Superiority of a novel flow-electrode capacitive deionization (FCDI) based on a battery material at high applied voltage

Abstract

Flow-electrode capacitive deionization (FCDI) provides the opportunity for continuous desalination operation of high concentration saline water. In this study, we firstly report the application of a battery material (a Prussian blue analogue, copper hexacyanoferrate, CuHCF) as flowable electrode in FCDI system, where it is coupled with activated carbon (AC). Its desalination performance under different voltage is evaluated when dealing with 10 g L−1 NaCl solution. Results show that the salt removal rate and salt removal efficiency of the designed FCDI is enhanced as increasing in applied voltage from 1.2 to 2.8 V. Moreover, benefiting from the high capacity of CuHCF material, the novel FCDI based on CuHCF-AC pair shows superiority over conventional FCDI with AC-AC pair when operates at high voltage over 2.0 V (e.g. salt removal rate of 0.12 vs. 0.11 mg cm−2 min−1, salt removal efficiency of ~91 vs. 84% and current efficiency of ~96 vs. 95% at 2.8 V), even though the pH of the concentrated water changes more significantly. The results indicate that FCDI based on CuHCF-AC electrode pair is effective in dealing with high saline water at high voltage. Other sodium ion intercalation material may also be applied in FCDI.