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.