engleski

Impedance Spectra of the Hydrogen Evolution Reaction at Low Cathodic Overpotentials

Impedance spectra of the hydrogen evolution reaction, HER, at low cathodic overpotentials are analysed on the basis of theoretical admittance/frequency function, initially derived for the Volmer-Heyrovsky-Tafel reaction mechanism involving hydrogen insertion (absorption + diffusion )step. General priciples of the impedance spectroscopy for HER are discussed by use of schematically constructed impedance spectra. In order to characterize influence of each impedance parameter on the shape of the spectrum, some simulationa of impedance spectra are performed with different values of impedance parameters. Comparative impedance measurements are carried out on deposited rhodium and ruthenium electrodes at -0.040 v vs. rhe, in 0.5 mol dm-3 H2SO4. Impedance parameter values are estimated by curve fitting between theoretical and experimental impedance spectra. In addition to the electron transfer, formation of adsorbed hydrogen and H2 desorption step, a participation of bulk diffusion step of hydrogen is indicated for both electrodes at the lowest frequencies. Comparison between impedance parameter values of two electrodes suggested faster kinetics of HER at the rhodium electrode.

impedance spectra; hydrogen evolution reaction; ruthenium electrode; rhodium electrode

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