Improved performance of flow-electrode capacitive mixing through N-doping of activated carbon

Flow electrodes, which are integral to flow-electrode capacitive mixing (F-CapMix), primarily consist of activated carbon (AC), conductive additive and an aqueous electrolyte with a salt. For the better performance of F-CapMix, the AC must have a high surface area and excellent electrical conductivity to facilitate efficient charge percolation and electron transport between the AC particles within the flow electrode. In this study, nitrogen-doped activated carbon (N-doped AC) was synthesized through a straightforward process involving the heating of a mixture of raw AC and melamine in a covered container. The resulting N-doped AC powder exhibited an average of 20 % higher electrical conductivity than raw AC powder without sacrificing the surface area (AC: 2284.7 m2/g vs N-doped AC: 2125.6 m2/g) owing to the incorporation of graphitic nitrogen and oxidized nitrogen into the raw AC surface. The surface characteristics of N-doped AC were found to be similar to those of raw AC. Electrochemical impedance spectroscopy analysis of F-CapMix utilizing N-doped AC in the flow electrode revealed reduced resistance and increased capacitance, leading to an enhancement in power density from 0.706 to 0.828 W/m2. Consequently, integrating N-doped AC into the flow electrode can contribute to the improved performance of F-CapMix.