This thesis presents surface-loaded cobalt oxide nanoparticles (CoOx) on semiconductor photocatalysts to investigate the precise characterization and modification effects for photocatalytic water oxidation. CoOx is widely known as a water oxidation reaction site (so-called cocatalyst) in photocatalytic water splitting with solar energy. However, while this cocatalyst has been recognized as a tool to enhance the photocatalytic activity the exact elements that determine the activity have not yet been well studied. 

In this book three topics are described, the first topic is quantitative investigation of the catalytic water oxidation ability of CoOx by surface localized plasmonic resonance effect. The second topic discussed is the promotion of water oxidation reaction with the electron transition effect between surface loaded CoOx and semiconductor support such as titania. The final topic presented is the determination of chemical potential of electrons in CoOx nanoparticle for water oxidation, that should be deeply related to the water oxidation efficiency. Through these studies, it was clarified that CoOx is not only empirically but also theoretically suitable for water oxidation even under surface-loaded condition on semiconductors. The author expects that obtained guidelines for cocatalyst design for water oxidation is useful for readers.

Megumi Okazaki got her Ph. D. degree in 2022 from the department of chemistry at Tokyo Institute of Technology. Her research field is photochemistry, especially artificial photosynthesis and semiconductor photocatalysis. She has investigated characteristics of metal oxide nanoparticle loaded onto semiconductor photocatalyst as reaction site of water oxidation.