Anions-capture materials for electrochemical electrode deionization: Mechanism, performance, and development prospects

Desalination is a critical process to resolve the crisis of insufficient freshwater resources. Among desalination technologies, electrochemical electrode deionization (EEDI) has attracted wide attention because of the advantages in low cost, no secondary pollution, and low energy consumption etc. Electrode materials are the critical factors for determining the performance of EEDI. However, the traditional EEDI with carbon electrode (capacitive deionization, CDI) often showed inefficient desalination capacity, charge efficiency, cycle stability as well as ions selectivity due to the anode oxidation. Therefore, the development of anions-capture materials is crucial for the development of EEDI devices. In this review, the anions-capture materials are classified into four categories according to their capture mechanisms: (i) Electrosorption materials, mainly including conventional and modified carbon materials; (ii) conversion reaction materials, mainly including Ag/AgCl and Bi/BiOCl couples; (iii) redox reactions materials including polypyrrole (PPY), poly (2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA) and poly (vinylferrocene) (PVFc); (iv) ions intercalation materials including layered double hydroxides/layered metal oxides (LDHs/LMOs), Mxenes. This review summarizes all currently known anions-capture materials and discussing their mechanisms and performance in detail. Future research focus and other vital issues that need to be addressed are also outlined.