Chapter 7: Particulate Photocatalyst Sheets for Efficient and Scalable Water Splitting

Sunlight-driven water splitting using particulate semiconductor photocatalysts has the potential to enable the large-scale production of inexpensive, renewable solar hydrogen, representing an environmentally-benign fuel and industrial feedstock. This is possible because particulate photocatalysts can be readily spread over wide areas. However, despite decades of intensive research, there are several critical challenges associated with this technology; specifically, upgrading the solar-to-hydrogen energy conversion efficiency (STH) and demonstrating scalability. Recently, particulate photocatalyst sheets based on hydrogen evolution photocatalysts and oxygen evolution photocatalysts embedded in conductive layers using a particle transfer technique have been studied as a means of realising efficient, scalable Z-scheme water splitting via two-step excitation. The most advanced photocatalyst sheets are capable of splitting water into hydrogen and oxygen in a stable manner with STH values of 1.0% at atmospheric pressure, with even higher values at reduced pressure. Notably, such photocatalyst sheets are directly scalable without any loss in activity, because hydrogen and oxygen are generated in close proximity to one another, mitigating problems with mass transfer in the reaction solution. In this chapter, the structures, reaction properties, and working mechanisms of state-of-the-art photocatalyst sheets with various surface modifications are described.