An activated bio-carbon for electrochemical double-layer capacitor used commercialized potato starch powder as the starting material to produce high-purity spherical carbon using a hydrothermal synthesis method with various reaction times. Chemical activation of the KOH coated bio-carbon spheres was heat treatment from 700-900 °C. The activated bio-carbon activated at 900 °C exhibited as specific surface area of 1579.4 m²/g, average pore size of 2.9663 nm and pore size distribution was mostly concentrated in the range of 1.3–3.5 nm.

As results of the electrochemical characteristics for the electrode of activated bio-carbon synthesized for 12 hrs and activated at 900 °C, in 6 M KOH aqueous electrolyte, the specific capacitance variations were 160.6 F/g at 5 mV/s, 142 F/g at 100 mV/s, and 123.5 F/g at 500 mV/s.