Tungsten Oxide Hydrogenation Effect

To further elucidate the effect of hydrogenation and determine the surface chemical state of tungsten oxide, we performed X-ray photoelectron spectroscopy analysis on tungsten oxide. Shown are the XPS full spectrum, W-4f spectrum and O-1s spectrum of three tungsten oxide samples. As can be seen from the figure, the three tungsten oxide samples contain W element, O element and a small amount of C element. The presence of the C-1s peak is attributed to unnatural hydrocarbons from the XPS instrument itself. And from the full spectrum of view, the three samples showed no significant change in each peak.

Three tungsten oxide samples have two peak binding energies present in bulk tungsten oxide. 37.7 and 35.5 eV, corresponding to W-4f_{5 / 2} and W-f_{7 / 2} orbitals of hexavalent tungsten ions, respectively. In the W-300 sample, in addition to these two binding energies, two new binding energy peaks exist. 36.4 and 34.3 eV, corresponding to the W-4f_{5 / 2} and W-f_{7 / 2} orbitals of the pentavalent tungsten ions. That is, the presence of pentavalent tungsten ions under hydrogenation at 300°C indicates the presence of oxygen vacancies in the sample. However, when hydrogenated at 400 ° C, two new binding energy peaks exist: 33.4 and 35.5 eV, corresponding to tetravalent tungsten ions.

That is, as the hydrogenation temperature increases, pentavalent tungsten ions and tetravalent tungsten ions are generated at 400°C. The formation of pentavalent tungsten ions and tetravalent tungsten ions indicates that the surface of the tungsten oxide is partially reduced and the O / W ratio is reduced to form oxygen vacancies on the surface to form an oxygen-deficient structure. And compared with the pentavalent tungsten ions, the formation of tetravalent tungsten ions makes the ratio of oxygen and tungsten decreased more obvious, the more the oxygen vacancies generated, the more obvious oxygen defects. The formation of pentavalent tungsten ions and tetravalent tungsten ions is the reason why the sample turns blue.

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