Divalent and halide dual-ion storage of a redox-active symmetric cell for an efficient wastewater-energy nexus

Here, we design an energy-efficient ion management and high-performance energy storage system based on a redox-active symmetric cell based on a divalent and halide dual-ion storage mechanism of V₂O₃ nanocrystal/carbon hybrids grown on reduced graphene oxide (V₂O₃@C/rGO). Experimental and computational analyses confirm the Ca²⁺ insertion-based ion storage and redox-mediating Br⁻ conversion mechanism of the V₂O₃@C/rGO. The symmetric cells of two V₂O₃@C/rGO electrodes can function as an energy-dense aqueous divalent metal-halogen battery with a high rate and long cycles, as well as an energy-efficient redox-active capacitive deionization (RACDI) device with high salt adsorption capacity and rate in both high and low concentrations of wastewater. Particularly, the total energy consumption of our RACDI is 76 Wh kg⁻¹, which is lower than that of existing CDI technologies, by means of spontaneous electrode regeneration without an ion-exchange membrane. This work provides a new concept of highly efficient and stable energy storage-desalination integrated functional systems for a sustainable wastewater-energy nexus.