CHEN Jingyuan

FacultyApplied Physics
Teacher OrganizationApplied Physics
Education and
 Research Organization
Faculty of Engineering /Graduate School of Engineering
PositionProfessor
Last Updated: 19/07/23 18:54

Researcher Profile & Settings

Name

    CHEN Jingyuan

Profile & Settings

Affiliation

  •  Applied Physics Professor

Education

  • Apr. 1993Mar. 1996Fukui University 物質工学
  • Apr. 1991Mar. 1993Fukui University 生物応用化学専攻
  • Apr. 1990Mar. 1991Fukui University Postgraduate Department of Biotechnology and Applied Chemistry
  • Feb. 1978Feb. 1982Tianjin University of Science and Technology School of Ocean Science and Engineering Chemical Engineering

Degree

  • Ph. D.
  • Bachelor Degree
  • Master's degree

Academic & Professional Experience

  • Apr. 2017University of Fukui Department of Applied Physics Professor
  • Apr. 2003Department of Applied Physics, University of Fukui Associate Professor
  • Jan. 2001Mar. 2002Department of Applied Physics, University of Fukui Senior Assistant Professor
  • Sep. 2000Aug. 2001Department of Chemistry, University of Utah Visiting Scholar
  • Jan. 1998Sep. 2000Faculty of Science, Kanazawa University Senior Assistant Professor
  • Apr. 1996Sep. 1998MAEDA KOSEN Company Limited. Senior Researcher
  • Feb. 1982Mar. 1990The electrochemical company Engineer, Head of the department of technology and development
  • Jul. 1975Feb. 1978Guankou people’s public corporation, Fujian Farmer

Association Memberships

    the Royal Society of Chemistry member,the Society for Electroanalytical Chemistry other,American chemical society member, International Society of Electrochemistry member,The Electrochemical Society member,Electrochemical Society of Japan member,Chemistry Society of Japan member,The polarographic Society of Japan councilor,

Overseas travel history

  • Lausanne, Swizerland 65th Annual Meeting of International Society of Electrochemistry Aug.  2014- Sep. 2014
  • Wells, Somerset, UK 10th ECHEMS Meeting Jun.  2014- Jun. 2014
  • Chicago, IL USA 2014 Pittsburgh Conference Mar.  2014- Mar. 2014
  • Santiago de Queretaro, Mexico 64th Annual Meeting of International Society of Electrochemistry Sep.  2013- Sep. 2013
  • Changchun, China 13th International Symposium on Electroanalytical Chemistry Aug.  2013- Aug. 2013
  • Durham University, UK Faraday Discussion 164 - Electroanalysis at the Nanoscale Jul.  2013- Jul. 2013
  • Lochow, Poland 9th ECHEMS Meeting Jun.  2013- Jul. 2013
  • Prague, Czech Republic 63rd Annual Meeting of International Society of Electrochemistry Aug.  2012- Aug. 2012
  • Slovenia, Portoro? The 14th International Conference on Electroanalysis Jun.  2012- Jun. 2012
  • Shanghai, China Department of Chemistry, Jiao Tong University Mar.  2012- Mar. 2012
  • Shanghai, China Department of Chemistry, Tongji University, Mar.  2012- Mar. 2012
  • Shanghai, China Department of Chemistry, Fudan University, Mar.  2012- Mar. 2012
  • Changsha, China State Key lab of Powder Metallurgy Powder Metallurgy, Research Institute Central South University, Mar.  2012- Mar. 2012
  • Changchun, China 13th International Symposium on Electroanalytical Chemistry Aug.  2011- Aug. 2011
  • Xiamen, China The State Key Lab, Xiamen University, Aug.  2011- Aug. 2011
  • Atlanta, GA. USA 61th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Mar.  2011- Mar. 2011
  • Hawaii, USA Pacifichem 2010 Dec.  2010- Dec. 2010
  • France 61th Annual Meeting of International Society of Electrochemistry Sep.  2010- Oct. 2010
  • China Fudan University, Tongji University Jul.  2010- Jul. 2010
  • Shanghai, China Department of Chemistry, Tongji University, Jun.  2010- Jun. 2010
  • Shanghai, China Department of Chemistry, Fudan University, Jun.  2010- Jun. 2010
  • Hsin-Chu, Taiwan, China Department of Chemical Engineering, National Tsing Hua University, Mar.  2010- Mar. 2010
  • Taiwan, China National Tsing Hua University Mar.  2010- Mar. 2010
  • Poland Institute of Physical Chemistry Polish Academy of Sciences Feb.  2010- Mar. 2010
  • Xiamen, China International Symposium on Nanoelectrochemistry and Spectroelectrochemistry, Aug.  2009- Aug. 2009
  • Beijing, China 60th Annual Meeting of International Society of Electrochemistry Aug.  2009- Aug. 2009
  • Changchun, China 12th International Symposium on Electroanalytical Chemistry Aug.  2009- Aug. 2009
  • Prague, Czech Republic 42th Heyrovsky Discussion Jun.  2009- Jun. 2009
  • Weingarten, Germany 5th ECHEMS Meeting Jun.  2009- Jun. 2009
  • Freiburg, Germany (IAF) Institute Angewandte Fraunhofer/ Freiburg, Jun.  2009- Jun. 2009
  • Tianjin, China Tianjin University of Science and Technology, Apr.  2009- Apr. 2009
  • USA 214th Meeting of the Electrochemical Society Oct.  2008- Oct. 2008
  • UK ELECTROCHEM 08, Liverpool, Sep.  2008- Sep. 2008
  • Spain 59th Annual Meeting of International Society of Electrochemistry Sep.  2008- Sep. 2008
  • San Sebastian, Spain CIDETEC, Centro de Tecnologias Electroquimicas, Parque Tecnologico de San Sebastian, Sep.  2008- Sep. 2008
  • Taibei, China 5th Asian Conference on Electrochemistry May  2008- May 2008
  • USA 58th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Feb.  2008- Mar. 2008
  • Canada 58th Annual Meeting of International Society of Electrochemistry Sep.  2007- Sep. 2007
  • China 11th International and First Sino-Japan Bilateral Symposium on Electroanalytical Chemistry Aug.  2007- Aug. 2007
  • USA 211th Meeting of the Electrochemical Society May  2007- May 2007
  • UK University of Bath Sep.  2006- Sep. 2006
  • UK 57th Annual Meeting of International Society of Electrochemistry Aug.  2006- Sep. 2006
  • Warsaw, Poland Faculty of Chemistry, Warsaw University Aug.  2006- Aug. 2006
  • Poland Department of Electrode Processes, Institute of Physical Chemistry Polish Academy of Sciences Aug.  2006- Aug. 2006
  • France 11th International Conference on Electroanalysis Jun.  2006- Jun. 2006
  • USA 209th Meeting of The Electrochemical Society May  2006- May 2006
  • USA 57th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Mar.  2006- Mar. 2006
  • USA Pacifichem 2005 Dec.  2005- Dec. 2005
  • Korea 56th Annual Meeting of International Society of Electrochemistry Sep.  2005- Oct. 2005
  • Canada 207th ECS Meeting of The Electrochemical Society May  2005- May 2005
  • Utah, USA Department of Chemistry, University of Utah, Mar.  2005- Mar. 2005
  • USA 56th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Feb.  2005- Mar. 2005
  • Bangladesh Bangladesh Chemical Congress 2004 Dec.  2004- Dec. 2004
  • USA 206th Meeting of The Electrochemical Society Oct.  2004- Oct. 2004
  • Greece 55th Annual Meeting of International Society of Electrochemistry Sep.  2004- Sep. 2004
  • USA 205th Meeting of The Electrochemical Society May  2004- May 2004
  • Cleveland, USA Eveready Battery Co. May  2004- May 2004
  • Detroit, USA Passive safety and advanced engineering research department, Ford Research & Advanced Engineering, Mar.  2004- Mar. 2004
  • USA 55th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Mar.  2004- Mar. 2004
  • China 9th International Seminar on Electroanalytical Chemistry Oct.  2003- Oct. 2003
  • France 203rd Meeting of The Electrochemical Society Apr.  2003- May 2003
  • USA 54th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Mar.  2003- Mar. 2003
  • USA 202nd Meeting of the Electrochemical Society Oct.  2002- Oct. 2002
  • USA 53th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Mar.  2002- Mar. 2002
  • USA Department of Chemistry, University of Utah Sep.  2000- Aug. 2001
  • USA The International Chemical Congress of Pacific Basin Societies Dec.  1995- Dec. 1995

