Date of Award

12-2010

Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Deyang Qu

Second Advisor

Bela Török

Third Advisor

Jonathan Rochford

Abstract

The effect of Nafion-montmorillonite nanocomposite membranes on hydrogen and methanol crossover in a PEM fuel cell was studied. Several analytical methods were used to determine the amount of fuel crossover and the ionic conductivity of the membranes. The fabrication of Nafion-montmorillonite nanocomposite membranes was studied with assistance of the statistical design-of-experiment method. Four process parameters were selected: choice of mixer, clay content, curing temperature, and curing time. Fuel crossover (hydrogen and methanol) and conductivity (in-plane and through-plane) were measured for each of the membranes. The results for each test were used to determine how the four parameters affected the membranes' properties, thus the process parameters were optimized. Curing time is critical for hydrogen crossover reduction. Four different two-factor interactions are critical for methanol crossover reduction: clay content and curing temperature; mixer and curing temperature; mixer and clay content; and curing temperature and time. Clay content and curing temperature individually influence in-plane conductivity as does the interaction between the mixer and clay content. The factors that influence through-plane conductivity are the mixer and clay content individually and the interaction between clay content and curing temperature.

Additional membranes were made using the optimized process and varying the type of clay and clay content. Analogous crossover and conductivity studies were performed. The Nafion-clay nanocomposites demonstrated significantly reduced permeability to both methanol and hydrogen relative to un-doped Nafion membranes. The reduction of hydrogen and methanol crossover was compared and the possible mechanistic difference was discussed. The ionic conductivities for both in-plane and through-plane were measured using ac-impedance techniques. The ionic conductivities of the Nafion-clay nanocomposites were lower than a pure Nafion membrane of the same thickness.

Comments

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