A novel method to tailor the porous structure of KOH-activated biochar and its application in Capacitive Deionization and energy storage Dehkhoda, Amir Mehdi; Gyenge, Előd; Ellis, Naoko
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°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 to 2670 m ² g-¹, 0.04 to 0.72 cm³ g-¹, and 0.05 to 1.70 cm³ 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 (N₂-dried activated at 675°C) showed promising capacitances between 220-245 F g-¹. Addition of mesoporous structure resulted in capacitances between 182-240 F g-¹ with significantly reduced electrode resistance and improved capacitive behaviour as evidenced by Impedance Spectroscopy and Galvanostatic Charge/Discharge tests.
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