Spatially resolved simulation on PEM fuel cells meets experiments - which model complexity is enough under which conditions?

Spatially resolved measurements on PEM fuel cells have been performed for at least two decades [1] and this measurement technique has provided better understanding of the coupled processes inside the cell. Especially, variations along the channel (ATC), such as gas concentrations, membrane humidification, water saturation and others can be depicted and their impact on the overall cell performance can be analysed. At Fraunhofer ISE, we developed the next version of our segmented ATC PEM fuel cell with 50 cm² active area divided in 25 segments along the gas channel. Together with a new multichannel characterisation system, fast voltage / current and impedance measurements are available. 3D CFD Models for PEM fuel cells are also developed and improved since more than 20 years [2] and are currently available most commercial CFD software codes; they can provide more detailed insights on the local effects in each dimension like channel-rib variations or through-plane gradients in the GDL and electrodes. But they come with relatively long simulation time in the range of some hours for steady-state simulations of single cell parts or even days for dynamic or larger cell / stack simulations. To provide more flexible and faster results that can help the experimenter before or even during the experiments, e.g. under which conditions or in which segment, flooding, drying or concentration issues can be expected, we developed a dynamic ATC model that calculates mass and heat balance in a discrete number of coupled segments (e.g. 25) along the two gas channel sides. It uses simplified kinetics using a Tafel approach, water transport through the membrane and heat transfer between the gas channels, solids and surrounding. This work compares and analyses specially resolved measurement results from the ATC fuel cell together with simulation results from a commercial CFD-Code (AVL FireM) and results from our simplified ATC model. It shows computation times, under which conditions and for which purposes, the simplified model approach is appropriate enough for predicting local variations and which limitations have to be considered. Limits in operating conditions like cell voltage, stoichiometry and humidity are discussed in which local effects like channel-rib-differences or through-plane humidity variations can or cannot be neglected and shows possible advantages and drawbacks of the simplification.