Sub-4-nm Pt₄FeCoNiCu HEI nanocrystals via borophene-mediated co-anchoring for efficient and durable electrocatalysis

Pt-based intermetallic compounds with atomically ordered arrangements are highly promising catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. However, the mutual constraint between high-temperature ordering and small-size stability (especially at high metal loadings), as well as the corrosion of both metal particles and carbon supports under operating conditions, severely limit their mass activity and long-term durability. Here, we report a borophene-mediated multimetal site co-anchoring strategy to synthesize sub-4-nanometer high-entropy Pt₄FeCoNiCu intermetallic catalysts (MMCA-HEIMCs) supported on pristine carbon, which enables simultaneous anchoring of Pt and non-noble metals onto the carbon support. The strong metal-borophene interaction suppresses particle sintering during high temperature annealing (1000°C) and enables a high metal loading of 36 wt % at a small particle size. The resulting L1₀-ordered structure with a unique FeCoNiCu atomic stacking configuration is confirmed by electron microscopy and x-ray absorption spectroscopy. The catalyst achieves an exceptional H₂-air fuel cell peak power density of 1.055 watts per square centimeter and an ORR mass activity of 1.4 amperes per milligram of Pt at 0.9 volts in H₂-O₂ fuel cells. Owing to the high-entropy stabilization effect and the robust borophene co-anchoring effect, the catalyst retains 72% of its peak power density and 80% of its initial mass activity after 30,000 durability cycles. Moreover, the borophene interlayer mitigates Pt-catalyzed carbon corrosion, as verified by a 5000 startup/shutdown cycling test and online mass spectrometry. This work demonstrates a general strategy to overcome the activity-durability trade-off in multicomponent intermetallic catalysts through strong metal-support interactions.