Biomass-derived nitrogen-doped porous carbon as a sustainable flow-electrode material for enhanced capacitive deionization

Freshwater scarcity has emerged as a critical global environmental challenge. Flow-electrode capacitive deionization (FCDI) represents a promising technology for achieving efficient and low-energy seawater desalination. This study presents a novel flow-electrode material, nitrogen-doped porous carbon (NPC), which is derived from biomass and demonstrates both cost-effectiveness and high performance. The NPC material is synthesized from bean shells through high-temperature pre-carbonization followed by activation with KHCO₃, resulting in a rich porous structure, increased specific surface area, and high graphitization degree, which collectively confer superior capacitance performance compared to activated carbon (AC). Desalination experiments indicate that the FCDI performance of the NPC flow-electrode surpasses that of the AC flow-electrode. Specifically, at a voltage of 2.5 V in a 6 g·L⁻¹ NaCl solution, the NPC system achieves an average salt removal rate (ASRR) of 104.9 μg·cm⁻²·min⁻¹, with a charge efficiency (CE) of 94.0% and an energy consumption (EC) of only 4.4 kJ·g⁻¹. Furthermore, the NPC-based FCDI system exhibits commendable desalination cycling stability, maintaining relatively stable energy consumption and efficiency after prolonged continuous desalination cycles. This research holds significant implications for the advancement of environmentally friendly, low-cost, high-performance FCDI systems for large-scale applications.