The thermodynamics of the so-called perfectly polarizable electrode was employed to analyze the voltammograms of a Pt(111) electrode in KBr solutions with an excess of a supporting electrolyte (0.1 M HClO4 and 0.1 M KClO4 + 10(-3) M HClO4 + xM KBr where x varied between 5 x 10(-4) and 1 x 10(-2)). The surface Gibbs excess, the Gibbs energy of adsorption and the charge number at a constant electrode potential and a constant chemical potential have been determined. The effect of pH on the magnitude of these parameters has been evaluated. The thermodynamic parameters for bromide have been compared to the parameters determined from previous thermodynamic studies of (bi)sulfate, chloride and OH adsorption at the Pt(111) electrode surface. As expected, bromide adsorption is stronger than for the other anions and halide adsorption seems to be limited by close packing of the adlayer. The calculated charge number values suggest that Br adsorption involves a full charge transfer, as in the case of chloride. (c) 2006 Elsevier B.V. All rights reserved.