Simulating Morphology and Degradation of PEMFC Cathode Catalyst Layers with Porous Carbon Supports: Part I. Effect of Relative Humidity on Catalyst Utilization

We present a physical model of the cathode catalyst layer morphology which simulates the electrochemically active catalyst surface area at varying degrees of humidification. The model considers pore, particle and ionomer distributions and resulting interfaces on the nanoscale to create a unique mathematical representation of each material. Specifically, the model discriminates between catalyst particles on the support surface and inside primary pores of the support and their respective connection to the proton-conducting phase. Catalyst particles may be protonically activated by coverage with ionomer or water or be protonically inaccessible. The exact configuration depends on the particle size and location as well as the cell operating conditions, sensitizing the simulated catalyst utilization to these properties. Model results are compared against data for five samples with different support materials and ionomer loadings manufactured in-house. Further, trends in catalyst utilization which were observed in recent literature are reproduced with the model. This work provides a comprehensive analysis of material configurations and simulations at begin of test. In Part II, the presented model is integrated into a degradation model to predict the evolution of the electrode morphology and catalyst utilization during ageing.