Generic catalyst layer

The operation of generic catalyst layer is illustrated schematically in Figure 4.2. It shows the shapes of local variables and fluxes in a layer, where the axis x is directed from the interface with the electrolyte medium, viz., the PEM, toward the interface with a porous gas diffusion medium, viz., a porous transport layer (PTL) or gas diffusion layer (GDL). The ionic current arrives or leaves the CL at the electrolyte interface, while the feed molecules are supplied from the porous transport medium (Figure 4.2). 

FIGURE 4.2 A schematic of a generic catalyst layer. The through-plane shapes of the ionic current density j, the electron current density y e, the feed molecules concentration c, and the local overpotential jj. 

Figure 24 shows a cross section of a Nafion membrane catalyzed by direct application of catalyst inks to its two major surfaces, as observed by SEM [52], The thin slice of MEA required for SEM imaging was generated by microtome from the MEA encapsulated in epoxy. This figure actually describes an MEA prepared for a DMFC, with PtRu black and Pt black catalyst layers of relatively high loading, resulting in catalyst layers 10 and 14 pm thick (Fig. 24). The SEM image well depicts two generic characteristics of CCMs prepared by direct, ink-based application of the catalysts to the ionomeric membrane the interface between the catalyst layer and the membrane is sharp on the SEM scale and the thickness of the catalyst layer measured from the...

Fig. 3 Contaminant pathways summary. Contaminants are generically identified as X, X, Xj, and X (a molecule), X + (a cation), and X (a radical). The arrows for both unit cell and catalyst layer levels refer to species movements. At the catalyst level, arrows indicate either species adsorption/desorption or reactions between species. BP bipolar plate, CL catalyst layer, FFC flow-field channel, GDL gas-diffusion layer, M membrane...

Catalyst Layer Morphology The microstructure of the catalyst has a strong effect on the overall effectiveness of the catalyst. From the generic fuel cell description of Chapter 2, the catalyst structure is highly three dimensional, and the potential reaction locations are limited to those with immediate access to ionic and electronic conductors, catalyst, and reactant gas. Maximization of this triple phase boundary area will reduce the activatiou polarization losses for a given current density. A catalyst layer with very low triple-phase boundary area density will have reduced number of available reaction sites and reduced performance. 

Catalyst layer—mixed conductivity Figure 4.28 Schematic of electrodes and main electrolyte in generic fuel cell system. 

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