By employing an oxidative photodeposition of CrOx the Rh/CrOx co-catalyst system was prepared on Ga2O3 and Ta2O5 resulting in up to 25% higher overall water splitting activities.

Chemical vapor synthesis (CVS) is a unique method to prepare well-defined photocatalyst materials with both large specific surface area and a high degree of crystallinity. The obtained β-Ga O nanoparticles were optimized for photocatalysis by reductive photodeposition of the Rh/CrO co-catalyst system. The influence of the degree of crystallinity and the specific surface area on photocatalytic aqueous methanol reforming and overall water splitting (OWS) was investigated by synthesizing β-Ga O samples in the temperature range from 1000 °C to 1500 °C. With increasing temperature, the specific surface area and the microstrain were found to decrease, whereas the degree of crystallinity and the crystallite size increased. Whereas the photocatalyst with the highest specific surface area showed the highest aqueous methanol reforming activity, the highest OWS activity was that for the sample with an optimum ratio between high degree of crystallinity and specific surface area. Thus, it was possible to show that the facile aqueous methanol reforming and the demanding OWS have different requirements for high photocatalytic activity.

We report on a novel route of preparing molybdena-modified bismuth tungstates and their successful application in the photocatalytic oxygen evolution reaction and the oxidation of glycerol. Hierarchically assembled monocrystalline Bi 2 WO 6 nanoplatelets with a specific surface area of 10 m 2 /g were obtained applying a hydrothermal synthesis method using Na 2 WO 4 and Bi(NO 3 ) 3 as precursors, followed by a solvent-free chemical vapor deposition method using Mo(CO) 6 , resulting in highly dispersed molybdena species. Extensive characterization using X-ray photoelectron spectroscopy, low-energy ion scattering, and Raman spectroscopy showed that microcrystalline MoO 3 islands were formed on the bismuth tungstate surface that grew in height and lateral dimension with increasing loading. Correspondingly, the molybdena-modified materials were found to have favorable photocatalytic and photoelectrochemical properties in the oxygen evolution reaction and the selective oxidation of glycerol.

ZnO‐co‐doped GaN is a promising catalyst for photocatalytic overall water splitting in the visible light range. The conventional high‐temperature synthesis has the drawback that only low amounts of Zn2+ ions can be incorporated into the GaN:ZnO matrix due to a substantial loss of volatile Zn metal during the nitridation of the binary oxides in flowing NH3. By applying moisture‐assisted nitridation of a co‐precipitated GaZn precursor under milder conditions it was possible to significantly reduce the Zn loss during nitridation. Using a GaZn precursor with a high Zn content, GaN:ZnO nanoparticles containing high amounts of Zn were obtained. The bandgap was found to decrease nearly linearly with increasing Zn content. Concomitantly, the defect density and structural disorder increased with increasing Zn content.

We present an alternative synthesis strategy for developing nanocrystalline (Ga1−xZnx)(N1−xOx) semiconductors known to be very efficient photoabsorbers. In a first step we produce mixtures of highly crystalline β-Ga2O3 and wurtzite-type ZnO nanoparticles by chemical vapor synthesis. (Ga1−xZnx)(N1−xOx) nanoparticles of wurtzite structure are then formed by reaction of these precursor materials with ammonia. Microstructure as well as composition (zinc loss) changes with nitridation time: band gap energy, crystallite size and crystallinity increase, while defect density decreases with increasing nitridation time. Crystallite growth results in a corresponding decrease in specific surface area. In the UV regime photocatalytic activity for overall water splitting can be monitored for samples both before and after nitridation. We find a significantly lower photocatalytic activity in the nitrided samples, even though the crystallinity is significantly higher and the defect density is significantly lower after nitridation. Both properties should have led to a lower probability for charge carrier recombination, and, consequently, to a higher photocatalytic activity.