Transport phenomena and reactions in the catalyst layers

Although water transport is not specifically considered in this section, structures appropriate for effective platinum (Pt) utilization are discussed. Because electrons, protons, and oxygen are all 

Using the models and the calculated results, a simplified equation, termed an evaluation equation in this section, was derived to show the relationships among major parameters in the cathode catalyst structure (Tabe et al., 2011). From the analysis of the evaluation equation, optimal structural parameters were identified. The results indicate tiiat the dominant parameters of the CL structure are the polymer electrolyte thickness covering carbon agglomerates and the CL thickness. 

The proton current in the CL is generated by the oxygen consumption, and the change in the proton current density, ih+, is satisfied with the balance expressed by Equation (1.4). The change in the cathode overpotential, rj, corresponds to the voltage decrease due to the proton transport it is expressed by Equation (1.5) using the proton current density, in+, and the effective proton conductivity, 

In the catalyst layer, the effective proton conductivity of the polymer electrolyte and the effective diffusion coefficient in the pores of the catalyst layer depend on the catalyst layer structure. These properties, and were given using the Bruggeman correction factor as follows  

k is the proton conductivity of the polymer electrolyte, Df is the diffusion coefficient of the species i in the CL pores, and scl is the porosity of the CL. 

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