Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Committee Chair

Jian Xie

Committee Co-Chair

Steven F. Son

Committee Member 1

Lia A. Stanciu

Committee Member 2

Wenquan Lu

Committee Member 3

Chengjun Sun

Abstract

Two major parts consist of my work in this dissertation which are the study of the materials for fuel cell catalysts and lithium-ion battery cathodes,

In the first part, FeOF is studied as a new generation cathode material due to its high specific capacity. To overcome its weaknesses which are low conductivity and poor cycle life, graphene sheets are introduced into FeOF to form a FeOF/graphene hybrid. It has been found that introducing graphene sheets can greatly improve the reversibility of FeOF and improve the specific capacity and rate performance by increasing its electronic conductivity. The cycle life and columbic efficiency of FeOF/G is greatly improved compared to blank FeOF material. FeOF/G exhibited 621 mAh/g initial specific capacity and retained 80% of its initial capacity after 100 cycles at the rate of 0.1C. In-operando synchrotron XAS and high energy XRD is applied to study the behavior of FeOF/G during cycling. It is proved that the incorporation of graphene nanosheets can help to anchor the FeOF and its discharge product to make it more reversible.

The second part mainly focuses on the improvement of the stability/durability of the fuel cell catalyst and the design of a novel catalyst/ionomer interface. Graphene sheets which has the highest graphic structure have been used to replace amorphous carbon blacks as catalyst supports for proton exchange membrane fuel cells (PEM-FCs). It has been proved by electrochemical tests that graphene nanosheet can improve the durability of the catalyst greatly. The surface functional has also been used to improve the mass activity of the PEMFC catalysts by improving the distribution of Pt over catalyst support surface and decreasing the size of Pt nanoparticles. Surface functionalization can also help to control the catalyst/ionomer interface. The opposite surface charge can help to guide the distribution of the Nafion ionomer to form a thin film, thus the mass transport resistance can be greatly reduced.

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