Effect of puffing on electrochemical properties of sorghum seed based porous carbon materials in supercapacitors

Biomass-based carbon materials are renewable, affordable and environmentally friendly, possessing great potential in electrochemical energy storage as electrode materials in supercapacitors due to their large specific surface area and self-doped heteroatoms. However, the electrochemical properties of these carbon materials may be influenced to some extent by pretreatment procedures of carbon precursors. For this research, a range of porous carbon materials based on unpuffed and puffed sorghum seeds were synthesized under various pre‑carbonization and activation temperatures. Among them, the puffed sorghum seed-based porous carbon (PH-R6A7), prepared through pre‑carbonization at 600 °C and KOH activation at 700 °C, exhibits a higher graphitization degree, increased N and O content, as well as a greater variety of nitrogen-containing groups and significant increasing graphite nitrogen compared to unpuffed sorghum seed-based porous carbon (PC-R6A7) fabricated under similar conditions. These improvements result in enhanced conductivity and wettability of electrode materials, thereby boosting their electrochemical properties. In a three-electrode setup employing a 6 M solution of KOH, PH-R6A7 demonstrates an exceptional specific capacitance of 523.84 F g⁻¹ at 1 A g⁻¹ compared with PC-R6A7 of 366.00 F g⁻¹; even at a high current density of 20 A g⁻¹ it maintains a high level of capacitance at 387.94 F g⁻¹. When employed in a double-electrode configuration at the same current density (i.e., 1 A g⁻¹), PH-R6A7 also achieves higher specific capacitance of 357.83 F g⁻¹ than PC-R6A7 (286.89 F g⁻¹), accompanied by an increased energy density of 12.35 Wh kg⁻¹ and 8.85 Wh kg⁻¹ at a power density of 249.97 W kg⁻¹ and 4.98 kW kg⁻¹, respectively. Furthermore, after undergoing 10,000 cycles at 2 A g⁻¹, PH-R6A7 demonstrates a superior capacitance retention of 99.68 % and coulomb efficiency of 99.91 %. PH-R6A7 fabricated through the combination method of puffing pretreatment and carbonization activation merits acknowledgment as an electrode material of superior performance and notable practical importance.