Electron Pumping Overcomes Spin-Crossover Barrier to Lock High-Spin Single-Atom Sites for Sustained Oxygen Reduction.

Abstract

The oxygen reduction reaction (ORR) is kinetically limited by spin-dependent adsorption of O2 and intermediates at catalytic sites, yet the high-spin configuration that promotes O2 activation is inherently metastable and suffers from uncontrolled spin evolution. Herein, we propose an electron-pumping strategy to overcome the spin-forbidden energy barrier, which is achieved by the continuous and unidirectional electron extraction from Fe centers invariably to stabilize the active sites in high-spin state. The sustained high-spin state of FeIII (d5, S = 5/2) activates the eg orbitals to govern orbital hybridization and electronic coupling with intermediates, while simultaneously overcoming spin-crossover barrier to continuously drive O2 activation, thereby accelerating reaction onset and subsequent catalytic steps. Moreover, it reinforces O─O bond scission and eases *OH removal, synergistically enhancing the complete ORR dynamics. Consequently, the designed electrocatalyst delivers an outstanding half-wave potential of 0.93 V with only 7 mV decay after 10 000 cycles. The assembled anion exchange membrane fuel cell achieves a peak power density of 966 mW cm-2 and retains 97% of its initial voltage after 50 h at 0.5 A cm-2. This work establishes the electron-pumping regulation as a paradigm for achieving intrinsic and sustained high-spin stabilization, breaking the activity-stability trade-off in oxygen electrocatalysis.