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Investigation of p-type ZnO nanowire applicable to nanogenerator and photoelectrochemical water splitting

  • Leeseung Kang (강이승, 대학원 신소재공학과 신소재공학전공)

초록/요약

Nanotechnology and nanoscience have received increasing attention over the last decade. Currently, intensive worldwide effort is ongoing toward the efficacious synthesis and fabrication of nanostructures and nanodevices. In this dissertation, a systematic on the synthesis, characterization, and device fabrication of La-doped p-type ZnO nanostructures has been performed. In this process, the following goals were achieved: (1) rational design and growth control of La:ZnO nanowires (NWs), (2) improved chemical and physical understanding of the growth of La:ZnO NWs, (3) reporting of their piezoelectric output performance, and (4) improvement in their photoelectrochemical (PEC) properties using nanoparticle (NP) sensitizers. An improved understanding of the chemical and physical processes that occur during hydrothermal growth was adequately achieved via a systematic investigation of La:ZnO NWs. The optimum amount of La-dopant was determined based on the morphology of NWs; moreover, the lattice constant, bond length, crystal phase, and surface elemental compositions were observed. Further details are provided in Chapter 3. Using La:ZnO NWs as piezoelectric nanogenerators (NGs), the piezoelectric energy harvesting properties were investigated. When undoped ZnO NGs were compared to La:ZnO NGs, the output voltage of the former was measured to be 2.1 V, while that of the latter was higher, at 3.0 V. Further, the undoped ZnO NGs produced a small current of 0.24 μA compared to the 0.34 μA for the La:ZnO NGs. Thus, it is believed that La doping could enhance the output performance of ZnO NGs by acting as a p-type dopant. These results will be presented in further detail in Chapter 4. Finally, a photocathode based on La:ZnO NWs was fabricated and its PEC performance was investigated. To improve the PEC performance for water splitting, CdTe NP sensitized La:ZnO NWs were introduced. The CdTe NPs were synthesized via a non-toxic, facile, one-pot method using a non-dimethylcadmium precursor and non-injection-based synthesis. According to the results from Chapter 5, the heterostructured CdTe NP sensitized La:ZnO could be promising for improving H2 evolution. It is expected that the results of these studies will contribute to a deeper understanding of p-type ZnO NWs and reveal new opportunities and applications for p-type semiconductors.

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목차

ABSTRACT
LIST OF FIGURES
LIST OF TABLES
LIST OF ABBREVIATIONS AND ACRONYMS
Chapter 1. Introduction
1-1. Energy, eco-friendly and sustainable development
1-2. Research trend of ZnO materials and applications
1-3. Scope and objectives of research
Chapter 2. Theoretical background
2-1. One-dimensional nanostructures
2-1-1. One-dimensional metal oxide nanostructures
2-1-1-1. Nanowires
2-1-1-2. Nanotubes
2-1-1-3. Nanobelts
2-1-2. Fundamentals of ZnO nanowires
2-1-2-1. Crystal structure
2-1-2-2. Lattice parameters
2-1-2-3. n-type doping
2-1-2-4. p-type doping
2-1-3. Synthesis of ZnO nanowires
2-1-3-1. Vapor phase transport method
2-1-3-2. Hydrothermal method
2-2. Piezoelectric nanogenerator
2-2-1. Piezoelectric materials in energy harvesting
2-2-1-1. Inorganic piezoelectric materials
2-2-1-2. Piezoelectric polymers
2-2-1-3. Bio-piezoelectric materials
2-2-2. ZnO nanowire nanogenerator
2-2-2-1. Origin of Piezoelectricity in ZnO
2-2-2-2. Piezoelectric potential and charge generation
2-3. Photoelectrochemical water splitting
2-3-1. Hydrogen production for the renewable energy source
2-3-2. Fundamental processes in a PEC device
2-3-2-1. Thermodynamics of PEC water splitting
2-3-2-2. PEC water splitting reaction mechanism
2-3-2-3. Semiconductor-liquid interface
Chapter 3. Synthesis of La-doped ZnO nanowires
3-1. Introduction
3-2. Experimental procedure
3-2-1. Materials and preparation
3-2-2. Characterization
3-3. Results and discussion
3-4. Conclusions
Chapter 4. Effect of La doping on the enhanced piezoelectric performance of flexible ZnO nanogenerators
4-1. Introduction
4-2. Experimental procedure
4-2-1. Materials and preparation
4-2-2. Device fabrication
4-2-3. Calculation of the strain neutral plain and strains
4-2-4. Characterization
4-3. Results and discussion
4-4. Conclusions
Chapter 5. Heterostructured CdTe nanoparticle sensitized La-doped ZnO nanowires for photoelectrochemical water splitting
5-1. Introduction
5-2. Experimental procedure
5-2-1. Materials and preparation
5-2-1-1. La-doped ZnO nanowires on FTO substrate
5-2-1-2. CdTe nanoparticles
5-2-1-3. CdTe nanoparticles sensitized La-doped ZnO nanowires
5-2-2. Photoelectrochemical measurements
5-3. Results and discussion
5-3-1. PEC measurement for La-doped ZnO nanowires
5-3-2. Synthesis of CdTe nanoparticles
5-3-3. Heterostructured photocatalyst of CdTe nanoparticles sensitized La-doped ZnO nanowires
5-4. Conclusions
Chapter 6. Conclusions
Acknowledgments
References

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