Chapter 2
Quantum Chemistry in Perovskite
Fluoride and Hydride: Nanoscale
Hydride Ion Conduction
Taku Onishi
Abstract Hydride ion, which implies negatively charged hydrogen, has recently
attracted much scientific attention from the viewpoint of nanoscale fast ion transport. Molecular orbital calculations based on density functional theory were performed for perovskite fluoride and hydride, in order to investigate the hydride
ion-conducting mechanism. In hydride ion-doped KMgF 3 perovskite, it was found
that hydride ion conduction occurs, combined with “competitive fluctuation”, which
implies that fluorine anion also migrates around local minimum during hydride ion
conduction. The activation energy for hydride ion conduction was estimated to be
0.61–0.85 eV. It was also found that hydride ion conduction occurs in KMgH 3
perovskite. The activation energy for hydride ion conduction was estimated to
be 0.40–0.61 eV. From the viewpoint of structural stability at high temperature,
it was concluded that hydride ion-doped KMgF 3 perovskite is more favourable
than KMgH 3 perovskite. In comparison with proton-conducting perovskites, it
was concluded that hydride ion conducting perovskites can be utilized as fast ion
conductor. Finally, we discuss hydride ion safety and outlook.
Keywords Molecular orbital calculation · Perovskite fluoride · Hydride ion
conduction · Competitive fluctuation · Perovskite hydride · Hydrogen storage
material
2.1 Introduction
It is well known that perovskites exhibit lithium ion, proton and oxide ion conductivities. Since the discovery of lithium ion conducting perovskite titanium oxides
T. Onishi ()
Graduate School of Engineering, Mie University, Tsu, Japan
Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo,
Oslo, Norway
e-mail: taku@chem.mie-u.ac.jp; taku.onishi@kjemi.uio.no
© Springer Nature Singapore Pte Ltd. 2020
T. Onishi (ed.), Theoretical Chemistry for Advanced Nanomaterials,
https://doi.org/10.1007/978-981-15-0006-0_2
27
Quantum Chemistry in Perovskite
Fluoride and Hydride: Nanoscale
Hydride Ion Conduction
Taku Onishi
Abstract Hydride ion, which implies negatively charged hydrogen, has recently
attracted much scientific attention from the viewpoint of nanoscale fast ion transport. Molecular orbital calculations based on density functional theory were performed for perovskite fluoride and hydride, in order to investigate the hydride
ion-conducting mechanism. In hydride ion-doped KMgF 3 perovskite, it was found
that hydride ion conduction occurs, combined with “competitive fluctuation”, which
implies that fluorine anion also migrates around local minimum during hydride ion
conduction. The activation energy for hydride ion conduction was estimated to be
0.61–0.85 eV. It was also found that hydride ion conduction occurs in KMgH 3
perovskite. The activation energy for hydride ion conduction was estimated to
be 0.40–0.61 eV. From the viewpoint of structural stability at high temperature,
it was concluded that hydride ion-doped KMgF 3 perovskite is more favourable
than KMgH 3 perovskite. In comparison with proton-conducting perovskites, it
was concluded that hydride ion conducting perovskites can be utilized as fast ion
conductor. Finally, we discuss hydride ion safety and outlook.
Keywords Molecular orbital calculation · Perovskite fluoride · Hydride ion
conduction · Competitive fluctuation · Perovskite hydride · Hydrogen storage
material
2.1 Introduction
It is well known that perovskites exhibit lithium ion, proton and oxide ion conductivities. Since the discovery of lithium ion conducting perovskite titanium oxides
T. Onishi ()
Graduate School of Engineering, Mie University, Tsu, Japan
Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo,
Oslo, Norway
e-mail: taku@chem.mie-u.ac.jp; taku.onishi@kjemi.uio.no
© Springer Nature Singapore Pte Ltd. 2020
T. Onishi (ed.), Theoretical Chemistry for Advanced Nanomaterials,
https://doi.org/10.1007/978-981-15-0006-0_2
27