Mo incorporation in WO3 thin film photoanodes: Tailoring the electronic structure for photoelectrochemical hydrogen production

The electronic surface structure of Mo-incorporated WO3 (WO3:Mo) is investigated using direct and inverse photoemission and compared to that of pure (Mo-free) WO3. The films are found to be n-type with an electronic surface band gap of 3.27 (+/- 0.15) eV. The conduction band minimum (valence band maximum) is 0.64 (+/- 0.10) eV above [2.63 (+/- 0.10) eV below] the Fermi level and at most 0.38 (+/- 0.11) eV above the H+/H-2 reduction potential [at least 1.66 (+/- 0.11) eV below the H2O/O-2 oxidation potential]. The findings suggest an explanation why WO3:Mo/WO3 bilayer structures show improved photoelectrochemical performance compared to respective single layer photoanodes.