Research Activities

Published Papers

  • A Cationic Rectifier Based on a Graphene Oxide Covered Microhole: Theory and Experiment
    Budi Riza Putra, Koichi Jeremiah Aoki, Jingyuan Chen, Frank Marken
    Langmuir 35(6) 2055-2065 Jan.  2019 Refereed
    Cation transport through nano-channels in graphene oxide can be rectified to give ionic diode devices for future applications for example in desalination. A film of graphene oxide is applied to a 6 m thick poly-ethylene-terephthalate (PET) substrate with 20 m diameter microhole and immersed in aqueous HCl solution. Strong diode effects are observed even at high ionic strength (0.5 M). Switching between open and closed states, microhole size effects, and time dependent phenomena are explained based on a simplified theoretical model focusing on the field-driven transport within the microhole region. In aqueous NaCl, competition between Na+ transport and field-driven heterolytic water splitting are observed, but shown to be significant only at low ionic strength. Therefore, nanostructured graphene oxide is demonstrated to exhibit close to ideal behavior for future application in ionic diode desalination of seawater.
  • Insight of electrolyte-free voltammetry at microelectrodes
    Koichi Aoki, Jingyuan Chen
    Current Opinion in Electrochemistry 10 67-71 Apr.  2018 Refereed
    Electrode reactions without deliberately adding supporting electrolyte are complicated with electric migrations associated with redox reactions, formation of double layers and ion-ion interactions relevant to electrode reactions. The complications can be realized quantitatively through voltammetry at various sized microelectrodes, partly because of negligibly small solution resistance effects and partly because of steady-state voltammograms which can be analyzed theoretically without capacitive time-dependent current. The present review deals with i) techniques of fabrication of many sized microelectrodes, ii) conditions of keeping low electrolyte concentrations, iii) ionic contribution of forming double layers, iv) participation in counter ions for electrode reactions, and v) change in ionic environment by redox reactions.
  • Effects of the dipolar double layer on elemental electrode processes at micro- and macro-interfaces
    Koichi Aoki, Jingyuan Chen
    Faraday Discussions Jan.  2016 Refereed
  • Quantitative Relation of the Frequency Dispersion of Double Layer Capacitances to Surface Roughness
    Koichi Jeremiah Aoki, Jingyuan Chen, Zhaohao Wang
    Advances in Nanoscience and Nanotechnology 19(1) 1-7 Nov.  2018 Refereed
    Frequency dispersion of double layer (DL) capacitances, which can be represented by the power law of the frequency or the constant phase element, is modeled by the Arrhenius equation with the activation energy which has a linear relation with the free energy change in the orientation of solvent dipoles. The Arrhenius equation has a form of a differential equation of the number of oriented dipoles. The solution is the power law of the time, being equivalent to the DL capacitance with the power law of the frequency. The power number is associated with the surface roughness of the electrode on the assumption that a dipole is oriented with the help of interaction on a given local area of the electrode. Then it has an approximately linear relation with the surface roughness. Surface roughness of highly oriented pyrolytic graphite electrodes is varied unintentionally by peeling-off processes and intentionally by electrochemical oxidation. The power numbers determined by ac-impedance techniques are compared with surface roughness obtained by scanning probe microscopy. They are approximately proportional to the surface roughness factor when the scanned domain on the surface is less than (40 nm)2, which is much smaller than the domain for the fractal structure.
  • Capacitive Currents Flowing in the Direction Opposite to Redox Currents
    Koichi Aoki, Jingyuan Chen, Peng Tang
    The Journal of Physical Chemistry C 122 16727-16732 Jun.  2018 Refereed
    A simple electrode reaction provides negative values of the double layer (DL) capacitance because a dipole of electrochemically generated charge coupled with the imaged charge on the electrode is oriented in the direction opposite to that of solvent. Some properties such as dependence of the capacitive values on the dc-potentials, the frequency dependence and localization of the redox charge are herein discussed in order to comprehend the negative capacitance. The redox species used are a ferrocenyl derivative, hexaammineruthenium and hexachloroiridium, of which heterogeneous reaction rates are so fast that the faradaic currents should be controlled by diffusion or the Warburg impedance. The observed ac-current can be represented by a simple sum of the diffusion-controlled current and the DL charging current by solvent and that by the redox species. Subtraction of the observed imaginary part of the admittance from the real one eliminates the diffusion-contribution to extract the charging admittance. This admittance takes negative values at dc-potentials near the standard redox potential. It is formulated by the dipole of the redox charge paired with the mirror-imaged charge. The negative capacitance has frequency dispersion similar to the conventional DL capacitance. A pseudo-capacitor has enhanced cooperatively the charge from the sum of individual DL charge and the redox charge, but this advantage is open to question.
  • Frequency dispersion of double layer capacitance of polyaniline-coated electrodes under the conducting state
    Zhaohao Wang, Koichi Aoki, Jingyuan Chen, Xiangong Zeng
    Int. J. Chem., 10(2) 25-35 Apr.  2018 Refereed
    The double layer capacitance of polyaniline (PANI)-coated electrode in acidic solution exhibited little frequency dispersion under the emeraldine (electrically conducting) state, while it showed large frequency dispersion under the insulating state. The former has a possibility of working as such an ideal capacitor that it may generate neither heat in iterative charge-discharge processes nor leakage of stored charge. The frequency dispersion is generally expressed by f - for ac-frequency f and a constant . This power law is ascribed to orientation of solvent dipoles rather than non-uniform distribution of ions. The value of  under the conducting state was close to zero, implying the orientation to be facilitated by less interaction of solvents. The less interaction was supported indirectly with strain-stress curves of PANI by atomic force microscopy. -Values close to zero were retained even for thick PANI films.
  • Double Layer Impedance in Mixtures of Acetonitrile and Water
    Koichi Aoki, Jingyuan Chen, Peng Tang
    Electroanalysis 30(8) 1634-1641 Mar.  2018 Refereed
    Double layer (DL) impedances were evaluated in mixed solutions of water and acetonitrile at various ratios in the polarized potential domain in order to find competitive orientation of the two solvent molecules on the platinum electrode. The DL capacitance at any ratio of the mixture shows the common power law of the ac-frequency. The capacitance at molar fractions of water less than 0.2 increases linearly with the fraction, and reaches the value for aqueous solution. This variation indicates accumulation of water molecules on the electrode excluding acetonitrile molecules. It is modelled on the concept of the Langmuir-type isotherm in which water and acetonitrile molecules have competitive interaction with the electrode. The experimental variations by the use of the isotherm yield the difference in the interaction energy, 6 kJ mol-1. The accumulation of water in the DL is supported by the formation of the adsorbed layer by insoluble ferrocene.
  • Volumetry of Hydrogen Micro-bubbles Dispersed in Water
    Koichi Aoki, Shimpei Yamaguchi, Jingyuan Chen
    J Material Sci Eng. B 8(1-2) 13-20 Mar.  2018 Refereed
    When hydrogen gas is bubbled in water until saturation, micro-bubbles with ca. 0.5 m in diameter have been detected in water by the dynamic light scattering, reportedly. A part of saturated hydrogen may take gas form, whereas it may take hydrated form. A question is how much molar ratio of the two forms. If hydrogen molecule is oxidized to hydronium ion, the volume of the solution including bubbles should decrease by the amount of gas form more predominantly than that of the hydronium one. Herein we oxidized the saturated hydrogen gas with potassium permanganate in the presence of platinum wire as catalyst. The decrease in the volume of the gas was compensated for addition of water so that the pressure of the hydrogen gas was able to be kept to the atmospheric pressure. From the decrease in the volume under the steady state, concentrations of H2 in the gaseous form were evaluated at several temperatures to be ca. 0.4 mM, which is a half the saturated concentration of H2. They were almost independent of the temperature of bubbling.
  • Decrease in the double layer capacitance by faradaic current
    Koichi Aoki, Jingyuan Chen, Xiangdong Zeng, Zhaohao Wang
    RSC Advances 7 22501-22509 2017 Refereed
    This work is on the reverse of the well-known double layer effects on charge transfer kinetics in a relationship between a cause and an effect. The reversible redox reaction of the ferrocenyl derivative decreased the capacitive values of the double layer impedance up to negative values, corresponding to an inductive component. This observation is disclosed by the subtraction of the real admittance from the imaginary one, which can extract the net double layer capacitance from the Warburg impedance. The inductance-like behavior is caused by the two: i) The double layer capacitance in the polarized potential domain is determined by such low concentrations of field-oriented solvent dipoles as redox concentrations conventionally employed; ii) The double layer capacitance is caused by the orientation of the dipoles in the same direction as the electric field, whereas the redox reaction generates charge in the direction opposite to the field. The Faradaic effect is demonstrated with ac-impedance data of the ferrocenyl compound in KCl solution in the unpolarized potential domain at 1 Hz - 3 kHz frequency. The negative admittance is proportional to the frequency. The theory on the negative capacitance is presented by combining the mirror-image surface charge with the Nernst equation.
  • Functionality of reduced graphene oxide flakes at the growth of conducting zone in polyaniline-graphenecomposite films
    Xiandong Zeng, Koichi Jeremiah Aoki, Jingyuan Chen
    Electrochim. Acta. 228 125-130 2017 Refereed
    When reduced graphene oxide (RGO) flakes were included in polyaniline (PANI), the PANI-RGO composite film exhibited faster redox conversion than the PANI film did. A reason of the enhancement of the conversion rate was searched by examining the growth rates of the conducting zone which appeared at the boundary between the oxidized and the reduced PANI in the film when the reduced composite was oxidized electrochemically from one end the film. The film was prepared by drying PANI-RGO colloidal suspensions, which were formed by coating flaky RGO particles with PANI. Higher anodic potentials and higher ratio of RGO fractions enhanced the growth rates. There are several possible reasons for the increase in the rates; electro-catalytic properties for the oxidation, enhancement of the conductivity by RGO, the electric percolation, and enhancement of specific surface area of RGO. The growth rate was modeled with the oxidation at the Tafel-typed rate, which was restrained by the IR-drop between the conducting front and the electrode. The growth length was expressed by a time-dependent non-linear differential equation. The numerical solution allowed us to analyze the experimental data of the time variation of the growth length. RGO functions as an increase in the rough surface area of the oxidation rather than electric percolation, enhancement of conductivity and catalytic effects.
  • Preface (Special issue in honor of Koichi Aoki)
    Jingyuan Chen, Nianjun Yang, Hiroshi Nishihara,
    Journal of Electroanalytical Chemistry 779 1-6 Oct.  2016 Refereed
  • Power law for frequency-dependence of double layer capacitance of graphene flakes
    H.Wang, K.Aoki, J.Chen, T.Nishiumi, X.Zeng, X,Ma
    J. Electroanal. Chem 741 114-119 Mar.  2015 Refereed
    The double layer capacitance per weight of graphene (GN) flakes in aqueous solution at the polarized potential increases with a decrease in the ac-frequency, obeying the inverse of the power law of the frequency. The power law is demonstrated to be equivalent to the constant phase element. The frequency-dependence increases with the thickness of the GN films. Thus, the lower the frequency and the thinner the film is, the larger is the capacitance density per weight. This is confirmed by cyclic voltammetry for several thickness of GN films and several scan rates. Resistance-like voltammograms at thick films are caused by frequency-dispersion. The overall capacitive properties of the GN films are as follows: the thickness of one GN flake is estimated to be 2 nm in average from the comparison of the thickness with the capacitances at the HOPG, which is consistent with values by the STM and AFM images.
  • Conditions of predominant occurrence of catalytic reduction of O-2 by ferrous hemin over formation of ferrous hemin-O-2 adduct
    Li, Wenwen;Aoki, Koichi Jeremiah;Chen, Jingyuan;Nishiumi, Toyohiko
    J. Electroanal. Chem., 743 134-138 Apr.  2015 Refereed
    Hemin, an iron porphyrin, functions as a carriage of dioxygen in mammalian respiration in the ferrous form. It works also as an electrochemical catalyst of the reduction of dioxygen by reproducing the ferrous form from the ferric one. Since the carriage requires stabilization of the dioxygen adduct, the catalytic reduction of dioxygen with the ferric form might hinder the stabilization. This work aims at finding the discrimination between the functions of the carriage and of the catalysis. A hint of the finding lies in the difference between the remarkable catalytic currents in high concentrations of hemin and negligibly small ones in very low concentrations. The catalytic current at the hemin-coated electrode is confirmed to occur at the stoichiometry of two hemin molecules and one dioxygen molecule. When this stoichiometry is applied to the dioxygen adduct of hemin as an intermediate species of the catalysis, high concentrations of dissolved hemin should provide the catalytic current. Spectro-electrochemistry demonstrates that ferrous hemin is not oxidized simply to the ferric form but is converted to other species, e.g. the dioxygen adduct.
