WO/BiVO Photoanodes: Facets Matching at the Heterojunction and BiVO Layer Thickness Effects.

Photoelectrochemical solar energy conversion offers a way to directly store light into energy-rich chemicals. Photoanodes based on the WO/BiVO heterojunction are most effective mainly thanks to the efficient separation of photogenerated charges. The WO/BiVO interfacial space region in the heterojunction is investigated here with the increasing thickness of the BiVO layer over a WO scaffold. On the basis of X-ray diffraction analysis results, density functional theory simulations show a BiVO growth over the WO layer along the BiVO {010} face, driven by the formation of a stable interface with new covalent bonds, with a favorable band alignment and band bending between the two oxides. This crystal facet phase matching allows a smooth transition between the electronic states of the two oxides and may be a key factor ensuring the high efficiency attained with this heterojunction. The photoelectrochemical activity of the WO/BiVO photoanodes depends on both the irradiation wavelength and the thickness of the visible-light-absorbing BiVO layer, a 75 nm thick BiVO layer on WO being best performing.