Lamella-like electrode with high Br2-entrapping capability and activity enabled by adsorption and spatial confinement effects for bromine-based flow battery

Bromine-based flow batteries (Br-FBs) are well suitable for stationary energy storage owing to their high energy density and low cost. However, their power density and lifespan are limited by relatively low reaction kinetics of Br2/Br- couple and serious self-discharge caused by bromine migration. Herein, lamella-like porous carbon nitride nanosheets (PCNS) with adsorption and spatial confinement effects are used to modify cathodes for Br-FBs. The large specific surface area and plentiful N-containing groups enable PCNS with excellent adsorption capacity, which captures bromine species into the pores on PCNS layers. The captured bromine species is subsequently confined in PCNS interlayers due to the strong interaction between bromine species and N-containing groups, thus effectively depressing bromine diffusion/migration. Moreover, the strong bromine adsorption capacity significantly improves the electrochemical activity of PCNS. Consequently, a zinc-bromine flow battery (ZBFB) employing PCNS-modified cathode achieves a high current density of 180 mA cm-2, with an ultra-high coulombic efficiency of 99.22%. It also exhibits better self-discharge performance and a long cycle life of 500 cycles. Furthermore, a complexing agent-free ZBFB is successfully realized based on the superior bromine-entrapping/retaining capacity of the PCNS-modified cathode. Consequently, this work provides a promising strategy toward electrode modifications for high-performance and long-lifespan Br-FBs.