INSITU PROBING OF STEP AND TERRACE SITES ON PT(S)-[N(111)X(111)] ELECTRODES

The electrochemical adsorption behaviour of fifteen platinum orientations taken in the [110] zone corresponding to Pt(S)-[n(111) × (111)] has been investigated by voltammetry at various sulphuric acid concentrations. The change of the voltammetric profile with the step density makes obvious the identification of the step contribution in the hydrogen adsorption process. Taking the step-terrace model as a guide, a counting of the step and terrace sites may be achieved. A new method to take into account the double-layer contribution is proposed. The results lead to the conclusion that the adsorption states on the terraces which may be divided into two main states (a weakly adsorbed state and a so-called unusual state) correspond together to the transfer of one electron per site and per adspecies. Adsorbed hydrogen atom is the more likely species. Each state corresponds to 2 3 and 1 3 respectively of the amount of the species adsorbed on the terrace sites for terraces wider than seven atomic rows. The sharp reversible peak observed in the unusual hydrogen adsorption state is studied as a function of terrace widths. © 1990.