Boron, Boron Hyperdoped Silicon and Silicon Nanoparticle Synthesis by Laser Pyrolysis with Applications in Energy Storage
Başlık:
Boron, Boron Hyperdoped Silicon and Silicon Nanoparticle Synthesis by Laser Pyrolysis with Applications in Energy Storage
Yazar:
Rohani, Parham, author. (orcid)0000-0003-2716-7372
ISBN:
9780438050358
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (157 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Mark T. Swihart Committee members: Edward Furlani; Gang Wu.
Özet:
This dissertation presents three examples of how laser pyrolysis synthesis can be used to develop new nanomaterials for energy applications. In the first chapter, we will discuss synthesis, characterization and application of boron nanoparticles for on-demand hydrogen generation application. In the second chapter, we will discuss synthesis, characterization and application of silicon nanoparticles for lithium-ion battery applications. In the third chapter, we will discuss synthesis and characterization of boron hyper-doped silicon nanoparticles for semiconductor and plasmonic applications.
Boron nanoparticles (BNPs) are of great interest for applications such as neutron capture therapy of cancer cells, hydrogen generation from water, and high energy density fuels. Boron is particularly interesting for chemical water splitting, because of its high gravimetric hydrogen generation potential of 277 g H2 per kg B. However, only a few studies of water splitting by reaction with boron are available, and those have used high temperature steam with external heating. Room-temperature boron hydrolysis is of great interest from both scientific and practical perspectives. The studies presented in chapter I demonstrate that high purity amorphous BNPs can be oxidized by water to produce hydrogen at room temperature, without external energy input, in the presence of catalytic quantities of an alkali metal or alkali metal hydride. The BNPs are produced in a single step gas phase process via CO 2 laser-induced pyrolysis of mixtures of B2H6 and SF6. The BNPs are spherical with a primary particle diameter of 10--15 nm, narrow size distribution, and specific surface area exceeding 250 m2g-1. This first demonstration of room-temperature chemical splitting of liquid water using boron opens up exciting new possibilities for on-demand hydrogen generation at high gravimetric capacity.
Electronic properties of silicon, the most important semiconductor material, are controlled through doping. The range of achievable properties can be extended by hyperdoping, i.e. doping to concentrations beyond the nominal equilibrium solubility of the dopant. In chapter II, hyperdoping was achieved in a laser pyrolysis reactor capable of providing non-equilibrium conditions, where doping is governed by kinetics rather than thermodynamics. The boron atom distribution in the hyperdoped nanoparticles is relatively uniform. The hyperdoped nanoparticles demonstrate tunable localized surface plasmon resonance (LSPR) and are stable in air for periods of at least one year. The hyperdoped nanoparticles are also stable upon annealing at temperatures up to 600°C. Furthermore, boron hyperdoping did not change the diamond cubic crystal structure of silicon, as demonstrated in detail by high flux synchrotron X-ray diffraction and pair distribution function (PDF) analysis.
Silicon is one of the best anode materials for lithium-ion batteries. Its theoretical gravimetric capacity is more than ten times that of graphite. However, practical use of silicon as an anode material has been limited by very poor cycling performance due to mechanical failure and pulverization. Nano-sized structures can accommodate significantly greater stress and strain without fracturing, compared with bulk silicon. Furthermore, nanoscale silicon increases the surface area accessible to the electrolyte while decreasing electronic and ionic transport distances, improving rate capabilities. However, limited electrical conductivity and disruption of the solid electrolyte interface (SEI) layer can severely limit the performance of even nanostructured silicon electrodes. One strategy to eliminate these effects is to encapsulate silicon within structures that can accommodate silicon volume changes during lithiation and delithiation. While such "yolk-shell" and "pomegranate" type structures have been demonstrated, and have shown promise, urgent needs remain for improved performance, which is achievable by using smaller silicon structures. In chapter III, we synthesized silicon nanoparticles with the primary size of 30 nm via laser-induced pyrolysis of silane. We then employed a combination of wet chemistry and gas phase processes to encapsulate these silicon nanoparticles within a network of graphene-type carbon shells, with void space surrounding each silicon nanoparticle. The carbon coating provides electrical conductivity and may promote formation of a stable SEI layer, while the void spaces within the nanocomposite structure accommodate volume changes during lithiation and delithiation. We compare their performance to that of similar structures prepared using larger silicon particles (~100 nm) and to anodes prepared without a void space. In this study, we demonstrate that the 30 nm silicon nanoparticles perform much better than the 100 nm silicon nanoparticles, and attribute this improved performance to shorter electronic and ionic transport distances in the smaller nanoparticles.
Notlar:
School code: 0656
Tüzel Kişi Ek Girişi:
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(682093.1) | 682093-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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