Investigation of electronic structure, morphological features, optical, colorimetric, and supercapacitor electrode properties of CoWO4 crystals

Abstract

Cobalt tungstate (CoWO4) crystals were synthesized by the co-precipitation (CP) and polymeric precursor (PP) methods with posterior heat treatment at 800 °C for 4 h. The electronic structure, morphological features, optical, colorimetric, and supercapacitive properties were investigated in detail. X-ray diffraction, Rietveld refinement data, micro-Raman spectra, and Fourier transform-infrared spectra proved the crystallization of both CoWO4 materials with a wolframite-type monoclinic structure. Rietveld refinement data were employed as input data to simulate all clusters found in this crystalline structure as well as electron density maps. These results indicated the existence of distortions in both octahedral [CoO6] and [WO6] clusters, yielding an inhomogeneous charge distribution in the monoclinic lattice. Field emission scanning electron microscopy and transmission electron microscopy techniques show the presence of asymmetrical CoWO4 crystals. The ultraviolet–visible diffuse reflectance spectroscopy revealed optical band energy values of 2.84 and 2.89 eV for CoWO4 crystals prepared by the CP and PP methods, respectively. Colorimetric results indicated that the CoWO4 crystals have a desirable feature for the development of blue inorganic pigments. The experimental specific capacitance measurements of CoWO4 crystals as an electrode (CP and PP) were 192.5 Fg−1 and 249.1 Fg−1 at 40 mV s−1 and 5 mV s−1 in an electrode with 0.4 mg and 0.8 mg of electroactive materials in 1 M Na2SO4 solution, respectively.