Formation of Structure and Function in Catalyst Layers

As first demonstrated by Ian D. Raistrick at Los Alamos National Laboratory (LANL), these improvements enabled a dramatic reduction of catalyst loading (Raistrick, 1986, 1989). The ink-based fabrication approach, later refined at LANL (Wilson and Gottesfeld, 1992), evolved into the standard method of catalyst 

FIGURE 3.2 A high-resolution TEM, obtained from image analysis of weU-dispersed Pt nanoparticles. They are deposited on a high-surface-area carbon support, together with the normalized particle radius distribution of Pt. 

Impregnation of the porous network with PFSA-type ionomer imparts high proton concentration and conductivity to the layer. The high proton concentration is beneficial for the ORR activity of the CCL but it is detrimental for catalyst stability. Simultaneous percolation in the interpenetrating networks of the solid Pt/carbon matrix, ionomer electrolyte, and pores ensures efficient transport of electrons, protons, chemical reactants (H2, methanol, O2, etc.), and product water to or from Pt. 

The required electronic conductivity of the support material depends strongly on IcL- A simple model of the interplay of local current generation and transport of electrons in the support phase can be used to obtain an estimate of the minimal electronic conductivity required. The underlying model is identical to models that evaluate the interplay of proton transport limitations and reaction in CCLs, discussed for instance in Eikerling et al. (2007a). 

The model shows that the electron transport effects do not affect the CL performance if the conductivity of the electron-conducting phase obeys the following requirement  

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