Sub‐3‐nm Pt ₂ MnZn Intermetallic Compound for Stable Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are restricted by sluggish oxygen reduction reaction (ORR) kinetics and insufficient catalyst durability. Platinum (Pt) remains irreplaceable for commercial PEMFCs. Although there have been many efforts to improve performance of Pt through alloying, insufficient stability remains a major challenge. Herein, we report a sub‐3‐nm ordered phase Pt ₂ MnZn intermetallic compound (IMC) on carbon black (O‐Pt ₂ MnZn) that achieves superior activity and durability for ORR. The electronegativity differences among Pt, Mn, and Zn endow the alloy with intrinsic thermodynamic stability, while the ordered structure provides beneficial strain and coordination effects. O‐Pt ₂ MnZn exhibited a high mass activity of 1.15 A mg _Pt ⁻¹ and 88.7% retention after 10,000 accelerated stress test (AST) cycles in rotating disk electrode. In practical fuel cells with an ultralow cathode Pt loading of 0.05 mg _Pt cm ⁻² , O‐Pt ₂ MnZn delivered a peak power density of 0.85 W cm ⁻² and 95.3% retention after 10,000 AST cycles, far exceeding commercial Pt/C (0.75 W cm ⁻² , 69.3% retention). This work demonstrates that engineering Pt‐based IMC with appropriately electronegative metals offers a viable route to durable high‐performance PEMFC cathode catalysts.