Unveiling the Catalytic Potential of Facet Heterojunctions in Platinum Alloys for Oxygen Reduction Reaction

Ensuring high-quality activity of proton exchange membrane fuel cells (PEMFCs) while mitigating the degradation of Pt-based alloy catalysts remains challenging. A platinum-skinned truncated octahedral PtNi alloy with (100)/(111) facet heterostructures is synthesized through a low-temperature thermally driven etching strategy, demonstrating exceptional oxygen reduction reaction (ORR) activity and stability. The heterostructure of the Pt_skin-PtNi(111) facet destabilizes the *OOH intermediate and promotes the preferential O─O bond cleavage, leading to the optimization of ORR pathway. A linear correlation between the generalized coordination number ( $\overline{\mathrm{CN}}$ ) and ΔG_*OH demonstrates that the facet hetero-sites optimize the adsorption of *OH to the theoretically optimal state through ligand and geometric effects. The optimized PNZC-5A160 catalyst exhibits enhanced ORR activity (2.97 A mg_Pt ^-1 at 0.9 V vs. RHE) and superior H₂-O₂ single PEMFC performance [mass activity (MA) of 0.5 A mg_Pt ^-1 at 0.9 V_iR-free; peak power density of 1.42 W cm^-2, exceeding the U.S. Department of Energy 2025 targets. After accelerated stress tests, the loss in MA at 0.9 V_iR-free and in potential at 0.8 A cm^-2 is only 8% and 3.7 mV, respectively, due to the enhanced binding of subsurface Pt and Ni to surface Pt atoms through Pt skin, thereby inhibiting the dissolution of Pt and Ni.