1 Water Desalination using Capacitive Deionization with Microporous Carbon Electrodes

Capacitive deionization (CDI) is a water desalination technology in which salt ions are removed from brackish water by flowing through a spacer channel with porous electrodes on each side. Upon apply-ing a voltage difference between the two electrodes, cations move to and are accumulated in electro-static double layers inside the negatively charged cathode and the anions are removed by the posi-tively charged anode. One of the key parameters for commercial realization of CDI is the salt adsorp-tion capacity of the electrodes. State-of-the-art electrode materials are based on porous activated carbon particles or carbon aerogels. Here we report the use for CDI of carbide-derived carbon (CDC), a porous material with well-defined and tunable pore sizes in the sub-nanometer range. When com-paring electrodes made with CDC with electrodes based on activated carbon, we find a significantly higher salt adsorption capacity in the relevant cell voltage window of 1.2-1.4 V. The measured adsorp-tion capacity for four materials tested negatively correlates with known metrics for pore structure of the carbon powders such as total pore volume and BET-area, but is positively correlated with the vol-ume of pores of sizes <1 nm, suggesting the relevance of these sub-nm pores for ion adsorption. The charge efficiency, being the ratio of equilibrium salt adsorption over charge, does not depend much o