Heterogeneous Au–Pt nanostructures with enhanced catalytic activity toward oxygen reduction

Abstract

Heterogeneous Au–Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core–shell Au–Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H₂PtCl₆ solution, whose chemical reaction can be described as 4Ag + PtCl₆²⁻ → Pt + 4AgCl + 2Cl⁻, is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag–Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core–shell Au–Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au–Pt nanostructures. The heterogeneous Au–Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.