UC Riverside

The present work employs a variety of approaches and techniques to explore the photocatalytic watersplitting phenomena of a well-known particulate photocatalyst—Gallium Zinc Oxynitride (GaNZnO) from two aspects: reaction kinetics and charge transfer phenomena.

Cocatalyst loading onto n-type semiconductors has been proven to be a highly effective approach to promote the activity of catalysts in photocatalytic processes. Watersplitting by particulate photocatalyst (PPC) systems, as a phenomenon, are usually studied via a macroscopic approach developed for Photoelectrochemical Cell (PEC) systems. However, the macroscopic nature of the PEC systems may have overlooked the subtle while intrinsic aspects of the PPC systems due to challenges in characterization techniques and biased views in describing such microscopic systems. Thus, a fundamental re-investigation of watersplitting process by cocatalyst-loaded PPC systems via exploring rate-limiting reaction kinetics and charge transfer phenomena could provide more insights for the study and the improvement of PPC systems in watersplitting.

The watersplitting kinetics of GaNZnO PPC systems were explored through overall watersplitting (OWS) and half-reaction experiments. The photoelectron tracing experiment was developed specifically to clarify the charge transfer direction on GaNZnO surface. In addition, various characterization techniques, such as: UV-VIS, XRD, HRTEM, Dark-field STEM and EDS were applied to gain more knowledge of the PPC system before and after reactions. From the kinetic experiments, we observed unusual rate trends which contradict or deviate from results predicted by PEC models. Further investigation indicates that those unusual behaviors were explained by an opposite charge transfer direction previously proposed by PEC models.