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Lithium polysulfide battery with improved capacity and cycle performance using carbon black coated free-standing carbon cloth
Title
Lithium polysulfide battery with improved capacity and cycle performance using carbon black coated free-standing carbon cloth.
Creator
Wei, Zhen, Kushima, Akihiro, Yang, Yang, Feng, Xiaofeng, University of Central Florida
Abstract / Description
Lithium ion batteries (LIBs) have been used in various applications such as portable electronics, grid storages, and electric vehicles (EVs). Despite its commercial success, further advancement of the battery is necessary to satisfy the increasing demands for low-cost and high- performance energy storage devices as LIB is reaching its theoretical limits. Lithium sulfur battery (LSB) is one of the promising candidates for the next generation energy storage technologies. LSB uses sulfur cathode...
Show moreLithium ion batteries (LIBs) have been used in various applications such as portable electronics, grid storages, and electric vehicles (EVs). Despite its commercial success, further advancement of the battery is necessary to satisfy the increasing demands for low-cost and high- performance energy storage devices as LIB is reaching its theoretical limits. Lithium sulfur battery (LSB) is one of the promising candidates for the next generation energy storage technologies. LSB uses sulfur cathode which is a low-cost and earth abundant material with an extremely high theoretical capacity of 2600 Wh kg-1. Although there have been numerous researches aiming to establish the LSB technology, it is still in a development stage. Some of the major challenges are; low-electric conductivity, dissolution of the intermediate lithium-polysulfide reactants, and the low Coulombic efficiency. These issues must be overcome before LSBs can become practical.The objective of this work is to develop an LSB cathode that solves the above issues and contributes to advancing the development of the LSB technology. We focus on improving the electrical conductivity while reducing the shuttle effect, a parasitic reaction of the polysulfides at the anode lithium surface. To achieve this goal, we developed a carbon black coated free-standing carbon cloth. It is infiltrated with a Li2S8-containing catholyte as an active material, and its carbon framework serves as an entrapment of the polysulfides. The electrode composite enabled high- sulfur-loading, and its high surface area increased the reaction sites allowing the effective utilization of the sulfur that lead to the high capacity. It also showed high capacity retention by successfully trapping the polysulfides within the electrode. This facile and low-cost solution contributes to the realization of the LSBs.
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Date Issued
2019
Identifier
CFE0007873, ucf:52791
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007873
Catalyst Design and Mechanism Study with Computational Method for Small Molecule Activation
Title
Catalyst Design and Mechanism Study with Computational Method for Small Molecule Activation.
Creator
Liu, Muqiong, Zou, Shengli, Harper, James, Dixon, Donovan, Chen, Gang, Feng, Xiaofeng, University of Central Florida
Abstract / Description
Computational chemistry is a branch of modern chemistry that utilizes the computers to solve chemical problems. The fundamental of computational chemistry is Schr(&)#246;dinger equation. To solve the equation, researchers developed many methods based on Born-Oppenheimer Approximation, such as Hartree-Fock method and DFT method, etc. Computational chemistry is now widely used on reaction mechanism study and new chemical designing.In the first project described in Chapter 3, we designed...
Show moreComputational chemistry is a branch of modern chemistry that utilizes the computers to solve chemical problems. The fundamental of computational chemistry is Schr(&)#246;dinger equation. To solve the equation, researchers developed many methods based on Born-Oppenheimer Approximation, such as Hartree-Fock method and DFT method, etc. Computational chemistry is now widely used on reaction mechanism study and new chemical designing.In the first project described in Chapter 3, we designed phosphine oxide modified Ag3, Au3 and Cu3 nanocluster catalysts with DFT method. We found that these catalysts were able to catalyze the activation of H2 by cleaving the H-H bond asymmetrically. The activated catalyst-2H complex can be further used as reducing agent to hydrogenate CO molecule to afford HCHO. The mechanism study of these catalysts showed that the electron transfer from electron-rich metal clusters to O atom on the phosphine oxide ligand is the major driving force for H2 activation. In addition, different substituent groups on phosphine oxide ligand were tested. Both H affinity of metal and the substituent groups on ligand can both affect the activation energy.Another project described in Chapter 4 is the modelling of catalyst with DFT. We chose borane/NHC frustrated Lewis pair (FLP) catalyzed methane activation reaction as example to establish a relationship between activation energy and catalysts' physical properties. After performing simulation, we further proved the well-accepted theory that the electron transfer is the main driving force of catalysis. Furthermore, we were able to establish a linearivrelationship for each borane between activation energy and the geometrical mean value of HOMO/LUMO energy gap (?EMO). Based on that, we introduced the formation energy of borane/NHC complex (?EF) and successfully established a generalized relationship between Ea and geometrical mean value of ?EMO and ?EF. This model can be used to predict reactivity of catalysts.
