Nitrogen–oxygen co-doped porous carbons prepared by mild potassium hydroxide activation of cicada slough for high-performance supercapacitors

•CPCKx are prepared from cicada slough under low KOH/precursor mass ratio.•Inherently distinct features of cicada slough determine the properties of CPCKx.•Evidence of the effect of surface wettability on the electrochemical performance.•High energy density of 10.3 Wh kg−1 at 10.1 kW kg−1 in Li2SO4 electrolyte.•Impressive energy density of 30 Wh kg−1 at 15.1 kW kg−1 in EMIMBF4 electrolyte.