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

Abstract

Flow-electrode capacitive deionization (FCDI) based on suspension or semisolid electrodes is a promising alternative for largescale 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 Fe 3 O 4 @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.

Asymmetric Fe2+/Fe3+-Mediated Flow-Electrode Capacitive Deionization for the Removal of Chloride Ions in Reclaimed Water

“…Figure S5b showed the survey of the samples, which showed a similar peak shape. The peaks of C 1s and O 1s were almost unchanged as seen in Figures S5c and S4d 3,19,50 The XPS results also demonstrated that AC was not oxidized. This stable operation of FCDI was attributed to the voltage drop across all components of the FCDI cell.…”

“…The increase in RE was due to the capacitive contribution of FCDI. 19 That was, when chloride ions migrate into the anode solution and were then transiently stored on the AC, a double electric layer was formed on the surface of the AC. 36 The contribution of the capacitive process was 27.48%.…”

“…17,18 In both approaches, the transfer of electrons is facilitated by lowering the resistance between the electrode particles, which then increases the adsorption capacity of the flow electrode. 19 Although the method of adding conductive materials is simple and effective, adding too much solid material will inevitably increase the viscosity of the flow electrodes, in addition to increasing energy consumption, and may even clog the tiny flow channel. 20 For example, Liang et al found that when the carbon black concentration reached 2 wt %, the flow electrodes flow slowly or even become immobile.…”

A Hexagonal Honeycomb-Shaped Flow Channel for High-Efficient Desalination and Flowability in Flow-Electrode Capacitive Deionization

“…Although the electrode particles within the SS-channel appear to accumulate similarly to the RC-channel, there is a high risk for the stability of the FCDI system in long-term operation due to the narrow nature of the flow channel, such as channel blocking and slurry leakage. Except for the bend, the high-velocity shear flow generated by the single-track channel can weaken the hydrodynamic boundary layer on the surface of the straight channel, which is detrimental to charge percolation networks and electron conduction . Importantly, the HH-FCDI exhibited superior stability in desalination performance compared to RC-FCDI and SS-FCDI systems (Figure f), both C / C 0 were always steady during the continued operation, and the SR, CE, and ENRS ended up at 64.89%, 96.06%, and 5.76 μmol J –1 , respectively (Table S7).…”

“…Except for the bend, the high-velocity shear flow generated by the single-track channel can weaken the hydrodynamic boundary layer on the surface of the straight channel, which is detrimental to charge percolation networks and electron conduction. 53 Importantly, the HH-FCDI exhibited superior stability in desalination performance compared to RC-FCDI and SS-FCDI systems (Figure 7f), both C/C 0 were always steady during the continued operation, and the SR, CE, and ENRS ended up at 64.89%, 96.06%, and 5.76 μmol J −1 , respectively (Table S7). The average ASRR (2.05 μmol cm −2 min −1 ) in the whole operation of the HH-FCDI system was significantly faster than the FCDI system with a conventional flow channel (Figure 7g).…”