Adsorbate interactions and phase transitions at the stepped platinum/electrolyte interface : experiment compared with Monte Carlo simulations

By comparison of the experimental and simulated voltammetric curves of a series of stepped platinum electrodes in contact with a sulfuric acid electrolyte, we show that hydrogen adsorbed on steps and on terraces exhibit very different lateral interactions. Hydrogen on terraces have repulsive lateral interaction energies, whereas hydrogen adatoms on steps attract each other. We believe that the most likely interpretation of the attractive interaction between the hydrogens on the steps is a H-induced local surface reconstruction of the steps under electrochemical conditions. We also demonstrate that, in agreement with experiment, diluting the quasi-perfect (1 1 1) surface with periodic steps suppresses the singular "butterfly" feature related to an order–disorder transition in the sulfate adlayer, due to the perturbation of the surface long-range order.