A new standard metric describing the adsorption capacity of carbon electrode used in membrane capacitive deionization.

Abstract A new standard metric has been developed to express the actual adsorption capacity of the carbon electrode in consideration of the electrode reactions. The adsorption experiments were carried out by changing the cell potentials (0.6–1.6 V) in the MCDI unit cell. The point at which the electrode reactions occur was determined from the change in instantaneous charge efficiency during the adsorption process. Then, the total charge supplied to the carbon electrode at this point was defined as the maximum allowable charge (MAC). The MAC values were constant at 59 C/g irrespective of cell potentials. In addition, the salt adsorption capacity (S A C M A C ) and the charge efficiency at MAC were approximately 16 mg/g and 91%, respectively, regardless of the cell potentials. Furthermore, the equivalent circuit analysis for the MCDI cell revealed that Faradaic reactions rarely occur at the MAC. The MAC is the maximum charge that can be supplied to the carbon electrode without electrode reactions. It is also unaffected by the cell components and operating conditions of the MCDI cell. Therefore, the MAC is expected to be a useful metric to objectively express the actual adsorption capacity of the carbon electrode. Graphical abstract Image 1 Highlights • The total charge supplied until Faradaic reactions occurred is defined as MAC. • The MAC values of the carbon electrode were constant regardless of the cell potentials. • The desalination performances at MAC were constant irrespective of the cell potentials. • MAC can be a useful metric to describe the adsorption capacity of carbon electrodes. [ABSTRACT FROM AUTHOR]