The effect of electrochemical CO annealing on platinum-cobalt nanoparticles in acid medium and their correlation to the oxygen reduction reaction

This paper describes a modification of the surface properties of a carbon-supported Pt(3)Co catalyst resulting from an electrochemical cycling treatment in a 0.1 M HClO(4) and in a CO-saturated 0.1 M HClO(4) solution (electrochemical CO-annealing). The procedure generated a Pt-rich surface with electrochemical properties different from that presented by the as-received (untreated) sample. This was evidenced by a shift in the CO stripping peak to more positive potentials in the CO stripping voltammetry, and by an increased charge of H(upd) region and a modification of the oxide reduction peak observed in the base cyclic voltammogram. In situ X-ray absorption spectroscopy experiments conducted in the dispersive mode revealed differences in the electronic 5d band occupancy after the CO annealing, whereas the behavior of the intensity of the white-line as function of the potential for this material approached that found for pure Pt/C nanoparticles, in contrast to the small potential dependence profile exhibited by the as-received Pt(3)Co nanoparticles. Mass activities towards the oxygen reduction reaction measured by rotating disk experiments carried out at 1600 rpm in a O(2)-saturated solution at 25 degrees C increased from 0.10 A/mg of Pt to 0.19 A/mg of Pt, evidencing the higher Pt utilization in the CO-annealed Pt(3)Co/C electrocatalyst. The origin of the different electrochemical behavior is discussed. (C) 2011 Elsevier Ltd. All rights reserved.