Large-scale synthesis of functional tungsten oxide with controlled oxygen-deficiency by a continuous screw reactor

Oxygen-deficient tungsten oxide is one of the promising materials for broad applications due to its enhanced characteristics owing to the oxygen-deficiency. Development of a mass production process is crucial in consideration of the increasing demand of this material in industrial purposes. A continuous screw reactor was employed to the production of oxygen-deficient tungsten oxide. The effects of hydrogen concentration and the reduction time on the composition of products were investigated. The maximum WO_2.72 mole fraction of 0.95 was achieved by optimum hydrogen concentration and reduction time. X-ray Photoelectron Spectroscopy (XPS) spectra of the products indicated the introduction of oxygen-deficiency. Anisotropic crystal growth in the (010) direction is found in the cross-section observation by Scanning Electron Microscope (SEM). The displacing value from High-Resolution Transmission Electron Microscope (HR-TEM) demonstrated the existence of WO_2.72. The reaction kinetic was investigated by thermogravimetric analysis. Estimated activation energy supported the results from the continuous process. This work suggests the promising process for the large-scale production of functional materials.