Screening of high-performance flow electrodes for fluoride removal using flow-electrode capacitive deionization

Flow-electrode capacitive deionization (FCDI) shows promise for treating fluoride-containing wastewater, yet its performance remains limited by the choice of electrode materials. In this study, activated carbon (AC) and carbon black (CB) were systematically compared as flow-electrode materials for fluoride removal. The CB-based system achieved 98.7% fluoride removal within 120 min at 1.0 V, substantially outperforming the AC system (60.9%), representing a 37.8‑percentage‑point improvement. This enhancement is attributed to the higher specific surface area and well-developed mesoporous structure of CB, which provide abundant electrosorption sites and facilitate ion diffusion. CB also exhibited superior electrochemical performance, with higher charge efficiency (81.1% vs. 59.2%) and lower energy consumption (5.32 vs. 8.50 kWh/mol) than AC. Electrochemical impedance and rheological analyses revealed that the improved performance of CB is associated with a more uniform conductive network, reduced charge-transfer resistance, and enhanced ion transport. Furthermore, fluoride accumulated in the electrolyte was recovered as lithium fluoride (LiF) via chemical precipitation, demonstrating the feasibility of integrating contaminant removal with preliminary resource recovery. This study fills the gap in systematic comparison of AC and CB for FCDI defluoridation, establishes a multi-dimensional structure–performance correlation, and provides a basis for developing efficient and resource-oriented FCDI processes for fluoride-containing wastewater treatment.