Bridging the charge gap: Nb2CTx/Nb2O5 Schottky heterojunctions as electronic highways in vanadium redox flow battery

Vanadium redox flow battery (VRFB), as a potential technology for next-generation energy storage system, is restricted by the slow redox kinetics of vanadium ions. Implementing interface engineering strategies to functionalize the surface of MXene can effectively address this challenge. Herein, a Nb2CTx/Nb2O5 Schottky heterostructure is constructed to facilitate high-speed charge transfer at the VRFB electrode through controllable in-situ oxidation. The loading amount of Nb2O5 nanorods on the surface of Nb2CTx nanosheets was regulated by varying the hydrothermal reaction time. Density functional theory calculations confirm that the Schottky barrier formed between Nb2CTx and Nb2O5 leads to the establishment of an internal electric field and reconfigures the electronic structure of surficial active sites. The rich pore structure of Nb2CTx/Nb2O5 electrode effectively shortens the diffusion path for vanadium ions, while its excellent hydrophilicity enhances the interaction between vanadium ions and the electrodes. Compared with graphite felt, Nb2CTx/Nb2O5-2@GF cell shows a 20 % increase in energy efficiency (EE) at 150 mA cm−2 cycling, reaching 75 %, while maintaining stable performance for over 800 cycles. This means a significant advancement in the development of high-performance electrodes for VRFBs. This work offers an efficient and scalable strategy for the design of redox flow batteries.