Correlating Ex-Situ and In Situ Measurement for Proton Exchange Membrane Fuel Cells

In the development of proton exchange membrane fuel cells (PEMFCs), the contamination effect on PEMFC durability can retard commercialization.^1-4 To understand contamination mechanisms and their impacts on PEMFCs, experimental studies conducted and found the sensitivity of performance to the low levels of contamination. ^1-9 Also, a simple isothermal model for contamination of a PEMFC which includes adsorption on the Pt catalyst, absorption into the membrane, and ion-exchange with ionomeric components was developed and presented. ^8-9 In this paper, we discuss the relationship between ex-situ measurements using thin film electrodes and the in-situ performance of PEMFCs. The isotherms from ex-situ measurements for each mechanism provide a quantitative effect of coverage by contaminants and are shown to predict in-situvoltage losses when the proper dimensionless variables are used.

       For the Pt coverage the ex-situ measurements are performed on thin-film electrodes, which have typically lower Pt loadings (e.g., 0.02mg/cm² vs. 0.4mg/cm²) and smaller geometric electrode areas (e.g., 0.24cm² vs. 50cm²). As shown in Figure 1, these ex-situ Pt coverage data can be obtained with contaminants in the liquid phase. In contrast, for the in-situ performance, transport of contaminants can be through the gas phase. To establish the relationship between the coverage measured with ex-situ liquid concentration and the coverage corresponding to in-situ gas phase concentration, scaling techniques are required. Data are presented and discussed to test the scaling and the dimensionless groups.

Acknowledgements

The authors gratefully acknowledge support for this work by the DOE EERE Fuel Cell Technologies Office (DE-AC36- 08GO28308) under a subcontract from NREL (ZGB-0-99180- 1) to the University of South Carolina

References

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