Simulation, synthesis, and characterization of Ni-Co and its co-doping in ZnO for energy applications

Pristine ZnO, ZnO doped with nickel (Ni), cobalt (Co), and their co-doped form (NiCo) nanoparticles were successfully synthesized via the sol-gel method to explore their potential for energy-related applications. The structural, morphological, and optical characteristics of the prepared samples were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), photoluminescence (PL), and UV-vis spectroscopy. The XRD analysis confirmed that all samples retained a hexagonal wurtzite structure, with minor peak shifts indicating successful incorporation of dopant ions into the ZnO lattice. The EDX spectra verified the presence of Zn, Ni, Co, and O elements, while FTIR spectra confirmed the characteristic functional groups and chemical bonds within the ZnO matrix. SEM imaging revealed that co-doping produced smaller, more uniform nanoparticles with increased surface roughness, beneficial for surface-related applications. Photoluminescence studies showed a red shift in emission from 371 nm (pure ZnO) to 379 nm (NiCo-ZnO) and a reduced optical bandgap from 3.34 eV to 3.27 eV, indicating enhanced defect states and improved charge carrier dynamics. UV-vis absorption spectra further revealed a bandgap of 3.35 eV for NiCo-ZnO at 370 nm, reflecting complex optical behavior due to co-doping. To optimize synthesis conditions, a fuzzy logic-based simulation was employed, providing predictive insights into bandgap, crystallite size, and optical properties. Notably, the simulation results closely matched the experimental data, validating the modeling approach. The co-doped ZnO samples demonstrated good reproducibility and optical stability over time, maintaining consistent optical absorption and emission characteristics after multiple testing cycles and storage under ambient conditions. These findings highlight that Ni and Co co-doping effectively tailors the optical and electronic properties of ZnO, making it a promising material for energy storage devices, photocatalytic applications, and sensing technologies. The enhanced defect states, increased surface area, and modified band structure collectively contribute to improved performance in real-world functional devices.