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

Abstract 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 .