Chapter 3: Metal Oxide-based Catalysts

Since the initial report of the Honda–Fujishima effect, various metal oxide-based photocatalysts have been studied, owing to the high catalytic activity and superior durability of these materials. The development of efficient photocatalysts requires the rational design of both the bulk and surfaces of these semiconductor particles. This chapter presents strategies that have been devised over the years to develop efficient ultraviolet light-responsive metal oxide photocatalysts, along with specific examples of highly efficient particulate metal oxide photocatalysts. These examples demonstrate that photocatalytic overall water splitting with an apparent quantum efficiency close to the ideal value of 100% in response to ultraviolet light has been achieved. Even so, the vast majority of solar radiation consists of visible light, and so the fabrication of efficient visible light-responsive photocatalysts is a prerequisite for achieving high solar-to-hydrogen energy conversion efficiencies. This chapter reviews various approaches to the design of visible light-responsive metal oxide photocatalysts and introduces recent concepts for solar hydrogen generation devices intended for future large-scale installations. Trends and progress in the field of photocatalyst research related to materials chemistry and chemical engineering are discussed, together with future challenges associated with the large-scale implementation of this technology.