In this article, Hafnium oxide (HfO2) overlayer was reported to be loaded on the surface of WO3 nanoparticles by a simple solvothermal method for the first time. HfO2 powders were dissolved in the concentrated sulfuric acid as raw material. The physicochemical properties of WO3 nanoparticles with and without HfO2 passivation layer were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). For the film electrode prepared with doctor-blade method, scanning electron mic...