Chapter 7 - Particulate photocatalysts for overall water splitting and implications regarding panel reactors for large-scale applications

Abstract

Using particulate photocatalysts, solar-driven overall water splitting (OWS) can enable large-scale hydrogen production as an inexpensive, renewable, environmentally friendly, and carbon-neutral fuel. One of the most promising means of realizing OWS is to develop systems in which photocatalysts are embedded in large panel arrays. At present, the primary obstacle to the commercialization of this technology is the limited solar-to-hydrogen (STH) conversion efficiencies of available photocatalysts. Numerous visible-light-driven photocatalysts have been studied to obtain improved water splitting activity by suppressing surface defects or by loading co-catalysts with different functions to promote the kinetics of the water reduction and oxidation reactions. Recent studies of photocatalyst sheets incorporating two photocatalysts and a solid-state electron mediator have shown this technology to be readily scalable with no loss of activity. The best performing system comprising Rh, La co-doped SrTiO3, and Mo-doped BiVO4 embedded in a thin conductive Au layer achieved an STH of 1.0% at near-ambient pressure. Narrow bandgap nonoxide photocatalysts can provide better performance on a thermodynamic basis at present, but the activities of these materials are currently inferior to those of OWS systems composed of metal oxides. This chapter describes various strategies for developing highly active, narrow bandgap photocatalysts, and the working mechanisms of powder suspension and photocatalyst sheets with various surface modifications. Recent progress in photocatalyst panels is also discussed, focusing on the separation of gaseous products and safety issues.