Symmetric and Asymmetric Capacitive Deionization Cells Using Modified Porous Carbon Electrodes

Abstract

Capacitive deionization (CDI) is an emerging approach to water treatment that makes use of common porous carbon materials to electrostatically remove ions from a solution.(1-3) Desalination using CDI is achieved in a flow cell consisted of a minimum of a pair of porous carbon electrodes separated by a water channel as sketched in Fig. 1(a). Often, constant-voltage operation is adopted to investigate ion transport of a CDI cell with a charging voltage (V ch) for ion adsorption and a discharge voltage (V dis) for ion desorption.(2)Details are illustrated in Fig. 1(b) by using an ionic charge curve plotted in a potential distribution diagram, where the ionic charge curve is defined by the modified Donnan (mD) model with chemical surface charge for a single carbon electrode according to reference (4, 5). Ion adsorption-desorption by a CDI cell depends upon the placement of the potential of zero charge (E PZC) versusE oin a potential distribution diagram,(6)where E PZC commonly defines a potential when the electrode has a minimum in ion adsorption,(7)as depicted at the lowest point on the ionic charge curves in Fig. 1(b). In this work, by modifying carbon surface chemistry using carbon oxidation, scenarios of different E PZCversus E o are created to investigate the effect of carbon surface charge on ion adsorption-desorption of a CDI cell. A comprehensive study will be performed to demonstrate the importance of the E PZCparameter in a potential distribution diagram on resulting adsorption-desorption characteristics, primarily including real-time measurements of the potential drops at the CDI electrodes during charging and discharging, and developments of a new approach to estimate the E PZCaccording to the mD model with chemical surface charge. References J. Landon, X. Gao, B. Kulengowski, J. K. Neathery and K. Liu, J. Electrochem. Soc., 159, A1861 (2012). X. Gao, J. Landon, J. K. Neathery and K. Liu, J. Electrochem.Soc., 160, E106 (2013). A. Omosebi, X. Gao, J. Landon and K. Liu, ACS Appl. Mater. Interf., 6, 12640 (2014). X. Gao, A. Omosebi, J. Landon and K. Liu, J. Phys. Chem. C, 122, 1158 (2018). P. M. Biesheuvel, H. Hamelers and M. Suss, Colloids Interf. Sci. Commun., 9, 1 (2015). E. Avraham, M. Noked, I. Cohen, A. Soffer and D. Aurbach, J. Electrochem. Soc., 158, P168 (2011). A. J. Bard and L. R. Faulkner, Electrochemical Methods - Fundamentals and Applications, John Wiley & Sons, New York (2001). Acknowledgement This work is supported by the Crosscutting Research, National Energy Technology Laboratory, U.S. Department of Energy (DE-FE0031555). Figure 1