Surface‐Selective Pt Enrichment for Stabilizing Ultrathin 2D PtCu Nanosheets Toward Durable Oxygen Reduction

ABSTRACT Ultrathin Pt‐based 2D alloy nanosheets are promising electrocatalysts for the oxygen reduction reaction (ORR) due to their high surface‐to‐volume ratios and favorable facet‐dependent activity. However, their thermodynamic instability and susceptibility to transition metal dissolution present critical barriers to their practical application. While surface Pt enrichment could mitigate such degradation, constructing Pt‐rich surfaces on 2D nanosheets remains challenging, as conventional approaches often induce structural collapse or undesired thickening. Herein, we report a surface‐selective Pt enrichment strategy via galvanic replacement to stabilize ultrathin PtCu nanosheets (PtCu NS/C) while preserving their unique 2D integrity. PtCu@Pt NS/C features a Pt‐enriched outer region and an alloyed subsurface, which effectively suppresses Cu exposure while maintaining beneficial electronic interactions. PtCu@Pt NS/C delivers high ORR activity, outperforming commercial Pt/C. More importantly, PtCu@Pt NS/C exhibits remarkable durability, with 17.5% mass activity loss after 30 000 accelerated stress test cycles. Notably, in single‐cell PEMFC configurations, PtCu@Pt NS/C demonstrates outstanding voltage stability with a minimal loss of 4 mV at 0.2 A cm −2 , whereas PtCu NS/C and Pt/C suffer much larger losses of 41 and 38 mV, respectively. This work demonstrates that preferential near‐surface Pt enrichment effectively stabilizes PtCu nanosheets, offering a surface‐engineering approach for improving the durability of ultrathin 2D alloy electrocatalysts.