High Proton Conductivity in β‐Ba<sub>2</sub>ScAlO<sub>5</sub> Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers

Murakami, Taito; Avdeev, Maxim; Morikawa, Riho; Hester, James; Yashima, Masatomo

doi:10.1002/adfm.202206777

Cited by 14 publications

(16 citation statements)

References 80 publications

(145 reference statements)

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“…For instance, Ba 7 Nb 5 MoO 20 hexagonal perovskite displays high proton conduction in a wet atmosphere (σ t ≈ 4.0 × 10 –3 S·cm –1 at 500 °C; proton transport number ∼0.8 at 500 °C), as well as good chemical stability under reducing conditions. Noticeably, these compounds display native proton conduction through the oxygen-deficient hexagonal or cubic layers, and thereby inducing oxygen vacancies through acceptor doping strategies is not required . In these compounds, the proton conduction is assisted by the tetrahedral units which could paves the way for the next generation of proton conductors for the H-SOFCs.…”

Section: Cubic Perovskite Derivative Oxide Ion Conductorsmentioning

confidence: 99%

“…Noticeably, these compounds display native proton conduction through the oxygen-deficient hexagonal or cubic layers, and thereby inducing oxygen vacancies through acceptor doping strategies is not required. 260 In these compounds, the proton conduction is assisted by the tetrahedral units which could paves the way for the next generation of proton conductors for the H-SOFCs.…”

Section: Cubic Perovskite Derivative Oxide Ion Conductorsmentioning

confidence: 99%

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Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

2023

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This Review presents an overview from the perspective of tetrahedral chemistry on various oxide ion-conducting materials containing tetrahedral moieties which have received continuous growing attention as candidates for key components of various devices, including solid oxide fuel cells and oxygen sensors, due to the deformation and rotation flexibility of tetrahedral units facilitating oxide ion transport. Emphasis is placed on the structural and mechanistic features of various systems ranging from crystalline to amorphous materials, which include a variety of gallates, silicates, germanates, molybdates, tungstates, vanadates, aluminates, niobate, titanates, indium oxides, and the newly reported borates. They contain tetrahedral units in either isolated or linked manners forming different polyhedral dimensionality (0 to 3) with various defect properties and transport mechanisms. The development of oxide ion conductors containing tetrahedral moieties and the elucidation of the roles of tetrahedral units in oxide ion migration have demonstrated diverse opportunities for discovering superior electrolytes for solid oxide fuel cells and other related devices and provided useful clues for uncovering the key factors directing fast oxide ion conduction.

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Section: Cubic Perovskite Derivative Oxide Ion Conductorsmentioning

confidence: 99%

Section: Cubic Perovskite Derivative Oxide Ion Conductorsmentioning

confidence: 99%

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

2023

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“…Second, water will be produced at the cathode and anode, and external gas humidification is not required, which will significantly simplify the fuel cell system . Recently, dual-ion, oxide-ion, and proton conducting hexagonal perovskite-related oxides such as Ba 7 Nb 4 MoO 20 -based materials, have attracted much attention due to high oxide-ion and proton conductivity. ,,− The bulk conductivities of Ba 7 Nb 4 MoO 20 are 2.9 mS cm –1 at 500 °C under wet air and 3.0 mS cm –1 at 593 °C under dry air, but these conductivities are not sufficiently high. Therefore, in this work, we investigate the electrical conductivity of Ba 7 Nb 4– x Mo 1+ x O 20+ x /2 materials with excess Mo compositions, which can lead to a larger amount of excess oxygen atoms and higher conductivities.…”

Section: Introductionmentioning

confidence: 99%

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Sakuda,

Murakami,

Avdeev

et al. 2023

Chem. Mater.

