Electrocatalytic oxidation of preadsorbed monolayer of CO on polycrystalline Pt 60–Ru 40 electrocatalyst: nucleation and growth of oxygen-containing species

Abstract

The kinetics and mechanism of nucleation and growth of oxygen-containing-species, during the electro-oxidation of preadsorbed saturated monolayer of CO on polycrystalline Pt 60–Ru 40 electrodeposited catalysts, were investigated in a CO-free perchloric acidic solution, using stripping voltammetry and potentiostatic pulse technique. The surface composition of investigated catalysts was determined using XPS. The plots of CO oxidation rate vs. time ( j– t curves) displayed responses quite typical for the processes controlled by the nucleation and growth phenomena. Therefore, the overall rate of the CO oxidation reaction can be expressed in terms of the rate of nucleation and growth of oxygen-containing species in adsorbed CO monolayer. With the increase in CO oxidation potential above +0.5 V vs. NHE, the change from a 2D-kinetically controlled nucleation to a 3D-diffusionally controlled nucleation mechanism was observed. Enhanced electrocatalytic activity of the investigated Pt–Ru surface toward CO electro-oxidation, compared to pure Pt surface, was discussed in terms of the propensity of Ru atoms nucleation sites toward the adsorption of oxygen-containing species and in respect to the observed difference in the intrinsic rate constants for CO oxidation on Pt vs. Ru surface atoms. Potentiostatic and voltammetric CO stripping experiments clearly showed the bifunctional character of our Pt–Ru catalyst, with enhanced synergistic properties.