Exploring the Synergistic Effects of Fe3+ and Cu2+ Co-Doping in Hydrothermally Synthesized NiO Nanoparticles for Enhanced Supercapacitor Performance

The current experimental investigation emphases on the synthetization and characterizations of pure and Fe³⁺& Cu²⁺ co-doped [Ni_0.5Fe_0.02Cu_0.06O_x, Ni_0.5Fe_0.04Cu_0.04O_x, and Ni_0.5Fe_0.06Cu_0.02O_x] NiO nanoparticles (NPs) prepared through the hydrothermal method for improved supercapacitor performance. The synthesized NiO NPs were subjected to annealing at 800 °C and subsequently examined using a range of characterization methods.The XRD analysis verified the existence of a face-centered cubic (FCC) structure.The FESEM-EDAX confirmed successful dopant incorporation, revealing changes in surface morphology and particle size. An enhancementin the optical bandgap from 3.15 to 3.45 eV was found by the UV–Vis-DRS study, indicating the possibility of quantum confinement effects. The XPS provided insights into the surface chemistry, confirming the presence and concentrations of Ni²⁺, Fe³⁺ and Cu²⁺ ions in their respective chemical states. BET analysis indicated a reduction in the specific surface areafrom 18.59 m²/g (pure NiO) to 11.04 m²/g (co-doped NiO), but an increase in pore diameter facilitates ion diffusion. Electrochemical analysis showed that [Ni_0.5Fe_0.06Cu_0.02O_x] achieved a highest specific capacitance of 546 F g⁻¹, at 10 mVs⁻¹exhibiting significantly superior performance than pure NiO NPs.This study highlighted the potential of Fe³⁺ and Cu²⁺ co-doped NiO NPs in enhancing the electrochemical performance of supercapacitors through improved charge storage capacity and conductivity.Furthermore, cyclic stability testing revealed that the co-doped sample retained approximately 92.12% of its initial capacitance after 2000 charge–discharge cycles, demonstrating excellent long-term electrochemical durability. These results underline the importance of doping in optimizing material properties for next-generation energy storage devices, making these nanoparticles a promising candidate for sustainable and high-performance supercapacitors.