Spin-state regulation of heteronuclear Cu-Co dual-atomic sites via tuning electronic asymmetry for enhanced oxygen reduction

Abstract

Modulating electronic asymmetry of transition metal (TM) sites attributes to switching their spin state and regulating bonding to oxygen-containing intermediates, thereby facilitating their performance for oxygen reduction reaction (ORR). Herein, we engineer the local coordination structure of the Cu-Co dual-atomic site by integrating phosphorous. The constructed CuCoNPC therefore possesses asymmetric active sites (CoN₃-CuN₃P), leading to a high spin-state of reactive Co sites. The accordingly tuned d_yz orbital occupation consequently triggers the rate-determining step of ORR switching from first (*O₂→*OOH) to the last protonation (*OH → H₂O). As a result, the CuCoNPC exhibits exceptional ORR activity, with j_k of 54 mA cm⁻² at 0.75 V_RHE and half-wave potential (E_1/2) of 0.86 V_RHE, overwhelming that of Pt in alkaline electrolyte. Meanwhile, it also displays a Pt-comparable onset (0.82 V_RHE) and E_1/2 (0.72 V_RHE) in acidic media. Finally, the CuCoNPC catalyst superior performance in liquid-form (P_max = 194 mW cm⁻²) and all-solid-state flexible (OCP = 1.51 V) zinc-air batteries. This work provides valuable guidance in developing active TM-based ORR catalysts via tuning electronic asymmetry.