A TiN Nanorod Array 3D Hierarchical Composite Electrode for Ultrahigh‐Power‐Density Bromine‐Based Flow Batteries

Bromine-based flow batteries are well suited for stationary energy storage due to attractive features of high energy density and low cost. However, the bromine-based flow battery suffers from low power density and large materials consumption due to the relatively high polarization of the Br2 /Br- couple on the electrodes. Herein, a self-supporting 3D hierarchical composite electrode based on a TiN nanorod array is designed to improve the activity of the Br2 /Br- couple and increase the power density of the bromine-based flow battery. In this design, a carbon felt provides a composite electrode with a 3D electron conductive framework to guarantee high electronic conductivity, while the TiN nanorods possess excellent catalytic activity for the Br2 /Br- electrochemical reaction to reduce the electrochemical polarization. Moreover, the 3D micro-nano hierarchical nanorod-array alignment structure contributes to a high electrolyte penetration and a high ion-transfer rate to reduce diffusion polarization. As a result, a zinc-bromine flow battery with the designed composite electrode can be operated at a current density of up to 160 mA cm-2 , which is the highest current density ever reported. These results exhibit a promising strategy to fabricate electrodes for ultrahigh-power-density bromine-based flow batteries and accelerate the development of bromine-based flow batteries.