Preparation and performance of PVA-PQ hydrogel electrode for capacitive deionization

Capacitive deionization is an emerging water treatment technology that leverages the principles of electrical double-layer formation, specifically targeting water with moderate to low salinity. However, due to the presence of the co-ion effect, both the desalination rate and charge efficiency are reduced. To address this issue, a PVA-based composite hydrogel electrode modified with an ion-exchange polymer was developed. PVA hydrogel electrodes with satisfactory mechanical and desalination properties were obtained by adjusting the crosslinking density and the concentration of the ion exchange polymer. The composite hydrogel electrode exhibits a more hydrophilic surface due to the PVA matrix. When used as cathode in an asymmetric CDI device, the composite electrode adsorbs cations (Na⁺) and reaches a salt adsorption capacity of 8.49 mg·g^-1 and a specific capacitance of 118.0 F·g^-1. While the charge efficiency of CDI device is 53.82%. The quaternary ammonium groups of the ion-exchange polymer on the cathode surface repel co-ions (Cl^-) via Donnan exclusion, effectively mitigating the co-ion effect. In addition, it exhibits excellent long-time durability. After 50 cycles, the electrode exhibited a specific capacitance of 118.0 F·g^-1 with 93.66% retention of its initial capacitance (126.1 F·g^-1), demonstrating minimal performance degradation. Notably, the salt adsorption capacity retention rate remained stable at 92.4% under continuous charge-discharge operation, further confirming the structural robustness of the PVA composite gel matrix. The composite hydrogel electrode provides a novel strategy for the development of CDI technology.