Boosting Kinetics of Ce³⁺/Ce⁴⁺ Redox Reaction by Constructing TiC/TiO₂ Heterojunction for Cerium-Based Flow Batteries

Cerium, a unique rare earth element, possesses a relatively high abundance, low cost, and high redox voltage, making it an attractive candidate for redox flow batteries. However, the sluggish kinetics and corrosion nature of the Ce3+/Ce4+ electrolyte result in overpotential and degradation of carbon felt (CF) electrodes, which hinders the development of cerium-based flow batteries. Therefore, it is essential to develop an electrode with high catalytic activity and corrosion resistance to the Ce3+/Ce4+ electrolyte. Herein, a TiC/TiO2 coated carbon felt (TiC/TiO2-CF) electrode is proposed. Remarkably, the TiC/TiO2 coating effectively minimizes the exposure of the CF to the highly corrosive cerium electrolyte, consequently enhancing the electrode's corrosion resistance. Additionally, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy characterizations reveal the formation of a heterojunction between TiC and TiO2, which significantly enhances the redox reaction kinetics of the Ce3+/Ce4+ redox couple. Eventually, the practical application of TiC/TiO2-CF catalytic electrode in a Ce-Fe flow battery is demonstrated. This study sheds light on the synthesis conditions of the TiC/TiO2-CF electrode, elucidates its heterojunction structure, and presents a novel Ce-Fe flow battery system.