Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

John W Van Zee

Abstract

This dissertation considers contamination of a proton exchange membrane fuel cell (PEMC) that may result from chemicals that leach from balance of plant (BOP) materials. Both model predictions and experimental data are presented. The model is used to predict the cathode contamination impact on the Pt/C electrode and the membrane assuming no transport of contaminant from cathode to anode. The model prediction accounts for the contamination mechanisms such as adsorption, ion-exchange, absorption and three sources of voltage (i.e., performance) loss. The simple 2-D time-dependent model is developed by considering well known chemical engineering concepts of Langmuir adsorption, partition coefficients, plug flow reactors (PFRs), and dimensionless analysis. The three important dimensionless groups that result from the analysis are the Da (contamination reaction rate), fÕ (capacity ratio), and ,,C (coverage ratio). For the experiments, selected model compounds were identified in leachate solutions during the screening of off-the-shelf BOP materials. Ex-situ studies using a rotating disk electrode and a membrane conductivity device allow the preparation of isotherms based on functionality and fundamental mechanisms. The isotherms for each mechanism provide a quantitative effect of coverage by these compounds. The in-situ data obtained from segmented cell experiments is also reported. The comparison of the model predictions with in-situ experiment data shows consistent predicted coverage and performance loss. The prediction results for different species that drive the contamination mechanisms agree with experimentally determined voltage losses for each mechanism. The voltage loss for the ionomer by an ion-exchange mechanism shows the slowest contamination rate but the greatest performance loss relative to other mechanisms (i.e., adsorption/absorption). That is, voltage losses by ion-exchange continued with feed contaminant until the cell totally lost the performance. In addition, the maximum coverage by contaminants with absorption and adsorption mechanisms is determined by the leachate concentration. Finally, the tolerance limit for the each mechanism is provided from the predictions allows for the establishment of qualification standards for BOP materials.

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