Carbon-supported Pt⁁Ag nanostructures as cathode catalysts for oxygen reduction reaction

Abstract

Pt_m⁁Ag nanostructures (m being the atomic Pt/Ag ratio, m = 0.1–0.6) were prepared by reflux citrate reduction of PtCl₆²⁻ ions in aqueous solution containing colloidal Ag (6.3 ± 3.9 nm). A distinct alloying of Pt with Ag was detected due to an involvement of the galvanic replacement reaction between PtCl₆²⁻ and metallic Ag colloids. The nanostructure transformed from a structure with an Ag-core and an alloyed PtAg-shell to a hollow PtAg alloy structure with the increase in m. Compared to a commercial E-TEK Pt/C catalyst, the catalytic performance of Pt in the Pt_m⁁Ag/C samples for the cathode oxygen reduction reaction (ORR) strongly correlated with the electronic structure of Pt, as a consequence of varied Pt dispersion and Pt–Ag interaction. With either H₂SO₄ or KOH as an electrolyte, Pt in the Pt_m⁁Ag nanostructures with a relatively high m (≥0.4) showed significantly enhanced intrinsic activity whereas Pt in those catalysts with low m (≤0.2) appeared less active than the Pt/C catalyst. These data are used to discuss the role of electronic structure and geometric effects of Pt toward ORR.