Recent advances in capacitive deionization: a comprehensive review on electrode materials

Capacitive deionization (CDI)technology has shown practicality and cost-effectiveness for water desalination. However, electrode development remains a major challenge. Carbon electrodes, commonly used in CDI, have limited adsorption capacity, necessitating the improvement of their physicochemical and electrochemical properties. To address these limitations, Faradaic electrodes based on the redox process have emerged as an alternative. Faradaic reactions in CDI systems offer benefits such as pseudocapacitive/intercalation effects and the development of charged species. Different types of Faradaic reactions include anodic oxidation reactions (to be avoided in CDI), cathodic oxygen reduction reactions, and Faradaic ion storage processes involving intercalation effects. Faradaic electrodes exhibit higher ion storage capacity due to their redox reactions and have been produced in various forms, expanding the range of available CDI electrodes. This indicates a promising future for Faradaic materials in CDI technology. The review highlights recent strategies in the development of capacitive and Faradaic electrode materials for CDI, along with progress in material synthesis and its impact on desalination. The review also introduces approaches to address complexities in defining optimal electrode parameters and achieve material optimization in electrochemical desalination. Overall, advancements in material development for electrochemical desalination processes are overviewed.