VOLUME 72 : 2024

Supercapacitors, known for high power and long cycle lives, can be made from sustainable materials like
biochar, which is highly porous and derived from abundant raw materials. Rice straw is converted into
biochar via pyrolysis in a tube furnace under N2. Various treatments were explored to enhance biochar’s
porosity and capacitance: (1) varying pyrolysis temperatures (700, 800, 900 °C), (2) chemical treatments
(HNO3 treatment before and after pyrolysis, reflux with HNO3, and high-temperature flash), and (3)
physical treatments (carbon black spiking and wet-milling with a planetary ball mill). Biochar pyrolyzed
at 700 °C showed higher areal capacitance values than those at higher temperatures. Untreated biochar
(UB) had the highest capacitance (55.30 mF/cm2 at 5 mV/s), followed by post-treated biochar (POTB)
at 31.65 mF/cm2. Carbon black spiking further improved these values. BET analysis revealed UB had
a lower surface area and pore volume (44.10 m2/g and 0.0142 m3/g). HNO3 treatment (167.66 m2/g and
0.0916 m3/g) and milling (224.85 m2/g and 0.2257 m3/g) significantly increased these metrics. Milled
biochar (MRB) achieved 53.76 mF/cm2 capacitance with better repeatability, highlighting that optimizing
the preparation conditions of rice straw biochar can significantly increase its porosity, surface area, and
electrochemical performance, repurposing the agricultural waste for supercapacitor applications.