In situ vertically aligned MoS${}_2$ arrays electrodes for complexing agent-free bromine-based flow batteries with high power density and long lifespan

Bromine-based flow batteries (Br-FBs) are highly competitive for stationary energy storage due to their high energy density and cost-effectiveness. However, adding bromine complexing agents (BCAs) to electrolytes slows down Br${}_2$/Br${}^{-}$ reaction kinetics, causing higher polarization and lower power density of Br-FBs. Herein, in situ vertically aligned MoS${}_2$ nanosheet arrays on traditional carbon felt substrates as electrodes to construct high power-density BCA-free Br-FBs are proposed. MoS${}_2$ arrays exhibit strong adsorption capacity to bromine, which helps the electrodes capture and retain bromine species. Even without BCAs, the battery self-discharge caused by bromine diffusion is also inhibited. Moreover, the rate-determining step of Br${}_2$/Br${}^{-}$ reactions is boosted and the vertically aligned array structure provides sufficient sites, motivating Br${}_2$/Br${}^{-}$ reaction kinetics and decreasing the battery polarization. The capacity retention rate of the BCA-free Br-FB based on MoS${}_2$ arrays-based electrodes reaches 46.34% after the 24-h standing test at 80 mA cm${}^{-2}$, meeting the requirements of practical applications. Most importantly, this BCA-free Br-FB exhibits a high Coulombic efficiency of 97.00% and an ultralong cycle life of 1000 cycles at a high current density of 200 mA cm${}^{-2}$. This work provides an available approach to developing advanced electrode materials for high power-density and long-lifespan Br-FBs. (© 2023 Wiley‐VCH GmbH)