Surface textural and rheological properties of rice husk-derived carbonaceous electrodes pyrolyzed under CO2 atmosphere controlling brackish water desalination performance of flow-electrode capacitive deionization: Effects of pyrolysis temperatures

초록

Flow-electrode capacitive deionization (FCDI) has emerged as a sustainable and energy-efficient brackish water desalination technique to solve water shortage. Among various components, electrode materials are mainly responsible for deciding brackish water desalination performance of the FCDI process. In this study, four different rice husk-derived carbonaceous electrodes (RHCEx; x: pyrolysis temperatures) under CO2 atmosphere were synthesized at 500 degrees C, 650 degrees C, 800 degrees C, and 950 degrees C to investigate systematically the effects of pyrolysis temperatures on their surface textural and rheological characteristics determining brackish water desalination performance of the FCDI process. RHCEx produced at higher temperatures was advantageous for the FCDI process due to superior surface textural features, high aromaticity, high bulk conductivity, and solid-like rheological nature. Hence, the FCDI stack employing RHCE950 showed the excellent electrochemical performance (specific capacitance (C-S) = 0.25 F/g) compared to RHCE500 (C-S = 0.12 F/g), RHCE650 (C-S = 0.14 F/g), and RHCE800 (C-S = 0.22 F/g) which led to the better brackish water desalination performance of the FCDI process. Despite the higher ASRR value of RHCE950 (0.0363 mg/cm(2)<middle dot>min), RHCE800 (ASRR = 0.0348 mg/cm(2)<middle dot>min) was regarded to be the most promising for the FCDI process owing to its highest yield-normalized ASRR value (RHCE800 (0.0093 mg/cm(2)<middle dot>min) > RHCE950 (0.0046 mg/cm(2)<middle dot>min) > RHCE650(0.0015 mg/cm(2)<middle dot>min) > RHCE500 (0.0007 mg/cm(2)<middle dot>min)). Electrosorption was mainly responsible for the elimination of charged ions from brackish water by the FCDI process employing RHCE800 under various operating conditions, where electrodialysis and Faradaic reaction partially contributed. Moreover, brackish water desalination performance of the FCDI process employing RHCE800 at 10 cycles remained 91 % compared to first cycle. Based on these observations, RHCE800 was considered as an alternative to activated carbon-based electrodes for the FCDI process capable of alleviating the water shortage problems.

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