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Oxide-ion and proton conductors have found diverse applications such as in electrolytes of solid-oxide, proton-conducting, and hybrid-ion fuel cells. Research of fuel cells with higher energy efficiency at lower operating temperature has stimulated the search for ion conductors and improved the understanding of the ion-diffusion mechanism. Ion conduction in hexagonal perovskite-related materials is rare, and the mechanism of ion diffusion is unclear. Herein, we report high oxide-ion and proton conductivity (bulk conductivities in wet air: 11 and 2.7 mS cm −1 at 537 and 326 °C, respectively), high chemical, and electrical stability in a new hexagonal perovskite-related oxide Ba 7 Nb 3.8 Mo 1.2 O 20.1 . Total direct current conductivity at 400 °C in wet air of Ba 7 Nb 3.8 Mo 1.2 O 20.1 was 13 times higher than that of Ba 7 Nb 4 MoO 20 . We also report a unique dimer-mediated cooperative mechanism of the high oxide-ion conduction of Ba 7 Nb 3.8 Mo 1.2 O 20.1 (bulk conductivities in dry air: 10 mS cm −1 at 593 °C and 1.1 mS cm −1 at 306 °C). Ab initio molecular dynamics (AIMD) simulations, neutron-diffraction experiments at 800 °C, and neutron scattering length density analyses of Ba 7 Nb 3.8 Mo 1.2 O 20.1 indicated that the excess oxygen atoms are incorporated by the formation of both 5-fold coordinated (Nb/Mo)O 5 monomer and its (Nb/Mo) 2 O 9 dimer with a corner-sharing oxygen atom and that the breaking and reforming of the dimers lead to the high oxide-ion conduction in the oxygen-deficient BaO 2.1 c′ layer. The long distance between Nb/Mo and Ba cations sandwiching the c′ layer of Ba 7 Nb 3.8 Mo 1.2 O 20.1 was found to be responsible for its low activation energy for oxide-ion conduction, leading to high conductivity at low temperatures. AIMD simulations showed that high proton conduction can be attributed to proton migration in the hexagonal close-packed BaO 3 layers of Ba 7 Nb 3.8 Mo 1.2 O 20.1 . The present findings hold a great promise for the development and design of ion conductors.

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“…Among these, yttrium-substituted barium zirconate or barium cerate with moderate substitution levels, Ba(Zr/Ce) 1– x Y x O 3 H x with x ≤ 0.2, , have been the gold standard achieving the best proton conductivities at intermediate temperatures. Recently, however, high proton conductivities have been also reported in non-cubic systems, such as monoclinic − and hexagonal − perovskite derivatives, oxides with palmierite or scheelite − structures, and Ruddlesden–Popper phases. , …”

Section: Introductionmentioning

confidence: 99%

Proton Diffusion Mechanism in Hydrated Barium Indate Oxides

et al. 2023

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We report on quasielastic neutron scattering (QENS) and ab initio molecular dynamics (AIMD) simulations of the mechanism of proton diffusion in the partially and fully hydrated barium indate oxide proton conductors Ba 2 In 2 O 5 (H 2 O) x (x = 0.30 and 0.92). Structurally, these materials are featured by an intergrowth of cubic and "pseudo-cubic" layers of InO 6 octahedra, wherein two distinct proton sites, H(1) and H(2), are present. We show that the main localized dynamics of these protons can be described as rotational diffusion of O−H(1) species and H(2) proton transfers between neighboring oxygen atoms. The mean residence times of both processes are in the order of picoseconds in the two studied materials. For the fully hydrated material, Ba 2 In 2 O 5 (H 2 O) 0.92 , we also reveal the presence of a third proton site, H(3), which becomes occupied upon increasing the temperature and serves as a saddle state for the interexchange between H(1) and H(2) protons. Crucially, the occupation of the H(3) site enables long-range diffusion of protons, which is highly anisotropic in nature and occurs through a two-dimensional pathway. For the partially hydrated material, Ba 2 In 2 O 5 (H 2 O) 0.30 , the occupation of the H(3) site and subsequent long-range diffusion are not observed, which is rationalized by hindered dynamics of H(2) protons in the vicinity of oxygen vacancies. A comparison to state-of-the-art proton-conducting oxides, such as barium zirconate-based materials, suggests that the generally lower proton conductivity in Ba 2 In 2 O 5 (H 2 O) x is due to a large occupation of the H(1) and H(2) sites, which, in turn, means that there are few sites available for proton diffusion. This insight suggests that the chemical substitution of indium by cations with higher oxidation states offers a novel route toward higher proton conductivity because it reduces the proton site occupancy while preserving an oxygen-vacancy-free structure.

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High Proton Conductivity in β‐Ba₂ScAlO₅ Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers

Cited by 14 publications

References 80 publications

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Proton Diffusion Mechanism in Hydrated Barium Indate Oxides

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High Proton Conductivity in β‐Ba2ScAlO5 Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers

Cited by 14 publications

References 80 publications

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Proton Diffusion Mechanism in Hydrated Barium Indate Oxides

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High Proton Conductivity in β‐Ba₂ScAlO₅ Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers