Oxygen-Terminated Nb₂CO₂ MXene with Interfacial Self-Assembled COF as a Bifunctional Catalyst for Durable Zinc-Air Batteries

The desirable air cathode in Zn-air batteries (ZABs) that can effectively balance oxygen evolution and oxygen reduction reactions not only needs to adjust the electronic structure of the catalyst but also needs a unique physical structure to cope with the complex gas-liquid environment. In this work, first-principles calculations were carried out to prove that oxygen-terminated Nb₂CO₂ MXene played an active role in enhancing the sluggish reaction of oxygen intermediates. Nb₂CO₂ MXene could also stimulate the spatial accumulation of discharge products, which was beneficial to improve the stability of secondary ZABs. Molecular dynamics simulation was used to show that the confinement effect of COF could effectively regulate the concentration of O₂ on the surface of Nb₂CO₂@COF, which was conducive to an efficient and durable reaction. COF-LZU1 was self-assembled on the interface of Nb₂CO₂ MXene (Nb₂CO₂@COF) for the first time. The Nb₂CO₂@COF electrode had excellent OER/ORR overpotentials with the potential difference (ΔE) of 0.79 V. When applied to the configuration of ZABs, Nb₂CO₂@COF showed a power density of 75 mW cm^-2 and favorable long-term charge/discharge stability, so it could be used as a potential candidate cathode for noble-metal-based catalysts. This idea of combining MXenes and COFs sheds some light on the design of ZABs.