Deciphering the bidirectional reconstructions and lattice oxygen activation for high-performance bifunctional oxygen electrocatalysis in Zn-air batteries

Despite the pivotal role of bifunctional oxygen electrocatalysis in rechargeable Zn-air batteries (ZABs), the true active phases under realistic conditions remain largely uncharted, leaving a critical gap in mechanistic understanding. To tackle this issue, a Fe-doped NiMoO₄ (NiFeMoO₄) pre-catalyst is evaluated for efficient bifunctional oxygen electrolysis. In-situ spectroscopic analyses prove that the NiFeMoO₄ undergoes rapid surface reconstructions. The active phases for oxygen evolution and reduction reactions (OER/ORR) are essentially determined as NiFe-oxyhydroxides and FeOOH/NiFe(OH)_x, respectively. A combination of ¹⁸O-isotopic labeling mass spectroscopy, in-situ Fourier transform infrared spectra, and theoretical calculations, validates that Fe doping triggers the involvement of lattice oxygen and promotes the desorption of O₂, which in turn accelerates the intrinsic OER activity. The reconstructed catalyst exhibits considerable bifunctional performance and enables a ZAB battery with a maximum power density of 210.2 mW cm⁻² and exceptional stability of 800 h. Our study not only demonstrates the great potential of NiFeMoO₄ pre-catalyst, but presents a new perspective for rational design of highly efficient earth-abundant oxygen electrocatalysts.