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

Abstract

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.