High-performance bifunctional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is the keystone for the industrialization of rechargeable zinc-air battery (ZAB). In this work, the modulation in the spin state of Fe single atom on nitrogen doped carbon (Fe₁-NC) is devised by Co₃O₄ (Co₃O₄@Fe₁-NC), and a mediate spin state is recorded. Besides, the d band center of Fe is downshifted associated with the increment in e_g filling revealing the weakened interaction with OH^* moiety, resulting in a boosted ORR performance. The ORR kinetic current density of Co₃O₄@Fe₁-NC is 2.0- and 5.6 times higher than Fe₁-NC and commercial Pt/C, respectively. Moreover, high spin state is found for Co in Co₃O₄@Fe₁-NC contributing to the accelerated surface reconstruction of Co₃O₄ witnessed by operando Raman and electrochemical impedance spectroscopies. A robust OER activity with overpotential of 352 mV at 50 mA cm^-2 is achieved, decreased by 18 and 60 mV by comparison with Co₃O₄@NC and IrO₂. The operando Raman reveals a balanced adsorption of OH^* species and its deprotonation leading to robust stability. The ZAB performance of Co₃O₄@Fe₁-NC is 193.2 mW cm^-2 and maintains for 200 h. Furthermore, the all-solid-state ZAB shows a promising battery performance of 163.1 mW cm^-2.

Shiao Zhu

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