Bromide Adsorption on Pt(111) over a Wide Range of pH: Cyclic Voltammetry and CO Displacement Experiments

Abstract

Bromide adsorption on Pt(111) is investigated by means of cyclic voltammetry and CO displacement experiments at different pH values. In acidic pH, bromide adsorption is strongly overlapped with hydrogen desorption process. However, as the pH increases, hydrogen adsorption process displaces toward negative potentials while bromide adsorption remains nearly in the same potential region. In consequence, both processes decouple at higher pH values. The structural transition from Pt(111)-(1×1) to Pt(111)(3×3)-4Br is pH independent, in the SHE scale, and not observed for pH > 9.1. Values of pztc are extracted from the combination of voltammetric and CO displaced charges. An alternative approach to obtain charge curves is based on the coincidence of the curves at the structural transition characteristic of the bromide adlayer completion. Pztc values obtained from different approaches with and without bromide are compared, and their dependence on pH discussed. A thermodynamic analysis is carried out to obtain hydrogen Gibbs excess and charge number from the Esin Markov analysis.