Host–Guest Engineering of Dual-Metal Nitrogen Carbides as Bifunctional Oxygen Electrocatalysts for Long-Cycle Rechargeable Zn-Air Battery

Abstract

The key to obtaining high intrinsic catalytic activity of Me-N_x-C electrocatalysts for Zn-air batteries is to form high-density bifunctional Me-N_x active sites during the pyrolysis of the precursor while maintaining structural stability. In this study, a host–guest spatial confinement strategy was utilized to synthesize a composite catalyst consisting of Co₃Fe₇ nanoparticles confined in an N-doped carbon network. The coupling between the host (MIL-88B) and guest (cobalt porphyrin, CoPP) produces high-density bimetallic atomic active sites. By controlling the mass of guest molecules, it is possible to construct precursors with the highest activity potential. The Co₃Fe₇/NC material with a certain amount of the guest displays a better electrocatalytic performance for both oxygen reduction reaction and oxygen evolution reaction with a half-wave potential (E_1/2) of 0.85 V and an overpotential of 1.59 V at 10 mA cm⁻², respectively. The specific structure of bimetallic active centers is verified to be FeN₂-CoN₄ using experimental characterizations, and the oxygen reaction mechanism is explored by in-situ characterization techniques and first-principles calculations. The Zn-air battery assembled with Co₃Fe₇/NC cathode exhibits a remarkable open-circuit voltage of 1.52 V, an exceptional peak power density of 248.1 mW cm⁻², and stable cycling stability over 1000 h. Particularly, the corresponding flexible Zn-air battery affords prominent cycling performance under different bending angles. This study supplies the idea and method of designing catalysts with specific structures at the atomic and electronic scales for breaking through the large-scale application of electrocatalysts based on oxygen reactions in fuel cells/metal-air batteries.