Superior Intermetallic Pt-Co/C Catalysts With Optimized Triply Metal-Loading, Size, and Ordering-Degree for High-Efficiency and Stable H₂-Air Fuel Cells.

Abstract

Pt-based intermetallic compounds (IMCs) are promising electrocatalysts for oxygen reduction reaction (ORR). This work presents small-sized (2-4 nm) Pt-Co IMCs with both high Pt loading (40-60 wt.%) and ordering degree (42%-91%) via an optimized L-cysteine hydrochloride-assisted impregnation. Besides heating rate and calcination temperature, metal loading is identified as a critical factor governing IMCs formation. Quantitative XRD analysis reveals that the IMCs fraction reaches 78.8% (29.4% L1₀-PtCo-IMC + 50.4% L1₂-Pt₃Co-IMC) at 40% loading, peaks at 94.5% (68.4% L1₀-PtCo-IMC + 26.1% L1₂-Pt₃Co-IMC) at 50% loading, and declines to 31.6% (solely L1₀-PtCo-IMC) at 60% loading. The 50% Pt-Co-IMCs/C with the highest L1₀-PtCo content delivers the best ORR performance, achieving a mass activity of 0.80 A mg_Pt ^-1-1.7 times that of commercial PtCo-TKK. In membrane electrode assembly tests under H₂-air with a low Pt usage of 0.16 mg cm^- ², a voltage of 0.603 V is achieved at 2.0 A cm^- ², with only 11.4% voltage decay after 30 000 cycles. Density functional theory calculations corroborate the activity trend of L1₀-PtCo >L1₂-Pt₃Co >disordered PtCo, thereby rationalizing the loading-dependent ORR activity. The synergistic effect between optimized ^*OH desorption kinetics in the rate-determining step and strong Pt-Co d-d orbital coupling jointly enhances the activity and stability.