Neodymium-Driven Surface-Modified WO ₃ Nanomaterials for Superior Electrochemical Hydrogen Evolution Reaction

In the present work, the hydrothermal synthesis method was employed to synthesize tungsten trioxide (WO3) and neodymium-doped tungsten trioxide (Nd:WO3) nanoparticles. XRD techniques revealed that both tungsten oxide (WO3) and neodymium-doped tungsten oxide (Nd-doped WO3) exhibit a monoclinic crystalline structure with crystalline sizes in the nanoscale range. Increasing concentrations of Nd doping (1%, 3%, 5%, and 7%) had a negligible effect on crystallinity and particle sizes. The energy value of the bandgap was determined using UV–visible absorption spectroscopy, while SEM analysis of pure WO3 revealed cuboidal or rectangular-shaped structures. Significantly, the addition of Nd did change the morphology to plate-like or nanosheet structures, and it is also apparent that the addition of Nd as a dopant affects the growth and morphology of material particles significantly. Overall, as the doping concentration increases, we observe an initial increase, followed by a decrease in particle size. The obtained particle sizes are 30, 45, 51, 57, and 52 nm for pure, 1, 3, 5 and 7% Nd doped WO3, respectively. TEM analysis helps to observe the surface topography, structure, and perceived internal particle arrangement of the synthesized NPs. To examine the electrochemical performance of the synthesized WO3 and Nd-doped WO3 NPs, cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) were used. CV analysis indicated that Nd doping significantly improved both Cs (specific capacitance) and ED (energy density), which reached a maximum of 908 F/g and 113 Wh/kg for the 5 wt % Nd-doped WO3 sample. In addition, LSV showed improved hydrogen evolution reaction (HER) activity, and a minimum overpotential of 190 mV (iR-corrected) at a current density of 10 mA/cm2 was noted with the same 5 wt % doping. The EIS results verified these results through attaining the least charge transfer resistance for the 5 wt % Nd:WO3 nanoparticles. XPS analysis confirmed the presence of Nd in the WO3 lattice and identified the elements W, O, and Nd, along with the corresponding oxidation states. In conclusion, the results of this work have demonstrated how Nd doping could significantly enhance the structural, micromorphological, and electrochemical performance of WO3, supported by confirming that Nd:WO3 is a feasible and advantageous electrocatalyst for water electrolysis.