Enhanced Charge Efficiency and Electrode Separation Utilizing Magnetic Carbon in Flow Electrode Capacitive Deionization

Flow electrode capacitive deionization (FCDI) holds great advantage and potential compared with conventional CDI as it enables continuously water desalination. However, efficient electrode separation to prevent its runoff is a great challenge that has not been well addressed. In this study, we demonstrated an FCDI process tailored for ion electrosorption using magnetic activated carbons (MACs) synthesized by simple coprecipitation of Fe3O4 on carbon substrate. The Fe3O4 provides the magnetism necessary for magnetic separation, while the carbon substrate endows electrosorption sites for ions. When used as electrodes in desalination cycles, the MACs exhibit similar salt removal rate with bare activated carbon but extremely high charge efficiency (>100%) and energy efficiency because of enhanced interparticle aggregation increasing electric conductivity and causing charge imbalance in the electrode chambers. The MAC also exhibited excellent magnetic separation efficiency (>99.81%) with its half retention lifetime 2 orders of magnitude higher than activated carbon and high stability with a lifetime of thousands of cycles. This study provides an easy and "contactless" separation of the fluidized electrodes in the FCDI system, which is safe and friendly for FCDI operation and maintenance in practical application.