Hierarchical hollow carbon spheres as advanced flow electrodes for high-efficiency capacitive desalination

Flow-electrode capacitive deionization (FCDI) has emerged as an intriguing desalination technology. However, the performance of FCDI is fundamentally limited by the transport properties of the flow-electrode materials. In this study, hierarchical hollow carbon nanospheres (HCNSs) were evaluated as advanced flow-electrode materials for FCDI. Benefiting from their well-defined hollow interiors and hierarchical porous structures, the HCNSs-based flow electrode exhibits favorable rheological behavior, reduced electrical resistance, and enhanced ion diffusion compared to commercial activated carbon (AC) and hollow mesoporous carbon nanospheres (HMCNs). Under optimized conditions (1.2 V, 5 wt% carbon content), the HCNSs-based FCDI achieved an average salt removal rate (ASRR) of 66.86 μg cm −2 min −1 , a charge efficiency of 91.03%, and low energy consumption of 0.037 kWh mol −1 . Impressively, the HCNSs flow electrode maintained structural integrity after six consecutive desalination cycles, and sustained an ASRR of 57.85 μg cm −2 min −1 over 12 h of non-stop operation. These results highlight the structural advantages of HCNSs in promoting both electronic and ionic transport, offering a rational design strategy for advancing the development of efficient FCDI systems.