On the electrochemical behavior of the Pt(1 0 0) vicinal surfaces in bromide solutions

Abstract

The electrochemical behavior of the stepped electrodes vicinal to the Pt(1 0 0) surface in bromide containing solutions has been studied by cyclic voltammetry, STM and the CO displacement method. The studied electrodes belong to the [0 1 1̄] and [0 0 1] zones, which nominally have n atom-wide terraces with (1 0 0) symmetry and (1 1 1) or (1 0 0) monoatomic steps, respectively. The voltammetric behavior of these electrodes indicates that the processes on the terrace sites, namely hydrogen and bromide competitive adsorption/desorption take place in a peak centered at 0.19 V, whereas the processes on the step sites occur at potentials below 0.15 V. The STM images obtained after the flame annealing treatment indicate that the electrodes with (1 1 1) steps have a surface topography that corresponds to the nominal structure. On the other hand, the electrodes with (1 0 0) steps appear to be reconstructed, with terrace edges having a zigzag shape. The adsorbed bromide arranges in a c(2 × 2) structure on the (1 0 0) terraces. The CO displacement method has allowed estimating the pztc (potential of zero total charge) for the surfaces. The variation of the pztc is much smaller than that found in other electrolyte solutions, due to the high pseudocapacity of the hydrogen/bromide adsorption processes on the terrace. The total charge at different potentials has been compared to the values predicted from the hard-sphere model. For the electrodes with (1 1 1) steps, the experimental values agree with the model, which facilitates the understanding of the general behavior of these surfaces.