Impact of carbon dioxide-assisted activation on Millettia pinnata shell-derived porous activated carbon for enhanced performance in symmetric supercapacitors

This paper presents a successful application of the physical activation method to convert agricultural biowaste, specifically Millettia pinnata (MP) shells, into activated carbon (AC) for use in cost-effective and environmentally sustainable high-performance supercapacitors. The AC derived from MP shells exhibited remarkable porosity, with a high surface area of 710 m2 g−1 and a total pore volume of 0.143 cm3 g−1, as determined by Brunauer–Emmett–Teller (BET) analysis. Electrochemical assessments revealed that the prepared AC materials demonstrated exceptional electrochemical performance. Experimental results indicate that the AC material achieved a notable specific capacitance of 314.5 F g−1 at 0.5 A g−1 and retains 80 F g−1 at 20 A g−1 in 6.0 M KOH electrolyte. The symmetric supercapacitors constructed using MPAC exhibit an impressive specific capacitance of 120.4 F g−1 at 0.2 A g−1 and energy density of 16.72 W h kg−1 at a power density of 200 W kg−1. Furthermore, these supercapacitors demonstrate good cyclability with capacity retention of 77.1