Designing NiCo₂S₄-Acetylene black engrained nitrogen-doped porous reduced graphene oxide nanocomposites conducting network: As positive/negative electrode combinations for high energy density of asymmetric supercapacitor and hydrogen evolution reaction

The development of two-dimensional composite materials for energy conversion/storage applications is crucial in light of the current high energy demand. Herein, we report the synthesis of nitrogen-doped porous reduced graphene oxide (N-prGO), NiCo₂S₄-acetylene black (NiCo₂S₄-AB), and their composite by hydrothermal method for supercapacitor (EC) and hydrogen evolution reaction (HER) applications. The morphology of the N-prGO/NiCo₂S₄-AB composite appeared as clusters bound in a few thin layers, confirmed by SEM, HR-TEM characterizations. EDAX mapping and elemental analysis confirmed the structural compositions. The synthesized composite materials were used for the fabrication of four different EC combinations of anode and cathode materials to study the performance of symmetric EC (SEC) and Asymmetric EC (AEC). Among them, the ACE type N-prGO (negative)/NiCo₂S₄-AB (positive) electrode combination showed the highest specific capacitance of 321.75 Fg^-1 at 2 mVs⁻¹ high energy density of 59.7 WhKg⁻¹ along with good power density of 450 WKg^-1 and time constant of 345 s. Furthermore, the N-prGO/NiCo₂S₄-AB composite studied as the electrode for HER, showed the lowest overpotential (198 mV) and Tafel slope (98 mV dec⁻¹) values, thus indicating a potential electrode for hydrogen production. The synergetic effect between morphology and mesoporosity of the N-prGO/NiCo₂S₄-AB composite plays a vital role in improving charge transfer which ultimately showed the superior performance of the N-prGO/NiCo₂S₄-AB composite towards dual applications.