Influence of Ni doping on the structural, morphological, optical, and electrochemical behaviors of CeO2 thin films

Cerium oxide (CeO 2 ) represents a promising candidate for energy storage owing to its mixed-valence states (Ce 3+ /Ce 4+ ) and outstanding chemical stability. Despite these advantages, its low intrinsic electrical conductivity remains a major obstacle to achieving high electrochemical performance. Nickel incorporation is proposed here as a suitable solution to overcome this limitation and improve the charge storage capacity of CeO 2 thin films. Herein, Ce 1-x Ni x O 2 (x = 0, 3, 5, and 7 at%) thin films were successfully deposited via the spray pyrolysis method onto both glass and ITO-coated glass substrates at 450°C. Structural characterization using X-ray diffraction (XRD) and Raman spectroscopy confirmed the formation of a single-phase cubic fluorite structure, with the characteristic active mode detected at 462 cm −1 . Scanning electron microscopy (SEM) indicated that Ni incorporation significantly modified the morphology of CeO 2 thin films. The UV-Vis-NIR spectra showed high transparency (above 70%) in the visible range, accompanied by a slight decrease in the band gap from 3.34 to 3.24 eV upon Ni doping. Electrochemical tests showed that nickel doping improved the energy storage capacity. Specifically, the sample with 5 at% Ni achieved a specific capacitance of 12.2 Fg −1 at 5 mVs −1 and 45.04 Fg −1 at 0.4 Ag −1 , higher than that of the undoped sample. Additionally, the CNi5 sustained high capacity retention over 100 cycles. These findings indicate that nickel-doped CeO 2 thin films emerge as an efficient electrode material for energy storage applications.