Trace-LiCl-assisted synthesis of high-loading ordered Pt3Co intermetallic catalysts for the oxygen reduction reaction in fuel cells

Abstract

The synthesis of high-loading platinum intermetallic compounds (IMCs) for proton exchange membrane fuel cells (PEMFCs) remains challenging due to severe nanoparticle agglomeration and inhomogeneity during high-temperature annealing. Here, we report a trace lithium chloride (LiCl)-assisted strategy that enables the synthesis of highly ordered Pt₃Co IMCs with ultrahigh metal loading (50.43 wt% Pt) and a small particle size (∼3.58 nm). Comprehensive characterization reveals that LiCl lowers the activation barrier for Pt/Co salt reduction by a strong polarization force, while its molten-salt phase accelerates Co diffusion into the Pt lattice and surface atomic rearrangement. The resulting Pt₃Co/C catalyst achieves a record oxygen reduction reaction (ORR) mass activity (MA) of 0.86 ± 0.04 A mg_pt⁻¹ in rotating disk electrode (RDE) tests. When integrated into PEMFC cathodes, it delivers peak power densities (PPD) of 2.92 W cm⁻² (H₂–O₂) and 1.23 W cm⁻² (H₂–air) at 80 °C, alongside exceptional stability. Crucially, the MA at 0.9 V reaches 0.61 A mg_pt⁻¹, surpassing the U.S. DOE 2025 target (0.44 A mg_pt⁻¹) by 39%. This work pioneers a barrier-lowering synthesis paradigm that resolves the fundamental ordering–sintering trade-off in high-temperature IMC fabrication.