A novel method to tailor the porous structure of KOH-activated biochar and its application in capacitive deionization and energy storage

This study reveals a novel method to tailor the micro- and meso-porous structures of activated biochar by exploiting the interaction between pre-carbonization drying conditions and carbonization temperature in KOH activation. Biochar samples were mixed with concentrated KOH and then dried under air or nitrogen for various periods of time (0-280 h) followed by carbonization at 475, 675 or 875 degrees C. It is confirmed that by manipulating drying conditions and carbonization temperatures, the KOH activated biochar can have a predominantly microporous, mesoporous or a combined (micro/meso) porous structure. The surface area, micropore and mesopore volumes tailored between: 488-2670 m(2) g(-1), 0.04 -0.72 cm(3) g(-1), and 0.05-1.70 cm(3) g(-1), respectively. The mechanism of porosity development was investigated by FTIR analysis suggesting conversion of KOH to K2CO3 due to different drying conditions as a major role in tailoring the structure. The application of activated biochar with tailored porosity was investigated for Electric Double Layer adsorption of NaCl/NaOH to be employed in water treatment (capacitive deionization) or energy storage (supercapacitor) processes. The majorly microporous activated biochar (N-2-dried activated at 675 degrees C) showed promising capacitances between 220 and 245 F g(-1). Addition of mesoporous structure resulted in capacitances between 182 and 240 F g(-1) with significantly reduced electrode resistance and improved capacitive behavior as evidenced by Impedance Spectroscopy and Galvanostatic Charge/Discharge tests. (C) 2016 Elsevier Ltd. All rights reserved.