Influence of ammonium fluoride concentration on the morphological, structural, optical and electrochemical properties of nanoporous WO₃ films

This paper reports the synthesis and characterization of tungsten oxide by anodization method for 1 h using (1 M H₂SO₄, 1 M Na₂SO₄) electrolyte solution while varying NH₄F concentration. The influence of NH₄F concentration on structural, morphological, optical, and photocatalytic properties is examined. Scanning electron microscopy images show  the formation of a thin layer with porous nanostructure attributed to the dissolution of anodic oxide by H⁺ and F⁻ ions in the electrolyte under UV radiation of 365 nm. X-ray diffraction analysis  reveals a mixed-phase crystal system of WO₃, consisting of both monoclinic and tetragonal phases The crystallite size is found  in the range 5.5‒18.2 nm with increasing NH₄F concentration. UV–Vis spectroscopy analysis indicates a narrowing in the energy bandgap from 3.06 to 2.35 eV. Cyclic voltammetry manifests  a decrease in the anodic peak current density with the rise in the concentration rate of NH₄F. These findings extend a better understanding of the influence of NH₄F concentration on the structural and electrochemical characteristics of the anodized nanoporous WO₃ film as a potential candidate for hydrogen generation by the water-splitting process.