Pseudocapacitive Coating for Effective Capacitive Deionization

Abstract

Capacitive deionization (CDI) features a low-cost and energy-efficient desalination approach based on electrosorption of saline ions. To enhance the salt electrosorption capacity of CDI electrodes, we coat ion-selective pseudocapacitive layers (MnO₂ and Ag) onto porous carbon electrodes (activated carbon cloth) with only minimal use of a conductive additive and a polymer binder (<1 wt % in total). Optimized pseudocapacitive electrodes result in excellent single-electrode specific capacitance (>300 F/g) and great cell stability (70% retention after 500 cycles). A CDI cell out of these pseudocapacitive electrodes yields as high charge efficiency as 83% and a remarkable salt adsorption capacity up to 17.8 mg/g. Our finding of outstanding CDI performance of the pseudocapacitive electrodes with no use of costly ion-exchange membranes highlights the significant role of a pseudocapacitive layer in the electrosorption process.