Core–Shell Fe3O4@C Conductive Additives for Magnetic Flow-Electrode Capacitive Deionization: Reconstruction of Charge Percolation Networks

Flow-electrode capacitive deionization (FCDI) based on suspension or semisolid electrodes is a promising alternative for large-scale applications, yet precise control over their transport behavior has not yet been accomplished. Here, we report a general approach for remotely manipulating the transport of the hybrid suspension electrodes composed of core–shell Fe3O4@C nanoparticles and powdered activated carbon (AC) simply by employing a magnetic field. Benefiting from the reconfiguration of the charge percolation networks, the average salt removal rate (ASRR) of magnetic FCDI was increased by 61.7% compared to that of FCDI without the magnetic field. The mechanism of magnetic field-magnetic carbon (MC) coupling includes three main pathways: (i) increasing the local concentration of active electrodes on the current collector surface, (ii) increasing the contact sites available to the current collector, and (iii) shortening the ion transport distance. It was also demonstrated that MC could be used as a novel active electrode by further increasing the adsorption capacity of the carbon shell. Under a moderate magnetic flux (Φ = 45 mT), the ASRR and charge efficiency reached 0.16 μm cm–2 min–1 and 94.3%, respectively. In addition, MC is mechanically and chemically robust and can be recovered and reused in long-term operation by magnetic separation. In brief, our study introduces a general strategy to enhance charge transport in suspension electrodes and demonstrates the promising potential of magnetic FCDI for efficient and low-cost desalination.