Capacitive deionization (CDI) is a promising desalination technology but is often limited by the low ion removal capacity of carbon-based electrodes. In this study, a hybrid capacitive deionization (HCDI) system employing an asymmetric silver/activated carbon (Ag/AC) electrode configuration was investigated under constant-current operation and compared with a conventional membrane capacitive deionization (MCDI) system. Desalination performance was evaluated using CDI Ragone plot analysis, while galvanostatic charge–discharge measurements were used to examine the potential evolution of individual electrodes. The results show that the Faradaic Ag/AgCl reaction stabilizes the cell voltage and expands the usable potential window of the activated carbon electrode. As a result, the HCDI system consistently outperformed MCDI, achieving a maximum salt adsorption capacity of 36.5 mg g⁻¹ in a 10 mM NaCl solution, more than twice that of MCDI (17.0 mg g⁻¹), along with a faster ion removal rate. These findings demonstrate that integrating Faradaic electrodes effectively overcomes the intrinsic capacity limitations of conventional CDI systems.
Jaehan Lee (Wed,) studied this question.