  • Voltammetry of Suspensions of Polyaniline-coated Graphene Composites
    J.Chen, X,Zeng, K.J.Aoki, T.Nishiumi
    Int. J. Chem., 7(2) 1-11 Jul.  2015 Refereed
    Flaky particles of polyaniline (PANI)-graphene (GN) with rectangular size of 1.0-1.5 mm are dispersed in aqueous solution so that their suspension is stable for one day without aggregation. The weight fraction of PANI in the particle is 75 %, which is independent of the loaded fraction of PANI in the synthesis. The PANI-GN film made of the suspension forms a self-standing, elastic, conductive film. The PANI-GN suspension exhibits both the reduction and the oxidation waves at potentials similar to those of PANI adsorbed on an electrode, whereas the PANI-GO suspension shows only the voltammetric reduction wave. The redox peak currents are controlled by diffusion of PANI-GN flakes. The PANI-GN film cast on the electrode shows voltammetric peaks for PANI, of which redox charge is larger than that of the electrochemically polymerized PANI film with the common weight of PANI. This fact can be explained in terms of the electrochemically exhaustive oxidation of PANI through the electric conduction of GN.
  • Examination of the Gouy?Chapman theory for double layer capacitance in deionized latex suspensions
    Xiaoyu Zhao, Koichi Aoki, Jingyuan Chen, Toyohiko Nishiumi
    RSC Adv. 108(4) 63171-63181 Sep.  2014 Refereed
    Electric double layer capacitance at platinum electrodes is controlled by dipole moments of the solvent in the diffuse layer rather than that by ionic distribution, being different from that at mercury electrodes. The controlling step is found by comparing capacitance vs. electrode potential curves in ionic solutions with those in deionized latex suspensions. The curves do not involve a valley shape of Gouy–Chapman (GC)-Stern's type until ionic concentrations are less than 0.05 mM, because measured capacitance is controlled by the inner layer. The valley shape at low concentrations can be measured in deionized sulfonic latex suspensions, whose conductance is brought about by the ionic latex particles rather than the dissociated hydrogen ions. An expression for the capacitance by the ionic latex suspension is derived, which is demonstrated to be the same form of the potential dependence as for mono-valence ions. Ac-impedance data are obtained at parallel polycrystalline platinum wires without an insulating shield. The valley shape is found, which is analyzed by the inverse plot of the capacitance against the hyperbolic cosine of the dimensionless applied potential. The linearity of the plots seems to support the GC-theory, but the capacitance values are much larger than those calculated from the GC-theory. The extra amount can be attributed quantitatively to the orientation of solvent molecules by combining Debye's theory with the GC-theory.
  • Irreversibility of catalytic reduction of dioxygen by dissolved hemin
    K.Aoki, W.Li, J.Chen, T.Nishiumi
    J. Electroanal. Chem., 713 131-135 Jan.  2014 Refereed
    Hemin in aerated dimethylsulfoxide catalyzes the reduction of dioxygen at glassy carbon electrodes with a gain voltage for the catalysis, 0.5 V. The catalytic rate, observed as the reduction current, increases with an increase in concentrations of dioxygen, but reaches a maximum at 6% of the saturated concentration. The voltammetric peak current has a linear relation with the scan rate. These variations are different from the ordinary catalytic mechanism, in which hemin oxidized by dioxygen might be reused for the electrochemical reduction. The voltammetric peak current in deaerated hemin solution is diffusion controlled, whereas that in aerated solution is represented as a sum of the diffusion current and a surface wave. The catalytic current is caused by hemin incorporated with dioxygen, of which adsorption density is close to an amount of a monolayer. Therefore hemin films are not suitable for continuous reduction of dioxygen. Once the adsorbed layer is electrochemically oxidized to remove the adsorption film, the catalytic reduction wave is retrieved.
  • Three following, four virtue
    Electrochemistry 82(1) 65 Jan.  2014 Refereed
  • Electrochemically Focus-Tunable Convex Lenses by Oil-Sessile Drop
    J.Yu, J.Chen, K.Aoki, T.Nishiumi
    ECS Electrochem. Letters 3(11) H39-H40 Aug.  2014 Refereed
    A sessile drop of nitrobenzene (NB) mounted on the transparent electrode immersed in the aqueous solution works as an optical lens of which focus can be controlled by electrode potential when the solution includes K3Fe(CN)6 and tetrapentylammonium (TPA+) chloride. K3Fe(CN)6 functions as a redox species, whereas TPACl does as supporting electrolyte as well as a surfactant. The focal length decreases in the reduction potential domain. The switching between the long and the short focuses is almost reversible for 1 h by the potential control, synchronized with voltammograms. The size of a real image of an object varies with the potential.
  • Solvent Variables Controlling Electric Double Layer Capacitance at the Metal?Solution Interface
    Y.Hou, K.Aoki, J.Chen, T.Nishiumi
    J. Phys. Chem. C., 118(19) 10153-10158 Apr.  2014 Refereed
    This paper aims at finding the experimentally controllable variables of solvent for the electric double layer capacitance obtained at two parallel platinum wire electrodes in the polarized potential domain. The equivalent circuit used is the frequency-dependent double layer impedance in series with solution resistance. The evaluated capacitance shows no systematic relation with the dielectric constants, viscosity, boiling temperatures, or dipole moments of the solvents but is proportional to the inverse of the lengths of field-oriented molecules. The proportionality indicates common saturated dielectric constants, 6, of 13 solvents. The variables controlling the capacitance are the saturated dielectric constants and the lengths of solvent molecules along the dipole.
  • Participation in Self-Emulsification by Oil-Thin Film Voltammetry
    K.Aoki, J.Yu, J.Chen, T.Nishiumi
    Int. J. Chem., 6(2) 73-81 Apr.  2014 Refereed
    When an oil phase comes in contact with an aqueous phase, emulsions are formed spontaneously in each phase even without surfactant. The self-emulsification seems inconsistent with the electron transfer model proposed by Anson, in which ferricyanide in the aqueous phase is reduced at the oil/water interface by decamethylferrocene of the thin nitrobenzene phase. Anson’s experimental data were here reproduced at slow scan voltammetry. However, the electron transfer model did not agree with our experimental results at high scan rates, in that the reduction wave of ferricyanide appeared without decamethylferrocene. Ferricyanide was demonstrated to pass through the nitrobenzene film in the form of aqueous droplets, which were adsorbed on the electrode surface. Formation of aqueous droplets can explain electrode reactions at carbon paste electrodes without including redox species in paste.
  • Formation of graphite oxide nano-disks by electrochemical oxidation of HOPG
    K.Aoki, H.Wang, J.Chen, T.Nishiumi
    Electrochim. Acta., 130(1) 381-386 Mar.  2014 Refereed
    When HOPG (highly oriented pyrolytic graphite) was electrochemically oxidized in alkali solution, STM observation showed that graphite oxide with homo-sized disks 15 nm in diameter and 0.5 nm in thickness was formed dispersively on the HOPG surface. With an increase in the anodic charge, the number of the disks enhanced, and covered finally the HOPG surface without overlap at the maximum coverage, 70%. The projected area of the disks was proportional to the anodic charge when the charge was small. The disks were hydrophilic. The double layer capacitance of the oxidized HOPG increased slightly with the anodic charge, implying that the disks should be an electrical insulator. The fully disk-coated HOPG did not block the diffusion-controlled current of the redox species. The layer of the disks must be porous for ions or solutions. The formation of the uniform size may be ascribed to the difference between the density of graphite oxide and that of the basal plane of graphite. The formation of nano-disks and their properties are inconsistent with such an image of intercalation that ions are inserted into layers of graphenes of HOPG.
  • Which Controls Conductivity of Sulfonic Latex Suspension, Hydrogen Ion or Latex Core?
    X.Zhao, J.Chen, K.Aoki, T.Nishiumi
    Int. J. Electrochem. Sci. 9 2649-2661 Mar.  2014 Refereed
    The answer of the title by conductometry of the deionized suspension is that the latex core controls, although a major charge carrier in the suspension seems intuitively to be hydrogen ion. Our experimental result is supported partially by the thermodynamic theory that the conductivity should be proportional to squares of the charge number, z, per ion, where the net charge number of the sulfonate latex is of order of 105. In contrast, the ionic conductivity of the latex seems to be rather small because the diffusion coefficient, D, of the latex core is much smaller than D of hydrogen ion. In order to respond to this competition between z and D, we synthesized four kinds of polystyrene sulfonic latex, ranging from 1 to 3 m in diameter. Conductivity of the deionized suspensions was evaluated from the dependence of an in-phase component of ac-impedance on inter-distances of two parallel wire electrodes. Then it did not include contribution of electric double layers or adsorption of latex. The values of z determined from the conductivity were 1 % of the loaded amounts of sulfonate moieties. They were proportional to a cube of the particle diameter. The relation of the ionic molar conductivity, =Dz2F2/RT, was confirmed by the proportionality of /D to z2 for four latexes, and mono-ions. The conductivity was mainly provided by the latex anions rather than hydrogen ion.
  • Voltammetry in viscous poly(ethylene glycol) solutions at microelectrodes
    Y.Guo, K.Aoki, J.Chen, T.Nishiumi
    Electrochemica Acta Mar.  2011 Refereed
  • Voltammetry of Mn(III) Porphyrin in Trihexyl(tetradecyl)-phosphonium Tris(pentafluoroethyl) trifluorophosphate Supported Toluene in Contact with an Aqueous Electrolyte
    W. Adamiak, G. Shul, E.Rozniecka, M. Satoh, J.Chen, M. Opallo
    Electroanalysis 23(8) 1921-1927 Jun.  2011 Refereed
    Voltammetry of manganese tetraphenylporphyrinato chloride in trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate solution in toluene reveals its unexpectedly low diffusion coefficient. UV-vis spectra confirm significant Cl− exchange with large phosphate anion at the axial position of the complex. Experiments performed with a glassy carbon electrode covered by a liquid film of the same solution and immersed in an aqueous electrolyte solution show a peak potential dependence on the nature and concentration of the aqueous electrolyte anion described by a Nernst type equation. Electron transfer is followed by anion expulsion where the anion effect results from the lability of the axial coordination site of the porphyrin and from spontaneous ion exchange.
  • Voltammetry of latexes
    J.Chen, K.Aoki, Q.Ke, Y.Gao, L.Han, H.Chen, T.Li
    International Symposium on Nanoelectrochemistry and Spectroelectrochemistry O13 Aug.  2009
  • Diffusion-controlled behavior of ferrocenyl derivative in viscous solutions
    Y.Guo, K.Aoki, J.Chen
    60th Annual Meeting of International Society of Electrochemistry s10-P-012 Aug.  2009
  • Electrically conductive polyaniline-coated polystyrene latex particles
    H.Chen, K.Aoki, J.Chen
    60th Annual Meeting of International Society of Electrochemistry s08-P-035 Aug.  2009
  • Electrochemical properties of 1,4-benzoquinone by microelectrode voltammetry
    H.Zhang, K.Aoki, J.Chen
    60th Annual Meeting of International Society of Electrochemistry s08-0802860 Aug.  2009
  • Potential-dependent motion by the charged droplets at the water/oil interface
    M.Li, K.Aoki, J.Chen
    60th Annual Meeting of International Society of Electrochemistry s09-0802819 Aug.  2009
  • An electrochemically driven air bubble on the O|W interface under the three-phase boundary reactions of ferrocene
    J.Chen, K.Aoki, T.Imamura, H.Toda, M.Satoh
    60th Annual Meeting of International Society of Electrochemistry s09-083742 Aug.  2009
  • Electrode reaction of suspended redox latex
    J.Chen, K.Aoki, H.Chen, T.Li
    12th International Symposium on Electroanalytical Chemistry I-32 Aug.  2009
  • An Driven Air Bubble on the O/W Interface by the Three Phase Boundary Reaction of Ferrocene
    J.Chen
    42th Heyrovsky Discussion Jun.  2009
  • Driven motion of an air bubble on the oil | water interface by three-phase boundary reactions
    J.Chen, M.Satoh, T.Imamura, H.Toda, K.Aoki
    5th ECHEMS Meeting 7 Jun.  2009
  • Electrical conduction of colloidal suspensions formed by polyaniline
    F.Kawaguchi, K.Aoki, T.Nishiumi, J.Chen
    5th ECHEMS Meeting 47 Jun.  2009
  • Possibility of coalescence of water droplets in W/O emulsions by means of surface processes
    J. Fukushima, H.Tatsuta, N. Ishii, J.Chen, T.Nishiumi, K.Aoki
    Colloids and Surfaces A 333 53-58 2009 Refereed
  • Spontaneous emulsification at oil|water interface by tetraalkylammonium chloride
    K.Aoki, M.Li, J.Chen, T.Nishiumi
    Electrochem. Commun 11 239-241 2009 Refereed
  • Diffusion-controlled currents in viscous solutions of polyethylene glycols
    K.Aoki, Y.Guo, J.Chen
    J. Electroanal. Chem., 629 73-77 2009 Refereed
  • Dissociation kinetics at polyacrylic latex-coated electrodes
    T.Li, K.Aoki, J.Chen, T.Nishiumi
    J. Electroanal. Chem 633 319-326 2009 Refereed
