Neutron Diffraction Study of a Sintered Iron Electrode In Operando

Journal Article (2021)
Author(s)

Bernhard M.H. Weninger (TU Delft - ChemE/Materials for Energy Conversion and Storage)

M. A. Thijs (TU Delft - RST/Neutron and Positron Methods in Materials)

Jeroen A.C. Nijman (Independent researcher)

L van Eijck (TU Delft - RST/Neutron and Positron Methods in Materials)

F.M. Mulder (TU Delft - ChemE/Materials for Energy Conversion and Storage)

Research Group
ChemE/Materials for Energy Conversion and Storage
Copyright
© 2021 B. Weninger, M.A. Thijs, Jeroen A.C. Nijman, L. van Eijck, F.M. Mulder
DOI related publication
https://doi.org/10.1021/acs.jpcc.1c03263
More Info
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Publication Year
2021
Language
English
Copyright
© 2021 B. Weninger, M.A. Thijs, Jeroen A.C. Nijman, L. van Eijck, F.M. Mulder
Research Group
ChemE/Materials for Energy Conversion and Storage
Issue number
30
Volume number
125
Pages (from-to)
16391-16402
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Abstract

Iron is a promising, earth-abundant material for future energy applications. In this study, we use a neutron diffractometer to investigate the properties of an iron electrode in an alkaline environment. As neutrons penetrate deeply into materials, neutron scattering gives us a unique insight into what is happening inside the electrode. We made our measurements while the electrode was charging or discharging. Our key questions are: Which phases occur for the first and second discharge plateaus? And why are iron electrodes less responsive at higher discharge rates? We conclude that metallic iron and iron hydroxide form the redox pair for the first discharge plateau. For the second discharge plateau, we found a phase similar to feroxyhyte but with symmetrical and equally spaced arrangement of hydrogen atoms. The data suggest that no other iron oxide or iron (oxy)hydroxide formed. Remarkable findings include the following: (1) substantial amounts of iron hydroxide are always present inside the electrode. (2) Passivation is mostly caused by iron hydroxide that is unable to recharge. (3) Iron fractions change as expected, while iron hydroxide fractions are delayed, resulting in substantial amounts of
amorphous, undetectable iron phases. About 40% of the participating iron of the first plateau and about 55% of the participating iron for the second plateau are undetectable. (4) Massive and unexpected precipitation of iron hydroxide occurs in the transition from discharging to charging. (2), (3), and (4) together cause accumulation of iron hydroxide inside the electrode.