Specificity of the kinetics of H2 evolution to the structure of single-crystal Pt surfaces, and the relation between opd and upd H

It is well known that transition metals exhibit a wide range of catalytic activities for various processes. One of the best examples is the dependence of H2 evolution kinetics on the nature of the cathode metal. This leads to an expectation that a similar specific dependence would also be observed at various single-crystal surfaces of Pt. In earlier literature this has, however, not been found. In the present paper, it is shown that such conclusions arise from the actual surface-specific electrode kinetics being obscured by effects associated with diffusion of H2 from a supersaturated region generated near the electrode. By means of Tafel polarization and impedance measurements at several Pt single-crystal surfaces rotated at 3500 rpm, it is shown that there are, in fact, clear specific dependences of the H2 evolution kinetic parameters on the Pt surface lattice geometry which are related to upd H deposition kinetics and to the well-known surface specificity of the H upd behaviour at Pt as seen in cyclic voltammetry. The question of how the opd H, additional to the upd H, is accommodated at cathodic overpotentials, is addressed.