Influence of the concentration of KOH-based aqueous electrolyte on the electrochemical behavior of NiO thin film

Abstract

In this research, we explored the influence of varying concentrations of KOH electrolyte (0.5, 1, and 2 M) on the electrochemical characteristics of Nickel Oxide (NiO) thin film. The deposition of NiO material onto glass and Fluor Tin Oxide (FTO) coated glass substrates was achieved through the chemical spray pyrolysis method. Subsequent examinations encompassed structural, morphological, optical, and electrochemical assessments, employing X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS), UV-VIS-NIR spectrophotometry, and cyclic voltammetry (CV), respectively. XRD analysis unveiled a polycrystalline cubic structure of NiO with a preference for orientation along the (111) plane. Raman spectroscopy confirmed the presence of the NiO phase, whereas SEM images depicted the emergence of interconnected nanograins with occasional minor cracks. EDS examination and elemental mapping further substantiated a homogeneous dispersion of elements. Optical analysis disclosed a band gap energy of 3.54 eV and an average transmittance of 71 % in the visible range. Electrochemical analysis indicated that the specific capacitance reached its peak at [1 M] (70 F. g−1). The [2 M] electrolyte exhibited the highest optical modulation (29 %), the most substantial charge density (Qi = 9.5 mC/cm2), and the most favorable switching kinetics. However, the coloration efficiency slightly decreased from 30.94 cm2/C in [1 M] to 30.47 cm2/C in the [2 M] solution, despite these improvements.