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You searched for +publisher:"Oregon State University" +contributor:("Ji, Xiulei"). Showing records 1 – 3 of 3 total matches.

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Oregon State University

1. Wang, Xingfeng. New Chemistry for Electrochemical Energy Storage Applications.

Degree: PhD, 2017, Oregon State University

Electrochemical capacitors and batteries are two major electrochemical energy storage technologies, which have been investigated extensively to meet the rapidly-growing demand for higher energy, higher power, lower cost and enhanced safety in the past few decades. With the charge storage mechanism of electrostatic charge adsorption/desorption via electrical double layers, electrochemical capacitors deliver higher power, but store less energy, compared to batteries, where redox reactions usually take place inside bulk electrode materials. Depending on the electrolytes, electrochemical capacitors can be divided into aqueous and non-aqueous capacitors. Aqueous electrolytes are more electrically conductive, non-flammable, and more sustainable, compared to non-aqueous electrolytes. However, non-aqueous electrolytes are overwhelmingly dominating the electrochemical capacitor markets, because they provide a larger electrochemical window, and consequently enable capacitors to store more energy. To take advantages of aqueous electrolytes and facilitate safer and more sustainable electrochemical capacitors, tremendous research has been conducted to increase energy density of aqueous capacitors. Traditional approach is to utilize redox-active electrodes, e.g. metal oxide and conducting polymers in pseudocapacitors, most of which increase energy density at the expense of largely sacrificing power and cycle life. It is important to make progress in one performance aspect of electrochemical capacitors, while retaining other desirable properties as much as possible. There are two effective ways to store more energy in electrochemical capacitors. One is by increasing capacitance, and the other one is by increasing operating voltages. Higher capacitance can be obtained when introducing redox reactions in electrochemical capacitors. Instead of employing redox-active electrodes, which may experience ion diffusion in solid, aqueous redox-active electrolyte was studied to retain high power while storing more energy. The redox pair of IOx-/I- in 4 M KI and 1 M KOH is reported for the first time, which enables aqueous capacitors to store a maximum energy of 7.1 Wh/kg, on a par with state-of-the-art non-aqueous capacitors, while delivering a maximum power of 6222 W/kg, and retaining 93% capacitance after 14,000 cycles. Higher operating voltages are realized in aqueous electrochemical capacitors by maintaining pH 1 and pH 10 at the positive and negative electrode, respectively, with a bipolar assembly of ion-exchange membranes. The theoretical electrochemical window of aqueous electrolytes is expanded from 1.23 to 1.76 V. A practical operating voltage of 1.8 V is proved to be safe for aqueous capacitors with the bipolar assembly, which allows to store a specific energy of 12.7 Wh/kg, as well as retain 97% capacitance after 10,000 cycles. Although batteries, especially lithium-ion batteries, have been successful in different fields, e.g. portable electronics, electric vehicles, etc., an intrinsic drawback still exists: low abundance of… Advisors/Committee Members: Ji, Xiulei (advisor), Lerner, Michael M. (committee member).

Subjects/Keywords: Electrochemical

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APA (6th Edition):

Wang, X. (2017). New Chemistry for Electrochemical Energy Storage Applications. (Doctoral Dissertation). Oregon State University. Retrieved from http://hdl.handle.net/1957/61859

Chicago Manual of Style (16th Edition):

Wang, Xingfeng. “New Chemistry for Electrochemical Energy Storage Applications.” 2017. Doctoral Dissertation, Oregon State University. Accessed February 19, 2019. http://hdl.handle.net/1957/61859.

MLA Handbook (7th Edition):

Wang, Xingfeng. “New Chemistry for Electrochemical Energy Storage Applications.” 2017. Web. 19 Feb 2019.

Vancouver:

Wang X. New Chemistry for Electrochemical Energy Storage Applications. [Internet] [Doctoral dissertation]. Oregon State University; 2017. [cited 2019 Feb 19]. Available from: http://hdl.handle.net/1957/61859.

Council of Science Editors:

Wang X. New Chemistry for Electrochemical Energy Storage Applications. [Doctoral Dissertation]. Oregon State University; 2017. Available from: http://hdl.handle.net/1957/61859


Oregon State University

2. Fang, Zhen. Iron Chalcogenide-based Thin Films Fabricated by Inkjet Printing.

Degree: MS, Chemical Engineering, 2015, Oregon State University

Digital printing techniques offer several advantages in manufacturing electronics such as direct writing of materials, reduction of chemical waste, and scalability. In particular, printing can significantly simplify manufacturing processes by directly defining the channel area, the gate, and the source and drain contacts, allowing for lower costs and higher throughput manufacture of Thin Film Transistors (TFTs). Pyrite (FeS₂) and ternary compound iron germanium sulfide (Fe₂GeS₄) are compound semiconductors which consist of earth abundant elements. Both materials are being studied as promising candidates for thin film photovoltaics. In this study, iron sulfide and iron germanium sulfide thin films were fabricated by ink-jet printing for the first time. The films were formed by simply inkjet printing iron and germanium salts followed by air annealing and sulfurization. Thin films were characterized by Ultraviolet-visible spectroscopy, X-ray diffraction, Scanning electron microscopy, Atomic force microscopy and Hall-effect measurements. The characterization results indicate P-type iron sulfide and iron germanium sulfide thin films were successfully fabricated. TFTs were fabricated and characterized using inkjet printed FeS₂ thin films on SiO₂/Mo/Glass substrates. The devices clearly show linear increment of the drain current as a function drain voltage and could be modulated by varying the gate voltage. However, the TFTs seem to show ambipolar behaviors. Better understandings of defects and electrical properties are needed to develop strategies that could improve pyrite-based TFT performance. Advisors/Committee Members: Chang, Chih-Hung (advisor), Ji, Xiulei (committee member).

