Structural and electrochemical properties of opaque sol–gel deposited WO3 layers

The preparation of thick and opaque WO3 layers by a simple sol–gel method is presented. The structure and morphology of these films has been assessed by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sol–gel WO3 layers were found to have oxygen replaced by a significant amount of hydroxyls and water incorporated in their structure. They consist of particles with dimensions of several microns, have high porosity and increased surface area, which renders them suitable for gas sensing applications. Their color changes reversibly from yellowish green to dark blue upon insertion of lithium ions. They are electrochemically stable and can withstand more than 1000 voltammetric coloration–bleaching cycles.