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Date Issued
2018
Identifier
CFE0007343, ucf:52112
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007343
INTERFACIAL BEHAVIOR IN POLYMER DERIVED CERAMICS AND SALT WATER PURIFICATION VIA 2D MOS2
Title
INTERFACIAL BEHAVIOR IN POLYMER DERIVED CERAMICS AND SALT WATER PURIFICATION VIA 2D MOS2.
Creator
Li, Hao, An, Linan, Jung, YeonWoong, Zhai, Lei, Feng, Xiaofeng, Yu, Xiaoming, University of Central Florida
Abstract / Description
In the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedancespectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150?(&)deg;C, as well as different annealing temperatures (1100-1400 (&)deg;C). All spectra,...
Show moreIn the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedancespectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150?(&)deg;C, as well as different annealing temperatures (1100-1400 (&)deg;C). All spectra, regardless of temperature and bias, consist of two semi-circular arcs,corresponding to the free-carbon phase and the interface, respectively. The impedance of the free-carbon phase is independent of the bias, while that of the interface decreased significantly with increasing dc bias. It is shown that the change of the interfacial capacitance with the bias can be explained using the double Schottky barrier model. The charge-carrier concentration and potential barrier height were estimated by comparing the experimental data and the model.The results revealed that increasing testing temperature led to an increased charge-carrier concentration and a reduced barrier height, both following Arrhenius dependence, whereas the increase in annealing temperature resulted in increased charge-carrier concentration and barrier height. The phenomena were explained in terms of the unique bi-phasic microstructures of the material. The research findings reveal valuable microstructural information of temperaturedependent properties of polymer derived ceramics, and should contribute towards more precise understanding and control of the electrical as well as dielectric properties of polymer derivedceramics. Furthermore, the desalination performances and underlying mechanisms of two-dimensional CVD-grown MoS2 layers membranes have been experimentally assessed. Based on a successful large-area few-layer 2D materials growth, transfer and integration method, the 2D MoS2 layers membranes showed preserved chemical and microstructural integrity after integration. The few-layer 2D MoS2 layers demonstrated superior desalination capability towards various types of seawater salt solutions approaching theoretically-predicted values. Such performances are attributed to the dimensional and geometrical effect, as well as the electrostatic interaction of the inherently-present CVD-induced atomic vacancies for governingboth water permeation and ionic sieving at the solution/2D-layer interfaces.
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Date Issued
2019
Identifier
CFE0007830, ucf:52813
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007830
Engineering Noble-metal Nanostructures for Biosensing Applications
Title
Engineering Noble-metal Nanostructures for Biosensing Applications.
Creator
Ye, Haihang, Xia, Xiaohu, Kuebler, Stephen, Chen, Gang, Beazley, Melanie, Feng, Xiaofeng, University of Central Florida
Abstract / Description
The ability to engineer noble-metal nanostructures (NMNSs) in a controllable manner and to understand the structure-dependent properties greatly boost our knowledge in rational design of biosensing technologies. In particular, as a type of highly efficient peroxidase mimics, NMNSs hold promising potential to break through the bottleneck of conventional enzyme-based in vitro diagnostics.During the time of my Ph.D. study, I have successfully: 1) directed a two-step method involving seed...
Show moreThe ability to engineer noble-metal nanostructures (NMNSs) in a controllable manner and to understand the structure-dependent properties greatly boost our knowledge in rational design of biosensing technologies. In particular, as a type of highly efficient peroxidase mimics, NMNSs hold promising potential to break through the bottleneck of conventional enzyme-based in vitro diagnostics.During the time of my Ph.D. study, I have successfully: 1) directed a two-step method involving seed-mediated growth and chemical etching for the synthesis of Ru nanoframes (RuNFs) with face-centered cubic crystal phase and enhanced catalytic activities; 2) demonstrated, for the first time, the inherent peroxidase-like activity of RuNFs as a type of efficient peroxidase mimics, opening up possibilities for their bioapplications; 3) developed an enzyme-free signal amplification technique for ultrasensitive colorimetric assay of disease biomarkers by using Pd-Ir nanooctahedra encapsulated gold vesicles as labels; 4) prepared polyvinylpyrrolidone (PVP)-capped Pt nanocubes with superior peroxidase-like catalytic activity and record-high specific catalytic activity; 5) developed a facile colorimetric method for the detection of Ag(I) ions with picomolar sensitivity by using the PVP-capped Pt nanocubes as the probes; 6) developed a non-enzyme cascade amplification strategy for colorimetric assay of disease biomarkers by taking advantage of the interaction between the Ag(I) ions and PVP-capped Pt nanocubes; and 7) established a highly sensitive colorimetric lateral flow assay platform by using Au@Pt core-shell nanoparticles as the labels that possess both plasmonic and catalytic properties.
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Date Issued
2019
Identifier
CFE0007559, ucf:52626
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007559