UV−visible diffuse reflectance spectroscopy was used to probe the electronic structure and domain size of tungsten oxide species in crystalline isopolytungstates, monoclinic WO3, and dispersed WOx species on ZrO2 surfaces. UV−visible absorption edge analysis, CO2 chemisorption, and Raman spectroscopic results show that three distinct regions of WOx coverage on ZrO2 supports appear with increasing WOx surface density:  submonolayer region (0−4 W nm-2), polytungstate growth region (4−8 W nm-2), and polytungstate/crystalline WO3 coexistence region (>8 W nm-2). The structure and catalytic activity of WOx species on ZrO2 is controlled only by WOx surface density (W nm-2), irrespective of the WOx concentration, oxidation temperature, and ZrO2 surface area used to obtain a particular density. The submonolayer region is characterized by distorted octahedral WOx species that are well dispersed on the ZrO2 surface. These species show a constant absorption edge energy, they are difficult to reduce, and contain few a...

/pdf/structure-and-electronic-properties-of-solid-acids-based-on-2ikoo481kf.pdf

Structure and Electronic Properties of Solid Acids Based on Tungsten Oxide Nanostructures

http://iglesia.cchem.berkeley.edu/Publications/JournalofCatalysis_181_57_1999.pdf

Structural and Catalytic Characterization of Solid Acids Based on Zirconia Modified by Tungsten Oxide

The faradaic efficiency for O2(g) evolution at thin-film WO3 photoanodes has been evaluated in a series of acidic aqueous electrolytes. In 1.0 M H2SO4, persulfate was the predominant photoelectrochemical oxidation product, and no O2 was detected unless catalytic quantities of Ag+(aq) were added to the electrolyte. In contact with 1.0 M HClO4, dissolved O2 was observed with nearly unity faradaic efficiency, but addition of a hole scavenger, 4-cyanopyridine N-oxide, completely suppressed O2 formation. In 1.0 M HCl, Cl2(g) was the primary oxidation product. These results indicate that at WO3 photoanodes, water oxidation is dominated by oxidation of the acid anions in 1.0 M HCl, H2SO4, and HClO4, respectively.

/pdf/a-quantitative-assessment-of-the-competition-between-water-2a9dxlrdyr.pdf

A quantitative assessment of the competition between water and anion oxidation at WO3 photoanodes in acidic aqueous electrolytes

Various hybrid functionals combined with both plane wave and localized basis sets have been used for a systematic study of the structural and electronic properties of all phases of WO3. It is found that hybrid functionals work at least as well as the standard DFT/GGA functional in predicting lattice constants and equilibrium volumes. However, the adoption of hybrid functionals has the advantage to considerably improve the Kohn−Sham band gap which is always severely underestimated by the standard DFT calculations. The HSE06 functional in combination with a plane wave basis set describes well the band gap of WO3, while the B3LYP functional associated with a localized basis set slightly overestimates it. The band gap can be made fully consistent with experiment by fixing the amount of Hartree−Fock exchange in the hybrid functional to 15%.

P. Boldrini

Papers

Neutron diffraction investigation of WO3