Elucidation of the Hematite Direct Reduction Mechanism Using In Situ Spectroscopy
4 affiliations
- 1Physical and Computational Sciences Directorate
- 2Pacific Northwest National Laboratory
- 3Department of Chemistry and Biochemistry and the Oregon Center for Electrochemistry
- 4University of Oregon
Abstract
Research on alternative energy storage technologies continues, especially in the grid-scale long duration space where traditional battery technologies (including lithium-ion) suffer from either cost or safety concerns. Conversion anodes leveraging multi-valent iron promise high capacities, but key microscopic details of the mechanism for conversion are unknown. Towards this objective, this study aims to use in situ electrochemical cells combined with NMR and EPR spectroscopy to search for reaction intermediates directly, expanding on previous studies where largely ex situ methods or carefully constructed surfaces and morphologies were employed. Performing the spectroscopic measurements under realistic electrochemical cell conditions which maximize the reaction conditions (strongly alkaline media, elevated temperatures > 60 °C) and using synthetic hematite aggregates demonstrated i) a lack of dissolved Fe3+ and ii) the presence of solvated Fe2+ species which scaled with applied current density. Leveraging ex situ Mössbauer spectroscopy in combination with the in situ measurements yielded evidence for an initial reduction step of Fe3+ to Fe2+ within the hematite structure. Collectively, these findings point to a solid-state reduction mechanism for hematite via a maghemite intermediate, followed by rupture and dissolution/reduction, with the steady-state solvated Fe2+ concentration gradually dissipating after the applied potential is removed. Detailed mechanistic knowledge will help inform future efforts to engineer further improvements to the direct electrochemical iron oxide reduction process.
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BibTeX
@misc{mezerkor2026elucidation,
title = {{Elucidation of the Hematite Direct Reduction Mechanism Using In Situ Spectroscopy}},
author = {Casey S. Mezerkor and Ravi K. Kukkadapu and Carinna L. Lapson and Mark Bowden and Raj Shekhar and Eric D. Walter and Paul A. Kempler and J. David Bazak},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010105/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010105/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Elucidation of the Hematite Direct Reduction Mechanism Using In Situ Spectroscopy
AU - Casey S. Mezerkor
AU - Ravi K. Kukkadapu
AU - Carinna L. Lapson
AU - Mark Bowden
AU - Raj Shekhar
AU - Eric D. Walter
AU - Paul A. Kempler
AU - J. David Bazak
PY - 2026
DA - 2026/10/08
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010105/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010105/v1
AB - Research on alternative energy storage technologies continues, especially in the grid-scale long duration space where traditional battery technologies (including lithium-ion) suffer from either cost or safety concerns. Conversion anodes leveraging multi-valent iron promise high capacities, but key microscopic details of the mechanism for conversion are unknown. Towards this objective, this study aims to use in situ electrochemical cells combined with NMR and EPR spectroscopy to search for reaction intermediates directly, expanding on previous studies where largely ex situ methods or carefully constructed surfaces and morphologies were employed. Performing the spectroscopic measurements under realistic electrochemical cell conditions which maximize the reaction conditions (strongly alkaline media, elevated temperatures > 60 °C) and using synthetic hematite aggregates demonstrated i) a lack of dissolved Fe3+ and ii) the presence of solvated Fe2+ species which scaled with applied current density. Leveraging ex situ Mössbauer spectroscopy in combination with the in situ measurements yielded evidence for an initial reduction step of Fe3+ to Fe2+ within the hematite structure. Collectively, these findings point to a solid-state reduction mechanism for hematite via a maghemite intermediate, followed by rupture and dissolution/reduction, with the steady-state solvated Fe2+ concentration gradually dissipating after the applied potential is removed. Detailed mechanistic knowledge will help inform future efforts to engineer further improvements to the direct electrochemical iron oxide reduction process.
ER -