Next-generation calcium oxide nanoparticles: A breakthrough in energy storage and humidity sensing

Chemical precipitation method was applied to synthesize CaO nanoparticles. The synthesized nanoparticles were then characterized by using different analytical methods including X-ray Diffraction, Fourier Transform Infrared spectroscopy, Field Emission Scanning Electron Microscopy, X-ray photoelectron spectroscopy, UV–Visible spectroscopy, thermogravimetric analysis and nitrogen adsorption-desorption analysis. Average crystallite size determined from XRD was found to be 42 nm, whereas average particle size obtained from FESEM images was 163 nm. In the FTIR analysis, the observed bands at 2040 and 873 cm⁻¹, corresponding to Ca-OH and Ca[sbnd]O stretching vibrations, confirmed the successful synthesis of CaO nanoparticles. XPS analysis confirmed that the sample was mainly composed of calcium [25.34 %], and oxygen [63.53 %]. TGA showed two significant weight losses, the former 9.81 % at 390–420 °C due to thermal decomposition of calcium hydroxide to calcium oxide and water and the later 18.98 % at 600–700 °C due to removal of chemical adsorbed water molecules and disintegration of the left over CaCO₃. Electrochemical performance such as supercapacitance and cyclic stability of the prepared sample were evaluated by studying different electrochemical factors like Cyclic Voltammetry, Galvanostatic Charge Discharge and Electrochemical Impedance Spectroscopy. Supercapacitance calculated from CV study was 23.45–72.22 F/g at different scan rates ranging from 2.5 to 100 mV/s, while supercapacitance values obtained from GCD study were 11.77 to 30.18 F.g⁻¹ at various current density ranges from 0.5 to 5 A.g⁻¹. Humidity sensor measurements were performed by determining changes in resistance of the sensing material applying LCR (Q) meter due to changes in humidity levels in a close chamber. Humidity sensing response/recovery times of CaO nanoparticles were noted as 79 s and 147 s. The evaluation of the examined factors concluded that the synthesized CaO nanoparticles can be successfully applied for supercapacitance and humidity sensing.