Percolation Behavior in Catalytic Porous Material

Abstract

Proper water management in Polymer Exchange Membrane (PEM) fuel cell is important to achieve high performance. Understanding the percolation of the produced water at the cathode catalyst layer (CL), is critical for any robust water management technique. The CL consists of a complex structure to allow reactants to pass through and reach the reaction catalyst site. The complex structure is made by a support structure (mostly carbon) that allows the transport of electrons, an ionomer that conducts protons, and voids that have the double role of oxygen breathing and exit paths for the generated water. In this work, a pseudo-Hele–Shaw experimental setup is used to investigate immiscible fluid displacement inside the CL under controlled conditions. Since water can be retained by ionomer, making it swell and caused a shift in the pore size distribution, fluor-inert is used as a working fluid. The evolution of percolation pressure and the projected area of the injected fluid are recorded simultaneously. Preliminary results show a high consistency in the measured data at high flow rate percolation. However, at low flow rate there is some variation in the data due to relative humidity effect. The experimental data is considered as an input to the (Ce-t^*) scale. This scaling has been previously developed (Medici & Allen, 2011) to study two phase flow in thin porous layers. The dimensionless energy scale (Ce) based on the ratio between the injected and dissipated energies. The other dimensionless time scale (t^*) is arises from the important of the time of percolation, where in capillary regime is in order of hours while in stable displacement is in order of minutes, so it characterizes the relative effects of viscous and capillary effect. This scaling collapses transient pressure and saturation to a linear, non-dimensional and unique correlation for each material.