Study of the kinetics and influence of Bi_irr on formic acid oxidation at Pt2Ru3/C

Abstract

Electrochemical oxidation of HCOOH in H2SO4 and HClO4 solutions was examined on thin film Pt2Ru3/C electrode. XRD pattern revealed that Pt2Ru3 alloy consisted of the solid solution of Ru in Pt and the small amount of Ru or solid solution of Pt in Ru. According to STM images, Pt2Ru3 particles size was between 2 and 6 nm. It was established that electrochemical oxidation of HCOOH commenced at −0.1 V versus SCE at Pt sites in the catalyst. Kinetic parameters indicated that dehydrogenation path was predominant. Dehydration occurs in parallel, but without significant poisoning by COad owing to oxidative removal by OH species on Ru atoms. The coverage of Pt2Ru3 surface by CO preadsorbed from the solution was found to be 24% lower when the surface was modified by irreversibly adsorbed Bi. Modification by Bi also shifted the onset potential for HCOOH oxidation for about 50 mV towards more negative values and consequently, increased the reaction rate for a factor of two. It was proposed that Ru acts through bifunctional mechanism, i.e. OH species adsorbed on Ru oxidizes COad from Pt sites, while Bi hinders the adsorption of CO on Pt sites via electronic and/or ensemble effects.