Exploration of electrodeposited platinum alloy catalysts for methanol electro-oxidation in 1 M H2SO4: Pt-Au system

Applied chemistry

The electrocatalytic activity of electrodeposited Platinum (Pt)-Gold (Au) alloy layers on an inert substrate electrode for methanol oxidation reaction. Analyses using energy-dispersive fluorescent X-ray analysis and powder X-ray diffrac-tometry confirm alloying of Pt with Au in a range of compositions. Steady-state polarisation measurements in 1 M methanol+1 M H2SO4 solutions clearly show that the onset of electro-oxidation shifts to less anodic potential values (approximately 160 mV), while also exhibiting current enhancements up to _15 times the currents obtained for the pure Pt electrodeposit. A linear relationship between the cyclic voltammetric peak (oxidation) current and [MeOH] is observed at a scan rate of 50 mVs)1, thus indicating reduced influence of adsorbed CO (COads) surface poison. A critical com-position, Pt (92%)/Au (8%) [denoted Pt-Au(3) alloy] is found to exhibit maximum electrocatalytic activity, be-yond which the activity drops, whereas pure Au does not catalyse the reaction. While the promotion of electro-oxidation is understood to be largely due to the alloy catalyst, surface redox species of Au oxide formed during the electro-oxidation process may also contribute to the oxygenation of COads, thereby enhancing the oxidation current. Plausible mechanisms of methanol oxidation on Pt/ transition metal alloy electrocatalysts are discussed in terms of electron transfer (in the alloy) and the role of Au oxide species.

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