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 H-2 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 H-2 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 H-2 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-2 additional to the upd H-2 is accommodated at cathodic overpotentials, is addressed. (C) 1998 Elsevier Science S.A. All rights reserved.