Performance and characterization of a Pt–Sn(oxidized)/C cathode catalyst with a SnO2-decorated Pt3Sn nanostructure for oxygen reduction reaction in a polymer electrolyte fuel cell

Abstract

We have prepared and characterized a SnO₂-decorated Pt–Sn(oxidized)/C cathode catalyst in a polymer electrolyte fuel cell (PEFC). Oxygen reduction reaction (ORR) performance of Pt/C (TEC10E50E) remained almost unchanged or even tended to reduce in repeated I–V load cycles, whereas the I–V load performance of the Pt–Sn(oxidized)/C prepared by controlled oxidation of a Pt–Sn alloy/C sample with the Pt₃Sn phase revealed a significant increase with increasing I–V load cycles. The unique increase in the ORR performance of the Pt–Sn(oxidized)/C catalyst was ascribed to a promoting effect of SnO₂ nano-islands formed on the surface of Pt₃Sn core nanoparticles. Also in a rotating disk electrode (RDE) setup, the mass activity of an oxidized Pt₃Sn/C catalyst was initially much lower than that of a Pt/C catalyst, but it increased remarkably after 5000 rectangular durability cycles and became higher than that of the fresh Pt/C. The maximum power density per electrochemical surface area for the Pt–Sn(oxidized)/C catalyst in a PEFC was about 5 times higher than that for the Pt/C catalyst at 0.1–0.8 A cm⁻² of the current density. In situ X-ray absorption near-edge structure (XANES) analysis at the Pt L_III-edge in increasing/decreasing potential operations and at the Sn K-edge in the I–V load cycles revealed a remarkable suppression of Pt oxidation compared with the Pt/C catalyst at higher potentials and no change in the Sn oxidation state, respectively, resulting in higher performance and stability of the Pt–Sn(oxidized)/C catalyst due to the SnO₂ nano-islands under the PEFC operation conditions. The SnO₂ nano-island decorated Pt–Sn(oxidized)/C catalyst with a Pt₃Sn alloy nanostructure is regarded as a promising candidate for a PEFC cathode catalyst.