Sonication-assisted activation of empty fruit bunches to produce activated carbon for supercapacitor's electrodes: Surface chemistry and morphology characterization

Thermochemical treatment of empty fruit bunches (EFBs) had been proven to be the fastest way of converting this agro-industrial waste into value. Two-step carbonization and activation was used to convert the EFB to activated carbon with high specific surface area (SSA) and porosity. Hydrothermal carbonization was done at 225 to 275 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>°C</mml:mo></mml:mrow> </mml:math> ; at retention time of 1-3 h. Activation was done at 800 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>°C</mml:mo></mml:mrow> </mml:math> for 1 h, using KOH at two different concentrations. The BET surface area, porosity and surface functional groups of the activated carbon were investigated. The samples experienced change in colourations, with the degree of colouration increases with the time and temperature of the reaction. The increase in these parameters also led to increase in the alkane functional groups and corresponding decreased in the hydroxyl functional groups. The specific surface area was measured using BET and maximum surface of 1375.26 m²/g was obtained when the biomass was carbonized at 275 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>°C</mml:mo></mml:mrow> </mml:math> for 1 h, and activated at 800 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>°C</mml:mo></mml:mrow> </mml:math> using KOH at a concentration of 1:1 to the hydrochar. Ultrasonic post-treatment of the activated carbon enhanced the BET surface area and pore volume to about 1.13 and 1.16 times, respectively. The corresponding pore diameter and volume at this optimum condition were 3.32 nm and 0.73 cm³/g, respectively. The material demonstrated a high specific surface area for electronic and ionic diffusions.