  • Partial charge transfer of latex particles
    J.Chen
    ELECTROCHEM 08 5 Sep.  2008
  • Size-dependent efficiency of electron transfer at suspended redox latex
    K.Aoki, J.Chen
    59th Annual Meeting of International Society of Electrochemistry 59 Sep.  2008
  • Redox latex
    J.Chen
    5th Asian Conference on Electrochemistry, 118 May  2008
  • Examination of electrochemical activity at the carboxyl latex particles coated-electrodes by redox reaction of FcTMA+ and Fe(CN)64-,
    J.Chen, T.Li
    58th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy 1870-4 Mar.  2008
  • Synthesis and the electrolyte of the functional polystyren-based latex
    T.Sakata, K.Aoki, J.Chen
    214th Meeting of the Electrochemical Society 139 Jan.  2008
  • Motion of an air bubble on oil|water interface
    K.Aoki, J.Chen, T.Imamura
    214th Meeting of the Electrochemical Society 93 Jan.  2008
  • Voltammetry of suspended jumbo particles
    J.Chen, K.Aoki
    214th Meeting of the Electrochemical Society 2739 Jan.  2008
  • Electrochemically Instantaneous Reduction of Conducting Polyaniline-coated Latex Particles
    H.Chen, K.Aoki, J.Chen
    214th Meeting of the Electrochemical Society 219 Jan.  2008
  • Voltammetric electrodes coated with carboxyl latex particles
    K.Aoki, T.Li, J.Chen, T.Nishiumi
    J. Electroanal. Chem. 613(1) 42012 2008 Refereed
  • Electrically conducting suspensions formed by polyaniline
    K.Aoki, F.Kawaguchi, T.Nishiumi, J.Chen
    Electrochim. Acta 53 3798-3902 2008 Refereed
  • Electrically driven motion of an air bubble on hemispherical oil | water interface by three-phase boundary reactions
    M.Satoh, K.Aoki, J.Chen
     24 4364-4369 2008 Refereed
  • Electrochemically instantaneous reduction of conducting polyaniline-coated latex particles dispersed in acidic solution
    H.Chen, J.Chen, K.Aoki, T.Nishiumi
    Electrochim. Acta, 53 7100-7106 2008 Refereed
  • Characteristic of electrically conducting of polyaniline-coated latex particles
    H.Chen, J.Chen, K.Aoki
    58th Annual Meeting of International Society of Electrochemistry S08-P-008 Sep.  2007
  • Catalytic generation of chlorine at small overpotential by micellar ferrocene
    Jingyuan Chen, H.Chen, Koichi Aoki
    The 11th International and First Sino-Japan Bilateral Symposium on Electroanalytical Chemistry I-48 Aug.  2007
  • Measurement of Interfacial Tension by Locating an Air Bubble on the Oil|Water Interface
    M.Sato, G.Shul, Koichi Aoki, M.Opallo, Jingyuan Chen
    International Conference on Electrified Interfaces 2007 42181 Jun.  2007
  • Electrogenerated Ion Transfer Across Toluene+Ionic Liquid Mixture / Aqueous Solution Interface
    M.Satoh, G.Shul, J.Chen, M.Opallo
    International Conference on Electrified Interfaces 2007 42211 Jun.  2007
  • Motion of an air bubble caused by three-phase boundary reaction
    Jingyuan Chen, Masanori Satoh, Koichi Aoki
    211th Meeting of the Electrochemical Society 1188 May  2007
  • Determination of nitric oxide by quenching electro-chemiluminescence of tris(2,2’-bipyridyl)ruthenium in flow injection analysis
    J.Chen, M.Miyake, Y.Chi, T.Nishiumi, K.Aoki
    Electroanalysis 19(42038) 181-184 Jan.  2007 Refereed
  • Comparison of fast scan voltammetry with microelectrode voltammetry of reduction of 1,4-benzoquinone
    K.Aoki, Jingyuan Chen, Hua Zhang
    J. Electroanal. Chem. 610 211-217 2007 Refereed
  • Catalytic generation of chlorine with slight overpotential by micellar ferrocene
    K.Aoki, J.Chen, H.Chen
    Electrochem. communi. 9 2304-2307 2007 Refereed
  • Carbon nanoparticle stabilised liquid|liquid micro-interfaces for electrochemi- cally driven ion-transfer processes
    S.M.MacDonald, P.D.I.Fletcher, Z-g.Cui, M.Opallo, J.Chen, F.Marken
    Electrochim. Acta 53 1175-1181 2007 Refereed
  • Size-dependent efficiency of electron transfer at suspended ferrocenyl jumbo particles
    L.Han, J.Chen, K.Aoki
    J. Electroanal. Chem. 602 123-130 2007 Refereed
  • Colloidal submicron-palladium particles stabilized with acetate
    K.Aoki, Y.Zhao, J.Chen
    Electrochim. Acta 52 2485-2491 2007 Refereed
  • Electrochemical motion of an air bubble at oil|water interface
    M.Sato, J.Chen
    57th Annual Meeting of International Society of Electrochemistry 57 S6-P-28 Aug.  2006
  • Ion Transfer Across Supported o-Nitrophenyloctylether | Aqueous Electrolyte Solution Interface Coupled to Electrochemical Redox Reaction
    J.Niedziolka, E.Rozniecka, J.Chen, M.Opallo
    57th Annual Meeting of International Society of Electrochemistry 57 S6-P-27 Aug.  2006
  • Electrochemical reaction at oil|water|electrode boundary
    J.Chen, M.Sato
    57th Annual Meeting of International Society of Electrochemistry 57 Aug.  2006
  • Voltammetry of suspensions of hollow particles with ferrocene-immobilized polyallylamine shell
    J.Chen, K.Aoki, T.Nishiumi, T.Li
    Langmuir 22 10510-10514 Aug.  2006 Refereed
  • A miniaturized flow injection analytical system for determining nitric oxide by inhibited electrogenerated chemiluminescence
    Jingyuan Chen, M.Miyake, Y.Chi
    11th International Conference on Electroanalysis 11 Mini05 Jun.  2006
  • Redox-active of latex dependence on particle size for the multiple electron transfer
    Jingyuan Chen, L.Han
    209th Meeting of The Electrochemical Society 209 1067 May  2006
  • Fabrication of an electrochemical generation-detection unit for nitric oxide with the help of iron porphyrin
    Jingyuan Chen, M.Miyake
    The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy 57 1520-14 Mar.  2006
  • Changing the direction of ion transfer across o-nitrophenyloctyletherwater interface coupled to electrochemical redox reaction
    J.Niedziolka, E.Rozniecka, J.Chen, M.Opallo
    Electrochem. communi., 8 941-945 2006 Refereed
  • Convection caused by three-phase boundary reactions
    K.Aoki, M.Satoh, J.Chen, T.Nishiumi
    J. Electroanal. Chem., 595 103-108 2006 Refereed
  • Micro-cylinder biosensors for phenol and catechol based on layer-by-layer immobilization of tyrosinase on latex particles: Theory and experiment, P.Rijiravanich
    P.Rijiravanich, K.Aoki, J.Chen, W.Surareungchai, M.Somasundrum
    J. Electroanal. Chem. 589 249-258 2006 Refereed
  • Partition of ferrocene in water by reaction at the water|oil|electrode three-phase boundary
    M.Sato, J.Chen
     1200 Dec.  2005
  • Charge transfer process in reduction of TCNQ at nanometer-scaled electrdes
    M.Taniguchi, J.Chen
    (1202) Dec.  2005
  • Electrochemical characterization of mono-dispersed redox latex
    J.Chen, L.Han
    (920) Dec.  2005
  • Electrochemical generation of nitric oxide
    M.Miyake, J.Chen, T.Nishiumi
     1196 Dec.  2005
  • Voltammetry of mono-dispersed redox latex particle
    J.Chen
    56th Annual Meeting of International Society of Electrochemistry 56 070-096 Sep.  2005
  • Synthesis and the multi-charge transfer of the functional polystyren-based latex
    J.Chen, Z.Zhang
    207th Meeting of The Electrochemical Society, 207 1047 May  2005
  • Size-dependence of faradaic current of monodispersed ferrocenyl-anchored polystyrene particles
    Jingyuan Chen, Z.Zhang, L.Han
    The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy 56 1210-5 Feb.  2005
  • Diffusion-controlled currents of redox latex particles with polystyrene-core and polyallylamine-ferrocenyl shell
    J.Chen, Z.Zhang
    J. Electroanal. Chem. 583 116-123 2005 Refereed
  • Electrocatalysis of carbon dioxide with hemin and hemin-coated latex
    Y.Gao, J.Chen
    J. Electroanal. Chem. 583 286-291 2005 Refereed
  • Integration of electrochemical generator and detector of nitric oxide
    Y.Chi, J.Chen, M.Miyake
    Electrochem. communi. 7 1205-1208 2005 Refereed
  • Preparation of ferrocenyl-immobilized polystyrene mono-dispersed latex particle
    L.Han, J.Chen, I.Ikeda
    Chemistry letters 34(11) 1512-1513 2005 Refereed
  • Redox reaction of hemin-immobilized polyallylamine-polystyrene latex suspensions
    Y.Gao, J.Chen
    J. Electroanal. Chem. 578 129-136 2005 Refereed
  • Measurements of Charge Transfer Rate Constants Using Nanometer-Electrode
    J.Chen
    Bangladesh Chemical Congress 2004 27 IL A4 Dec.  2004
  • Reactions at oil|water|electrode interfaces by ion-insoluble polydimethylsiloxane droplet
    J.Chen, M.Sato
    55th Annual Meeting of International Society of Electrochemistry 55 SIFP11 Sep.  2004
  • Voltammetry of silver stearate coated nanoparticles in suspensions
    J.Chen, N.Yang
    205th Meeting of The Electrochemical Society 204 A2-51 May  2004
  • Visualization of electrode reactions for monodisperse polyaniline-coated latex particles
    J.Chen, Q.Ke
    The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy 55 9400 Mar.  2004
  • The formation of emulsion at water|oil|electrode three-phase boundary
    J.Chen, M.Sato
    206th Meeting of The Electrochemical Society 205 2276 Jan.  2004
  • Potential shifts of ferrocene-derivatives at ultra-small microelectrodes
    A.Mori, J.Chen
    206th Meeting of The Electrochemical Society, 205 56 Jan.  2004
  • Reactions at oil|water|electrode interfaces by ion-insoluble polydimethylsiloxane droplet - formation emulsion
    M.Sato, J.Chen
    206th Meeting of The Electrochemical Society 205 69 Jan.  2004
  • Steady-state current at oil|water|electrode interfaces using ion-insoluble polydimethylsiloxane droplets
    Jingyuan Chen, M.Sato
    J. Electroanal. Chem. 572 153-159 2004 Refereed
  • Electrochemical Generation of Free Nitric Oxide from Nitrite Catalyzed by Iron meso-Tetrakis(4-N- methylpyridiniumyl)porphyrin
    Y.Chi, J.Chen, K.Aoki
    Inorg. Chem., 43(26) 8437 -8446 2004 Refereed
  • Competition between polymerization and dissolution of poly(3-methylthiophene) films
    K.Aoki, I.Mukoyama, J.Chen
    R. J. Electrochem. 40 319-324 2004 Refereed
  • Electrode reactions of catechol at tyrosinase-immobilized latex suspensions
    P.Rijiravanich, K.Aoki, J.Chen, W.Surareungchai, M.Somasundrum
    Electroanalysis 16 605-611 2004 Refereed
  • Coalescence of O/W emulsion by potential application
    J.Chen, J.Yoshida, Y.Zhao, K.Aoki,
     203 2638 Apr.  2003
  • Electrode reactions of catechol at tyrosinase-immobilized latex suspensions
    P.Rijiravanich, K.Aoki, J.Chen, W.Surareungchai, M.Somasundram
    203rd Meeting of The Electrochemical Society S1-1701 Apr.  2003
  • Ferrocene redox behavior at nano-scale three-phase boundary
    T.Porntip, J.Chen, K.Aoki
    203rd Meeting of The Electrochemical Society A1-36 Apr.  2003
  • Electrode reactions at nanometer-scaled oil|water|electrode interfaces
    J.Chen, P.Tasakorn
    he Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 54 220-10 Mar.  2003
  • Charge transfer rate constants at electrodes of nanometer dimensions
    J.Chen
    9th International Seminar on Electroanalytical Chemistry, Changchun, China 1-41 Jan.  2003
  • Zeptomole Voltammetric Detection and Electron-Transfer Rate Measurements Using Platinum Electrodes of Nanometer Dimensions
    J.J.Watkins, JingyuanChen, H.S.White, H.D.Abruna, E.Maisonhaute, C.Amatore
    Anal. Chem., 75(16) 3962-3971 2003 Refereed
  • Electrode reactions at sub-micron oil|water|electrode interfaces
    K.Aoki, P.Tasakorn, J.Chen
     542 51-60 2003 Refereed
  • Suspensions of poly(vinylferrocene)-coated latex particles
    J.Chen, K.Aoki, C.Xu
    J. Electroanal. Chem. 546 79 -86 2003 Refereed
  • Redox reactions of polyaniline-coated latex suspensions
    K.Aoki, J.Chen, Q.Ke, S.P.Armes, D.P.Randall
    Langmuir 19 5511-5516 2003 Refereed
  • Partial charge transfer of polyvinylferrocene-coated latex particles adsorbed on pyrolytic graphite electrode
    C.Xu, J.Chen, K.Aoki
     5 506-510 2003 Refereed
  • Electrochemical coalescence of nitrobenzene|water emulsions
    J.Yoshida, J.Chen, K.Aoki
     553 117-124 2003 Refereed
  • Charge transfer reactions of silver stearate coated nanoparticles in suspensions
    K.Aoki, J.Chen, N.Yang, H.Nagasawa
    Langmuir 19 9904-9909 2003 Refereed
  • Electrochemically driven polystyrene-sulfonic acid particles in deionized suspension: microscope analysis
    K.Aoki, C.Wang, J.Chen
    J. Electroanal. Chem., 540 135-143 2003 Refereed
  • Redox mechanism of nitric oxide in the iron porphyrin,
    J.Chen, O.Ikeda
    The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy 53 1378 Mar.  2002
  • Electrochemical behavior of the ferrocene-coated microparticles
    J.Chen, C.Xu, K.Aoki
    202nd Meeting of the Electrochemical Society U3-911 Jan.  2002
  • Competition of dissolution and polymerization of polythiophene films
    K.Aoki, J.Chen, I.Mukouyama,
    202nd Meeting of the Electrochemical Society A1-29 Jan.  2002
  • Temperature-variation of capacitance of alkanethiol monolayer films
    T.Nakamura, K.Aoki, J.Chen
    Electrochim. Acta 47 2407-2411 2002 Refereed
  • Critical thermal variation of displacement of alkanethiols in self-assembled films
    K.Aoki, J.Chen, T.Nakamura
    Electrochem. Commun. 4 521-526 2002 Refereed
  • Voltammetry of a single oil droplet on a large electrode
    P.Tasakorn, J.Chen, K.Aoki
    J. Electroanal. Chem. 533 119-126 2002 Refereed
  • Concentration-dependence of faradaic currents and conductivity in polystyrene sulfonic latex suspension
    C.Wang, T.Nagahashi, K.Aoki, J.Chen
    J. Electroanal. Chem. 530 47-52 2002 Refereed
  • Overestimation of heterogeneous rate constants of hexacyanoferrate at nanometer-sized ultramicroelectrodes
    J.Chen, K.Aoki
    Electrochem. Commun. 4 24-29 2002 Refereed
  • Electrochemical Dissolution of Polythiophene Films
    I.Mukoyama, K.Aoki, J.Chen
    J. Electroanal. Chem. 531 133-139 2002 Refereed
  • Redox mechanism of NO in water-soluble iron porphyrin
    Jingyuan Chen, O.Ikeda
    Electroanalysis 13 1076-1081 2001 Refereed
  • Electrode reaction of ferrocene in a nitrobenzene-water emulsion
    J.Chen, O.Ikeda, K.Aoki
    J. Electroanal. Chem 496 88-94 2001 Refereed
  • Electrode reaction of ferrocene in nitrobenzene-water emulsion
    J.Chen, K.Aoki
    Pacifichem 2000 Dec.  2000
  • Curing of epoxy resin contaminated with water
    J.Chen, T.Nakamura, K.Aoki, Y.Aoki, T.Utsunomiya
    J. Appl. Polym. Sci. 79 214-220 2000 Refereed
  • Redox potentials of polynuclear metal complexes by pai-conjugated metal-interaction
