Graduation Year

2009

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Mechanical Engineering

Major Professor

Ashok Kumar, Ph.D.

Co-Major Professor

Elias K. Stefanakos, Ph.D.

Keywords

Polyaniline, Chemisorption, Kinetics, Complex hydride, Physisorption

Abstract

Over the past few years, the need for a clean and renewable fuel has sharply risen. This is due to increasing fossil fuel costs and the desire to limit or eliminate harmful by-products which are created during the burning of these fuels. Hydrogen is the most abundant element in the universe and can be used in either fuel cells or traditional internal combustion engines to produce energy with no harmful emissions. One of the main obstacles facing the implementation of a hydrogen economy is its storage. Classical methods of storage involve either high and unsafe pressures or liquid storage involving a large amount of energy. Two alternative hydrogen storage methods are investigated - physisorption, which is the weak chemical bonding to a material, as well as chemisorption, which is a strong chemical bond of hydrogen to a host material.

Polyaniline, a conducting polymer, is investigated in both its bulk form as well as in nanostructured forms, more precisely nanofibers and nanospheres, to store hydrogen via physisorption. It is found the bulk form of polyaniline can store only approximately 0.5wt.% hydrogen, which is far short of the 6wt.% required for practical applications. Nanofibers and nanospheres, however, have been developed, which can store between 4wt.% and 10wt.% of hydrogen at room temperature with varying kinetics. A new complex metal hydride comprised of LiBH4, LiNH2 and MgH2 has been developed to store hydrogen via chemisorption.

While the parent compounds require high temperatures and suffer of slow kinetics for hydrogen sorption, the work performed as part of this dissertation shows that optimized processing conditions reduce the hydrogen release temperature from 250°C to approximately 150°C, while the addition of nano sized materials has been found to increase the kinetics of hydrogen sorption as well as further decrease the hydrogen release temperature, making this one of the first viable hydrogen storage materials available. This is the first time that nanostructured polyaniline has been investigated for its hydrogen performance. Additionally, the thorough investigation of the effects of nano sized additives and processing parameter optimization of the multinary hydride are first reported in this dissertation.

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