Enhancing Co<sub>3</sub>O<sub>4</sub> nanoparticles: Investigating the impact of nickel doping and high-temperature annealing on NiCo<sub>2</sub>O<sub>4</sub>/CoO heterostructures

<p>In this study, we investigated the phase transition of cobalt spinel (Co₃O₄) nanoparticles into Co_3-xNi_xO₄/CoO heterostructures by introducing varying amounts of nickel (x = 0.0–0.16) and subjecting the particles to high annealing temperatures of 1000 ℃. X-ray diffraction (XRD) analysis confirmed the Co_3-xNi_xO₄CoO structure for all samples. Transmission electron microscopy (TEM) provided further insights into the phase or heterostructure of the samples after annealing, revealing the arrangement of the two phases. Fourier-transform infrared spectroscopy measurements demonstrated a band shift around 537 cm^-¹ with increasing Ni content, while ultraviolet-visible (UV-Vis) measurements indicated the energy band (<italic>Eg</italic>). Significant morphological changes were observed in scanning electron microscope (SEM) measurements at 0.16 Ni, displaying irregular agglomerates. Our findings suggest that introducing Ni into the Co₃O₄ structure and increasing the annealing temperature to 1000 ℃ can lead to the formation of a heterostructured system. Furthermore, our study's significance is highlighted by the streamlined synthesis of NiCo₂O₄/CoO using the sol-gel method followed by calcination. This departure from complex techniques provides an efficient route to acquiring the NiCo₂O₄/CoO system, a promissory material for advancing supercapacitor research.</p>