INFLUENCE OF POROUS ELECTRODE STRUCTURE ON PEM FUEL CELLS DESIGN AND PERFORMANCE

摘要

Gas flow in fuel cell porous electrodes is usually modelled with Darcy's law, which requires the definition of a resistance constant for the material. This can be done directly via experimentation or indirectly via numerical tuning to fit experimental data on cell behaviour. Both methods lack generality, as they do not take into account the particular porous structure of each electrode. In the present work, a numerical procedure for calculating the resistance constant for a given porous structure is presented. This procedure is based on Lattice Boltzmann models, which treat the problem from a microscopic point of view, reproducing collisions between fluid molecules and solid particles. It can be demonstrated that under certain hypotheses, these models yield Navier-Stokes equations on a macroscopic scale, hence obeying fluid mechanics laws. Here the flow in a set of thirty randomly generated porous structures was analyzed, thus obtaining a distribution of values for Darcy's constant. The analysis was repeated for ten different pressure gradients applied to a portion of the electrode and for three different volume porosities. The results showed that, for a given volume porosity, the value of Darcy's constant is strongly affected by the material porous structure. On the other hand, the mean value of resistance remained almost constant while varying the applied load, thus correctly reproducing the linear dependence between velocity and pressure gradient, as stated by Darcy's law.