Decoupling the Effects of High Crystallinity and Surface Area on the Photocatalytic Overall Water Splitting over β-Ga O Nanoparticles by Chemical Vapor Synthesis.

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.