Sub-Nanometer PtSn Interlayer Tuning Ligand and Strain Effects Boosts Oxygen Reduction Electrocatalysis

The integration of ligand and strain effects in core/shell architectures offers a compelling avenue for boosting the catalytic efficiency of noble metals. However, conventional thin-Pt-shell catalysts incorporating small-radius transition metals suffer from an over-compressed Pt lattice, leading to limited oxygen reduction reaction (ORR) performance toward fuel cell devices. Herein, we report a class of PdSn/PtSn/Pt sandwich-structured nanowires based on large-radius Sn elements, taking advantage of its diffusion inclination to Pt, to construct the sub-nanometer PtSn interlayer so as to address this trade-off issue. We demonstrate that the intermetallic Pt-Sn bonds with elevated covalency downshift the d-band center of Pt through strengthened ligand effect, and the diffusion of large-radius Sn atoms from PdSn core to Pt shell surprisingly offsets an optimally compressive strain for surface Pt. Thanks to such two-tier tuning from PtSn interlayer, the resulting PdSn/(PtSn/Pt)_2-3L NWs with the thinnest Pt shell exhibit exceptional catalytic behaviors by achieving a mass activity of 4.26 A mg_Pt+Pd ^-1 (13.91 A mg_Pt ^-1) at 0.9 V_RHE, with < 30% decay after 20 000 cycles, overweighing most reported Pt/Pd-based ORR catalysts. The corresponding H₂-O₂ anion-exchange-membrane fuel cell device delivers a very high peak power density of 1.64 W cm^-2, with an impressive Pt utilization up to 11.71 W mg_Pt ^-1.