Z‐Scheme Water Splitting Systems Based on Solid‐State Electron Conductors

Abstract Z‐scheme systems based on two‐step photoexcitation are thought to be a promising means of converting solar energy into hydrogen using long‐wavelength visible light. Electron transfer between the hydrogen evolution photocatalyst (HEP) and oxygen evolution photocatalyst (OEP) can greatly affect the performance of such systems, and the use of electron mediators providing efficient electron transfer is thus helpful. Ionic redox couples have been widely employed in particle suspension systems in this regard. In such systems, ions providing electron transfer diffuse through a stirred solution and react on the HEP and OEP. Solid‐state electron mediators can also promote electron transfer while simultaneously holding the HEP and OEP in place. This is a convenient means of immobilizing the particulate photocatalysts and may be applicable to large‐scale production. Accordingly, it would be desirable to increase the efficiency of charge transfer between the HEP and OEP by combining various solid‐state electron conductors. The present review examines the latest advances in Z‐scheme water splitting systems, focusing on solid‐state electron mediators. Both particle suspension and immobilized systems are assessed. Potential approaches to the construction of large‐scale Z‐scheme water splitting operations are discussed in detail together with important future challenges.