INFLUENCE OF ADSORPTION OF ORGANIC-COMPOUNDS AND SURFACE HETEROGENEITY ON THE HYDROGEN EVOLUTION REACTION

The hydrogen evolution reaction on rough or porous surfaces often lead s to low Tafel slopes that cannot be explained in terms of the Volmer- Heyrovsky-Tafel mechanism. In addition, adsorption of organic compound s and ions causes an increase in the Tafel slopes. To explain such beh avior, a concept of distribution of adsorption energies on heterogeneo us surfaces, leading to a distributed kinetics, was studied. Simulatio ns of the dependence of the current and the surface coverage by adsorb ed hydrogen on overpotential are presented for different values of the kinetic parameters in the absence and presence of the adsorbed foreig n substances. These results were compared with those obtained using th e Frumkin/Temkin adsorption isotherm. It was found that for some kinet ic parameters and a flat distribution of adsorption energies, low Tafe l slopes, similar to those observed experimentally, are obtained.