    R. Polarography 46 87-104 2000 Refereed
  • Capacitance of a solid sulfonated epoxy resin-coated electrode
    J.Chen, K.Aoki, T.Totsuka, T.Utsunomiya
    J. Appl. Electrochem 29 1457-1461 Jun.  1999 Refereed
  • Oxidation of NO mediated by water-soluble iron porphyrin
    J.Chen, O.Ikeda, T.Hatasa
    Pacifichem 1999 Jan.  1999
  • Oxidation of NO mediated by water-soluble iron porphyrin
    J.Chen, O.Ikeda, T.Hatasa, A.Kitajima, M.Miyake, A.Yamatodani
     1 274-277 1999 Refereed
  • Configurational stabilization of mixed-valence states in the star-burst tetranuclear ruthenium complex bridged with acetylene links,
    K.Aoki, H.Kamo, J.Chen, Y.Hoshino
    J. Electroanal. Chem., 420 189-193 1997 Refereed
  • Redox properties of oligo(1,1’-Dihexylferrocenylene)s
    H.Nishihara, T.Hirao, K.Aramaki, K.Aoki, J.Chen
    International Conference on Science and Technology of Synthetic Metals 288 Aug.  1996
  • Redox interaction in mixed-valence tri-nuclear ring complexes by means of quantum chemical approach,
    J.Chen, K.Aoki
     402 189-193 1996 Refereed
  • Interaction over three redox centers at conjugated oligomeric ferrocenes with N (=2-6) nuclei,
    K.Aoki, J.Chen, H.Nishihara, T.hirao
    J. Electroanal. Chem., 416 151-155 1996 Refereed
  • Redox interaction of tetranuclear complex with ethynyl bridges
    J.Chen, K.Aoki, H.Kamo
    Pacifichem 1995 288 Dec.  1995
  • Redox interaction of star-burst tetranuclear complex
    J.Chen, K.Aoki
    1st Asian Conference on Electrocahemistry 2A-20 May  1995
  • Statistical thermodynamics of multi-nuclear linear complexes with mixed valance states by means of correlated-walk,
    K.Aoki, J.Chen
     380 35-45 1995 Refereed
  • Redox interaction of star-burst tetranuclear complex
    K.Aoki, J.Chen, M.Haga
    J. Electroanal. Chem., 396 309-316 1995 Refereed
  • Construction of functional polymer-modified electrode prepared by electrolytic polymerization of o-nitroaniline
    Yoshiharu Nakamura, J.-Y. Cheng, Isao Tabata, Shin-ichiro SUYE, Mitsugi Senda
    Electrochemistry 62(12) 1235-1237 1994 Refereed
  • Invariance of double layer capacitance to polarized potential in halide solutions
    Y.Hou, K.Aoki, J.Chen, T.Nishiumi
    Univ. J. Chem. 1 162-169 Sep.  1913 Refereed
  • Heterogeneous reaction rate constants by steady-state microelectrode techniques and fast scan voltammetry
    K.Aoki, C.Zhang, J.Chen, T.Nishiumi
    J. Electroanal. Chem 706 40-47 May  1913 Refereed
  • Blocking of two-electron reduction of non-charged species in the absence of supporting
    C.Zhang, K.Aoki, J.Chen, T.Nishiumi
    J. Electroanal. Chem. 708 101-107 May  1913 Refereed
  • Slow scan voltammetry for diffusion-controlled currents in sodium alginate solutions
    B.Wang, K.Aoki, J.Chen, Toyohiko Nishiumi
    J. Electroanal. Chem. 700 60-64 Apr.  1913 Refereed
  • Salt-free electrolysis of water facilitated by hydrogen gas in thin layer cell
    C.Li, K.Aoki, T.Nishiumi, J.Chen
    Report in Electrochemistry, 3 42200 Apr.  1913 Refereed
  • Voltammetry in low concentration of electrolyte supported by ionic latex suspensions
    K.Aoki, X.Zhao, J.Chen, T. Nishiumi
    J. Electroanal. Chem. 697 42133 Mar.  1913 Refereed
  • Self-dispersion of mercury droplets from saturated calomel electrodes into solutions
    J.Chen, K. Iwama, K.Aoki, T.Nishiumi
    International Journal of Electrochemical Science, 8 7394-7400 Mar.  1913 Refereed
  • Determination of concentration of saturated ferrocene in aqueous solution
    C.Ouyang, K.Aoki, J.Chen, T.Nishiumi, B.Wang
    Reports in Electrochemistry 3 17-23 Mar.  1913 Refereed
  • Electrolysis of pure water in a thin layer cell
    K.Aoki, C.Li, T.Nishiumi, J.Chen
    J. Electroanal. Chem. 695 24-29 Feb.  1913 Refereed
  • Resistance associated with measurements of capacitance in electric double layers
    K.Aoki, Y.Hou, T.Nishiumi, J.Chen
    J. Electroanal. Chem 689 124-129 Jan.  1913 Refereed
  • Diffusion coefficients in viscous sodium alginate solutions
    K.Aoki, B.Wang, J.Chen, T.Nishiumi
    Electrochim. Act 83 348-353 Nov.  1912 Refereed
  • Self-dispersion of mercury metal into aqueous solutions
    K.Aoki, C.Li, T.Nishiumi, J.Chen
    J. Electroanal. Chem. 682 66-71 Aug.  1912 Refereed
  • Comparison of diameters of disk microelectrodes obtained from microscopes with those evaluated from steady-state currents
    K.Aoki, C.Ouyang, Z.Chaofu, J.Chen, T. Nishiumi
    International J. Electrochemistry 7 5880-5892 Jul.  1912 Refereed
  • Is hydrogen gas in water present as bubbles or hydrated form?
    K.Aoki, H. Toda, J. Yamamoto, J.Chen, T. Nishiumi
    J. Electroanal. Chem 668 83-89 Feb.  1912 Refereed
  • Diffusion-controlled current at elliptically deformed microelectrodes
    K.Aoki, C.Ouyang, J.Chen, T.Nishiumi
    J. Solid State Electrochem 15 1010-1019 Nov.  1911 Refereed
  • Radii of microelectrodes undervalued from steady-state currents
    K.Aoki, H.Takeuchi, J.Chen, T. Nishiumi
    Review of Polarography 57(2) 101-119 Nov.  1911 Refereed
  • Voltammetry of Ferrocenyl Derivatives at Glass-coated Platinum Nano-electrodes
    K.Aoki, C. Zhang, Jingyuan Chen
    62th Annual Meeting of International Society of Electrochemistry s14-48 Sep.  1911
  • Voltammetry of Carboxyl Functionalized Particle Films
    T.Li, J.Chen, K.Aoki
    13th International Symposium on Electroanalytical Chemistry I-55 Sep.  1911
  • Multistep Spontaneously Formed Emulsions at Water|Nitrobenzene Interface
    M.Li, K.Aoki, J.Chen
    13th International Symposium on Electroanalytical Chemistry P124 Aug.  1911
  • Voltammetric Determination of Nano-electrodes
    K.Aoki, J.Chen
    13th International Symposium on Electroanalytical Chemistry I19 Aug.  1911
  • Voltammetric determination of both concentration and diffusion coefficient by combinational use of regular and micro electrodes
    K.Aoki, H.Zhang, J.Chen, T.Nishiumi
    Electroanalysis May  1911 Refereed
  • Voltammetric variations with structure of latex particles
    K.Aoki, J.Chen
    International Symposium on Electroanalytical Chemistry Shikata Discussion 2011 2C12 May  1911 Not refereed
  • Voltammetric electrodes modified with swollen polyacrylic latex particles
    K.Aoki, T.Li, J.Chen, T.Nishiumi
    J. Electroanal. Chem Apr.  1911 Refereed
  • Voltammetric determination of concentrations of ferrocene-included nitrobenzene droplets in water
    M.Li, K.Aoki, J.Chen, T.Nishiumi
    J. Electroanal. Chem. Apr.  1911 Refereed
  • Voltammetry of the carboxylate functionalized particles-modified electrodes
    K.Aoki, T.Li, J.Chen
    61th The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy 440-29 Mar.  1911
  • Relation between oxidation current of hydrogen gas and amount of the bubbles inaqueous solution
    H.Toda, K.Aoki, J.Chen, T.Nishiumi
    Pacifichem 2010 157 Dec.  1910 Not refereed
  • Determination of concentration and diffusion coefficient by the combination of regular and micro electrodes
    H.Zhang, K.Aoki, H.Toda, J.Chen
    Pacifichem 2010 193-450 Dec.  1910 Not refereed
  • Comparison of Voltammograms at the Polymer-coated Nano-electrode with Those at the Glass Sealed One
    J.Chen, K.Aoki
    61th Annual Meeting of International Society of Electrochemistry s10-P-001 Sep.  1910
  • Fabrication of glass-coated electrodes with nano- and micrometer size by means
    K.Aoki, C..Zhang, J.Chen, T.Nishiumi
    Electrochimica Acta 24 7328-73337 Apr.  1910 Refereed
  • Voltammetric potentials of polyaniline varying with electric percolation
    H.Chen, K.Aoki, F.Kawaguchi, J.Chen, T.Nishiumi
    Electrochimica Acta, 55 6959-6963 Feb.  1910 Refereed
  • Blocking of two-electron reduction of non-charged species in the absence of supporting electrolyte at nanoelectrodes
    C.Zhang, K.Aoki, J.Chen, T.Nishiumi
    J. Electroanal. Chem., 708 101-107 Nov.  2013 Refereed
    1,4-Benzoquinone (BQ) and tetracyanoquinodimethane (TCNQ), which are reduced consecutively to mono-anions and dianions under conventionally voltammetric conditions, cannot be reduced up to the dianions without supporting electrolyte in acetonitrile solution. Effects of the IR-drop and the electrostatic force in low concentrations of supporting electrolyte are examined by use of the first reduction waves. They apply to the analysis of the second waves. Voltammograms without supporting electrolyte at microelectrodes with the diameters less than 0.4 μm do not include noticeably IR-drop. The large overpotential for the anions cannot be explained in terms of the electric migration which has been estimated from solutions of the Nernst–Planck equation and the Laplace equation. With an increase in the conductivity of the solution by addition of electrolyte, the second reduction wave appears, involving the potential shift. The electrolyte does not influence the first reduction waves but varies the second one. The salt effect specific to the second wave is ascribed to non-stoichiometric association of the redox anion with the salt cation.
  • Invariance of double layer capacitance to polarized potential in halide solutions
    Y.Hou, K.J.Aoki, J.Chen, T.Nishiumi,
    Universal Journal of Chemistry 1(4) 162-169 Nov.  2013 Refereed
    This paper aims at evaluating the dependence of double-layer capacitance at a platinum wire electrode both on concentrations of four kinds of halide ions and the dc potential in the double-layer region (from 0.0 to 0.4 V vs. Ag|AgCl) from a viewpoint of frequency-dispersion of the capacitance. Attention was paid to shape of the double layer capacitance vs. dc-potential curves. The equivalent circuit used for analysing the double-layer impedance was a parallel combination of a double layer capacitance and an apparent resistance. The latter is caused by the time-derivative of the capacitance, which belongs to an in-phase component. It was inversely proportional to the frequency and the electrode area, but unaffected by the potential and the variation of concentrations of halide ions. On the other hand, the parallel capacitance decreased linearly with logarithm of the frequency, and was proportional to the electrode area. It showed almost a value common to concentrations from 1 mM to 2 M (= mol∙dm-3) and four halide ions. Variations of the capacitance with the dc-potential in 0.1 M KF, KCl and KBr solutions are ca. 10 %. Therefore, the capacitance has negligible influence on the localization of ions by the Gouy-Chapman theory.
  • Heterogeneous reaction rate constants by steady-state microelectrode techniques and fast scan voltammetry
    K.Aoki, C.Zhang, J.Chen, T.Nishiumi
    J. Electroanal. Chem., 706 40-47 Oct.  2013 Refereed
    Rate constants of fast electron transfer reactions of hexachloroiridium, hexaammine ruthenium, aminoferrocene, tetracyanoquinodimethan (TCNQ), ferrocenecarboxylic acid and ferrocene, which have been determined equivocally by fast voltammetry, are attempted to be evaluated with steady-state voltammetric measurements at ultramicroelectrodes. This work is motivated by the experimental feasibility of high current density at ultramicroelectrodes without effects of capacitive currents or solution resistance. The theory of mass transport mentions that current densities by steady-state voltammetry at electrodes 10 μm and 1 μm in diameter correspond, respectively, to 2.1 V s−1 and 210 V s−1 scan rates at large electrodes. However, no potential shift is observed even at electrodes 0.01 μm in diameter for the six species. This fact implies that the heterogeneous rate constants are at least larger than 10 cm s−1. Fast scan voltammetry is carried out at a large electrode for scan rates less than 10 V s−1. Peak-to-peak potentials increase with an increase in the scan rates. This variation is fitted to the mass transport equation complicated by the electrode kinetics for the rate constant of 0.01–0.1 cm s−1. The inconsistency between the two methods is ascribed partly to solution resistance and partly to the resistance relevant to the electric double layer at fast scan voltammetry. The contribution of the solution resistance is demonstrated from the facts that the peak currents vary linearly with the peak potentials, that the slope of the linearity is independent of kinds of redox species, and that the slope corresponding to the conductivity has a linear relationship with concentration of supporting electrolyte.
  • Determination of concentration of saturated ferrocene in aqueous solution
    C.Ouyang, K.J.Aoki, J.Chen, T.Nishiumi, B.Wang
    Reports in Electrochem., 3 17-23 Jul.  2013 Refereed
    The solubility of ferrocene in aqueous solution is known to be approximately 0.04 mmol/dm3. The solubility values determined by voltammetry have been overestimated because of adsorption on electrodes. This work deals with discerning diffusion from adsorption by altering not only the voltammetric time scale but also the solvents used. Fast voltammetric responses by differential pulse voltammetry and fast scan voltammetry exhibited adsorption behavior. In contrast, quasi steady-state voltammetry showed the diffusion-control, the current of which seemed to evaluate the saturated concentration accurately. However, the currents in the solution including a small amount of organic solvent were smaller than those in the aqueous solution although the concentrations were identical. Solutions including organic solvents have often been used to obtain calibration curves. Therefore, the concentration evaluated from the calibration curve was estimated to be larger than the true concentration. The current in the organic solvent was explained in terms of the extra solvation energy by supersaturation, which was dissipated to low concentrated domains by diffusion. It was formulated in the form of diffusion coefficients. The true concentration was evaluated to be 0.01 mmol/dm3 by slow scan voltammetry in the solution without calibration curves.
  • Salt-free electrolysis of water facilitated by hydrogen gas in thin layer cell
    C.Li, K.J.Aoki, J.Chen, T.Nishiumi
    Reports in Electrochem., 3 7-15 Jul.  2013 Refereed
