Doctoral Dissertations

Date of Award

12-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Energy Science and Engineering

Major Professor

Thomas A. Zawodzinski

Committee Members

Dibyendu Mukherjee, Jagjit Nanda, David L. Wood III

Abstract

The high cost of platinum catalysts remains a major limitation to the development of proton exchange membrane fuel cells (PEMFCs). Despite a monumental research effort for platinum group metal free (PGM-free) catalysts, no viable alternative has been found that matches platinum in activity and stability. Further efforts to reduce cost have increased focus on anion exchange membrane fuel cells (AEMFCs) in recent years. Changing the conducting ion from protons in PEMs to hydroxide in AEMs changes the fuel cell environment from acidic to basic. Many PGM-free catalysts show increased activity and stability in basic environments.Considering the promise of AEMFCs a series of systematic studies was conducted on several cell components. The physical and catalytic properties of a family of PGM-free oxygen reduction catalysts was studied through various spectrographic and voltammetric techniques. A thorough study of the catalyst performance in a single cell fuel cell test was conducted, leading to the development of a PGM-free catalyst which matched the performance of platinum. The anode performance was found to be significantly lower than expected. A systematic investigation of AEMFC anodes attributed the poor performance to electrode flooding. Modification of the anode catalyst layer led to improved anode performance to the detriment of the whole-cell performance. These results highlighted the need for a greater level of understanding of water transport in AEMs. To this end, several anion exchange membranes were synthesized and the effect of cation structure on water uptake, conductivity, stability was measured. Additionally, water uptake, conductivity, and the electro-osmotic drag of water were studied in a commercial AEM.The knowledge of oxygen electrodes for AEMFCs was leveraged for the development of rechargeable zinc-air batteries (ZABs). ZABs utilize oxygen from the air as half the battery chemistry to dramatically reduce the size and weight of the cell. Rechargeable ZABs are expected to half energy densities 4-5x higher than lithium ion batteries. However, their development is hindered by zinc dendrite and passivation issues, poor oxygen catalysis, and electrolyte management. In this work, bifunctional oxygen reduction and evolution catalysts and novel anion exchange membrane are studied through ex-situ and in-situ methods.

Comments

Portions of this text were published in the Journal of Power Sources: A family of platinum group metal-free catalysts for oxygen reduction in alkaline media. Gabriel A.Goenaga, Asa L.Roy, Nelly M.Cantillo, ShaneFoister, Thomas A. Zawodzinski Jr. Journal of Power Sources (2018), 395, 148-157

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