Year: 2026
Type: preprint
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.
Source: ChemRxiv
Institutions: Pacific Northwest National Laboratory, University of Oregon
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7220925403