Date of Completion

5-3-2018

Embargo Period

4-14-2018

Keywords

Polymer Electrolyte Fuel Cells, Contamination, Durability, Transport Phenomena

Major Advisor

Ugur Pasaogullari

Associate Advisor

Aimy Bazylak

Associate Advisor

Wilson Chiu

Associate Advisor

Michael Pettes

Associate Advisor

Prabhakar Singh and Trent Molter

Field of Study

Mechanical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Polymer electrolyte fuel cells (PEFCs), while a promising clean energy technology, suffer from a lack of durability, especially tolerance to impurities. This work studies both foreign cationic contamination in the cathode, and detection of fuel impurities through the development of a hydrogen contaminant detector (HCD).

The role of mass transport in foreign cationic contamination of PEFCs is studied through the extraction of a gas diffusion media (GDM) from a cell that experienced sudden shutdown during in situ foreign cation contamination. Significant cation salt precipitation is examined using x-ray computed tomography, with the distribution examined using an in-house Matlab code. Results show that the microporous layer (MPL) restricted capillary transport of the dissolved cations towards the catalyst layer, causing the cationic salt concentration to build and precipitate within the GDM. A computational model is developed to model the coupled water and cation transport in the GDM and membrane electrode assembly (MEA), and further shows that the increased capillary resistance encountered as the water transitions from the macroporous carbon paper substrate to the MPL, acts to restrict the transport of water and foreign cations to the MEA.

The impact of foreign cations on catalyst layer thinning is subsequently examined. Four hundred hour long tests were run on baseline and calcium cationcontaminated PEFCs. Significant catalyst layer thinning observed only on the cation contaminated cell is proposed to occur due to proton depletion and subsequent carbon corrosion. The computational model is used to show that foreign cations accumulate towards the cathode (occupying 80% of the sulfonic acid sidechains), which result in a depletion of protons. To sustain oxygen reduction, it is hypothesized that carbon oxidation occurs to generate protons and continue oxygen reduction in the cathode.

Finally, development of a HCD is discussed; specifically work towards characterizing the response to carbon monoxide impurities. Electrochemical impedance spectroscopy measurements are performed and analyzed using electrochemical equivalent circuits (EEC). Fitting the data to EECs shows that different circuits are required to match the baseline and CO-contaminated EIS spectra, in which both the oxidizing and reducing electrodes contribute into the measured response.

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