The present study reports the synthesis of nickel-doped tungsten trioxide (Ni–WO₃) nanoparticles at doping concentrations of 2.5%, 5%, 7%, and 10% by a facile one-pot hydrothermal method and their systematic characterisation by X-ray diffraction (XRD), field-emission scanning electron microscopy with energy dispersive X-ray analysis (FE-SEM/EDAX), Fourier transform infrared spectroscopy (FTIR), UV–Visible spectroscopy, and cyclic voltammetry (CV). XRD confirmed the monoclinic gamma-WO₃ phase (JCPDS 43-1035) across all compositions, with progressive lattice expansion and crystallite size reduction from approximately 35 nm in undoped WO₃ to 22 nm at 7% Ni, attributed to partial substitution of W⁶⁺ (ionic radius 0.60 Å) by the larger Ni²⁺ (ionic radius 0.69 Å). FE-SEM revealed a systematic evolution from compact quasi-spherical particles in undoped WO₃ to a roughened, open-porous nanoparticle architecture at 7% Ni, with inter-particle voids of 10–50 nm highly favourable for electrolyte penetration. EDAX confirmed stoichiometric W–O composition with Ni atomic concentrations closely matching nominal values. FTIR demonstrated systematic shifts and broadening of the W–O–W bridging and terminal W=O stretching modes attributable to lattice distortion by the dopant. UV–Visible Tauc plot analysis revealed progressive optical band gap narrowing from 2.65 eV (undoped WO₃) to approximately 2.35 eV at 7% Ni, implying enhanced charge carrier density. Cyclic voltammetry in 1 M Na₂SO₄ electrolyte showed that 7% Ni–WO₃ delivered the highest specific capacitance among the series, with well-defined redox features corresponding to W⁶⁺/W⁵⁺ and supplementary Ni²⁺/Ni³⁺ transitions and satisfactory rate capability across 2–100 mV s⁻¹. The 7% doping level is identified as the optimum, simultaneously maximising lattice expansion, grain boundary density, morphological porosity, and electronic conductivity. These results establish Ni–WO₃ as a promising pseudocapacitive electrode material and provide a clear structure–property framework for further optimisation.
Publication Date: 2026-06-14