Facile preparation of a novel biomass-derived H3PO4 and Mn(NO₃)₂ activated carbon from citrus bergamia peels for high-performance supercapacitors

•An efficient method to produce high-quality activated carbons derived from renewable sources.•Activated carbon structures containing P, N and Mn3O4 dispersed along the carbon matrix.•Materials with excellent capacitive properties, reaching a specific capacitance of 289 F.g−1 in 6 M KOH.•Outstanding values of energy density in [EMIM][BF4] ionic liquid electrolyte, with maximum value of 50.8 Wh kg−1 at a power density of 240 W kg−1.