Electrochemical characterization of RuO2 and activated carbon (AC) electrodes using multivalent Ni(NO3)2 electrolyte for charge storage applications

•Ni-based aqueous electrolyte could be a good candidate for RuO2 and AC based supercapacitors.•Insertion of Ni2+ could result in increased crystallinity of RuO2 electrodes.•Large size of Ni2+ may limit its diffusion into the crystalline RuO2.•Irreversibility in Ni(OH)2 on the electrode surface may result in poor cyclic capacitance.