Synthesis and characterization of CuO/graphene (Core/shell) quantum dots for electrochemical applications

•The CuO/G QDs were synthesized through a simple and hydrothermal technique.•The capacitance has enhanced using the combined hybrid electrolyte (KOH + LiCl).•Specific capacitance exhibits 154 F g−1 at current density of 1 A g−1.•Cycling stability show 84% capacitance retention after 3,000 cycles.