TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method comprises performing a degradation/dehydration on the textile solid waste or plastic solid waste at a temperature of 100-200 degrees C under vacuum or at elevated pressure to form a char, washing the char, and drying or evaporating the washed char before performing pyrolysis. The activated carbon or its composite has the form of a composite material structure obtained by adding a composite forming additive including metal element or its metal oxide or a precursor to the textile or plastic solid waste to produce a metal/metal oxide activated carbon matrix during a physical or chemical activation that follows pyrolysis. The activated carbon or its composite is in the form of a composite material structure obtained by adding a composite forming additive including carbon nanotubes (CNTs) to the reactants during degradation/dehydration step. The pyrolysis is performed in the presence of graphite fibers or carbon fibers. The activated carbon or its composite is: further treated in a post-activation process; and grind milled to produce an average particle size of 3-50 mu m. The method further comprising fabricating an electrode by dissolving an optional binder in a solvent or dispersing the optional binder in a dispersion medium with the grind milled activated carbon or its composite to form a composition, applying the slurry to a collector, removing the solvent or the dispersion medium by drying, and leaving behind the binder and activated carbon or its composite on the collector. Preferred Components: The textile solid waste or plastic solid waste is free of virgin materials. The activated carbon or its composite has pores and surface area measured using density functional theory (DFT). The total number of pores are at least 40%, have a size of 2-50 nm. The activated carbon or its composite has a surface area of 900-3000 m2/g. The activated carbon or its composite has a pore volume of 0.400-0.900 cc/g.