Thermal annealing-induced structural modifications and electrochemical enhancement of NiO/CNT electrodes synthesized by spray pyrolysis for high-performance supercapacitors

This work studies the structural and electrochemical characteristics of nickel oxide (NiO) and nickel oxide/carbon nanotubes (NiO/CNT) nanocomposites prepared via spray pyrolysis and annealed at 350, 400, and 500 ${}^{°}C$. Structural characterization using X-ray diffraction (XRD) confirms phase purity and crystallinity. The NiO and NiO/CNT samples annealed at 400 °C (400-N and 400-NCT) exhibited optimal performance. Scanning electron microscopy (SEM) images of 400-NCT revealed a compact morphology with well-dispersed CNTs across the NiO nanoparticles. From Brunauer-Emmett-Teller (BET) analysis, its specific surface area was 93.82 m² g⁻¹, broader than 400-N's 35.63 m² g⁻¹, while its pore volume was 0.43 cm³ g⁻¹, larger than 0.13 cm³ g⁻¹ for 400-N. Moreover, 400-NCT displayed higher specific capacitance of 745 F g⁻¹ at 5 A g⁻¹, better rate capability (30.7 %), and superior cycle life (109 % @ 1000 cycles) than 400-N (16.20 F g⁻¹, 26 % rate retention, and 21 % longevity @ 1000 cycles) in 2 M KOH. From electrochemical impedance spectroscopy, 400-NCT portrayed the lowest series and charge transfer resistance (6.60 Ω; 2.28 Ω) than 400-N (7.83 Ω; 20.41 Ω), demonstrating enhanced conductivity. The synergistic combination of CNTs and NiO in the nanocomposite is responsible for the enhanced performance, which boosts the conductivity, enlarges the surface area, and optimizes the pore network for rapid ion transport and enhanced charge storage. These findings show how modifying a process parameter in a facile and affordable method like spray pyrolysis can yield optimal results, contributing to realizing Sustainable Development Goal 7 (SDG 7) of affordable and sustainable energy solutions.