Solid bromine complexing agents: long-term solution for corrosive conditions in redox-flow battery†

Redox flow batteries (RFBs) fulfill the requirements for long-duration energy storage (LDES), and the use of bromine as a catholyte has garnered substantial interest due to its high availability and low cost. However, at high states of charge, the vapor pressure of bromine presents significant safety concerns within the catholyte tank, while polybromide species have been shown to corrode the metals present in the stack. Traditionally, soluble bromine complexing agents (BCAs) have been employed to mitigate the concentration of free bromine, providing some improvement in safety; however, this has often resulted in significant reductions in power density and durability. In this study, we present the development of a solid BCA incorporated into the catholyte tank of a hydrogen-bromine RFB (HBRFB). The long-term separation of the bromine-rich solid phase from the flowing liquid phases enables sustained high performance for over 250 cycles. The effective complexing-dissociating equilibrium within the electrolyte tank ensures adequate bromine concentration for operation at high current densities. This advancement significantly enhances the viability of bromine-based RFB technology as a dependable solution for long-duration energy storage.