Differential PEMFC

The nature of the water present within a PEM can also have an effect upon its performance during PEMFC operahon. At /I > 6, water exists in the three forms previously mentioned in Section 3.2.1 free water, loosely bound water, and nonfreezable water. This has been established by Eourier transform infrared (FTIR) studies and more recently by calorimetry and gravimetric analysis. Pulse NMR has also been used in conjunchon with differential scanning calorimetry (DSC) to analyze the contributions of these three different types of water in Nation and BPSH membranes. These values can be seen in Table 3.1. 

K. Ito, K. Ashikaga, H. Masuda, et al. Estimation of flooding in PEMFC gas diffusion layer by differential pressure measurement. Journal of Power Sources 175 (2008) 732-738. 

For higher temperature operation, a polybenzimid-azole-based polymer electrolyte may be preferred. The PEMFC structures have good mechanical integrity under compression and expansion from differential temperature and pressure gradients that occur during operation. This system has minimal materials problems, except for the cost and operation characteristics of the membrane. The PEMFC operates at 1 A/cm at 0.7 V. The electrode reactions in acidic media have been discussed above. 

Table 6.1 shows a lack of homogeneity in the definition of bipolar plate requirements. Nevertheless, there has been a differentiation between graphitic and metallic bipolar plates for PEMFC since 2006, as the ways of fabrication and feasible geometries are widely different and stationary, portable and automotive applications are distinct. 

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