Modelling Electrochemical Cells with Porous Electrodes. The Proton Exchange Membrane Fuel Cell

摘要

We describe a method to find profiles for the electric potential, the concentration and the temperature across a heterogeneous cell, using the fuel cell as an example. The cell is divided into five layers: the electrolyte and the electrodes are treated as homogeneous layers, while the electrode interface regions are treated as planar Gibbs interfaces. The five sets of equations, one for each layer, are solved to give the three profiles. The model is checked for thermodynamic consistency. This reveals e.g. that water is not in equilibrium at the interfaces at high current densities. Also, interface transport properties, like Peltier and Soret effects, are essential for the profiles. The polarization curve at high current densities can be explained, not by diffusion limitations, but by a varying membrane resistance for current densities below 7500 A/m~2. The heat fluxes out of the cell vary largely with the boundary conditions that are imposed.