Hydrogen evolution reaction (HER) is one of the most prominent reactions in renewable-energy technology. A lot of research has been done to explore the kinetic and mechanism aspects of this reaction in dilute media. However, in a real hydrogen power station, this reaction literally occurs in highly concentrated media which its kinetic aspects on microelectrodes have not yet been discussed in literature. The present research was carried out to investigate the electrochemical behavior of highly concentrated electroactive species. The high concentration of electroactive species leads to large currents on millimeter size electrodes that are challenging to interpret due to high resistive (iR) losses. Electrodes in the nanometer scale provide measurable currents and also enable kinetic studies of the above-mentioned reactions. Electrochemically facile systems such as reduction of proton reduction, potassium ferri/ferrocyanide, and ruthenium hexaammine(III/II) are suitable choices to qualify the general aspects of highly concentrated systems.To track the surface dependence of current, we studied the three above-mentioned systems at 25�m, 10�m Pt electrodes. In parallel with experimental results, simulation studies were carried out using DigiElch 6.F. The influence of migration and rate of diffusion on the steady state current will be discussed in this seminar. For example, at large electrodes, apparent diffusion coefficients of electroactive species were larger than the common ones previously reported in literature.Interestingly, the above-mentioned systems, despite having facile kinetics, exhibit over voltages at high concentrations compared to resulting data in diluted media. In the case of potassium ferri/ferrocyanide, the resulting cyclic voltammograms deviated from expected voltammetric reversible behavior indicating the existence of a kinetic barrier, which will be discussed in the talk.

Electrochemical studies of highly concentrated redox active species

247th National Meeting (2014)

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