Breaking the linear scaling relation through synergistic modulation of d-band center and spin state via p-d hybridization for enhanced bifunctional oxygen electrocatalysis

The development of highly efficient and stable bifunctional electrocatalysts capable of simultaneously catalyzing the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is critical for advancing zinc-air batteries (ZABs). However, the linear scaling relationship (LSR) governing the adsorption energies of oxygen species imposes constraints on the concurrent enhancement of ORR and OER performance. In this study, we report the synthesis of a novel FeSn/NC catalyst that exhibits strong p-d orbital hybridization by incorporating p-block Sn metal into d-block Fe metal. This strategy facilitates the manipulation of the d-band center and enables the effective formation of low-spin (LS) Fe 3+ simultaneously. The regulation of the d-band center is identified as an effective strategy to enhance the adsorption energy of OOH* and OH* intermediates, while the LS Fe 3+ configuration can effectively weaken the adsorption strength of the O* intermediate. Consequently, this p-d hybridized Fe-based catalyst successfully overcomes the constraints imposed by LSR, thereby boosting bifunctional activity for both ORR and OER. The synthesized FeSn/NC catalyst demonstrates exceptional bifunctional performance with a potential difference (ΔE) of 0.65 V between ORR and OER activities. Furthermore, ZAB based on FeSn/NC achieves an impressive peak power density of 186.0 mW cm −2 , while maintaining stable operation over 700 h during cycling tests. This work offers new insights into designing high-performance bifunctional electrocatalysts through strategies involving synergistic modulation of d-band center and spin state.