Effect of cross-chamber flow electrode recirculation on pH and faradaic reactions in capacitive deionization

Mitigating faradaic reactions is critical for improving charge efficiency, reducing energy consumption, and protecting electrodes from degradation during desalination in capacitive deionization (CDI). In this study, we examined the influence of recirculating flow electrodes (FEs) within their respective anode and cathode chambers [within-chamber (WC)] or across them [cross-chamber (CC)] on pH, faradaic reactions, and energy demand under constant current operation. By changing from WC to CC (without FEs), the difference in pH between the anode and cathode chambers decreased from 10 to 4.5 units. Adding FEs to CC recirculation further reduced the pH gradient between anode and cathode chambers and resulted in the most stable pH (10.4 +/- 0.08) of all treatments. We attributed the improvements in CC recirculation to faradaic consumption of anode-generated H+ at the cathode and neutralization of H+ and OH- via water formation. The capacitive behavior of FEs reduced several faradaic reactions by decreasing the whole-cell voltage. The energy consumption by the electrodes was reduced by 25% for the anode and 35% for the cathode when FEs were operated in CC instead of WC recirculation. These findings indicate that continuously recirculating FEs across the anode and cathode chambers can minimize detrimental faradaic reactions and pH changes in FE-CDI.