Modelling current transients for the hydrogen evolution reaction on silver electrodes.

A. RUDERMAN; M.F. JUAREZ; L. AVALLE; G. BELTRAMO; E. SANTOS

Günzburg

Workshop; Workshop de DFG Research Unit FOR 1376: Theory meets Experiment; 2012

DEUTSCHE FORSCHUNGSGEMEINSCHAFT

On silver electrodes is quite well-known that the reaction goes through a two-steps mechanism, involving Volmer and Heyrovsky elementary steps. The total current for HER is determined then by the rate of both reactions. The rate of the Volmer reaction depends on the vacancies on the metal surface, while the speed of Heyrovsky depends on the hydrogen coverage. In 1955, Gerischer solved the corresponding kinetic equations, obtaining an analytical expression of total current as a function of time. After careful attempts we could not successfully fit our experimental results with the Gerischer formalism. We propose that the slow decay of the current is a manifestation of a more radical phenomenon at the surface: Anion adsorption. It has been proven experimentally and theoretically that sulfate adsorbs specifically on Ag(100). This adsorption increases asymptotically with the potential and the sulfate concentration in the solution bulk. The maximal experimental adsorption proposed is around 0.23 ML. We present here a so-called modified-Gerischer model were the phenomena of anion desorption is considered.