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Journal article
Tunnel Structural Heterogeneity in MnO 2 Polymorphs: Origins and Effect on Ion Transport
Meeting abstracts (Electrochemical Society), v MA2019-02(3), pp 150-150
01 Sep 2019
Abstract
The establishment of an accurate synthesis-structure-property relationship is the central scheme of materials science, which is particularly important for polymorphic materials possessing various structural forms with different properties. Manganese dioxide (MnO
2
) is a typical polymorphic material exhibiting various one-dimensional tunnel phases that are constructed by [MnO
6
] octahedra units, enabling its extensive applications in water desalination, (electro)catalysis and energy storage. Despite the long-range [MnO
6
] ordering confirmed by conventional diffraction tools, surprisingly, the electrochemical energy storage properties of a specific MnO
2
tunnel phase still vary significantly in literature with unclear structural origins.
Here, we demonstrate the existence of tunnel heterogeneity featuring localized tunnel intergrowths within single MnO
2
nanoparticles via atomically-resolved imaging. Furthermore, combining both
ex situ
and
in situ
transmission electron microscopy, the tunnel heterogeneity within one MnO
2
nanoparticle is demonstrated to significantly affect the energy storage kinetics in sodium ion battery even down to sub-nanometer scale.
The origins of such tunnel structural heterogeneity in MnO
2
are explored further, where a layer-to-tunnel (L-T) transition mechanism is identified to be responsible. The L-T transition is the essential step for the MnO
2
layered precursors to gradually transform to tunnel polymorphs during the hydrothermal synthesis. The intermediate state during the L-T transition is successfully obtained and analyzed to extract the critical information regarding the atomic reconfiguration, compositional evolution and electronic structure change during this transition. It is found that the L-T transition is not homogeneous but rather topotactically happening from the layer edges into the body, which leads to the gradual splitting of 2D MnO
2
layers into 1D nanowires possessing tunnel structure. The layers are transformed to 3×3 tunnels in multisteps via formation of intermediate tunnel phases exhibiting much larger openings. The transition starts by macroscopic layer distortion from adjacent Jahn-Teller active [Mn
3+
O
6
] octahedra, experiences Mn
3+
disproportionation reaction and layer-interlayer Mn migration, expels doped Mg
2+
out of the openings, and gradually builds the tunnels by reconstructing the Mn-O bonds.
Findings in this work could guide the controlled synthesis and selective size-engineering of MnO
2
tunnels for specific applications in various fields. We also expect it to call for renewed attention to the controlled synthesis of homogeneous tunnel-specific phases with predictable properties, and to yield a more precise structure-property relationship in polymorphic materials.
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Details
- Title
- Tunnel Structural Heterogeneity in MnO 2 Polymorphs: Origins and Effect on Ion Transport
- Creators
- Yifei YuanWentao YaoBryan BylesKun HeCong LiuBoao SongMeng ChengZhennan HuangKhalil AmineEkaterina PomerantsevaJun LuReza Shahbazian-Yassar
- Publication Details
- Meeting abstracts (Electrochemical Society), v MA2019-02(3), pp 150-150
- Publisher
- Institute of Physics (IOP)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Materials Science and Engineering
- Other Identifier
- 991020786014304721