Progress in energy recovery and graphene usage in capacitive deionization

Capacitive deionization (CDI) shows promising potential for water desalination due to its high performance, energy efficiency, and environmental friendliness. Because of their excellent conductivity, chemical stability, and high surface area, carbon derivatives are the most used capacitive deionization electrode materials. Among these carbon materials, graphene is quite attractive because of its exceptional electrical conductivity and very large surface area compared with other carbon materials. In addition to the low energy requirements of the CDI that in many scenarios outperforms reverse osmosis, further reduction in the energy can be realized through recovering some of the input energy. The recovered energy can be used to power additional CDI cells, stored in other energy storage devices such as supercapacitors, or used in any other application. This study summarizes recent progress in implementing graphene as an electrode material for CDI and the different methods used for recovering energy from CDI cells. Furthermore, the energy consumption in CDI with and without energy recovery is compared with the most common desalination technologies such as reverse osmosis, multiple-effect distillation, and multistage flash distillation.