Subjects/Keywords: Iron Chalcogenide; Thin film transistors

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Fang, Z. (2015). Iron Chalcogenide-based Thin Films Fabricated by Inkjet Printing. (Masters Thesis). Oregon State University. Retrieved from http://hdl.handle.net/1957/57722

Chicago Manual of Style (16th Edition):

Fang, Zhen. “Iron Chalcogenide-based Thin Films Fabricated by Inkjet Printing.” 2015. Masters Thesis, Oregon State University. Accessed February 19, 2019. http://hdl.handle.net/1957/57722.

MLA Handbook (7th Edition):

Fang, Zhen. “Iron Chalcogenide-based Thin Films Fabricated by Inkjet Printing.” 2015. Web. 19 Feb 2019.

Vancouver:

Fang Z. Iron Chalcogenide-based Thin Films Fabricated by Inkjet Printing. [Internet] [Masters thesis]. Oregon State University; 2015. [cited 2019 Feb 19]. Available from: http://hdl.handle.net/1957/57722.

Council of Science Editors:

Fang Z. Iron Chalcogenide-based Thin Films Fabricated by Inkjet Printing. [Masters Thesis]. Oregon State University; 2015. Available from: http://hdl.handle.net/1957/57722


Oregon State University

3. Xing, Zhenyu. Preparation and Properties of Porous Carbon Materials.

Degree: PhD, Chemistry, 2016, Oregon State University

Porous carbon is indispensable in modern technology applications. It is used for energy storage, gas separation, water purification, catalyst support, and chromatography. The diversity of its applications stems from its unique properties, including high specific surface area, tunable pore volume, and chemical stability. Specifically, the large surface area provides high capacitance for the electric double layer capacitor, and catalytic sites for the chemical reaction and binding substrate for other catalysts in the metal air battery, fuel cell, and water splitting. Tunable pore size holds the same importance as the high surface area. Micropores are always prerequisite for the high surface area, and dramatically affect the solvated ions in the capacitive behavior. Mesopores and macropores are necessary for the mass transfer, which is the most dominant process in drug delivery, gas separation, and ions diffusion in the capacitor and fuel cell. The carbon crystal structure always determines chemical stability. Always, the more graphitic or the more graphenic is, the more chemically stable the carbon is. On the contrary, the structure of amorphous carbon is apt to be damaged under high potentials or in the harsh chemical environments, such as strong acid or base. Porous carbon can be synthesized by inorganic template filling, polymer carbonization or catalytic activation; however, these methods are constrained by high cost, tedious preparation process and low yield, which further limit their practical application. In this thesis, I will introduce a porous graphene preparation by CO₂ activation and magnesiothermic reduction of CO₂. On one side, porous carbon preparation by physical activation, such as H₂O and CO₂, and chemical activation, such as ZnCl₂, H₃PO₄, and KOH, has been used industrially for decades, and plenty studies have been devoted to revealing the pore size or surface area changes during the activation, such as volume of micropores increased by H₃PO₄, lower activation temperature and higher yield by ZnCl₂ and increased surface area and graphitic feature by KOH. However, detailed study of the carbon structure evolution during the activation remains unknown. The reaction mechanism of carbon activated by CO₂ is the simplest due to the single product formation of CO, and the simplicity of this reaction makes possible the elucidation of structural evolution of carbon during CO₂ activation. After analyzing the structural evolution revealed by neutron total scattering, TEM, and other characterizations, we have come to the conclusion that the defective graphenic domains are removed, and turbostratic domains are thinned after the nanoporosity is generated in the initial activation. Furthermore, the tailor-designed porous carbon is synthesized in a short activation time with a high surface area with the guide of the mechanistic insights into the structural evolution of carbon. The synthesis of porous carbon by magnesiothermic reduction of CO₂ holds a very similar design principle as the widely… Advisors/Committee Members: Ji, Xiulei (advisor), Lerner, Michael (committee member).

Subjects/Keywords: porous carbon; Porous materials  – Synthesis

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Xing, Z. (2016). Preparation and Properties of Porous Carbon Materials. (Doctoral Dissertation). Oregon State University. Retrieved from http://hdl.handle.net/1957/60026

Chicago Manual of Style (16th Edition):

Xing, Zhenyu. “Preparation and Properties of Porous Carbon Materials.” 2016. Doctoral Dissertation, Oregon State University. Accessed February 19, 2019. http://hdl.handle.net/1957/60026.

MLA Handbook (7th Edition):

Xing, Zhenyu. “Preparation and Properties of Porous Carbon Materials.” 2016. Web. 19 Feb 2019.

Vancouver:

Xing Z. Preparation and Properties of Porous Carbon Materials. [Internet] [Doctoral dissertation]. Oregon State University; 2016. [cited 2019 Feb 19]. Available from: http://hdl.handle.net/1957/60026.

Council of Science Editors:

Xing Z. Preparation and Properties of Porous Carbon Materials. [Doctoral Dissertation]. Oregon State University; 2016. Available from: http://hdl.handle.net/1957/60026

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