A nontoxic, high-voltage zinc–bromine battery utilizing multi-oxidation-state bromine (Br−/BrO−/BrO3−) redox chemistry

Abstract

Zinc–bromine batteries suffer from significant bromine gas leakage, posing serious safety hazards. This work introduces a novel Br⁻/BrO⁻/BrO₃⁻ triple redox system within alkaline zinc–bromide batteries. This system facilitates the electrochemical conversion of Br⁻/BrO₃⁻ to the mediator species BrO⁻ via murexide organic chelation under alkaline conditions. The coordinated three-phase redox transition enables a multi-electron transfer mechanism, achieving a discharge plateau of 2.0 V while effectively suppressing Br₂ release. Through a synergistic electrolyte design incorporating acidic substances (oxalic acid) and urea-based complexes (murexide), bromine is confined to non-volatile ionic states, effectively mitigating persistent bromine leakage. The optimized system delivers an area capacity of 2.2 mAh cm⁻² and maintains 83% capacity retention over 700 cycles, demonstrating the practical viability of complete bromine containment in aqueous alkaline batteries. This system-level approach advances fundamental principles for designing multi-electron redox pairs in aqueous batteries and provides key insights into halogen-mediated reaction mechanisms relevant to electrocatalysis and environmental remediation.