Graduation Semester and Year

2014

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Brian Dennis

Abstract

The world's energy demand is expected to increase dramatically over the next few decades. At the same time the availability of cheap fossil fuels is expected to decrease. In addition to the increase in energy cost, the use of fossil fuels results in the release of greenhouse gases into the atmosphere. A lot research effort has been invested in the development of renewable energy resources that are cost competitive, sustainable, and emission free. Although these renewable technologies are available, many are not implemented widely due low efficiency and high capital cost. Therefore, fossil fuels are expected to remain a major source of the world's energy for several decades. The release of carbon dioxide by the burning of fossil fuels is particularly problematic as these emissions are believed by many scientists to be the cause of global warming. To solve this climate change challenge, many researchers believe the carbon dioxide levels in the atmosphere should be reduced. One approach to this problem is to employ methods that convert carbon dioxide into useful liquid or solid chemicals.It has been known for decades that a mixture of carbon dioxide and water can be converted to useful liquids such as acids and alcohols via thermo/electro/photo-chemical methods. The electro and photo chemical approaches have resulted in liquid products with low carbon numbers, such as methanol and formic acid, using catalysts composed of Ruthenium, Palladium, Titanium oxides, and Copper oxides. Alcohols have a high fuel value and are arguably most important product of electrochemical reduction of carbon dioxide. The reported Faradic efficiency of alcohols is not high and the few cases with good Faradic efficiency the production rate and energy efficiency is low. Besides these low efficiencies, the price of some the catalysts are too high to be considered for industrial scale production. In an effort to increase the energy efficiency, this work employs a hybrid photo-electrochemical approach that uses solar energy to reduce the electricity required for carbon dioxide reduction to liquids. A photo-electrochemical microreactor was developed to demonstrate this approach. This micro design increases the energy efficiency by decreasing the Ohmic losses while increasing production rates by improving mass transport of the reactants to the electrode surface. A novel nanostructured copper oxide surface is used as a semiconductor photoelectrode in this micro photo-electrochemical cell. Since the photoelectrode is produced from copper, an earth abundant element, it is more economical for industrial applications. The developed reactor has produced alcohols up to three carbons with high Faradic efficiency, which is novel and not reported by other researchers.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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