    Electrolysis of water without salt in a thin layer cell requires a voltage of more than 1.3 V. This voltage is found to be reduced to 0.4 V when hydrogen gas is dissolved in electrolyzed water. The decrease in the overvoltage can be used for the salt-free electrolysis of pure water. Thin layer electrolysis under steady state is often caused by redox cycling. The redox cycling model relevant to the reaction between H2 and H+ is theoretically analyzed here in a two-electrode cell. The validity and limitation are discussed on the basis of the experimental voltammograms of a solution containing H2 and H+. When a solution contains H2 without deliberately adding H+, hydrogen gas would not be expected at the cathode due to the small amount of H+. Consequently redox cycling might be blocked. However, experimental voltammograms, without the addition of H+, exhibited the steady state limiting current by redox cycling. The current was regarded as dissociation kinetics of water. The redox cycling in this case was theoretically analyzed to partially explain the experimental results. The oxidation of hydrogen gas at the anode facilitates the dissociation kinetics to produce redox cycling.
  • Slow scan voltammetry for diffusion-controlled currents in sodium alginate solutions
    B.Wang, K.J.Aoki, J.Chen, T.Nishiumi,
    J. Electroanal. Chem., 700 60-64 Apr.  2013 Refereed
    Slow scan voltammetry is useful for extracting Faradaic diffusion-controlled current from capacitive one, because the former and the latter are, respectively, proportional to the square-root of scan rate and the scan rate itself. This report shows clear, reproducible voltammograms of 0.5 μM redox species with the help of sodium alginate (SA) at scan rates less than 0.1 mV s−1. SA enhances viscosity of solution without any influence on diffusion coefficient of the redox species so that natural convention is suppressed during the slow scan. Therefore, it allowed us to obtain ideal voltammograms reproducibly at slow scans, retaining the Faradaic current. Especially, a wire electrode is demonstrated to be a powerful tool for detecting low concentrations by slow scan voltammetry because of the large electrode area in comparison with the length of the boundary between the electrode and the insulator. A voltammetric detection limit is obtained in the relationship between the scan rates and concentration of redox species.
  • Self-Dispersion of Mercury Droplets from Saturated Calomel Electrodes into Solutions
    J.Chen, K.Iwama, K.J.Aoki, T.Nishiumi
    Int. J. Electrochem. Sci., 8 7394-7400 May  2013 Refereed
    When mercury metal comes in quiescent contact with aqueous solution, it disperses spontaneously into the solution in micro-droplets form (J. Electroanal. Chem. 682 (2012) 66). The self-dispersion may occur from a saturated calomel electrode (SCE). This report deals with quantitative determination of mercury droplets dispersed in the solution to which the SCE was immersed quiescently for a day. The detection technique was anodic striping voltammetry at a gold electrode on which amalgam was formed spontaneously. The stripping anodic current was proportional to the periods of immersing the electrode into the solution. Calibration was made in the suspension of known concentration of mercury droplets. The concentration of self-dispersed mercury was 7 mg dm-3 or 0.036 mmol dm-3, which was by four orders of magnitude larger than the acceptable concentration limit in rivers.
  • Voltammetry in low concentration of electrolyte supported by ionic latex suspensions
    K.J.Aoki, X.Zhao, J.Chen, T.Nishiumi
    J. Electroanal. Chem., 697 5-9 May  2013 Refereed
    Since ionic conductivity has a linear relation with the square of the number of charge, ionic latex particles with a huge number of the charge could provide high conductance. It is expected that addition of only a small amount of latex particles into voltammetric solution enhances the conductance so much that voltammograms can be measured, overcoming ohmic drop. Conductivity of latex suspensions of polystyrene–polystyrenesulfonic acid with volume fractions less than 0.02, which were well deionized by centrifugation, was determined by ac-impedance at two parallel wire electrodes. Since the resistance was determined by the dependence of the in-phase component on the electrode distance, it did not include participation of electric double layers or adsorption of latex. The relationship between conductivity and a diffusion coefficient stated that the conductivity of the suspension was provided mainly by diffusion of latex particles with multiple charges rather than that of the counterion. The suspension with [H+] = 10−5 M, corresponding to 8.9 × 105 number mm−3, including hydrogen gas showed a voltammetric oxidation peak of hydrogen, whereas hydrochloric acid with [HCl] = 10−5 M showed a resistive current–potential curve.
  • Electrolysis of pure water in a thin layer cell
    K.J.Aoki, C.Li, T.Nishiumi, J.Chen
    J. Electroanal. Chem., 695 24-29 Apr.  2013 Refereed
    Current–voltage curves were obtained at parallel platinum electrodes in the thin layer cell including pure water. They were under the steady state in the voltage domain from 1.0 V to 1.3 V when the distance of the electrodes was less than 100 μm. The solution resistance obtained from the current–voltage curve was much smaller than that predicted from the resistivity of pure water. The reason can be explained in terms of generation and accumulation of hydrogen ion and hydroxide ion before the recombination reaction. These kinetically survived ions decrease the resistance, and enhance the electrolysis rate. We subtract the reaction-controlled current–voltage curves from the overall curves to evaluate ion-included solution resistance. The resistivity of the solution averaged in the cell increased with an increase in the distance between the electrodes. In order to understand the above behavior, we calculated concentration profiles of the ions and potential distribution in the cell on the basis of Nernst–Planck equation including dissociation kinetics of water.
  • Resistance associated with measurements of capacitance in electric double layers
    K.J.Aoki, Y.Hou, J.Chen, T.Nishiumi
    J. Electroanal. Chem., 689 124-129 Jan.  2013 Refereed
    The behavior of electric double layers at polarized interfaces in KCl solutions is revisited in order to examine properties of the constant phase element (CPE). We pay attention specifically to frequency-dependence of both the capacitance and the resistance. Two parallel platinum wires immersed in solution are used as insulator-free electrodes. They avoid stray capacitance or irreproducibility of impedance caused by incompleteness of electric shield of electrodes. The Nyquist plot takes approximately a straight line because the in-phase component, Z1 is inversely proportional to ac-frequency, similar to the capacitance. Since Z1 extrapolated to zero separation of the electrodes is non-zero, a resistance is present at the double layer in parallel form. It is not a Faradaic resistance because of absence of any electroactive species. The parallel resistance is inversely proportional to the frequency, whereas the capacitance decreases with a linear relation to logarithm of the frequency. The latter is responsible for the frequency-dependence of the former. The parallel resistance is the apparent one involved inevitably in ac-measurements of the capacitance. Values of the capacitance are independent of concentration of KCl in the domain from 0.1 mM to 3 M.
  • Diffusion coef?cients in viscous sodium alginate solutions
    K.Aoki, B.Wang, J.Chen, T.Nishiumi
    Electrochim. Acta., 83 348-353 Nov.  2012 Refereed
    Sodium alginate solution, being viscous hydrocolloid, was examined voltammetrically in the context of viscous effects by use of a ferrocenyl compound as a redox probe. Voltammograms were almost independent of concentrations of sodium alginate even in a solid-like state. Diffusion coefficients of the ferrocenyl compound did not vary with viscosity evaluated by a viscometer. Ionic conductivity of sodium alginate was also independent of the viscosity. In contrast, diffusion coefficients of the latex particle 0.84 μm in diameter decreased with an increase in the viscosity. The intrinsic viscosity was evaluated. The value is equivalent to the volume as large as 3 m3 of water in which one mole of the unit of sodium alginate polymer generates the viscosity. Consequently, redox species diffuse through water portions circumventing the alginate network. As an application, sodium alginate solutions were used for long-time chronoamperometry. The current was decayed with the time even of 1500 s without any effect of natural convection, whereas that in the aqueous solution was irreproducible for times longer than 20 s. The other application was electroplating of silver. The silver surface deposited in sodium alginate had no morphology by the SEM image, while the surface plated without sodium alginate showed morphology even on an optical microscopy scale.
  • Comparison of diameters of disk microelectrodes obtained from microscopes with those evaluated from steady-state currents
    K.Aoki, C.Ouyang, C.Zhang, J.Chen, T.Nishiumi,
    Int. J. Electrochem. Sci., 7 5880-5892 Jul.  2012 Refereed
    Diameters of disk microelectrodes evaluated from steady-state diffusion-controlled currents by use of Saito's equation were smaller than geometrical diameters obtained from a scanning electron microscope (SEM) when the diameters were less than 4 um. The smallest electrode that could be compared had the diameters 0.007 um by the current and 0.11 um by the SEM. With a decrease in the electrode, the observed currents were smaller than those predicted from Saito's equation. As a reason of the blocking of diffusion, memory diffusion was taken into account. It includes a delay or a displacement of the diffusion flux in the Fick's first law. The equation for memory diffusion was solved for the hemispherical and the disk electrode to give expressions for the steady-state currents. The experimental results allowed us to determine the displacement, 0.9 um, as a blocking parameter.
  • Self-dispersion of mercury metal into aqueous solutions
    K.Aoki, C.Li, T.Nishiumi, J.Chen
    J. Electroanal. Chem., 682 66-71 Aug.  2012 Refereed
    Mercury metal dispersed spontaneously into the aqueous solution as micro-droplets when it came in quiescent contact with the solution. The self-dispersion was observed by means of the dynamic light scattering method, thermogravimetry and voltammetry. The mercury microdroplets generated in water had ca. 0.3 μm in diameter. The diameter and the concentration of the droplets were stable. The concentration of mercury might be 1–3 μmol dm−3 if the droplets were to be dissolved homogeneously in water. The concentration exceeds the environmental limits by three orders of magnitude. The dispersed mercury was confirmed not to be ions or oxide of mercury but to be metal droplets. The self-dispersion of mercury belongs to the self-emulsification at liquid|liquid interfaces without surfactants.
  • Is hydrogen gas in water present as bubbles or hydrated form?
    K.Aoki, H.Toda, J.Yamamoto, J.Chen, T.Nishiumi,
    J. Electroanal. Chem., 668 83-89 Mar.  2012 Refereed
    When hydrogen gas is bubbled into water, it may well be present as stabilized bubbles rather than hydrated hydrogen molecules, as in the spontaneous emulsification at oil|water interfaces without surfactant. On this prediction, we used dynamic light scattering (DLS) to find bubbles 0.4–0.5 μm in diameter, which were stable for more than 9 h. The intensity of the scattering light, which was proved to be proportional to concentrations of polystyrene latex suspensions, was also kept in solution in contact with hydrogen gas atmosphere. The bubbles were stable even at 50 g (gravity) by centrifugation. Voltammograms of the bubble-included solution had the oxidation peak, of which current was proportional to the intensity of DLS. Concentration of hydrogen in solution was evaluated accurately by comparing voltammetric currents at a regular electrode and a small electrode. The oxidation of hydrogen should be caused by the hydrated hydrogen which was supplied by dissolution of bubbles. Kinetic data of the dissolution were obtained at microelectrodes by using the advantage of extracting kinetics from diffusion currents. Voltammetric currents at microelectrodes were smaller by 10 times than those predicted from diffusion of hydrated hydrogen. Therefore, the oxidation is controlled by the dissolution rate at the high current density. The rate was estimated to be 2 × 10−8 mol s−1 cm−2, which was converted to the linear transfer rate, 0.4 mm s−1, at gas|water interface.
  • Functionality of reduced graphene oxide flakes at the growth of conducting zone in polyaniline-graphene composite films
    Zeng, Xiangdong;Aoki, Koichi Jeremiah;Chen, Jingyuan
    ELECTROCHIMICA ACTA 228 125-130 Feb.  2017
  • Effects of the dipolar double layer on elemental electrode processes at micro- and macro-interfaces.
    Aoki Koichi Jeremiah;Chen Jingyuan
    Faraday discussions 2018
    :Determination of heterogeneous rate constants of redox reactions or charge transfer resistances always involves ambiguities due to their participation in double layer (DL) capacitances and solution resistances. The rate constants determined by steady-state voltammograms at ultra-microelectrodes are inconsistent with time-dependent voltammograms, implying participation of the DL impedance. We examine controlling factors of DLs through the frequency-dependence of the capacitance on the basis of the definition of the current and the capacitance. The capacitance obeys the power law of the frequency. It is controlled by the orientation of a limited amount of solvent dipoles, independent of salts. Redox species, dipoles of which are oriented oppositely to the solvent dipoles, decrease the DL capacitance and make the value negative at high concentrations of the species. The decrease in the capacitance increases the real impedance, as predicted from the phase angle, yielding an extra resistance. This may be a ghost charge transfer resistance. However, there are actually a number of well-defined charge transfer resistances, which are observed as transferring rates through films on electrodes.

