Dealloyed Pt−Cu Core−Shell Nanoparticle Electrocatalysts for Use in PEM Fuel Cell Cathodes

We report the synthesis, characterization, and single fuel cell testing of a novel class of nanostructured Pt−Cu alloy particle materials for use as oxygen reduction electrocatalyst in polymer electrolyte membrane fuel cells. The active phase of the Pt alloy nanoparticle catalysts is prepared by electrochemical dissolution (voltammetric dealloying) of Cu surface atoms from Cu-rich Pt−Cu alloy precursors. Bulk and surface structural and compositional characterization suggests that the dealloyed active catalyst phase consists of a core−shell structure in which a multilayer Pt rich shell is surrounding a Pt-poor alloy particle core. The electrocatalytic Pt mass activity of the dealloyed core−shell particles for the oxygen reduction reaction (ORR) exceeds that of state-of-the art Pt electrocatalyst by more than a factor of 4 and thus meets performance targets for fuel cell cathodes [Gasteiger, H. A.; Kocha, S. S.; Sompalli, B.; Wagner, F. T. Appl. Catal. B: Environ. 2005, 56, 9−35].1 It is hypothesized that a reduced Pt−Pt distance near the particle surface, stabilized by the lattice-contracted alloy core, may explain the modification of the surface catalytic reactivity. Dealloying of base-metal-rich noble metal alloy precursors is proposed as a more general strategy toward modifying the surface catalytic properties of noble metal surfaces.