Hydrogen in tungsten trioxide by membrane photoemission and density functional theory modeling

The measurement of hydrogen induced changes on the electronic structure transition metal oxides by X-ray photoelectron spectroscopy is a challenging endeavor, since origin cannot be unambiguously assigned to hydrogen. H-induced in tungsten trioxide have been known for more than 100 years, but are still being controversially debated. controversy stems from difficulty disentangling effects due hydrogenation oxygen deficiencies. Using membrane approach spectroscopy, combination with tuneable synchrotron radiation we measure simultaneously core levels and valence band up pressure 1000 mbar. Upon hydrogenation, intensities W$^{5+}$ level state close Fermi increase following pressure-composition isotherm curve bulk H$_x$WO$_3$. Combining experimental data density-functional theory description coloration proton polaron model corroborated. Although near edge, edge now dominated orbitals instead as case pristine oxide having wider implication its use (photo-electrochemical) catalyst.