Degradation, PEFC measurements

A key element of PEM fuel cell is the CCL, which contains a double layer capacitance connected to resistivities due to proton and oxygen transport. To understand measured CCL spectra, many works employ the equivalent circuit method (ECM). This method is based on the construction of an equivalent transmission line, which gives an EIS spectrum close to the spectrum of the system of interest. The components of the resulting circuit are then attributed to CL physical parameters. For example, in a recent work, Nara et al. (2011) used the ECM to study the CCL degradation mechanisms in the PEFC. 

Other online techniques can be used to examine the change in electrode or electrolyte materials. If parts of the electrode or electrolyte are lost due to reaction, finite vapor pressure, or other reasons, analysis of the effluent product can often be correlated to the particular loss mechanism. For example, in PEFCs, one mode of physicochemical electrolyte degradation is accompanied by loss of the fluorine ion, which can be detected by measurement of the effluent condensed water fluorine content. Also, if carbon corrosion is occurring, carbon monoxide or carbon dioxide gas is produced, and this can be measured with a sufficiently sensitive device. In general, if there is a chemical reaction causing the degradation, the product species from this can be detected in the effluent and correlated with the measured loss. 

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