Magnetic array for efficient and stable Flow-electrode capacitive deionization

Abstract

• A novel magnetic array-based magnetic FCDI system is introduced. • Core-shell magnetic carbon particles are used as a conductive additive. • The desalination performance of FCDI with low electrode content is enhanced. • The electron percolation efficiency near the current collector is enhanced. Magnetic flow-electrode capacitive deionization (FCDI) is a promising desalination technology; however, it still faces the risk of material stability and flow channel clogging during continuous operation. In this study, a new magnetic array design was introduced in the FCDI system to achieve efficient and stable desalination. Pairs of magnets were uniformly placed on the surface of the end plates along the flow channel to create alternating magnetic and magnetic field-free zones. Core-shell magnetic carbon (MC) was used as the conductive additive to guide the flow electrodes towards the magnet sides, thus creating a high concentration electrode area on the surface of the current collectors. When the flow electrode entered the magnetic field-free zones, the concentrated flow electrode returned to a homogeneous state. The results demonstrated that the desalination rate of FCDI with a low carbon content (1.0–2.0 wt%) increased by more than 120% after the application of a magnetic field. In the magnetic array, the working surface of the current collector significantly increased due to the aggregation effect of MC particles, which improved the electron transfer efficient and shortened the ion transport distance. In addition, the operational stability of FCDI in the magnetic field array was also demonstrated in a long-term operation. When the cell voltage was 1.2 V, the average salt removal rate (ASRR) and charge efficiency of FCDI were maintained at 0.35 μmol cm −2 ·min −1 and greater than 95%, respectively. In summary, magnetic array design offers the potential for FCDI to break through the trade-off between desalination performance and pumping energy consumption.