Hydride-ion transport mechanisms in oxyhydrides and nitride-hydrides: a neutron spectroscopy and computational approach
Doctoral thesis, 2025
This thesis investigates the fundamental mechanisms governing hydride-ion transport in the novel nitride-hydride Ca3CrN3H and oxyhydride perovskites ATiO3–x–yHx□y (A = Ba, Sr, and □ denotes anion vacancies), which are promising materials for energy and catalysis applications. However, key questions remain regarding the structure-dynamics relationships that govern their transport behavior. To address these, this thesis combines quasielastic and inelastic neutron scattering with density functional theory and molecular dynamics simulations to probe the diffusional and vibrational dynamics of hydride-ions. The aim is to provide a comprehensive understanding of the structural and chemical factors enabling hydride-ion transport and to guide the development of energy and catalytic devices based on these materials.
In the nitride-hydride Ca3CrN3H, the results reveal characteristic hydride-ion vibrational modes correlated with the hydride-ion site occupancy, and the analysis of the vibrational spectrum indicates the presence of vacant sites. These vacancies enable jump-diffusion dynamics, including localized, back-and-forth motions, and successive jumps across nearest-neighbor vacancies. Both dynamics are characterized by exceptionally low activation energies, which facilitates the hydride-ion transport.
In the oxyhydride perovskites ATiO3–x–yHx□y, hydride-ion diffusion similarly requires anion vacancies and proceeds via jumps to nearest-neighbor vacancies. The results suggest that both localized, back-and-forth jumps and long-range, successive jumps can occur on comparable timescales in regions with sufficient vacancy content. However, in regions of lower vacancy content, long-range transport is impeded due to the lack of continuous pathways of vacancies and hydride-ions. Additionally, the results show that localized electrons (i.e., polarons) increase the migration energy barrier of hydride-ions compared to delocalized electrons in the conduction band.
These findings showcase the critical role of both anion vacancy concentration and electronic structure in enabling efficient hydride-ion transport, providing design principles for developing next-generation nitride-hydride and oxyhydride hydride-ion conductors and catalysts.
In the nitride-hydride Ca3CrN3H, the results reveal characteristic hydride-ion vibrational modes correlated with the hydride-ion site occupancy, and the analysis of the vibrational spectrum indicates the presence of vacant sites. These vacancies enable jump-diffusion dynamics, including localized, back-and-forth motions, and successive jumps across nearest-neighbor vacancies. Both dynamics are characterized by exceptionally low activation energies, which facilitates the hydride-ion transport.
In the oxyhydride perovskites ATiO3–x–yHx□y, hydride-ion diffusion similarly requires anion vacancies and proceeds via jumps to nearest-neighbor vacancies. The results suggest that both localized, back-and-forth jumps and long-range, successive jumps can occur on comparable timescales in regions with sufficient vacancy content. However, in regions of lower vacancy content, long-range transport is impeded due to the lack of continuous pathways of vacancies and hydride-ions. Additionally, the results show that localized electrons (i.e., polarons) increase the migration energy barrier of hydride-ions compared to delocalized electrons in the conduction band.
These findings showcase the critical role of both anion vacancy concentration and electronic structure in enabling efficient hydride-ion transport, providing design principles for developing next-generation nitride-hydride and oxyhydride hydride-ion conductors and catalysts.
ionic transport
density functional theory
hydride-ion
nitride-hydride
molecular dynamics
neutron scattering
oxyhydride
KB, Kemigården 4, Chalmers
Opponent: Christopher Ling, School of Chemistry The University of Sydney NSW 2006, Australia
Author
Lucas Fine
Chalmers, Chemistry and Chemical Engineering, Energy and Material
Configuration and Dynamics of Hydride Ions in the Nitride-Hydride Catalyst Ca<inf>3</inf>CrN<inf>3</inf>H
Chemistry of Materials,;Vol. 37(2025)p. 489-496
Journal article
Fine, L. Laven, R. Wei, Z. Tsumori, T. Matsuura, M. Tamatsukuri, H. Kageyama, H. Koza, M. M. and Karlsson, M. One-dimensional Hydride-Ion Conduction in the Nitride-Hydride Ca3CrN3H
Mechanism of Hydride-Ion Diffusion in the Oxyhydride of Barium Titanate
Journal of Physical Chemistry C,;Vol. 129(2025)p. 12305-12311
Journal article
Unraveling the electronic control of hydride-ion diffusivity in oxyhydrides from model studies on BaTiO3−2xHx□x
Materials Advances,;(2025)
Journal article
Fine, L. Laven, R. Naumovska, E. Guo, H. Haussermann, U. Jaworski, A. Jimenez-Ruiz, M. Nilsen, G. J. Koza, M. M. and Karlsson, M. Localized Jump-Diffusion Dynamics of Hydride-Ions in an Oxyhydride of SrTiO3 Studied using Inelastic and Quasielastic Neutron Scattering
Novel materials for next-generation fuel cells and ammonia synthesis catalysts.
