ELECTROCATALYTIC OXIDATION OF PREADSORBED MONOLAYER OF CO ON POLYCRYSTALLINE PT-60-RU-40 ELECTROCATALYST - NUCLEATION AND GROWTH OF OXYGEN-CONTAINING SPECIES

The kinetics and mechanism of nucleation and growth of oxygen-containi ng-species, during the electro-oxidation of preadsorbed saturated mono layer of CO on polycrystalline Pt-60-Ru-40 electrodeposited catalysts, were investigated in a GO-free perchloric acidic solution, using stri pping voltammetry and potentiostatic pulse technique. The surface comp osition of investigated catalysts was determined using XPS. The plots of CO oxidation rate vs. time (j-t curves) displayed responses quite t ypical for the processes controlled by the nucleation and growth pheno mena. Therefore, the overall rate of the CO oxidation reaction can be expressed in terms of the rate of nucleation and growth of oxygen-cont aining species in adsorbed CO monolayer. With the increase in CO oxida tion potential above +0.5 V vs. NHE, the change from a 2D-kinetically controlled nucleation to a 3D-diffusionally controlled nucleation mech anism was observed. Enhanced electrocatalytic activity of the investig ated Pt-Ru surface toward CO electro-oxidation, compared to pure Pt su rface, was discussed in terms of the propensity of Ru atoms nucleation sites toward the adsorption of oxygen-containing species and in respe ct to the observed difference in the intrinsic rate constants for CO o xidation on Pt vs. Ru surface atoms. Potentiostatic and voltammetric C O stripping experiments clearly showed the bifunctional character of o ur Pt-Ru catalyst, with enhanced synergistic properties. (C) 1998 Else vier Science B.V. All rights reserved.