Improving the electrochemical response of nanostructured MoO3 electrodes by Co doping: Synthesis and characterization

CoxMo1-xO3 (x = 0, 0.03, 0.06, and 0.09) thin films were deposited on indium-doped tin oxide-coated and glass substrates by a sol-gel method. All the samples crystallized in the stable orthorhombic phase as revealed by X-ray diffraction patterns, with a granular shaped surface confirmed by field emission scanning electron microscopy. The optical band gaps of the samples were obtained by two different optical methods; namely, optical transmittance spectroscopy and diffuse reflectance spectroscopy. There was considerable agreement between the band gaps determined by the two methods. The experimental band gaps were compared with theoretically computed values obtained by density functional theory calculation of the density of states for x = 0 and x = 0.06. The theoretical band gaps served as qualitative confirmation for experimental ones. It was also revealed that the presence of Co as an impurity in MoO3 with an optimized incorporation amount of x = 0.06 refined the morphology and layered structure with an orthorhombic phase, which resulted in improvement of the electrochemical performance in both 1 M KOH electrolyte and LiClO4/propylene carbonate electrolyte.