Date of Award

8-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemical Engineering

Advisor

Goodwin, Jr., James G

Committee Member

Bruce , David A

Committee Member

Hwu , Shiou-Jyh

Committee Member

Kitchens , Christopher L

Abstract

Proton exchange membrane fuel cells are a highly efficient source of power generation that is needed to sustain the energy demands of today's more environmentally conscience society. However, the presence of impurities in the hydrogen fuel stream, such as CO, H2S, and NH3 from the steam reforming/partial oxidation of hydrocarbons/methanol, can severely poison the Pt electrocatalyst present in the fuel cell electrode causing degradation in the fuel cell performance. To counter these poisoning effects, fuel cell manufacturers are forced to use higher Pt loadings, which dramatically increases material costs and prevents the successful commercialization of the technology. The focus of the present research is the investigation of the impurity effects on the activity of a Pt fuel cell catalyst for the adsorption and activation of hydrogen at typical fuel cell conditions. The degree of impact from each impurity is observed in terms of Pt surface atom availability, which is then related to fuel cell performance results.
The effect of CO on hydrogen activation on Pt fuel cell catalysts were found to be severe even at as low as 10 ppm. In the presence of water vapor, the maximum CO surface coverage found on the Pt/C catalyst was between 0.5–0.7 monolayer at typical fuel cell operating conditions. Reversibility of the poisoning showed only a partial recovery in available Pt surface sites, however, the amount of Pt surface sites recovered was enough to return the hydrogen activation reaction back to equilibrium, which is equivalent to a full recovery observed in fuel cell performance. The poisoning effect from tetrachloroethylene appears to be a combination of the processes occurring at the anode and cathode. The presence of the hydrogen is required to help decompose the chlorocarbon at the low operating temperatures. Once decomposed, the oxygen enhances the poisoning by tetrachloroethylene or derivatives. Other impurities such as NH3, paraffins (C3–C7), inert gases (He, N2, Ar), and ethylene, were found to have little or no effect on the hydrogen activation on Pt fuel cell catalyst.

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