Novel strategy to enhance the desalination performance of flow-electrode capacitive deionization process via the assistance of electro-catalytic water splitting

Abstract Flow-electrode capacitive deionization (FCDI) has gained lots of attention for the continuous operation, fast and scalable desalination process. However, the flow electrode slurry is poorly conductive and resulting in the high ions transport resistance, which restricts its desalination efficiency. In this work, a novel FCDI system was constructed by using the porous nickel foam (NFM) as the current collector, and its desalination performance was enhanced via the assistance of electro-catalytic water splitting. In detail, the functionalized current collectors (NFM-Co3O4 with enhanced oxygen evolution activity and NFM-Co(OH)2 with enhanced hydrogen evolution activity) were prepared through a two-step procedure of electrodeposition and subsequently anodic reaction/cathodic reaction. A desalination efficiency of 90.22% was obtained by the FCDI system adopted functionalized NFM (F-NFM-FCDI) after 100 min operation at applied voltage of 2.0 V, which was much higher than that of the FCDI system adopted bare NFM (NFM-FCDI, 65.37%). Moreover, F-NFM-FCDI system possessed higher charge efficiency (CE) of 81.24% and lower normalized energy consumption (NEC) of 237.54 J·mmol-1 under this condition. Mechanism analysis demonstrated that the enhancement on the desalination performance of F-NFM-FCDI system was attributed to the improved conductivity in flow-electrode chamber, which was due to the increase in the concentration of H+ and OH- caused by the enhanced electro-catalytic water splitting reaction during charging. In summary, this work provided a novel and facile strategy to improve the desalination performance of FCDI system by coupling with electro-catalytic water splitting.