Chemical and Biological Engineering ETDs

Sarah Stariha

Publication Date

6-9-2016

Abstract

One of the biggest obstacles to commercializing polymer electrolyte membrane fuel cells is the use of platinum as a catalyst. One way to overcome this obstacle is to replace platinum with non-platinum group metal (non-PGM) catalysts, particularly for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The most realistic method of estimating the performance of non-PGM catalysts is testing within membrane electrode assemblies (MEAs). One key issue is that non-PGM catalysts are not as active as platinum. One way to increase their performance is to optimize the catalyst layer composition, specifically the components responsible for ionic and electronic conductivity. The first objective of this work was to determine the optimal ionomer-to-catalyst ratio and additional carbon content within the catalyst layer. Another problem that arises when replacing platinum with non-PGM catalysts is the catalyst layer thickness. Platinum catalyst layers are on the order of 10 μm whereas non-PGM catalyst layers are on the order of 60-120 μm. Although this increase in catalyst allows for more active sites it causes challenges in transport performance by elongating pore channels. From this the second objective of this work was to examine the chemistry and morphology of both the non-PGM catalysts and sprayed catalyst layers and their effects on MEA performance. Another polymer electrolyte membrane fuel cell and an alternative to PEMFCs are anion exchange membrane fuel cells (AEMFCs). Unlike the corrosive environment in PEMFCs, the alkaline environment of AEMFCs is much more conducive to non-PGM catalysts. The problem is that AEMFC technology is decades behind that of PEMFC, particularly the anion exchange membranes and their stability. Because of this there is very little data on alkaline MEA assembly and testing. The third objective of this work was to integrate new Ni-based hydrogen oxidation reaction (HOR) catalysts into alkaline MEAs. A large part of this objective was designing a reproducible protocol for making these MEAs. From this work it was concluded that within the catalyst layer the amount of ionomer plays a key role in MEA performance as does any additional carbon added. In general higher amounts of Nafion® ionomer lead to poor overall performance most likely do to pore and active site blocking and loss of electronic conductivity. This can be corrected with the addition of carbon. It was found that the catalyst layer morphology also plays an important role in MEA performance, specifically pore connectivity. Lastly it was shown that a reproducible protocol for making alkaline MEAs was established and is comparable to what has been reported in the literature. Also initial MEA data for Nickel-Molybdenum-Copper HOR catalysts was successfully acquired for the first time.

Keywords

Proton Exchange Membrane Fuel Cell (PEMFC), Alkaline Exchange Membrane Fuel Cell (AEMFC), Catalyst Layer Composition Optimization, Catalyst Layer Morphology, non-platinum group metal catalysts

Sponsors

Department of Energy Fuel Cell Technology Program

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Garzon, Fernando

Second Committee Member

Artyushkova, Kateryna

Third Committee Member

Serov, Alexey

Fourth Committee Member

Shuler, Andrew

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