In the context of a global transition to a decarbonized economy, materials science research focuses on identifying new, more efficient materials for use in energy-intensive sectors such as transportation and chemical production. Notable efforts aim to reduce the operating temperature below 300 °C in fuel cells—devices that convert decarbonized electricity into green fuels such as dihydrogen (H2) and vice versa—as well as in catalysts for ammonia synthesis, which use dihydrogen to produce ammonia (NH3), a molecule widely used in fertilizer production. A promising strategy explores novel material classes, specifically oxyhydride and nitride-hydride compounds, which show potential to compete with or even outperform the current technologies due to their high hydride-ion (H-) conductivity. However, a fundamental understanding of the hydride-ion transport mechanism, that is, how hydride-ions diffuse through these materials at the atomic scale, is still lacking. To this end, this thesis investigates various oxyhydride and nitride-hydride samples using neutron scattering techniques combined with computer simulations. The results show that hydride-ion diffusion strongly depends on the chemical composition (which species are present) and crystalline structure (how the atoms are arranged). In particular, the presence of anion vacancies (missing anions in the crystalline structure) creates pathways for hydride-ions to “hop” from site to site. When enough vacancies are present, these hops can connect and form networks that allow hydride-ions to be transported across macroscopic distances. The understanding of this behavior developed in this thesis helps to establish design criteria, such as the optimal chemical composition of oxyhydrides and nitride-hydrides, for developing materials that meet the performance requirements of low-temperature fuel cells and efficient ammonia synthesis catalysts.
In the context of a global transition to a decarbonized economy, materials science research focuses on identifying new, more efficient materials for use in energy-intensive sectors such as transportation and chemical production. Notable efforts aim to reduce the operating temperature below 300 °C in fuel cells—devices that convert decarbonized electricity into green fuels such as dihydrogen (H2) and vice versa—as well as in catalysts for ammonia synthesis, which use dihydrogen to produce ammonia (NH3), a molecule widely used in fertilizer production. A promising strategy explores novel material classes, specifically oxyhydride and nitride-hydride compounds, which show potential to compete with or even outperform the current technologies due to their high hydride-ion (H-) conductivity. However, a fundamental understanding of the hydride-ion transport mechanism, that is, how hydride-ions diffuse through these materials at the atomic scale, is still lacking. To this end, this thesis investigates various oxyhydride and nitride-hydride samples using neutron scattering techniques combined with computer simulations. The results show that hydride-ion diffusion strongly depends on the chemical composition (which species are present) and crystalline structure (how the atoms are arranged). In particular, the presence of anion vacancies (missing anions in the crystalline structure) creates pathways for hydride-ions to “hop” from site to site. When enough vacancies are present, these hops can connect and form networks that allow hydride-ions to be transported across macroscopic distances. The understanding of this behavior developed in this thesis helps to establish design criteria, such as the optimal chemical composition of oxyhydrides and nitride-hydrides, for developing materials that meet the performance requirements of low-temperature fuel cells and efficient ammonia synthesis catalysts.
Time-resolved spectroscopy of proton and hydride-ion conducting perovskites
Swedish Energy Agency (P2019-90169), 2020-01-01 -- 2024-12-31.
Subject Categories (SSIF 2025)
Materials Chemistry
Condensed Matter Physics
Driving Forces
Sustainable development
Areas of Advance
Energy
Materials Science
Roots
Basic sciences
Infrastructure
C3SE (-2020, Chalmers Centre for Computational Science and Engineering)
ISBN
978-91-8103-258-1
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5716
Publisher
Chalmers
KB, Kemigården 4, Chalmers
Opponent: Christopher Ling, School of Chemistry The University of Sydney NSW 2006, Australia