Ideal proton transport modeling

According to the model above, in experiments of Nordlund and Lindbergh, the approximation of ideal proton transport is justified for currents below 100 mA cm . To show this explicitly, it is advisable to plot the model shape of MOR rate along x. By definition, Rmor = -dj/dx. Using Equation 4.232 here, one obtains... 

Besides these generalities, little is known about proton transfer towards an electrode surface. Based on classical molecular dynamics, it has been suggested that the ratedetermining step is the orientation of the HsO with one proton towards the surface [Pecina and Schmickler, 1998] this would be in line with proton transport in bulk water, where the proton transfer itself occurs without a barrier, once the participating molecules have a suitable orientation. This is also supported by a recent quantum chemical study of hydrogen evolution on a Pt(lll) surface [Skulason et al., 2007], in which the barrier for proton transfer to the surface was found to be lower than 0.15 eV. This extensive study used a highly idealized model for the solution—a bilayer of water with a few protons added—and it is not clear how this simplification affects the result. However, a fully quantum chemical model must necessarily limit the number of particles, and this study is probably among the best that one can do at present. 

The polarization voltage of the cathode side is determined by reaction kinetics, transport of water and oxygen across the cell and by proton transport across the CCL. In this section, we will assume an ideal membrane humidification. We start with the model of the CCL. 

The mobility in the pore includes molecular mechanisms of proton transport in bulk water and along the array of charged surface groups. An idealized two-state approach based on this distinction was considered in [82]. This simple model can reproduce a continuous transition from surface-like to... 

Ideally, the membrane should be filled homogeneously with water at the value of water content that gives the best proton conductivity. In particular, models dwelling on fuel cell operation usually consider the membrane a homogeneously hydrated medium with constant transport coefficients [2, 3], This approximation corresponds to the assumption of an ul-trathin membrane [5, 6],... 

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