Anodic NiO nanoparticles as high-performance asymmetric supercapacitor devices in hybrid electrolytes

The energy storage capabilities of a supercapacitor are critically determined by the choice of electrode materials, electrolytes, and synthesis methods, making their appropriate selection indispensable for improving the electrochemical performance. This study presents the synthesis of nickel oxide (NiO) nanoparticles (NPs) by a low-cost, straightforward, and one-step anodization approach. FESEM, HRTEM, XRD, XPS, BET analysis, FTIR, and Raman spectroscopy were performed to determine the morphology, crystal structure, oxidation states, specific surface area, functional groups, and vibrational and rotational states of NiO NPs. The fabricated electrode was investigated for capacitive application in 1 M KOH, Na₂SO₄ and hybrid electrolytes. The electrode showed an enhanced capacitance of 1748 F g^-1 at 2.0 A g^-1 in the hybrid electrolyte compared to 1116 F g^-1 in KOH and 816 F g^-1 in Na₂SO₄. The fabricated asymmetric supercapacitor device (NiO//AC) achieved a specific capacitance of 172 F g^-1 at 2 A g^-1 with an energy density of 34.4 Wh kg^-1 at a power density of 900 W kg^-1. Notably, the device retained 94% capacitance after 8000 cycles at 5 A g^-1. The improved performance can be attributed to the high surface area of NiO NPs, enhanced conductivity, and improved charge kinetics in the hybrid electrolyte. This result demonstrates the potential of anodic NiO NPs as efficient materials in hybrid electrolytes for supercapacitor applications.