Porous interconnected NiCo₂O₄ nanosheets and nitrogen- and sulfur-codoped reduced graphene oxides for high-performance hybrid supercapacitors

We demonstrate a facile hydrothermal synthesis of the interconnected porous NiCo₂O₄ nanosheets for hybrid supercapacitor applications. The as-synthesized NiCo₂O₄ nanosheets show a high specific capacitance of 3137 F g⁻¹ at a current density of 2 A g⁻¹, which is much greater than 1916 and 1251 F g⁻¹ of Co₃O₄ and NiO, respectively. Interestingly, the total specific capacitance of the NiCo₂O₄ is almost close to the sum of the specific capacitance of the NiO and Co₃O₄. Furthermore, a hybrid supercapacitor is configured with the NiCo₂O₄ nanosheets and the nitrogen- and sulfur-codoped reduced graphene oxide as the positive and negative electrodes, respectively. This hybrid supercapacitor delivers a maximum energy density of 33.64 W h kg⁻¹ at a power density of 1196 W kg⁻¹ and excellent long-term cyclic stability over 12,000 charge/discharge cycles at the enlarged voltage window of 1.5 V. The remarkable supercapacitive performances of the hybrid device are attributed to the interconnected porous structure of NiCo₂O₄ nanosheets and three-dimensional continuous macropores of codoped reduced graphene oxides.