Synthesis and Structure of High-Purity BaCe0.25Mn0.75O3: An Improved Material for Thermochemical Water Splitting

Robert Bell, Nicholas Strange, Dan Plattenberger, Sarah Shulda, James Park, Andrea Ambrosini, Karen Heinselman, Joshua Sugar, Philip Parilla, Eric Coker, Anthony McDaniel, David Ginley

Research output: Contribution to journalArticlepeer-review

2 Scopus Citations


Solar thermochemical hydrogen production (STCH) via redox-active metal oxides is an approach for direct solar-driven hydrogen generation typically using a high-temperature redox cycle involving refractory oxides and steam. Typical cycles involve high-temperature reduction of oxides to form oxygen vacancies, followed by lower temperature reaction between oxygen vacancies and steam where the oxide is re-oxidized and the steam is reduced to hydrogen. Only a few materials have demonstrated reversible cycling under the typically harsh STCH conditions (e.g. 1500 degrees C reduction, 900 degrees C re-oxidation) and critical questions remain on the true reversibility of non-stoichiometric multi-cation oxide systems, significantly hampered by the lack of single-phase samples for these material systems. To date, most STCH processes have relied on CeO2 as a benchmark active material, but more recently, the 12R phase of BaCe0.25Mn0.75O3 (BCM) has demonstrated greater hydrogen-generation potential at lower peak temperatures. However, previous reports of 12R-BCM have included large fractions, >10 wt%, of secondary phases, which complicate analysis of the stability and performance. A comprehensive understanding of the redox mechanism and reversibility of the process in BCM can only be achieved with nearly single-phase samples which, to date, have been difficult to produce. Here two approaches to BCM synthesis are reported: solid state and sol-gel-based routes. It is demonstrated that both routes can be tuned to produce the 12R structure with >97 wt% yield when annealed =1450 degrees C. Herein synchrotron-based diffraction measurements of rhombohedral 12R-BCM enabled characterization of the anisotropy between thermal expansion along the c-axis and within the ab plane. The impact of high-temperature redox cycling on the stability and phase fraction of the 12R-BCM polytype was also investigated. These results offer two viable routes for synthesis of high-purity 12R-BCM critically needed for evaluating the efficacy of BCM as a STCH material and validate its ability to split water at lower temperatures over extended numbers of redox cycles.
Original languageAmerican English
Pages (from-to)884-892
Number of pages9
JournalActa crystallographica Section B, Structural science, crystal engineering and materials
Issue number6
StatePublished - 2022

NREL Publication Number

  • NREL/JA-5K00-79620


  • barium cerium manganate
  • hydrogen
  • solar thermochemical hydrogen
  • STCH
  • synthesis


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