Engineering the reversible redox electrochemistry on cuprous oxide for efficient chloride ion uptake

To address the dual challenges of freshwater scarcity and energy storage demands, battery deionization has emerged as a promising technology for simultaneous salt removal and energy recovery. Compared to the significant research advancement in cation-storage electrodes, anion-storage counterparts remain a critical bottleneck thus limiting the industrialization of battery deionization technique. Here, we employ Cu2O as a Cl− storage electrode material, by engineering the electrochemical-driven reversible synthesis-decomposition process between Cu2O and Cu2(OH)3Cl, the Cu2O electrode delivers the state-of-the-art high charge capacity of 286.3 ± 8.1 mAh g−1 and Cl− storage capacity of 203.5 ± 21.3 mg g−1 in natural seawater. Ex-situ liquid cell electrochemical transmission electron microscopy and in-situ powder X-ray diffraction unveil a continuous and spatial confirmed electrochemical-driven electrode oxidation, spatial migration and crystallization mechanism engaged in the reversible structural transformation between Cu2O and Cu2(OH)3Cl during battery deionization process. This work not only introduces a highly efficient electrode material for Cl− removal but also establishes a basis for leveraging the electrochemical-driven reversible synthesis-decomposition process and spatial confinement reversible structural transformation mechanism to design advanced electrode materials for diverse ion removal applications. Battery deionization is an emerging technology, with anion storage materials underexplored. Here, authors report Cu2O as a chloride anion storage electrode material with a reversible transformation between Cu2O and Cu2(OH)3Cl and demonstrate application to saltwater deionization.