Near-isothermal ferrite/alumina ("hercynite cycle") twostep Red/Ox cycle for solar-thermal water splitting

Christopher L. Muhich, Brian D. Ehrhart, Ibraheam Al-Shankiti, Alan W. Weimer

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Hydrogen productivity exceeding 350 micromoles H2/g total redox material has been demonstrated for near-isothermal processing using the "hercynite cycle" for oxidation with steam carried out at 1350°C following 1500°C reduction. This temperature difference driving the redox is quite narrow compared to standard 500oC temperature swing (T-swing) redox processing. Such processing substantially reduces the difficult solid/solid heat recuperation required for standard Tswing systems and the thermal stresses associated with heating/cooling active materials during redox cycling. Focused ion beam (FIB) milling followed by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) after 200 redox cycles shows that the ferrite/alumina is well-dispersed, indicating a robust active redox material. Efficiency analysis identifies isothermal processing with perfect steam/steam heat exchange as the highest theoretically possible efficiency. Since isothermal processing at the highest reduction temperatures is unlikely due to simultaneous redox (producing both H2 and O2 together), near-isothermal processing provides for the best scenario to achieve the highest solar-thermal process efficiency possible.

Original languageEnglish (US)
Title of host publicationOptics for Solar Energy, OSE 2014
PublisherOptical Society of America (OSA)
ISBN (Print)9781557527561
StatePublished - Nov 25 2014
Externally publishedYes
EventOptics for Solar Energy, OSE 2014 - Canberra, Australia
Duration: Dec 2 2014Dec 5 2014

Publication series

NameOptics for Solar Energy, OSE 2014


OtherOptics for Solar Energy, OSE 2014

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Atomic and Molecular Physics, and Optics
  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment


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