Cu/Cu₂O@polyvinyl alcohol/carbon nanotube conductive hydrogel for chloride ion removal in capacitive deionization

Cu₂O, as a cost-effective chloride ion (Cl^-) storage electrode material, has shown great potential in Cl^- removal applications. However, in the electrochemical process, Cu₂O as the anode is easily oxidized and dissolved by free copper ions (Cu²⁺), leading to the loss of copper components and causing electrode performance degradation. In this work, we introduced a three-dimensional (3D) self-supporting polyvinyl alcohol/carbon nanotube (PVA/CNTs) conductive hydrogel as the carrier of Cu₂O for capacitive deionization (CDI). Among them, PVA acts as an antioxidant to inhibit the conversion of Cu₂O to free Cu²⁺, CNTs act as the growth carrier of copper particles to make them more evenly distributed in the electrode materials, and the 3D hydrogel structure can accommodate a large amount of water, making Cu₂O fully contact with chloride ions in water and store them. At 1.4 V, the Cu/Cu₂O@PVA/CNTs conductive hydrogels (Cu@CHs) demonstrate 49.58 ± 3.27 mg g^-1 Cl^- storage capacity and significantly superior areal Cl^- storage capacity on the 13.66 ± 0.68 mg-Cl^- cm^-2, and there was no significant performance degradation in 100 cycles. This study, using PVA as the core component, proposes a simple strategy for constructing high areal performance 3D materials and provides optimization ideas for solving the oxidation dissolution problem of faradaic materials in the CDI process.