Talk Tilte: Toward Solar Hydrogen Production: Visible-Light-Induced Water Splitting via Z-scheme Photocatalysis Systems
Abstract:
Solar-light-driven water splitting using cheap and robust photocatalysts is one of the most promising ways to cleanly produce H2 as a renewable energy. Because almost half of the incident solar energy at the Earth’s surface falls in visible region, the efficient utilization of visible light is indispensable for realizing practically high efficiency in H2 production via the photocatalysis. However, achieving the photocatalytic water splitting under visible light had been hampered over many years. This is basically due to the lack of ideal semiconductor materials having both the appropriate band levels for this reaction and the sufficiently high stability. In 2001, the present author has for the first time demonstrated overall water splitting (i.e., simultaneous evolution of H2 and O2 with a stoichiometric ratio) under visible light based on a Z-scheme type water splitting system. In such Z-scheme water splitting system, two different photocatalysts, one for H2 evolution and the other for O2 evolution, are combined by using a shuttle redox couple (Red/Ox) in the solution. Over a H2-evolving photocatalyst (HEP) the photoexcited electrons (e–) reduce water to H2 and photogenerated holes (h+) oxidize a reductant (Red) to an oxidant (Ox). The Ox is reduced back to the Red by photoexcited electrons over an O2-evolving photocatalyst (OEP) on which the holes oxidize water to O2. By separating the overall reaction into two stages, the energy required to drive each photocatalysis process can be reduced, thereby enabling the efficient utilization of visible light compared to the conventional (i.e., one-step) water splitting system. We have first achieved overall water splitting by employing a strontium titanite doped with Cr (SrTiO3:Cr) and a tungsten trioxide (WO3) as the HEP and OEP, respectively, in the presence of as iodate/iodide (IO3–/I–) as the shuttle redox mediator. Then, various visible-light-responsive materials such as (oxy)nitrides, sulfides, oxyhalides and organic dyes were successfully applied to Z-scheme water splitting.
Biographical Sketch
Ryu Abe received his PhD in 2001 from the Tokyo Institute of Technology. He then worked as a postdoctoral fellow (2001–2002) and researcher (2002–2005) at the National Institute of Advanced Industrial Science and Technology (AIST). In 2005, he began his academic career as an associate professor at the Catalysis Research Center at Hokkaido University. In 2012, he was promoted to Professor at the Graduate School of Engineering at Kyoto University. His research focuses on developing highly efficient photocatalysts that can split water into hydrogen and oxygen under visible light irradiation, with a particular interest in Z-scheme type systems that mimic the light harvesting and electron transfer mechanisms in natural photosynthesis. He has received several awards, including the Encouragement Prize from the Japan Institute of Energy (2003), the Chemical Society of Japan Award for Young Chemists (2008), the Japanese Photochemistry Association Award (2019), the Chemical Society of Japan Award for Creative Work (2022) and the Nagakura Saburo Award (2022). He has published over 220 original papers (h-index: 65, Web of Science), and also serves as associate editor of Chemistry Letters (CSJ) and Sustainable Energy and Fuels (RSC), and as a senior editor of the Journal of Photochemistry and Photobiology A (Elsevier).