Fabrication of Low-Cost and Ecofriendly Porous Biocarbon Using Konjaku Flour as the Raw Material for High-Performance Supercapacitor Application

[Image: see text] Low-cost and ecofriendly porous biocarbons were fabricated from konjaku flour via precarbonization and potassium hydroxide (KOH) activation. The obtained biocarbon AC(K)-5 derived from a precarbonized carbon/potassium hydroxide (KOH) mass ratio of 1:5 possessed an ultrahigh specific surface area of 1403 m(2) g(–1) and hierarchical porous structures with the existence of micro- to macropores. When AC(K)-5 was employed as a supercapacitor electrode in 6 M KOH, it showed a high specific capacitance of 216 F g(–1) and excellent cycling stability with capacitance retention remaining 93.7% after 5000 cycles. Moreover, the AC(K)-5 sample acquired a supramaximal specific capacitance of 609 F g(–1), and the high energy density of AC(K)-5//AC(K)-5 symmetrical cells reached up to 9.2 Wh kg(–1) when p-phenylenediamine serving as a redox electrolyte was added into KOH electrolyte. The reported simple fabrication strategy would leverage a green biomass precursor for the preparation of supercapacitors.