Solar Fuels

1Materials Design Directions for Solar Thermochemical Water Splitting

Robert B. Wexler¹, Ellen B. Stechel² and Emily A. Carter¹*

¹Department of Mechanical and Aerospace Engineering and the Andlinger Center for Energy and the Environment, Princeton University, Princeton, NJ, United States

²ASU LightWorks® and the School of Molecular Sciences, Arizona State University, Tempe, Arizona, United States

Abstract

Solar thermochemical water splitting (STWS) offers a renewable route to hydrogen with the potential to help decarbonize several industries, including transportation, manufacturing, mining, metals processing, and electricity generation, as well as to provide sustainable hydrogen as a chemical feedstock. STWS uses high temperatures from concentrated sunlight or other sustainable means for high-temperature heat to produce hydrogen and oxygen from steam. For example, in its simplest form of a two-step thermochemical cycle, a redox-active metal oxide is heated to ≈1700 to 2000 K, driving off molecular oxygen while producing oxygen vacancies in the material. The reduced metal oxide then cools (ideally with the extracted heat recuperated for reuse) and, in a separate step, comes into contact with steam, which reacts with oxygen vacancies to produce molecular hydrogen while recovering the original state of the metal oxide. Despite its promising use of the entire solar spectrum to split water thermochemically, the estimated cost of hydrogen produced via STWS is ≈4 to 6× the U.S. Department ...