Spin-Matching Effect Triggering Enhanced Oxygen Reduction Reaction in Acidic and Alkaline Media.

The development of high-performance oxygen reduction reaction (ORR) electrocatalysts operable across broad pH ranges is hindered by strong adsorption of hydroxyl intermediates (*OH). This work introduces a conceptually novel strategy of spin-state modulation via interfacial engineering to regulate platinum nanocrystals anchored on atomically dispersed Fe-N-C substrates (Pt/FeSA-NC). Based on density functional theory (DFT) predictions, we construct a spin-state-tunable architecture by precisely controlling Pt particle size (2-8 nm), which induces spin-matching effects that effectively mitigate *OH over-binding in pH-dependent ORR path. Mechanistic studies indicate that the synergy between FeN4-mediated metal-support interactions and size-dependent spin polarization facilitates charge transfer, weakening *OH adsorption and promoting its desorption. In alkaline conditions, ∼2 nm Pt nanoclusters with moderate spin density achieve a peak power density of 179 mW cm-2 in Zn-air batteries with 150 h stability. Under acidic media, ∼8 nm Pt nanoparticles with low-spin configuration deliver a mass activity of 0.65 A mgPt -1 and a peak power density of 730 mW cm-2 in proton-exchange membrane fuel cells (PEMFCs), outperforming commercial Pt/C and retaining 90% activity after 3000 cycles. This finding provides a spin-engineering paradigm for designing advanced electrocatalysts with ultralow Pt loading.