Influence of Structural and Wetting Properties on Fuel Cell Performance

7 INFLUENCE OF STRUCTURAL AND WETTING PROPERTIES ON FUEL CELL PERFORMANCE 

The catalytic layers (CLs) of fuel cell electrodes can be represented as an assembly of two interconnected porous systems (1) a microstructure of porous catalysts (together with their supports) flooded by electrolyte, and (2) a macroslructure in hydrophilic CLs of wide gas pores or, in hydrophobized CLs, agglomerates of hydrophobic particles with gas pores between the particles. 

The most important parameter of CLs is the value of the surface area Sx dividing these two systems. According to Gurevich et al. (1974) and Fuller and Newman (1993), such an assembly can be treated mathematically as a system with distributed parameters one along coordinate x into the layer s depth, and a second along coordinate y perpendicular to the surface dividing the two porous systems. 

The current-producing electrochemical reactions take place in the CL. Gaseous reaction components are easily transported through gas pores to junctions with electrolyte-filled hydrophilic micro- and mesopores, where they are dissolved in the electrolyte. Then the dissolved reaction components are transported by (slow) diffusion to the catalyst s reaction sites. The stationary diffusion process in the y direction can be represented by the equation 

The microkinetics of the electrochemical reaction can be represented by a Volmer-type equation  

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