Theory of water desalination by porous electrodes with fixed chemical charge

Abstract

Water desalination by capacitive deionization (CDI) is performed via electrochemical cells consisting of two porous carbon electrodes. Upon transferring charge from one electrode to the other, ions are removed from the feedwater by electrosorption into electrical double layers (EDLs) within the micropores of the porous carbon. When using electrodes containing fixed chemical charge in the micropores, various counterintuitive observations have been made, such as "inverted CDI" where upon charging, ions are released from the electrode, and the feedwater is only desalinated when the cell is discharging. We set up an EDL model including chemical charge that explains these observations and makes predictions for a working range of enhanced desalination by CDI.