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

Yang, Songhe; Gu, Xiaosong; Feng, Xuezhen; Wang, Ranhao; Lou, Xiang-Yang; Wei, Wenfei; Chen, Hong · Nat Commun · 2025

basic_science · Level V

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Abstract

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 Cu<sub>2</sub>O as a Cl<sup>-</sup> storage electrode material, by engineering the electrochemical-driven reversible synthesis-decomposition process between Cu<sub>2</sub>O and Cu<sub>2</sub>(OH)<sub>3</sub>Cl, the Cu<sub>2</sub>O electrode delivers the state-of-the-art high charge capacity of 286.3 ± 8.1 mAh g<sup>-1</sup> and Cl<sup>-</sup> storage capacity of 203.5 ± 21.3 mg g<sup>-1</sup> 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 Cu<sub>2</sub>O and Cu<sub>2</sub>(OH)<sub>3</sub>Cl during battery deionization process. This work not only introduces a highly efficient electrode material for Cl<sup>-</sup> 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.