A Multiscale Modeling Approach to Identify and Quantify the Transport Limitations in Proton Exchange Membrane Fuel Cells
Authors: Jahnke Thomas , Gülicher Konrad , Morin Arnaud 
Published: February 2024

The reduction of platinum loading is essential for lowering the cost of Proton Exchange Membrane Fuel Cells (PEMFCs). However, low platinum loadings typically lead to performance losses due to reduced electrochemical active surface area as well as additional local transport losses within the catalyst layer. Experimentally, limiting current analysis provides a helpful tool to investigate the oxygen transport limitations. In this method the limiting current (obtained at cell voltages of about 0.2 V) is measured for different oxygen concentrations and total pressures. The oxygen transport resistance is then calculated from the ratio of oxygen concentration and limiting current. The pressure variation allows separating the pressure dependent and pressure independent parts of this resistance, which are related to transport in the channels, molecular diffusion in the Gas Diffusion Layer (GDL), Knudsen diffusion through the Micro Porous Layer (MPL) and cathode catalyst layer (CCL) plus local transport losses within the CCL, respectively. However, the method does not allow to easily break down the contributions of each cell component and processes to the total resistance, which requires the variation of the components[1].
Therefore, within the project FURTHER-FC[2] we develop a multiscale modeling approach for interpreting the experimentally observed transport losses and to quantify the contributions of the different cell components based on their microstructure. On the sub-µm scale a Lattice Boltzmann model is developed to describe the transport within the CCL on the agglomerate scale, taking into account the transport through the ionomer film. This model is used to parametrize the effective local transport resistance[3] for calculation of the reaction kinetics in the cell model. For the GDL/MPL Direct Numerical Simulation (DNS) applied to the real microstructures[4] is used to obtain the effective diffusion coefficients, which are then applied in the cell model. The 2D PEMFC model considers the multicomponent transport, i.e., free flow in the gas channels and transport through the porous media according to Darcy’s law, charge transport, water transport in the ionomer, energy transport as well as the electrochemical reactions. Model validation is performed with limiting current analysis on MEAs with different platinum loading under various pressures and relative humidity. By analyzing the local concentrations within the cell, the model is then used to quantify the contributions of each cell component to the overall oxygen transport resistance.

The project FURTHER-FC [2] has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No 875025. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.

[1] Daniel R. Baker et al, J. Electrochem. Soc. (2009) 156 B991
[2] https://further-fc.eu/
[3] T. Jahnke and A. Baricci, J. Electrochem. Soc. 169 (2022) 094514
[4] M. Ahmed-Maloum et al., Journal of Power Sources 561 (2023) 232735

Figure 1