Synergistic interplay of Zn and Rh-Cr promoters on Ga2O3-based photocatalysts for water splitting

Photocatalytic water splitting activity of a wide-bandgap material, Ga₂O₃, is greatly boosted with the addition of Zn and Rh-Cr co-catalyst at optimum loadings. To date, however, the exact roles of the co-catalysts and particularly the origin of their synergistic functions are not clarified. Herein, we present how the optimum Zn loading on Ga₂O₃ leads to creation of ZnGa₂O₄/Ga₂O₃ heterojunction favorable for charge separation through the information on the occupied and unoccupied electronic states of Zn and Ga elucidated by X-ray absorption and emission spectroscopic methods. The function of Rh-Cr as electron sink and reduction site was proven by photocatalytic experiments using an electron scavenger (Ag⁺) and by learning where Ag deposits and its effects on the photocatalytic activity. Finally, perturbation of Zn electronic structure by photo activation was evidenced by modulation excitation X-ray absorption spectroscopy. Importantly, Rh-Cr markedly enhanced the level of the perturbation, serving as a proof of direct communication and synergy between the electronic states of Zn, present in ZnGa₂O₄, and Rh-Cr deposited on Ga₂O₃.