Urchin-Like Mesoporous TiN Hollow Sphere Enabling Promoted Electrochemical Kinetics of Bromine-Based Flow Batteries

Bromine-based flow batteries (BFB) have always suffered from poor kinetics due to the sluggish Br₃ ^-/Br^- redox, hindering their practical applications. Developing cathode materials with high catalytic activity is critical to address this challenge. Herein, the in-depth investigation for the free energy of the bromine redox electrode is conducted initially through DFT calculations, establishing the posterior desorption during oxidation as the rate-determining step. An urchin-like titanium nitride hollow sphere (TNHS) composite is designed and synthesized as the catalyst for bromine redox. The large difference in Br^- and Br₃ ^- adsorption capability of TNHS promotes rapid desorption of generated Br₃ ^- during the oxidation process, liberating active sites timely to enable smooth ongoing reactions. Besides, the urchin-like microporous/mesoporous structure of TNHS provides abundant active surface for bromine redox reactions, and ample cavities for the bromine accommodation. The inherently high conductivity of TNHS enables facile electron transfer through multiple channels. Consequently, zinc-bromide flow batteries with TNHS catalyst exhibit significantly enhanced kinetics, stably operating at 80 mA cm^-2 with 82.78% energy efficiency. Overall, this study offers a solving strategy and catalyst design approach to the sluggish kinetics that has plagued bromine-based flow batteries.