Eutectic salt induced self-activation technique for porous graphene-like carbon nanosheets as the high-capacity cathodes for Zn-ion hybrid supercapacitors

•Graphene-like carbon nanosheets were obtained in different eutectic salts.•In-situ formed Na2CO3 can serve as a chemical activation agent.•The roles of eutectic salt have been revealed.•The carbon has a surface area of 1739.5 m2/g with hierarchical pores.•The carbon nanosheets achieved high specific capacity of 169.1 mAh g−1.