Colloidal atomically-thin inorganic nanoflowers for electrocatalytic hydrogen evolution
File(s)
Author(s)
Sokolikova, Maria
Type
Thesis
Abstract
Layered metal chalcogenides include several classes of inorganic solids characterised by weak van der Waals bonding between the two-dimensional structural blocks. Bulk counterparts of layered transition metal dichalcogenides have been extensively investigated for decades for applications in catalysis and energy storage, whereas bulk pnictogen chalcogenides have attracted a significant attention due to their excellent thermoelectric properties. Following the successful isolation of graphene, the exploration of two-dimensional materials derived from bulk crystals has begun. Compared to graphene, atomically-thin sheets of layered metal chalcogenides offer a variety of disparate electronic structures, ranging from semiconductors and semimetals to topological insulators, owing to the diverse compositions and lattice symmetry of individual layers.
In order to implement the isolated layers of metal chalcogenides in novel nanoelectronics and miniaturised electrochemical devices, methods to produce two-dimensional nanosheets with high yield and in a controllable manner need to be developed. Colloidal synthesis holds a great promise for a large-scale preparation of dispersions of atomically-thin metal chalcogenide nanosheets for applications not requiring high structural perfection of the material, such as catalysis. Furthermore, wet chemical synthesis is a particularly powerful approach to obtain the material with desired morphology, crystal phase, and composition via the accurate tailoring of the precursors’ reactivity. However, a controllable colloidal synthesis of metal chalcogenide nanosheets is still at a very early stage.
In this work, we design a colloidal synthesis of atomically-thin layered metal chalcogenide (MoSe2, MoTe2, Bi2Te3, WSe2) nanoflowers from molecular precursors. We systematically investigate the effect of synthesis parameters, such as type and stoichiometry of metal precursor, coordinating solvent and growth temperature, on the morphology (MoSe2) and lateral termination (Bi2Te3) of the colloidal branched nanosheets. We demonstrate how by optimising the precursor reactivity, the formation of chemically-unstable MoTe2 and direct growth of the metastable WSe2 polymorph can be achieved. The designed synthesis strategy was successfully modified to obtain doped material (Fe- and Cu-doped WSe2) and ternary compositions (WxMo1-xSe2), preserving the edge-rich morphology of colloidal nanoflowers. The colloidal nanoflowers were tested as a catalyst material for the hydrogen evolution reaction. Furthermore, potential improvement of the catalytic activity due to the composition variation and crystal phase engineering was examined.
In order to implement the isolated layers of metal chalcogenides in novel nanoelectronics and miniaturised electrochemical devices, methods to produce two-dimensional nanosheets with high yield and in a controllable manner need to be developed. Colloidal synthesis holds a great promise for a large-scale preparation of dispersions of atomically-thin metal chalcogenide nanosheets for applications not requiring high structural perfection of the material, such as catalysis. Furthermore, wet chemical synthesis is a particularly powerful approach to obtain the material with desired morphology, crystal phase, and composition via the accurate tailoring of the precursors’ reactivity. However, a controllable colloidal synthesis of metal chalcogenide nanosheets is still at a very early stage.
In this work, we design a colloidal synthesis of atomically-thin layered metal chalcogenide (MoSe2, MoTe2, Bi2Te3, WSe2) nanoflowers from molecular precursors. We systematically investigate the effect of synthesis parameters, such as type and stoichiometry of metal precursor, coordinating solvent and growth temperature, on the morphology (MoSe2) and lateral termination (Bi2Te3) of the colloidal branched nanosheets. We demonstrate how by optimising the precursor reactivity, the formation of chemically-unstable MoTe2 and direct growth of the metastable WSe2 polymorph can be achieved. The designed synthesis strategy was successfully modified to obtain doped material (Fe- and Cu-doped WSe2) and ternary compositions (WxMo1-xSe2), preserving the edge-rich morphology of colloidal nanoflowers. The colloidal nanoflowers were tested as a catalyst material for the hydrogen evolution reaction. Furthermore, potential improvement of the catalytic activity due to the composition variation and crystal phase engineering was examined.
Version
Open Access
Date Issued
2019-07
Date Awarded
2020-02
Copyright Statement
Creative Commons Attribution-Non Commercial 4.0 International Licence
License URL
Advisor
Mattevi, Cecilia
Giannini, Vincenzo
Sponsor
Imperial College London
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)