Density functional theory–based design of a Pt-skinned PtNi catalyst for the oxygen reduction reaction in fuel cells

Abstract

Pt-based binary alloys (Pt-M, M = transition metal) with optimal electronic and geometric properties may be used to secure the economic feasibility of fuel cells by reducing Pt content and increasing cathodic efficiency. Herein, the oxygen reduction reaction (ORR) on Pt-M alloys (Pt3M and PtM, M = Co, Ni, Mn, and Ir) was probed by density functional theory calculations to reveal that the oxygen dissociation pathway is optimal for Pt(111), Pt3M(111), and PtM(111) surfaces. However, as the above alloys were inferior to Pt catalysts, Pt/Pt-M alloys were designed by the addition of a single Pt skin layer at the top of Pt-M alloys, which enhanced ORR performance by decreasing the adsorption strengths of key intermediates (O* and OH*) to values below those observed for the Pt catalyst. Pt/PtNi and Pt/PtCo catalysts, which offer the benefit of decreased Pt content, showed particularly high performances. The results of electronic structure analysis demonstrated that the above decrease in adsorption strength was due to the inhibition of the high activity of the Pt-M(111) surface by the Pt skin layer. Finally, simple descriptors (optimal d-band center position and adsorption strength) were established to enable the further search for better fuel cell catalysts.