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.