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 Ptskin‐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 (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 mgPt‐1 at 0.9 V vs. RHE) and superior H2‐O2 single PEMFC performance (mass activity (MA) of 0.5 A mgPt‐1 at 0.9 ViR‐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 ViR‐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 platinum skin, thereby inhibiting the dissolution of Pt and Ni.