In-Situ Growth of 2D to 3D NiO on Nickel Foam with Enhanced Capacity Retention as Battery-Type Electrode for Asymmetric Supercapacitor

This work presents a systematic study to synthesize NiO on nickel foam (NF) using a straightforward and cost-efficient hydrothermal method, followed by calcination. Through comprehensive physicochemical analyses, it was demonstrated that the properties of the NF@NiO could be modulated by adjusting the concentration of the nickel (II) nitrate hexahydrate precursor. Notably, a morphological transition from a 2D sheet-like structure to a 3D rambutan-like formation was observed as the precursor concentration increased. The best-performing NF@NiO 4 mM showed a maximum areal capacity of 723 mC cm⁻² (equivalent to 547.73 F g⁻¹) at a current density of 0.5 mA cm⁻². This electrode also maintained remarkable cycle stability, retaining 78.9% of its capacitance after 10,000 cycles at a current density of 50 mA cm⁻² in 2 M KOH. Furthermore, the assembled asymmetric supercapacitor (ASC) (NiO 4 mM//AC) achieved a specific capacitance of 64.79 F g⁻¹ at a current density of 1 A g⁻¹ with an energy density of 17.63 Wh kg⁻¹ at a power density of 700 W kg⁻¹.