Books etc

  • Voltammetry
    Koichi Jeremiah Aoki and Jingyuan Chen
    IntechOpen Nov.  2018
    DOI: http://dx.doi.org/10.5772/intechopen.81341
    Theories of cyclic voltammetry, ac-impedance techniques and the double layer capacitive currents are described concisely to touch their principles. Applications of the theory to experimental data do not always lead to reasonable interpretation consistent with by other techniques. Several tips are presented not only in the experimental viewpoint but also in a perspective of the data analysis. Most of them are devoted to cyclic voltammetry. They include shape of voltammograms, peak currents and peak potentials, diffusion- and adsorption-controls, the number of electrons, reference and counter electrodes, usage of ac-impedance, heterogeneous charge transfer rates, and combination with data by scanning probe microscope. They belong partially to recommendation and partially prohibition.

Conference Activities & Talks

  • Electrochemical reactions of the composite films consisting of a suspension of the polyaniline coating graphene
    Jingyuan Chen
    The Electrochemical Society of Japan Sep.  2017 The Electrochemical Society of Japan
  • 参照極の無い無塩ボルタンメトリーの展開
    The Polarographic Society of Japan Nov.  2016 The Polarographic Society of Japan
  • イオン性高分子ラテックス懸濁液における電気二重層静電容量の測定
     Nov.  2015 The Polarographic Society of Japan
  • Electrochemical characteristics of conducting composite films that made from suspensions of polyaniline-coated graphene
    Jingyuan Chen
    The 16th International Symposium on Electroanalytical Chemistry Aug.  2017 International Symposium on Electroanalytical Chemistry
    Supercapacitor, made of conducting polymer, polyaniline (PANI) and reduced graphene oxide particles (RGO) composite, which can provide huge charge density, may be one of the most successful applications.1,2 In order to know reasons of the specific features, it is necessary to examine electrochemical mechanisms quantitatively in the composites. Here, we are concerned with finding these mechanisms by use of PANI-RGO suspension3, of which particle-particle interaction can be controlled in the preparation. Flaky particles of PANI-RGO with rectangular size of 1.0-1.5 m are dispersed in aqueous solution. The PANI- RGO film made of the suspension forms a self-standing, elastic, conductive film. The film exhibited faster redox conversion than the PANI film did. A reason of the enhancement of the conversion rate was searched by examining the growth rates of the conducting zone when the reduced composite was oxidized electrochemically from one end film, as shown in Fig.1. The length, x, of the growing conducting zone, was plotted against the time, t, of applying the oxidation potential, as shown in Fig. 2. The morphology of the cross section (Fig. 1) indicates that the reaction occurs at rough surface area rather than the projected area. An increase in  (= wRGO / (wRGO + wPANI)) necessarily increases the net surface area to enhance j0. We estimate the surface roughness quantitatively. The growth rate was modeled with the oxidation at the Tafel-typed rate, which was restrained by the IR-drop between the conducting front and the electrode. The growth length was expressed by a time-dependent non-linear differential equation. The numerical solution allowed us to analyze the experimental data of the time variation of the growth length. RGO functions as an increase in the rough surface area of the oxidation rather than electric percolation, enhancement of conductivity and catalytic effects.
  • Dependence of double layer on Warburg impedance
    Jingyuan Chen
    Faraday Discussion Sep.  2016 RSC
    This basic work was inspired by the frequency-dependence of the double layer (DL) capacitance, which is caused by the long-range interaction of solvent molecules [ ]. The relevance of the electrode reactions to the DL structure has been discussed in the context of acceleration or deceleration of heterogeneous rate constants of the charge transfer reactions [ ], called the Frumkin correction [ ]. Since heterogeneous kinetics can be observed as the second effect of mass transport, it is reasonable to discuss the effect of the DL capacitance on diffusion rather than the heterogeneous kinetics. A simple redox reaction is often controlled by both a charge transfer step and a diffusional step. The former is complicated directly with the DL impedance because of involvement of a surface process, whereas the latter may be distinguished from the DL effect in that it occurs in solution phase. We should at the first stage examine the latter, i.e. the effects of the Warburg impedance on the double layer impedance. If both impedances are independent each other, they can be represented as a parallel equivalent circuit. A real part of the Warburg impedance for infinite diffusion has the same value as that of the imaginary one, according to the solution of the diffusion equation [ , ], although complications occur at several geometries with combinations of reactions [ ]. As a result, values of the observed real admittance subtracted from the imaginary one should agree with those of the DL impedance without involving redox species. This is a point to examine a detailed relation between the Warburg impedance and the DL impedance here. We use here (ferrocenylmethyl) trimethylammonium (FcTMA) as a redox species without any effect of heterogeneous rates. Observed ac-currents necessarily include harmonic components on the assumption of a small value of the amplitude of the applied ac-voltage. The relation between the harmonics and the amplitude will be discussed here. Since a disk-exposed working electrode often yields such floating capacitance that the DL impedance may not be separated from the Warburg impedance, we use a platinum wire electrode without shielding. Dc-voltage and concentrations of FcTMA are varied in order not only to confirm the Warburg impedance but also to examine participation of adsorption of FcTMA. Results are different from the preconceived ideas. According to the conceptual diffusion-controlled impedance, the values of the real impedance are smaller than those of the negative imaginary ones owing to the double layer impedance. However, the opposite behaviour is found in the Nyquist plot at which the experimental data fell on the domain of |-Z2| < |Z1| in the dc-potential domain for the redox reaction. It can be explained in terms of either extreme enhancement of the DL resistance in the redox potential or generation of inductance at the DL layer caused by the redox reaction. The latter being possible will be discussed on this poster. Key words: generation of inductance; interplay of faradaic reaction and double layer capacitance; redox reaction of ferrocenyl derivative; ac impedance with frequency-dependence
  • Salt-free Electrolysis
    Jingyuan Chen
    Asia-Pacific Conference on Energy Storage and Conversion 2016 Sep.  2016 Asia-Pacific Conference on Energy Storage and Conversion
    Behavior of Faradaic currents at low concentration of electrolyte is a classical subject - . It has revived since currents at pico-ampere order microelectrodes have provided negligible amount of IR-drop of solution resistance without deliberately adding supporting electrolyte . The subject of the electrolyte-free can result conceptually not only in the IR-drop by solution resistance but also in the mass transport problem complicated by the electric field . The former is relevant to the potential distribution in a cell which varies mainly with geometry of a cell and electrodes, specifically with a distance between a working electrode and a counter electrode. This talk reports applications of two characteristics of salt-free electrolysis; one being (1) extremely high current density of nanoelectrodes and the other being (2) the kinetic mass transport problem of water electrolysis in a thin layer cell. (1) Single disk electrodes were fabricated by the previous method of which diameters range from 1 nm to 500 nm. When redox reactions occur by diffusion-control, the diffusion flux converges to a nanometer area of the electrode. Then the current density becomes extremely high. For example, electrodes 100 nm and 1 nm in diameter generate such high current density that a conventional electrode can produce at scan rates of 20 kV s-1 and 200 MV s-1 for cyclic voltammetry (CV), respectively. Very small currents at nanoelectrodes allows us to obtain voltammograms of neutral redox species without salt. Although voltammograms of tetracyanoquinodimethane (TCNQ) in the presence of salt show two waves for successive two-electron reduction, non-salt solution shows only the first reduction wave. This behavior is valid also for benzoquinone. Stability of di-anions requires high concentration of mono-valent salt. (2) Pure water was electrolyzed at parallel platinum electrodes with the distance was less than 100μm, of which structure is illustrated in Fig. . The solution resistance obtained from the current-voltage curve was much smaller than that predicted from the resistivity of pure water. The reason can be explained in terms of generation and accumulation of hydrogen ion and hydroxide ion before the recombination reaction. The resistivity of the solution averaged in the cell increased with an increase in the distance between the electrodes. In order to understand the above behavior, we calculated concentration profiles of the ions and potential distribution in the cell on the basis of the Nernst-Planck equation including dissociation kinetics of water. This behavior is valid also for hydrogen gas in water.
  • Conditions of salt-free electrolysis at a single nano-electrode
    Jingyuan Chen
    EMN (Energy materials nanotechnology) Hawaii Meeting Mar.  2016 EMN (Energy materials nanotechnology) Hawaii Meeting
    Behavior of Faradaic currents at low concentration of electrolyte is a classical subject - . It has revived since currents at pico-ampere order microelectrodes have provided negligible amount of IR-drop of solution resistance without deliberately adding supporting electrolyte . The subject of the electrolyte-free can result conceptually not only in the IR-drop by solution resistance but also in the mass transport problem complicated by the electric field . The former is relevant to the potential distribution in a cell which varies mainly with geometry of a cell and electrodes, specifically with a distance between a working electrode and a counter electrode. This talk reports applications of two characteristics of salt-free electrolysis; one being (1) extremely high current density of nanoelectrodes and the other being (2) the kinetic mass transport problem of water electrolysis in a thin layer cell. (1) Single disk electrodes were fabricated by the previous method of which diameters range from 1 nm to 500 nm. When redox reactions occur by diffusion-control, the diffusion flux converges to a nanometer area of the electrode. Then the current density becomes extremely high. For example, electrodes 100 nm and 1 nm in diameter generate such high current density that a conventional electrode can produce at scan rates of 20 kV s-1 and 200 MV s-1 for cyclic voltammetry (CV), respectively. Very small currents at nanoelectrodes allows us to obtain voltammograms of neutral redox species without salt. Although voltammograms of tetracyanoquinodimethane (TCNQ) in the presence of salt show two waves for successive two-electron reduction, non-salt solution shows only the first reduction wave. This behavior is valid also for benzoquinone. Stability of di-anions requires high concentration of mono-valent salt. (2) Pure water was electrolyzed at parallel platinum electrodes with the distance was less than 100μm, of which structure is illustrated in Fig.1 . The solution resistance obtained from the current-voltage curve was much smaller than that predicted from the resistivity of pure water. The reason can be explained in terms of generation and accumulation of hydrogen ion and hydroxide ion before the recombination reaction. The resistivity of the solution averaged in the cell increased with an increase in the distance between the electrodes. In order to understand the above behavior, we calculated concentration profiles of the ions and potential distribution in the cell on the basis of the Nernst-Planck equation including dissociation kinetics of water. This behavior is valid also for hydrogen gas in water.
  • Voltammetry at a single nanoelectrodes
    Jingyuan Chen
    Pacifichem 2015 Dec.  2015 Pacifichem 2015
    An ultramicroelectrode is a tool for probing into the identity of nano-material. An advantage of the voltammetric behavior at a microelectrode is to exhibit a steady-state current-voltage curve [ - ]. It is due to the existence of a mathematical solution for the 3D-diffusional Laplace equation [ ]. Since microelectrode exhibits high current density because diffusion flux of electroactive species converges to the electrode [ ], Steady-state currents of non-charged species can be obtained without addition of supporting electrolyte in the solution. There should be the other rate-determining step irrelevant to heterogeneous current density distributions. This lecture focus on (1) fabrication of single nanoelectrodes by combining the six steps, (2) electrode kinetics effect at the steady-state voltammograms, (3) measurement of ultrafast electrode kinetics, (4) variables controlling the capacitances, (5) undervalued radii of microelectrodes from steady-state currents, (6) the absolute and accurate determination of concentrations and the diffusion coefficients of redox species at two kinds of electrodes. Furthermore, limiting currents have no effect on electrode kinetics. There should be the other rate-determining step irrelevant to heterogeneous current density distributions.
  • Current-voltage curves at various diameters of single nanoelectrodes
    jingyuan chen
    7th International workshop on surface modification for chemical and biochemical sensing Nov.  2015
    This talk reports two characteristics of a single nanoelectrode, (1) extremely high current density and (2) very small current. Both are discussed when current-voltage curves are obtained at various electrode diameters. Both are discussed when current-voltage curves are obtained at various electrode diameters. Our concern is single disk electrodes of which diameters range from 1 nm to 500 nm. (1) The average current density by diffusion control at a microdisk electrode is inversely proportional to the diameter of the electrode. Consequently it increases tremendously with a decrease in the diameter. For example, electrodes 100 nm and 1 nm in diameter generate such high current density that a conventional electrode can produce at scan rates of 20 kV s-1 and 200 MV s-1 for cyclic voltammetry (CV), respectively. This comparison inspires us to determine fast heterogeneous reaction rate constants under the steady-state conditions. A question is that a common rate constant can be obtained both by steady-state voltammetry at namoelectrodes and by fast cyclic voltammetry at conventional electrodes. We predicted potential shifts of six kinds of redox species with a decrease in the electrode diameter. However, no shift of the current-voltage curves is observed even at 1 nm electrode. Potential shift by CV can be attributed to partially solution resistance and partially dynamic effects of the double layer capacitance. (2) Very small currents at nanoelectrodes allows us to obtain voltammograms of neutral redox species without deliberate addition of salt. When electrodes less than 0.3 m in diameter are used, sigmoidal current-voltage curves of TCNA in acetonitrile without salt can be obtain. Although voltammograms of TCNQ in the presence of salt show two waves for successive two-electron reduction, non-salt solution shows only the first reduction wave. This behavior is valid also for benzoquinone. Dianions may make complexes with mono-valent cations
  • Catalytic reduction of O2 by ferrous hemin over formation of ferrous hemin -O2 adduct
    Jingyuan Chen
    66th Annual Meeting of International Society of Electrochemistry Oct.  2015 International Society of Electrochemistry
    Hemin, an iron porphyrin, functions as a carriage of dioxygen in mammalian respiration in the ferrous form. It works also as an electrochemical catalyst of the reduction of dioxygen by reproducing the ferrous form from the ferric one. Since the carriage requires stabilization of the dioxygen adduct, the catalytic reduction of dioxygen with the ferric form might hinder the stabilization. This work aims at finding the discrimination between the functions of the carriage and of the catalysis. A hint of the finding lies in the difference between the remarkable catalytic currents in high concentrations of hemin and negligibly small ones in very low concentrations. The catalytic current (Fig.1 (b)) at the hemin-coated electrode is confirmed to occur at the stoichiometry of two hemin molecules and one dioxygen molecule. When this stoichiometry is applied to the dioxygen adduct of hemin as an intermediate species of the catalysis, high concentrations of dissolved hemin should provide the catalytic current. Spectro-electrochemistry (Fig.2) demonstrates that ferrous hemin is not oxidized simply to the ferric form but is converted to other species, e.g. the dioxygen adduct.
  • Focus-Tunable Convex Lenses by Oil-Sessile Drop
    Jingyuan Chen
    Electrochem 2015 Sep.  2015 イギリス化学会
    Electrowetting is a phenomenon of varying a contact angle of a sessile drop on an electrode with electrode voltage [ ]. Since it can control the size of drops reversibly [ ], it has been applied [ ] to transport of microfluidics, lab-on-chip made of droplets, adjustable lenses, electronic displays, fast responding electronic paper, and fast micro-switches. Electrodes in these applications are coated with dielectric films in order to avoid electrolysis of liquid [ ], because voltages required for variation of interfacial tension are as high as 100 V [1]. The principle of electrowetting is based on variations of surface tension at liquid|electrode interface with electrode voltage. It has been called electrocapillarity, found by Lippmann [ ]. Electrowetting has also been found when faradaic reactions occur, as is exemplified by polarographic maximum currents [ ]. Its interpretation involves complications relevant to redox reactions [ ] rather than the Lippmann's concept. Examples are reactions at droplets with liquid|liquid interfaces [ , ] and at three-phase boundaries [ - ]. The voltage-dependence of the size means that the curvature radius of the sessile drop can be controlled with the voltage. This report is devoted to demonstration of the adjustable lenses by the redox reaction-control. A sessile drop of oil (Nitrobenzene, Ethylene carbonate, etc.) mounted on the transparent electrode immersed in the aqueous solution works as an optical lens of which focus can be controlled by electrode potential when the solution includes K3Fe(CN)6 and tetrapentylammonium (TPA+) chloride. K3Fe(CN)6 functions as a redox species, whereas TPACl does as supporting electrolyte as well as a surfactant. The focal length decreases in the reduction potential domain. The switching between the long and the short focuses is almost reversible for 1 h by the potential control, synchronized with voltammograms. The size of a real image of an object varies with the potential.
  • Demonstration of electric double layer capacitance in deionized latex suspensions by ac-impedance
    Jingyuan Chen
    15th International Symposium on Electroanalytical Chemistry Aug.  2015 15th International Symposium on Electroanalytical Chemistry
