Alkali-activation as a facile way to reinforce porosity and defective aromatic structures of rice husk-based carbonaceous electrodes via C and Si etching governing brackish water desalination performance of flow-electrode capacitive deionization

초록

This study comprehensively compared rice husk-based carbonaceous electrodes (RHCE) and NaOH-activated RHCE (RHCESHx; x: NaOH concentrations) to investigate the feasibility of NaOH-based alkali-activation for enhancing porous and defective aromatic structures of RHCE directly associated with brackish water desalination performance of flow-electrode capacitive deionization (FCDI). Porous and defective aromatic structures were better developed on RHCE surfaces due to the etching of C and Si via facilitated corrosive reactions between alkaline metal oxides and/or reactive gases at higher NaOH concentrations during pyrolysis. These phenomena changed the rheological nature from fluid-like behavior to solid-like behavior of flow-electrode suspensions with RHCE. Consequently, the FCDI stack employing RHCESH4.0 (specific capacitance (C-S) = 0.39 F g(-1); total resistance (|Z|(0.01 Hz)) = 91.5 Omega) exhibited higher electrochemical performance than that using other RHCEs (C-S = 0.23-0.35 F g(-1); |Z|(0.01 Hz) = 96.9-177.4 Omega), leading to the greatest brackish water desalination performance of the FCDI process employing RHCESH4.0. In contrast, RHCESH2.0 appeared to be more cost-effective than other RHCEs in terms of yield-normalized average salt removal rate values (ASRR(YN)) of the FCDI process (ASRR(YN): RHCESH2.0 (0.0371 mg cm(-2) min(-1)) > other RHCEs (0.0292-0.0345 mg cm(-2) min(-1))). Electrosorption played a dominant role in eliminating charged ions, rather than electrodialysis, in the FCDI process employing RHCESH2.0 under various operational conditions. As the FCDI process employing RHCESH2.0 maintained excellent brackish water desalination performance at 10 cycles, it can be a promising option for stimulating practical applications of the FCDI process.

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