Operational Limits of Redox Metal Oxides Performing Thermochemical Water Splitting

Alicia Bayon, Alberto de la Calle, Ellen B. Stechel, Christopher Muhich

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Solar thermochemical hydrogen production is an attractive technology that stores intermittent solar energy in the form of chemical bonds. Efficient operation requires the identification of a redox-active metal oxide (MOx) material that can achieve high conversion of water to hydrogen at minimal energy input. Water splitting occurs by consecutive reduction and reoxidation reactions of MOx. MOx is reduced to MOx−δ and, in the second step, is reoxidized by water recovering the initial MOx and generate H2. The material must reduce at temperatures achievable in concentrated solar receiver/reactors, while maintaining a thermodynamic driving force to split water. At equilibrium, extent of reduction depends on temperature and oxygen partial pressure, and in this analysis, a set of thermodynamic properties, namely, enthalpy and entropy of oxygen vacancy formation, is sufficient to represent MOx. Herein, a method to easily classify materials based on these thermodynamic properties under any condition of oxygen partial pressure and temperature is presented. This method is based on fundamental thermodynamic principles and is applicable for any redox material with known thermodynamic properties. Despite the simplicity of the method, it is believed that this analysis will support future research in targeting thermodynamic properties of redox-active metal oxides.

Original languageEnglish (US)
Article number2100222
JournalEnergy Technology
Issue number1
StatePublished - Jan 2022

ASJC Scopus subject areas

  • General Energy


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