This work reports the hydrothermal synthesis and comprehensive characterisation of cobalt-doped molybdenum trioxide (Co–MoO₃) nanostructures at cobalt doping concentrations of 2.5%, 5%, 7%, and 10%. The orthorhombic alpha-MoO₃ crystal structure (JCPDS 05-0508) was retained across all compositions as confirmed by X-ray diffraction (XRD), with no secondary cobalt oxide or molybdate phases detected. Progressive Co²⁺ incorporation (ionic radius 0.745 Å) at Mo⁶⁺ sites (ionic radius 0.59 Å) induced systematic lattice expansion, with peak positions shifting monotonically to lower 2θ values, and crystallite size reduction from approximately 38 nm in undoped MoO₃ to 24 nm at 7% Co. Microstrain increased from 0.12% to 0.33% across the doping range. Field-emission scanning electron microscopy (FE-SEM) revealed that Co doping progressively transformed the characteristic plate-like belt morphology of alpha-MoO₃ into a faceted, irregularly aggregated nanoparticle texture with substantially higher inter-particle porosity, reaching an optimal open architecture at 7% Co. Energy dispersive X-ray (EDAX) analysis confirmed stoichiometric Mo–O elemental ratios with Co atomic percentages closely matching nominal synthesis values. FTIR spectra showed systematic changes in the Mo=O (990 cm⁻¹) and Mo–O–Mo (870, 820 cm⁻¹) vibrational modes with increasing Co content, alongside the emergence of a Co–O stretching feature near 560 cm⁻¹ above 5% doping. Optical band gap analysis by UV–Visible Tauc plots revealed progressive band gap narrowing from 3.1 eV (undoped MoO₃) to approximately 2.55 eV at 10% Co, attributed to intra-gap Co²⁺ d-states and associated oxygen vacancy donor levels. Cyclic voltammetry in 1 M Na₂SO₄ electrolyte demonstrated that 7% Co–MoO₃ achieved the highest specific capacitance in the series, benefiting from the synergistic enhancement of Mo⁶⁺/Mo⁵⁺ intercalation pseudocapacitance and supplementary Co²⁺/Co³⁺ redox charge storage. The results establish 7% as the optimum Co doping level and provide detailed structure–property correlations for the Co–MoO₃ system relevant to the design of high-performance metal oxide pseudocapacitor electrodes.
Publication Date: 2026-06-14