SnO‐Based Mesh‐Island Architecture Stabilizes PtCoSn Alloy Catalysts for Durable Hydrogen Fuel Cells

The large‐scale deployment of proton exchange membrane fuel cells is hindered by the intrinsic activity‐stability trade‐off in Pt‐based alloy catalysts, arising from transition metal dissolution and nanoparticle aggregation. Herein, we develop a mesh‐island confinement strategy to construct a ternary PtCoSn catalyst via alternating atomic layer deposition. In this design, Co preferentially occupies low‐coordination Pt sites, while Sn is selectively enriched on the nanoparticle surface and carbon support. Upon reduction, a PtCoSn alloy core is formed and stabilized by a surface SnO‐based mesh and support‐confined islands. This architecture enables the catalyst to achieve superior oxygen reduction reaction activity and significantly enhanced stability compared to conventional binary alloys by suppressing transition metal dissolution and inhibiting nanoparticle migration. The membrane electrode assembly achieves a peak power density of 1.46 W cm −2 and a mass activity of 0.73 A mg Pt −1 , with only 14.4% performance degradation after 30 000 accelerated durability cycles. This work establishes a general strategy for the rational construction of highly durable electrocatalysts through mesh‐island confinement.