Hydrogen evolution at Pt(111) - activation energy, frequency factor and hydrogen repulsion

Hydrogen evolution on Pt(111) is investigated as a function of temperature; the results are interpreted in terms of the theory of electrocatalysis. The current-potential curves are consistent with a Volmer-Tafel mechanism, in which the recombination of two weakly adsorbed hydrogen atoms determines the overall rate, and in which the adsorbed hydrogen shows a repulsive interaction. The pre-exponential factor of about 109A cm−2 is high and indicates a rate determining step that occurs only on the surface. The activation energy is of the order of 0.5 − 0.6 eV and concurs with previous theoretical estimates.