Sustainable processing of electrodes for membrane capacitive deionization (MCDI)

Membrane capacitive deionization has been explored as an alternative desalination technique which can lower the voltage requirement and the ability to regenerate the electrodes. Traditional materials used in electrode processing can lead to various environmental problems related to toxicity, biodegradability and depletion of natural resources. Herein the use of sustainable alternatives to electrode components is reported, focusing on the implementation of bio–derived and F–free binders and green solvents, respectively. These sustainably processed electrodes display improved hydrophilicity (water contact angles of between 6° and 36°), higher values for internal surface area (between 1640 m2g–1 and 2025 m2g–1) and improved gravimetric capacitance (up to 82 Fg–1) compared to activated carbon electrodes prepared with polyvinylidene fluoride binder. Green solvents such as γ-valerolactone and Agnique AMD 3L (N,N-dimethyl lactamide) were able to produce stable dispersions, demonstrating the feasibility of replacement of N-methyl-2-pyrrolidone solvent in electrode processing. The resultant electrodes were successfully employed in membrane capacitive deionization using various cell configurations, achieving high values of salt adsorption capacity (0.0147) and charge efficiency (94%). The implementation of cellulose acetate, carboxymethyl cellulose and polyacrylic acid binders, prepared in green solvents, has shown potential to increase salt removal and decrease the energy consumption of membrane capacitive deionization.