Engineering p–d Orbital Coupling and Vacancy-Rich Structure in Triatomic Iron–Bismuth–Iron Sites for Rechargeable Zinc–Air Batteries

The rational design of heteroatomic sites with synergistic electronic modulation remains a critical challenge for achieving bifunctional oxygen electrocatalysis in sustainable energy technologies such as fuel cells and metal-air batteries. Herein, a triatomic Fe₂BiN₅ configuration embedded in nitrogen-doped carbon (Fe₂BiN₅/C) with atomically dispersed FeN₂-BiN-FeN₂ sites and vacancy-rich structures is synthesized via a pyrolysis and etching strategy. The triatomic architecture endows Fe₂BiN₅/C with exceptional bifunctional activity, delivering a high oxygen reduction reaction half-wave potential of 0.918 V and an oxygen evolution reaction overpotential of 245 mV at 10 mA cm^-2, surpassing Pt/C and RuO₂. In situ X-ray absorption fine structure and Raman spectroscopy reveal dynamic structural evolution during electrocatalysis, where Fe acts as the primary active center with Bi regulating the electron distribution via long-range interactions, thereby optimizing adsorption/desorption energetics of oxygen intermediates. The theoretical calculations further elucidate that the Bi-induced p-d orbital coupling leads to the alteration in Fe d-orbitals energy level, downshift d-band center, weaken binding strength to the oxygen-based intermediates, and reduced energy barrier for oxygen electrocatalysis. This work provides an understanding of bifunctional triatomic site with p-block metal as electronic modulators embedded in transition-metal atoms toward enhanced oxygen catalysis.