PEFC model composition

The factors 4 and 4 accormt for the heterogeneity of the interface. The interfacial flux conditions. Equations (6.56) and (6.57), can be straightforwardly applied at plain interfaces of the PEM with adjacent homogeneous phases of water (either vapor or liquid). However, in PEFCs with ionomer-impregnated catalyst layers, the ionomer interfaces with vapor and liquid water are randomly dispersed inside the porous composite media. This leads to a highly distributed heterogeneous interface. An attempt to incorporate vaporization exchange into models of catalyst layer operation has been made and will be described in Section 6.9.4. 

Hydrogen Cell (PEFC) To apply the Q3D model to hydrogen PEFC, one has to modify the gas composition, the diffusion coefficients and the reaction rate parameters on the anode side. The parameters used for the PEFC simulation are listed in Table 7 (those parameters which are not shown here are the same as in Table 5). Since hydrogen oxidation... 

Such combined modeling/experimental diagnostics work for PEFC cathodes was described in [13]. The latter model addresses the cathode catalyst layer and gas-diffusion backing, as schematically presented in Fig. 44. The catalyst layer is considered in the model a composite film, typically 4-7 pm thick, of Pt/C catalyst intermixed with recast ionomer. The... 

Usually, the starting point of model derivation is either a physical description along the channel or across the membrane electrode assembly (MEA). For HT-PEFCs, the interaction of product water and electrolyte deserves special attention. Water is produced on the cathode side of the fuel cell and will either be released to the gas phase or become adsorbed in the electrolyte. As can be derived from electrochemical impedance spectroscopy (EIS) measurements [14], water production and removal are not equally fast Water uptake of the membrane is very fast because the water production takes place inside the electrolyte, whereas the transport of water vapor to the gas channels is difiusion limited. It takes several minutes before a stationary state is reached for a single cell. The electrolyte, which consists of phosphoric add, water, and the membrane polymer, changes composition as a function of temperature and water content [15-18]. As a consequence, the proton conductivity changes as a function of current density [14, 19, 20). 

At the cell level, the above-described mechanisms lead to the following consequences. The acid composition is a function of current density and cell temperature due to the delicate balance between internal water production and removal. Hence the conductivity changes as a function of current density, which can be observed experimentally during load changes in HT-PEFC operation [14], As the phosphoric acid takes up water, the volume of the membrane increases, that is, it swells as shown by synchrotron radiography experiments [53]. The resulting situation is depicted in Figure 29.2. At present, there is no model for an HT-PEFC which also... 

In order to analyze the processes in a fuel-ceU system, all units with a positive change in Gibbs energy and those with a negative change were summarized in two composite curves. Figure 32.3 shows the composite curves for a lOkWei HT-PEFC system based on C12H26 as a model fuel for kerosene. At 298 K, the black curve... 

Simple pore models (Srinivasan et al., 1967), thin-film models (Srinivasan and Hurwitz, 1967), macrohomogeneous models, and refined variants of agglomerate models are still being applied and further developed for the present generation of ionomer-bound composite catalyst layers in PEFCs (Gloaguen and Durand, 1997 Jaouen et al., 2002 Karan, 2007 Kulikovsky, 2002a, 2010b Sun et al., 2005). Effectiveness factor approaches have been elaborated as quantitative tools to compare... 

---