Modeling a Proton Exchange Membrane Fuel Cell Stack Cell by Cell: Illustration of a Mechanism for the Propagation of Degradations

Abstract

This paper is devoted to the modeling of a PEMFC fuel cell stack. First, to justify the hypotheses, original experimental results are presented and show that the gas flow rates feeding a cell in its stack environment highly depend on the thermal management. Then, the generic model of a cell in its stack environment is presented. A two-phase flow model is implemented to calculate the gas flow rates as a function of the pressure drops and considering the amount of liquid water present in both compartments. In this way, the dispatching of the total active gases flow rate between the different cells can therefore be described. Finally, a stack of five cells is numerically assembled by describing the thermal coupling between the cells. Two application examples are conducted. A first one considers a cooling defect and a second one simulates the case where one cell is more degraded than the others. It is shown how these types of malfunction can cause a fuel starvation event. At the end, and for the first time as far as we know, a mechanism of propagation of degradations from cell to cell is proposed. List of symbols SymbolDescriptionUnitSymbolDescriptionUnit Double-layer capacity of the cellF Protonic resistance of the membrane and electrodesΩ water vapor concentrationmol m−3 Thermal resistanceK W−1 Oxygen Concentrationmol m−3 Mass transfer reisstances m−3 Concentration of the saturated vapor at T mol m−3 Water saturation in the channels Specific heat capacity of plateJ/K.kg TemperatureK Effective water vapor diffusion coefficient through the GDLm2 s−1 Cell potentialV Water diffusion coefficient in the membranem2 s−1 Volume of channels m3 Effective oxygen diffusion coefficient through the GDLm2 s−1 Greek Letters Thickness of the GDLm Anodic charge transfer coefficient Standard cell potentialV Cathodic charge transfer coefficient Equivalent weight of the membranekg mol−1 Roughness factor of the electrode Faraday constantC mol−1 Pressure dropPa Current intensityA Electro-osmosis coefficient Exchange current densityA m−2 Water content of the membrane thermal capacity of the MEAJ K−1 Effective thermal conductivity of GDLW mK−1 thermal capacity of the anode/cathode platesJ K−1 Volumetric masskg m−3 Length of the active aream Cathode electrode potentialV Water latent heatkJ mol−1 Upper & lower scripts lower heating value of HydrogenkJ mol−1 in Inlet Molar mass of waterkg mol−1 out Outlet Dry air molar flow ratemol s−1 c Cathode Dry hydrogen molar flow ratemol s−1 a Anode Water vapor molar flow ratemol s−1 ch Channels Water vapor flow rate from electrode to channelsmol s−1 el Electrode Atmospheric pressuremol s−1 m Membrane Total pressure in the anode channelsPa cf Cooling fluid Total pressure in the cathode channelsPa n−1Preceding electrode Universal gas constantJ mol.K−1 n + 1Following electrode Electrical resistance of the cellΩ