Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Chemical Engineering

First Advisor

John W. Van Zee

Abstract

This dissertation investigated ammonia (NH3) as a fuel contaminant to the anode in Proton Exchange Membrane Fuel Cells (PEMFCs). Since NH3 is fed to the anode in a gas phase and transferred to the cathode, the effect of a contaminant is distributed through MEA and quite complicated. This study is focused on the investigation of mechanism of NH3 transport and the isolation of multiple effects to degrade the performance of fuel cell. External Reference Electrode (ERE) was employed to decouple the effect of individual electrode and explain the mechanism of NH3 contamination.

A NH3 transport mechanism is supported by data for various inlet conditions in a N2/N2 laboratory-scale fuel cell at Open Circuit Condition (OCC). With a commercialized GORETM PRIMEA® 5631 MEAs at 70oC, the data were obtained with a material balance technique, which uses an ion selective electrode (ISE) to determine the concentration of ammonium ion in the process streams. The results indicate that ammonia was not transported across the membrane when the feeds to both electrodes were dry. However, with humidified feeds ammonia was transported from the anode to the cathode. The data also show the water content of in the MEA is the critical factor that causes NH3 crossover in the MEA.

An ERE was developed for PEM fuel cell by using a Nafion® strip and used to understand contamination mechanism. The voltage of anode electrode relative to ERE was measured during a polarization curve. The data showed the measurement of individual electrode was extremely affected by the misalignment between two electrodes. We compare the overpotential measured from the reference electrode and the calculated overpotential from subtracting the cell voltages between neat hydrogen and a 25 ppm CO in H2 stream at same current. The studies indicated that the overpotentials obtained from two different methods were same and the location of a Nafion® strip on MEA was not related to acquire the anode overpotentials.

When NH3 contaminant was introduced to the cell at OCC, thermodynamic potential of the anode electrode was measured for GORETM PRIMEA® 57 series MEA at 80°C. High Frequency Resistance (HFR) and material balance were also analyzed during the change of thermodynamic potential. It was shown that the injected NH3 was absorbed in the MEA until the ion exchange capacity was fully saturated and then NH3 reaction occurred on the electrode. Finally, we studied how NH3 contamination process occurs from transient voltage changes of the cell and an individual electrode.

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