Enhancing the electronic and ionic transport of flow-electrode capacitive deionization by hollow mesoporous carbon nanospheres

Flow-electrode capacitive deionization (FCDI) is a promising desalination technology by virtue of its infinite electrosorption capacity and possible continuous operation. However, FCDI still suffers from the limited electronic and ionic transport of its flow-electrode. Herein, we first employed hollow mesoporous carbon nanospheres (HMCNs) as flow-electrode to improve FCDI desalination performance. To understand the dependence of FCDI performance on the structural properties of flow-electrodes, two other samples, activated carbon (AC) and solid mesoporous carbon nanospheres (SMCNs), were selected for comparison. The results showed that HMCNs flow-electrode exhibited excellent rheological behaviors with good dispersibility and increased viscosity. EIS analysis proved that HMCNs flow-electrode had a decreased electrical resistance and enhanced ion diffusion. As expected, HMCNs exhibited improved desalination performance compared with AC and SMCNs. In particular, at 1.2 V with 10 % mass loading, the average salt removal rate, charge efficiency, and energy consumption reached 0.040 mg/cm2∙min, 92.9 %, and 0.035 kWh/mol, respectively. The excellent desalination performance should be attributed to the structural advantage of HMCNs in electronic and ionic transport. Overall, this study provides insights into the dependence of FCDI performance on the structural properties of flow-electrodes, thereby progressing the FCDI technology in relation to electronic/ionic transport.