<p>The precursor of reactant material plays a pivotal role in determining the charge storage behaviour of supercapacitors. In this work, a binder-free solvothermal route was employed to fabricate three-dimensional nickel oxide (NiO) microflower, by varying concentrations of nickel nitrate precursor (0.3, 0.4, and 0.5M) on stainless steel (SS) substrates labelled as N3-SS, N4-SS, and N5-SS. The 0.4M NiO optimized sample was also grown on nickel foam (Nf) named N4-Nf to compare NiO performance on both substrate for supercapacitor applications. The samples were comprehensively characterized using XRD, EDS, SEM, TEM, FTIR, BET, and XPS techniques. The NiO microflower revealed notable pseudocapacitive behaviour with good charge storage ability. Among all prepared samples, the N4-SS electrode demonstrated superior performance, achieving a maximum capacitance of 431 F g⁻¹ on SS and 855 F g⁻¹ on Nf at 0.5 A g⁻¹ in 2 M KOH electrolyte. Furthermore, the N4-Nf electrode delivered an energy density of 29.68 W h kg⁻¹ and a power density of 104 W kg⁻¹ at a current density of 0.5 A g⁻¹. It also retained 75% of its initial capacitance after 5000 charge–discharge cycles, confirming its good cycling durability. The synthesized NiO-based supercapacitor electrode exhibits appreciable capacitance, promising stability, favourable power output, and low impedance, highlighting its potential for practical energy storage applications.</p>