Influence of adsorption of organic compounds and surface heterogeneity on the hydrogen evolution reaction

The hydrogen evolution reaction on rough or porous surfaces often leads to low Tafel slopes that cannot be explained in terms of the Volmer-Heyrovsky-Tafel mechanism. In addition, adsorption of organic compounds and ions causes an increase in the Tafel slopes. To explain such behavior, a concept of distribution of adsorption energies on heterogeneous surfaces, leading to a distributed kinetics, was studied. Simulations of the dependence of the current and the surface coverage by adsorbed hydrogen on overpotential are presented for different values of the kinetic parameters in the absence and presence of the adsorbed foreign substances. These results were compared with those obtained using the Frumkin/Temkin adsorption isotherm. It was found that for some kinetic parameters and a flat distribution of adsorption energies, low Tafel slopes, similar to those observed experimentally, are obtained.