Modelling air-breathing PEMFC and validation by experimental characterisations

A mathematical model of an air-breathing PEMFC and its validation is presented. The aim of this work is to gain an understanding of the physical and electrochemical processes in an air-breathing PEMFC with an open cathode. The model is stationary and non-isothermal. The model geometry represents a two-dimensional symmetry element of the air-breathing sample cells that were used for the measurements. Multicomponent Stefan-Maxwell diffusion is used to describe the mass transport of the gaseous components (O2, H2O, N2) within the gas diffusion layer, the catalyst layer and the void space above the open cathode. Moreover, the model takes into account the exchange of water through the membrane due to diffusion and electro-osmotic drag, the charge transport of protons and electrons as well as the heat balance effects. Some of the heat balance effects include heat sources caused by irreversible losses and heat exchange to the exterior due to convective heat transport. The electrochemical reactions in the catalyst layer are described by an agglomerate model which takes into account the reaction and diffusion within the agglomerations of catalyst and electrolyte. The description of the mass transport of the gaseous components on the anodic side (H2, H2O) has been simplified by using Fickean diffusion. Calculations with this model are performed for cathodes with opening ratios of 33%, 50% and 80%.The experiments are made with three air-breathing sample cells having the aforementioned opening ratios. Each cell is characterised under floating temperature conditions by measurement of the current-voltage curve as well as measurements of the cell temperature and the cell impedances at 1 kHz. The model is validated by comparison of the measured current-voltage characteristics with the model predictions. Moreover, the ionic cell resistance that is predicted by the model agrees with experimental results for low hydrogen stoichiometry