CFD Modelling of PEM Fuel Cells

In the present Ph.D. research project Computational Fluid Dynamics (CFD) is used as the foundation to generate a model of a PEM fuel cell. The idea is to use a commercial available CFD code, which is capable of solving multi specie and multiphase problems. And into this code integrate additional modules which can handle the electrochemical and other specific fuel cell related, processes.Models of the electrochemistry, the different transport processes, phase transfer etc. will be developed and integrated into the commercial CFD code CFX4.4 to simulate both benchmark and complex applied cases. Through these simulations a deeper understanding of the coupled processes will be achieved. This will contribute with important knowledge of these processes coupling and influence on the fuel cells efficiency. Further, geometrical and material properties influence on the performance can be investigated, and thereby contribute to the future development of PEM fuel cells. Project results One, two and three dimensional fuel cell models have been established to evaluate the influence of different parameter on the fuel cells performance. It has been shown that modelling has to be extended in dimension, accordingly to which effects that has to be analysed. For estimation of certain processes under certain operational conditions, one-dimensional models are adequate, whereas for other the full three-dimensional model has to be applied.Currently the work is focused on the further development of a three dimensional model. The model consists of straight channels, porous gas diffusion layers, porous catalyst layers and a membrane. In this computational domain, important transport phenomena's are dealt with in detail. The model solves the convective and diffusive transport of the gaseous phases in the fuel cells and allows prediction of the concentration of the species present. A special feature of the model approach is a method that allows detailed modelling and prediction electrode kinetics. The transport of electrons in the gas diffusion layer and catalyst layer is accounted for, as well as the transport of protons in the membrane phase. This provides the possibility of predicting the three-dimensional distribution of the activation overpotential in the catalyst layer. The current density's dependency on the gas concentration and activation overpotential can hereby be fully addressed. The current model can for example show how the GDL electric conductivity affects the distribution of current density, and how this affects the fuel cells potential curve. Industrial Ph.D. Student Mads Bang Supervisors: Thomas Condra (AAU), Steen Yde-Andersen (IRD Fuel Cells A/S), Klaus Moth (APC Denmark), Eivind Skou (University Of Southern Denmark)