Black and white anatase, rutile and mixed forms: band-edges and photocatalytic activity.

Here we investigate the band-level energetics of "black" hydrogenated titania in different polymorphs using in situ photoelectrochemical measurements and XPS valence band measurements. We find that the conduction band of black rutile is higher in energy than in black anatase by 0.4 eV. For photocatalytic hydrogen generation, in a polymorph hetero-junction such as in black Degussa P25, thus black rutile can act as a photosensitizer while black anatase provides charge-mediation catalysis onto H2O to generate H2. By optimizing the thermal reduction conditions of black anatase/rutile junctions the H2 production can be significantly increased.