Crystal Field Engineering of Bioinspired Dual-Metal Single-Atom Catalysts Via Spin-State Modulation for Efficient...

The oxygen reduction reaction (ORR) is central to next-generation energy technologies, but its practical implementation is constrained by inherently sluggish kinetics. Herein, we propose a bioinspired strategy that synergistically integrate atomic-scale crystal field engineering and hierarchical porosity design, effectively tackling the intrinsic activity and mass transport limitations of ORR. This strategy is realized in a Fe/Co dual-metallic single-atom sites anchored on hierarchical meso/microporous N-doped carbon matrices (MPNC-FeCo-x). The optimized MPNC-FeCo-4 exhibits remarkable ORR performance with a half-wave potential of 0.923 V and a turnover frequency of 2.01 e^- site^-1 s^-1 in alkaline media. When deployed in zinc-air batteries, it delivers an ultrahigh peak power density of 232.81 mW cm^-2 and unprecedented cycling stability over 800 h. Mechanistic studies reveal that Co atoms modulate the crystal field to induce the spin transition of Fe species to medium spin (t_2g ⁴e_g ¹ configuration), while the hierarchical pore architecture enhancing charge and mass transfer. Advanced stepwise interfacial kinetic analysis quantifies how the enhanced intrinsic activity and the optimized mass transport cooperate to enhance ORR performance. This work establishes a paradigm for manipulating spin states via rational crystal field design in multi-metallic single-atom systems, providing fundamental insights into structure-activity relationships for energy conversion technologies.