Hierarchical NiCo/NiO/NiCo₂O₄ composite formation by solvothermal reaction as a potential electrode material for hydrogen evolutions and asymmetric supercapacitors

Electrochemical energy storage and conversion mechanisms are highly viable routes in the current scenario, and hence supercapacitor and electrolysis of water splitting have gained significant attention in recent times. Thus, transition metal nickel cobalt oxides are widely inspected as promising electrode materials for electrocatalysis and supercapacitors. However, the pure NiCo₂O₄ was highly hindered by its widespread uses due to low electronic conductivity and deficient active edges. This study is aimed to fabricate the NiCo/NiO/NiCo₂O₄ composite using a solvothermal process with different ratios of solvents. The inherent NiCo/NiO/NiCo₂O₄ composite holds plentiful active edges and improved electrical conductivity than the pure. Interestingly, the electrocatalytic results revealed that the NiCo/NiO/NiCo₂O₄ (NC) composite prepared by a solvent ratio of (double distilled water (DDW) to N, N-Dimethylformamide (DMF)) 2:1 (NC1) displayed the small overpotentials of 144 and 142 mV to realize 10 mA cm⁻² with the robust durability during a 24 hours hydrogen evolution reaction (HER) test in the acid and alkaline electrolyte, respectively. Moreover, the designed NC1 composite as a supercapacitor electrode exhibited considerable capacitance of 638 F g⁻¹ at a current density of 1 A g⁻¹. In comparison, the analog DDW to DMF ratio 1:1 (NC2) and 1:2 (NC3) structures showed 514 F g⁻¹ and 415 F g⁻¹, respectively. Further, a dual-electrode device was fabricated using the NC1 composite and activated carbon, exhibited an energy density of 28.14 W h kg⁻¹ at 414.45 W kg⁻¹ power density with excellent device stability (89.4%) for 10 000 charge/discharge cycles.