Enhanced salt removal performance of flow-electrode capacitive deionization via NaOH activation of coffee waste-derived carbonaceous electrodes: Roles of surface textural features

초록

The effects of NaOH activation on the surface textural features of coffee waste-derived carbonaceous electrodes (CWCE) governing the salt removal performance of the flow-electrode capacitive deionization (FCDI) process were comprehensively evaluated. Since NaOH activation significantly improved the textural characteristics (specific surface area, pore volume, mesoporosity, less hydrophobicity, and viscosity) of CWCE, the electrochemical performance of the FCDI stack utilizing NaOH-activated CWCE (CWCENA) was much superior to that with CWCE. Hence, the salt removal performance of the FCDI process utilizing CWCENA (average salt removal rate (ASRR) = 0.0276 mg/cm(2).min; charge efficiency (CE) = 58.1%) was approximately 8 times higher than that using CWCE (ASRR = 0.0032 mg/cm(2).min; CE = 52.1%). Under various operating conditions, the FCDI process with CWCENA eliminated effectively either positively or negatively charged ions from saline water, in which non-Faradaic electrosorption was found to be crucial for the salt removal of the FCDI process rather than electrodialysis. Furthermore, the tested FCDI process utilizing CWCENA achieved the highest salt removal performance even at 10 wt% dosage (ASRR = 0.0433 mg/cm(2).min; CE = 61.1%). This means that no occurrence of flow-electrode agglomeration at high dosage conditions might lead to the better salt removal performance of the FCDI process. Based on these reasons, it can be concluded that CWCENA has great potential as a carbonaceous electrode-based flow-electrode material for improving the salt removal performance of the FCDI process.

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