Structural and Electrochemical Studies of Pt Clusters Supported on High Surface Area Tungsten Carbide for Oxygen Reduction

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High-surface-area tungsten carbide (WC) was synthesized via a molten solvent route and investigated as a noncarbon electrocatalyst support for nanosized Pt clusters. Pt clusters less than ∼3 nm in size with a small particle size distribution were homogeneously deposited on the WC support by galvanic displacement with Cu. The activity of supported Pt clusters for the oxygen reduction reaction in acid media was studied. It was found that the activity of the Pt clusters is enhanced on WC compared with Pt clusters supported on carbon, and the most likely cause of this enhancement is electron transfer between the catalyst and support. The electrochemical stability of both raw and platinized WC was investigated by cyclic voltammetry, and the surface composition of the support was probed by X-ray photoelectron spectroscopy. It was found that WC is electrochemically stable at potentials less than 0.8 V vs the normal hydrogen electrode. At elevated potentials, the WC surface was oxidized to at least two different WOx species during electrochemical treatment. This transformation of the dominant surface species as well as the tungsten coordination and bonding caused the detachment of Pt clusters from the support surface, which facilitated the agglomeration of Pt clusters on the electrocatalyst support surface.