Modeling of Diffusive Convective and Electromechanical Processes in PEM fuel cells

Research output: Book/ReportPh.D. thesisResearch

Abstract

In the report, the transport phenomena in a proton exchange membrane fuel cell fueled by hydrogen and air, is analyzed, and a comprehensive three dimensional computerized model of the cell is presented. The model accounts for most of the major transport processes and allow the prediction of their impact on the operational performance of the fuel cell.

In the modelling work presented, the commercial CFD package CFX4.4 is used as the foundation to generate a model of a PEM fuel cell. The CFX4.4 platform provides the framework of solving the three-dimensional transport equations for mass, momentum and chemical species. Since analytical solutions to these three dimensional convections diffusion problems can rarely be obtained, the CFX code makes use of a finite volume discretization and numerical techniques, in order to obtain a solution.

The model developed solves the convective and diffusive transport of the gaseous phase in the fuel cell and allows prediction of the concentration of the species present. A special feature of the approach developed is a method that allows detailed modelling and prediction of electrode kinetics. The transport of electrons in the gas diffusion layer and catalyst layer, as well as the transport of protons in the membrane phase is accounted for. This provides the possibility of predicting the threedimensional distribution of the activation overpotential in the catalyst layer. The current density's dependency on the gas concentration and activation overpotential can thereby be addressed. The proposed model makes it possible to predict the effect of geometrical and material properties on fuel cells performance, which means that the model can predict how the gas diffusion layer (GDL) and catalyst layers physical properties affects the distribution of current density, and how this affects the fuel cells polarization curve and efficiency under operation.

It is shown that the conductivity and the effective porosity of the catalyst layer, may strongly affect the performance of the fuel cell, and that it therefore should be considered when fuel cell models are made.
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Details

In the report, the transport phenomena in a proton exchange membrane fuel cell fueled by hydrogen and air, is analyzed, and a comprehensive three dimensional computerized model of the cell is presented. The model accounts for most of the major transport processes and allow the prediction of their impact on the operational performance of the fuel cell.

In the modelling work presented, the commercial CFD package CFX4.4 is used as the foundation to generate a model of a PEM fuel cell. The CFX4.4 platform provides the framework of solving the three-dimensional transport equations for mass, momentum and chemical species. Since analytical solutions to these three dimensional convections diffusion problems can rarely be obtained, the CFX code makes use of a finite volume discretization and numerical techniques, in order to obtain a solution.

The model developed solves the convective and diffusive transport of the gaseous phase in the fuel cell and allows prediction of the concentration of the species present. A special feature of the approach developed is a method that allows detailed modelling and prediction of electrode kinetics. The transport of electrons in the gas diffusion layer and catalyst layer, as well as the transport of protons in the membrane phase is accounted for. This provides the possibility of predicting the threedimensional distribution of the activation overpotential in the catalyst layer. The current density's dependency on the gas concentration and activation overpotential can thereby be addressed. The proposed model makes it possible to predict the effect of geometrical and material properties on fuel cells performance, which means that the model can predict how the gas diffusion layer (GDL) and catalyst layers physical properties affects the distribution of current density, and how this affects the fuel cells polarization curve and efficiency under operation.

It is shown that the conductivity and the effective porosity of the catalyst layer, may strongly affect the performance of the fuel cell, and that it therefore should be considered when fuel cell models are made.
Original languageEnglish
Place of PublicationAalborg
PublisherInstitut for Energiteknik, Aalborg Universitet
StatePublished - 2005
Publication categoryResearch
ID: 17909258