    Electric double layer capacitance at platinum electrodes is controlled by oriented length of dipole solvent molecules on the electrode rather than that by ionic distribution, being different from at mercury electrodes. The controlling step is found by comparing capacitance vs. electrode potential curves in ionic solutions with those in deionized latex suspensions. The curves do not involve a valley shape of Gouy-Chapman (GC)'s type until ionic concentrations are less than 0.05 mM, because the measured capacitance is controlled by the inner layer. The valley shape at the low concentrations can be measured in deionized sulfonic latex suspensions, whose conductance is brought about by the ionic latex particles rather than the dissociated hydrogen ion. The expression for the capacitance by the ionic latex suspension is derived, which is demonstrated to be the same form of the potential dependence as for mono-valence ions. The ac-impedance data are obtained at parallel polycrystalline platinum wires without insulating shield. The valley shape is found, which is analyzed by the inverse plot of the capacitance against the hyperbolic cosine of the dimensionless applied potential. The linearity of the plots seems to support the GC-theory, but the capacitance values are much larger than those calculated from the GC-theory. The extra amount can be attributed quantitatively to the orientation of solvent molecules by combining Debye's theory with the GC-theory.
  • Fast electron-transfer kinetics at single nano disk electrodes
    Jingyuan Chen
    65th Annual Meeting of International Society of Electrochemistry Aug.  2014 International Society of Electrochemistry
    The kinetic data at ultra microelectrodes (UME) should be consistent with those by fast scan voltammetry. The relation of the radius a, at UME with the scan rate v, at a large electrode is given by v = 8.15RTD/Fa2. The values of reported data are changed in the context of diffusion layer thickness. For example, a = 1 nm corresponds to v = 210 MV/s at a large electrode. As a result, single nano electrode allows us to determine fast kinetic constants by changing electrode diameter, which is often too fast to be obtained with conventional electrodes. However, it is dangerous to consider simply v = 8.15RTD/Fa2 from the diffusion process, because the heterogeneous reaction occurs at electrode surfaces rather than in the diffusion layer. This question will be discussed by determination of rate constants of fast electron transfer reactions of hexachloroiridium, hexamine ruthenium, aminoferrocene, tetracyanoquinodimethan, benzoquinone, ferrocenecarboxylic acid and ferrocene. This work is motivated by the experimental feasibility of high current density at ultra microelectrodes without effects of capacitive currents or solution resistance. A number of nanoscale platinum electrodes which was sealed with a glass are stable (Fig.1). Half wave potential was refereed by a non-charged species which be used as reference potential (Fig.3). The potential can be accurately controlled even in high resistive solutions owing to eliminating ohmic effects. Mass-transport mechanisms can be analyzed from the ratio between the steady-state current of sample and that of the reference species. No potential shift is observed even at electrodes 10 nm in diameter for the six species (Fig.2). This fact implies that the heterogeneous rate constants are at least larger than 10 cm/s. Fast scan voltammetry is carried out at a large electrode for scan rates less than 10 V/s. The inconsistency between the two methods is ascribed partly to solution resistance and partly to the resistance relevant to the electric double layer at fast scan voltammetry. The contribution of the solution resistance is demonstrated from the facts that the peak currents vary linearly with the peak potentials, that the slope of the linearity is independent of kinds of redox species (Fig.3).
  • Is the dianion formed in the absence of salt?
    Jingyuan Chen
    10th ECHEMS Meeting, Jun.  2014 ECHEMS Scientific Committee
    This talk is an applications of the nano-electrodes in molecular electrochemical analysis. When diameters of electrodes are less than 400 nm, steady-state currents of non-charged species can be obtained without addition of salt in dry acetonitrile. Determined moleculars are 1,4-benzoquinone (BQ) and tetracyanoquinodimethane (TCNQ). They cannot be reduced up to the dianions without supporting electrolyte in acetonitrile solution. Effects of the IR-drop and the electrostatic force in low concentrations of supporting electrolyte are examined by use of the first reduction waves. Voltammograms without supporting electrolyte at nanoelectrodes do not include noticeably IR-drop. The large overpotential for the anions cannot be explained in terms of the electric migration which has been estimated from solutions of the Nernst-Planck equation and the Laplace equation. With an increase in the conductivity of the solution by addition of electrolyte, the second reduction wave appears, involving the potential shift. The electrolyte does not influence the first reduction waves but varies the second one. The salt effect specific to the second wave is ascribed to non-stoichiometric association of the redox anion with the salt cation.
  • Comparison of heterogeneous reaction rate constants by steady-state microelectrode techniques with those by fast scan voltammetry
    Jingyuan chen
    2014 Pittsburgh Conference Mar.  2014 The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Inc.
    The steady-state current at microelectrode a in radius is expressed by IL = 4Fc*Da. The average current density is jL = (4/)Fc*D/a. On the other hand, the voltammetric current density at a large electrode is enhanced with an increase in scan rates v. When the expression for the current density at the microelectrode is set equal to the equation for the peak current density by linear sweep voltammetry jp = 0.446Fc*(DvF/RT)1/2, the relation between the scan rate and the radius is expressed by v = 8.15RTD/Fa2. Typical values of v for a = 1 nm are 210 MV/s. Therefore the steady-state voltammetry at microelectrodes allows us to obtain such fast electron transfer kinetic data as not to be realized by the conventional fast scan voltammetry. However, it is dangerous to consider simply v = 8.15RTD/Fa2 from the diffusion process, because the heterogeneous reaction occurs at electrode surfaces rather than in the diffusion layer. This question will be discussed by determination of rate constants of fast electron transfer reactions of hexachloroiridium, hexaammine ruthenium, aminoferrocene, tetracyanoquinodimethan, ferrocenecarboxylic acid and ferrocene. This work is motivated by the experimental feasibility of high current density at ultramicroelectrodes without effects of capacitive currents or solution resistance. No potential shift is observed even at electrodes 0.01 m in diameter for the six species. This fact implies that the heterogeneous rate constants are at least larger than 10 cm/s. Fast scan voltammetry is carried out at a large electrode for scan rates less than 10 V/s. The inconsistency between the two methods is ascribed partly to solution resistance and partly to the resistance relevant to the electric double layer at fast scan voltammetry. The contribution of the solution resistance is demonstrated from the facts that the peak currents vary linearly with the peak potentials, that the slope of the linearity is independent of kinds of redox species.
  • Electrode reaction of bubbles, droplets and particles
    J.Chen, K.Aoki, Xiaoyu Zhao, Jie Yu
    64th Annual Meeting of International Society of Electrochemistry Sep.  2013 International Society of Electrochemistry
    Our concern is whether colloidal suspensions including redox species can take place electrode reactions in the same way as dispersed redox molecules. Redox colloidal suspensions are exemplified as metal particles, red blood cells, dispersed hydrogen gas, emulsified redox species, and redox latex suspensions. Possible steps different from molecules are (i) non-elastic collision with an electrode, (ii) limitation of reacting domain of colliding colloidal particle to the double layer, (iii) strong interaction among redox species in a particle, (iv) non-uniform distribution of potential within a particle, (v) satisfaction of electric neutrality condition, (vi) small diffusion coefficients, (vii) the number of electrons transferred per particle. There is no ideal colloidal particle that overcomes simultaneously these complications. Individual events of reactions, detected by isolated nano-electrodes, may bring out an image of a dynamic reacting path of the particle. J. Osteryoung showed that steady-state voltammetric reduction current of hydrogen ion in latex suspension decreased at lower concentration of supporting electrolyte. F. Marken reported enhancement of redox activity by emulsification at the three-phase junction of the oil|water|electrode. Behavior in latex suspensions and emulsions, belonging to colloids, has also been found in solution including nano-bubbles, nano-particles and droplets. The theory, the data analysis and applications have been developed by K. Aoki, and H. Girault. We report here some experimental results of hydrogen bubbles, redox latex particles, metal droplets , oil and aqueous droplets. Our latex particles used are polyaniline-coated polystyrene, ferrocene-immobilized polystyrene, polystyrene-sulfonic acid, hemine-immobilized polystyrene, polyacrylic latex, and tyrosinase-immobilized polystyrene. This work reports stable dispersions of both microbubbles of hydrogen in water and microdroplets of mercury in water. Some common behaviors were shown from voltammetric data, pointed out their electrode reactions was the same way as dispersed redox molecules.
  • Electrochemical quantitative analysis of colloidal suspensions of droplets/bubbles/particles
    J.Chen, K.Aoki
    14th International Symposium on Electroanalytical Chemistry Aug.  1913
  • Salt-Free Electrolysis of Water In a Thin Layer Cell
    C.Li, J.Chen, K.Aoki
    14th International Symposium on Electroanalytical Chemistry Aug.  2013
    Pure water containing no exogenous ions is an excellent insulator, but not even “deionized” water is completely free of ions. The concentration of hydroxide anion and hydrogen cation is 10-7mol/L, dispersed in water. When applied potential, the electrode surface in liquid may be charged by dissociation of H2O from the surrounding solution. In equilibrium, the surface charge is balanced by oppositely charged counterions in solution. The region near the surface enhanced counterion concentration. It is known that the theoretical electrical resistivity for pure water is approximately 18.2 MΩ·cm at 25℃, for this reason pure water can be electrolyzed into oxygen and hydrogen gases but this is a very slow process. If the distance between electrodes is very small, the products of electrode reactions diffuse in opposite directions across the cell to the electrodes, where they can react again. This is redox cycling, it can enhance the current, and hence improve the sensitivity and selectivity. The redox cycling can make the current be under steady state in thin layer cell electrolysis. Electrolyzed pure water at parallel platinum electrodes of which distance less than 100μm, the thin layer cell structure is illustrated in Fig.1. The relation between the electrolysis potential and current was obtained through linear sweeping voltammetry (LSV) in 0.1M NaClO4 aqueous solution on the assumption that there was no solution resistance. It obeyed the Tafel equation, which represented the electrode kinetic overpotential. When this kinetic overpotential was eliminated from the current-voltage curve of electrolysis, the potential drop should be caused by solution resistance. The resistivity of pure water was calculated from the potential difference at same current values. It increased with an increase in the distance between the electrodes, as exhibited in Fig.2. The value was however, smaller than the conventional concept of pure water resistivity. This was because generation and accumulation of hydrogen ion and hydroxide ion before the recombination reaction [1]. The conductance of water is provided by the products of H+ and OH- after electrolysis water, of which concentrations are satisfied with c+ + c- > 210-7 M. This fact is contrary to the common knowledge that pure water is hardly electrolyzed. The conductivity enhances with a decrease in the inter-distance. The enhancement is an evidence of the electrochemical formation of H+ and OH- which are far from the equilibrium.
  • Dependence of TCNQ Reduction on Supporting Electrolyte at Glass-coated Platinum Nano-electrodes
    C.Zhang, J.Chen, K.Aoki
    14th International Symposium on Electroanalytical Chemistry Aug.  1913
  • Voltammetry of hydrogen bubbles, latex particles and oil droplets,
    Jingyuan Chen
    9th ECHEMS Meeting Jun.  2013 Institute of Physical Chemistry Polish Academy of Sciences, Poland
    Our concern is whether colloidal suspensions including redox species can take place electrode reactions in the same way as dispersed redox molecules. Redox colloidal suspensions are exemplified as metal particles, red blood cells, dispersed hydrogen gas, emulsified redox species, and redox latex suspensions. Possible steps different from molecules are (i) non-elastic collision with an electrode, (ii) limitation of reacting domain of colliding colloidal particle to the double layer, (iii) strong interaction among redox species in a particle, (iv) non-uniform distribution of potential within a particle, (v) satisfaction of electric neutrality condition, (vi) small diffusion coefficients, (vii) the number of electrons transferred per particle. There is no ideal colloidal particle that overcomes simultaneously these complications. For example, polyaniline-coated latex suspension can solve complications (iv) because the electric conduction of polyaniline provides equi-potential on the particle surface. Individual events of reactions, detected by isolated nano-electrodes, may bring out an image of a dynamic reacting path of the particle. J. Osteryoung showed that steady-state voltammetric reduction current of hydrogen ion in latex suspension decreased at lower concentration of supporting electrolyte. F. Marken reported enhancement of redox activity by emulsification at the three-phase junction of the oil|water|electrode. Behavior in latex suspensions and emulsions, belonging to colloids, has also been found in solution including nano-bubbles, nano-particles and droplets. The theory, the data analysis and applications have been developed by K. Aoki, and H. Girault. We review here some experimental results of hydrogen bubbles, redox latex particles, oil and aqueous droplets, metal droplets, and specific geometry of solid|liquid|liquid three phase junction. Our latex particles used are polyaniline-coated polystyrene, ferrocene-immobilized polystyrene, polystyrene-sulfonic acid, hemine-immobilized polystyrene, polyacrylic latex, and tyrosinase-immobilized polystyrene.
  • 薄層油膜電極におけるエマルションが引 き起こす反応
    陳 競鳶, 青木 幸一, 西海豊彦
    The Polarographic Society of Japan Nov.  1912
  • Variation of reaction layer of three-phase boundaries with self-emulsification
    陳 競鳶, Qiang Wang, 青木 幸一, 西海豊彦
     Mar.  1912
  • ケルビン水滴誘導起電機による電荷分離
    青木 幸一, 松浦(まつうら)崇(たか)志(し), 西海, 陳 競鳶
     Dec.  1911
  • 電気化学法による油水界面に生成したエマルション量の測定
    陳 競鳶, 青木 幸一, 西海 豊彦
     Dec.  1911
  • Voltammetry of the carboxylate functionalized particles-modified electrodes
    J.Chen, K.Aoki, Tianbo Li
    Pittcon 2011 Mar.  1911
  • Determination of concentration and diffusion coefficient by the combination of regular and microelectrodes
    J.Chen, Hua Zhang, K.Aoki, Hirakazu Toda
    Pacifichem2010 Dec.  1910
  • ポリエチレングルコール高粘度溶液における微小電極のボルタンメトリー
    陳 競鳶, 青木 幸一, GuoYi
     Nov.  1910
  • Debate on nano-electrode voltammograms by coating with polymer and glass
    J.Chen, K.Aoki
     Sep.  1910
  • Potential difference between dispersed and adsorbed polyaniline
    青木 幸一, 川口 文彦, 陳 漢, 陳 競鳶, 西海 豊彦
     Mar.  1910
  • Fabrication and electrode reaction of glass-coated electrodes
    張朝富, 張華, 青木 幸一, 陳 競鳶
     Mar.  1910
  • Relation between oxidation current of hydrogen gas and amount of the bubbles in aqueous solution
    Hirokazu Toda, K.Aoki, J.Chen, Toyohiko Nishiumi
    Pacifichem2010 1910
  • ガラス封入ナノ電極の作製法
    青木 幸一, 陳 競鳶, 西海 豊彦, Zhang Chaofu
     Nov.  2009
  • An electrochemically driven air bubble on the O W interface under the three-phase boundary reactions of ferrocene
    J.Chen, Masanori SAatoh, Tomohiro Imamura, Hirokazu Toda, 青木 幸一
    ISA Aug.  2009
  • Electrochemical properties of 1,4-benzoquinone by microelectrode voltammetry
    青木 幸一, Zhang Hua, J.Chen
    ISA Aug.  2009
  • Potential-dependent motion by the charged droplets at the water oil interface
    Li Mengjuan, K.Aoki, J.Chen
    ISE Aug.  2009
  • Electrochemical properties of poly(styrene-acrylic acid) latex particle films
    Tianbau Li, J.Chen, Toyohiko Nishiumi, K.Aoki
    ISe Aug.  2009
  • Electrically conductive polyaniline-coated polystyrene latex particles
    Chen Han, J.Chen, K.Aoki, Toyohiko Nishiumi
    ISE Aug.  2009
  • Diffusion-controlled behavior of ferrocenyl derivative in viscous solutions
    Yi Guo, J.Chen, K.Aoki
    ISE Aug.  2009
  • Voltammograms in viscous solutions of PEG
    青木 幸一, Guo Yi, 陳 競鳶
     Mar.  2009
  • Reduction Kinetics of Hydrogen Ion at Films Composed of
    Tianbao Li, 青木 幸一, 陳 競鳶
     Nov.  2008
  • 電気伝導性コロイド粒子の合成と電極反応
    陳 競鳶, 陳漢, 青木 幸一
     Mar.  2008
  • Motion of An Air Bubble on Oil|Water Interface
    T. Imamura, K.Aoki, J.Chen
    214th ECS Meeting Jan.  2008
  • Synthesis and the Electrolyte of the Functional Polystyren-based Latex
    T. Sakata, K.Aoki, J.Chen
    214th ECS Meeting Jan.  2008
  • Electrochemically Instantaneous Reduction of Conducting Polyaniline-coated Latex Particles
    Han Chen, K.Aoki, J.Chen
    214th ECS Meeting Jan.  2008
  • イオン液体を支持塩とするトルエン滴における電極反応とそれに続くイオン移動
    佐藤 正則, Galyna Shul, Ewa Rozniecka, Wojciech Adamiak, Frank Marken, Marcin Opallo, 陳 競鳶, 青木 幸一
     Nov.  2007
  • カーボキシルラテックスで被覆されたボルタンメトリ用電極
    Tianbao Li, Jingyuan Chen, K.Aoki, Toyohiko Nishiumi
    The Polarographic Society of Japan Nov.  2007
  • ミセル化したフェロセンによる塩素の触媒生成
    Han Chen, Jingyuan Chen, Koichi Aoki
    The Polarographic Society of Japan Nov.  2007
  • ベンゾキノンの還元の高速ボルタンメトリーと微小電極ボルタンメトリーとの比較
    陳 競鳶, 青木 幸一, 張 華
    The Polarographic Society of Japan Nov.  2007
  • 三相界面での電極反応による空気泡の運動
    陳 競鳶, 佐藤 正則, 青木 幸一
     Mar.  2007
  • 界面活性剤や麦芽糖による三相界面の膨張と収縮
    佐藤 正則, 陳 競鳶, 青木 幸一
     Nov.  2006
  • ルテニウム錯体の電気化学発光を利用した一酸化窒素(NO)の検出
    三宅正輝, 陳 競鳶, 西海 豊彦, 青木 幸一
     Nov.  2006
  • コロイド粒子の構造に影響する電極反応
    陳 競鳶
     Sep.  2006
  • レドックスラテックスの粒径に依存した反応活性
    陳 競鳶, 韓 利民
     Apr.  2006
  • Fast electron-transfer kinetics at single nano disk electrodes
    J.Chen, K.Aoki, X.Zhao, J.Yu
    65th Annual Meeting of International Society of Electrochemistry Aug.  1914
  • Is the dianion formed in the absence of salt?
    J.Chen, K.Aoki
    10th ECHEMS Meeting Jun.  1914
  • Comparison of heterogeneous reaction rate constants by steady-state microelectrode techniques with those by fast scan voltammetry
    J.Chen, K.Aoki, X.Zhao
    2014 Pittsburgh Conference Mar.  1914

Recital

  • 電気化学ゼミナー
    How to make nano-electrodes? What can we do by using the nano-electrodes?
    Xiamen University, ChinaZhong-Qun Tian, State Key Lab. of Physical Chemistry of Solid Surfaces
    participants: 31 Sep.  2014- Sep. 2014

Works

  • 6th Asian Conference on Electrochemistry in Taipei
    J.Chen, Jun. 2008

Awards & Honors

  •  The 16th International Symposium on Electroanalytical Chemistry one of the top-ten excellent poster presentations Langmuir-typed double layer capacitance in water/acetonitrile solutionsAug. 2017
    one of the top-ten excellent poster presentations
  •  14th International Symposium on Electroanalytical Chemistry one of the top-ten excellent poster presentations An in phase component of double layer capacitanceAug. 2013
    one of the top-ten excellent poster presentations