Enhanced salt removal performance of flow electrode capacitive deionization with high cell operational potential

Capacitive deionization (CDI) is an emerging technology with great potential to be energy efficient and allow cost-effective operation for the removal of salt ions from saline water. The introduction of flow electrode to CDI greatly enhanced the salt removal performance at much higher salt concentration, even at seawater level, due to not needing a discharging process, which is required for conventional CDI desalination. Since the oxidation of carbon electrodes and water electrolysis leads to the decrease in desalination performance and long-term stability of the CDI cell, it has typically been operated at the potential difference < 1.2 V. However, due to the various resistances of CDI components, it is known that the electrode potential is lower than the applied cell potential difference. Based on such knowledge, in this study, we operated FCDI desalination at various operational potential differences from 1.2 to 4.5 V, and studied the carbon oxidation and electrochemical characteristics by FT-IR, Raman spectroscopy, and EIS measurements. Desalination efficiency and salt removal rate increase with higher operational potential difference. Our results confirmed that up to 2.5 V, no noticeable carbon oxidation and gas generation resulting from water electrolysis occurred.