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Published September 10, 2021 | Supplemental Material
Journal Article Open

Hydrogen from Sunlight and Water: A Side-by-Side Comparison between Photoelectrochemical and Solar Thermochemical Water-Splitting


Photoelectrochemical (PEC) and solar thermochemical (STCH) water-splitting represent two promising pathways for direct solar hydrogen generation. PEC water-splitting integrates multiple functional materials and utilizes energetic electrons and holes generated from sunlight to produce hydrogen and oxygen in two half-reactions, while STCH water-splitting couples a series of consecutive chemical reactions and uses absorbed heat from sunlight to generate hydrogen and oxygen in two full reactions. In this Focus Review, the basic operating principles, sunlight utilization, device architecture, reactor design, instantaneous and annually averaged solar-to-hydrogen (STH) conversion efficiency, and the operating conditions and constraints of both pathways are compared. A side-by-side comparison addresses some common sources of confusion and misinterpretation, especially in the evaluation of STH conversion efficiencies, and reveals distinct features and challenges in both PEC and STCH technologies. This Focus Review also addresses materials and device challenges in PEC and STCH for cost-competitive hydrogen generation.

Additional Information

© 2021 American Chemical Society. Received: April 9, 2021; Accepted: July 22, 2021; Published: August 16, 2021. W.-H.C. acknowledges the support from Ministry of Science and Technology (2030 Cross-Generation Young Scholars Program), Taiwan and Ministry of Education (Yushan Scholar Program), Taiwan. The authors acknowledge the support from the Fuel Cell Technologies Office, of the U.S. Department of Energy, Energy Efficiency and Renewable Energy under contract number DE-EE0008092. The PEC analysis was partly based on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266. This material is also partially based on work supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy (EERE) Solar Energy Technologies Office (SETO) under Award No. DE–EE0008991. Author Contributions: Wen-Hui Cheng and Alberto de la Calle contributed equally to this work. The authors declare no competing financial interest.

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