Polymer Electrolyte Membrane (PEM) fuel cell systems are heterogeneous catalytic systems. Although there are many computational models that describe the behavior of PEM fuel cells, few simulate the catalyst surface concentration of reactant gases at the catalyst layer-membrane layer inteface. Most PEM fuel cell models make no distinction between the bulk concentration of reactants and the catalyst surface concentration of reactants. It is the surface concentration that is key when studying PEM fuel cell systems: the reactions occur at the surface of the catalyst.;In addition, few model the dynamics within the non-continuum flow region near the solid surfaces of the fuel cell. Microscale and nanoscale fuel cells are not completely described by continuum mechanics. At the microscale and nanoscale, more specialized tools, which account for the increased surface forces and micro length scales, are needed to understand the dynamics of these micro-devices. The model simulates the microscale dynamics of a PEM fuel cell within the slip flow regime. Special attention is given to simulating the behavior of each reactant and product near each solid surface. To correct for non-equilibrium behavior near the solid surfaces, slip boundary conditions are used to account for velocity slip.;This analysis models a PEM fuel cell to determine both the bulk reactant concentrations and the catalyst surface concentrations at the catalyst layer-membrane layer interface and demonstrates that size has an impact on overall fuel cell performance. The model also shows a reduction of the Ohmic losses that is balanced by an increase in the parasitic losses within the fuel cell. Finally, it is shown that the bulk concentration at the membrane-catalyst layer interface is not zero.
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