Carbon electrodes with ionic functional groups for enhanced capacitive deionization performance

Operation of the AC-CDI cell assembled using the A-AC and S-AC electrodes where salts are adsorbed when potential is applied (charged step) and are desorbed at short circuit (discharged step). [Display omitted] Capacitive deionization (CDI) has proved to be a clean and green technology; however, the charge leakage in the electrode pores during the adsorption-desorption cycles lowers the desalination efficiency. In this work, commercially available activated carbon was chemically treated to give the activated carbon surface either immobilized amino groups or sulfonic acid groups. The amino group-containing and sulfonic group-containing carbon materials were used as anode and cathode electrodes, respectively, in assembling a CDI (AC-CDI) cell. The salt adsorption capacity, salt removal efficiency, and charge efficiency of the AC-CDI cell were over two times higher than those of the untreated carbon-based CDI cell and comparable with those of the membrane CDI (MCDI) cell. The greatly improved desalination performance of the AC-CDI cell was attributed to enhanced wettability, faster diffusion of counter ions to each electrode via electrostatic attraction, and the prevention of re-adsorption of ions via repulsion between the charged layers and co-ions during adsorption-desorption cycle. Thus, it can be concluded that chemically modified carbon-based CDI cell is highly promising for practical application.