A catalyst ink for proton exchange membrane fuel cells (PEMFCs) is generally prepared by various mixing methods by dispersing platinum or platinum alloy nanoparticles supported on carbon blacks with ionomers in a specific solvent or solvent combination. The catalyst ink is deposited on the surface of the membrane or diffusion media and is typically subjected to elevated temperatures to facilitate rapid removal of solvent. Large carbon agglomerates resulting from sub-optimal ink dispersion and drying conditions can limit catalyst utilization, inhibit mass transport in the catalyst layer, and damage the membrane and possibly also the gas diffusion media [1, 2]. Micro-structural evolution of the catalyst ink can be controlled by interactions of the ionomer in the catalyst-ionomer ink and by the effect of ink solvent composition on those interactions during the ink drying process. This presentation will describe the results of in-situ/ex-situ X-ray scattering studies of the evolution of the cathode catalyst layer during the ink drying process to determine the impact of solvent removal rates and solvent identity on the structural evolution of the cathode catalyst layer. These studies also included operando ink drying at room temperature, under an atmosphere containing the solvent, and a high temperature. Ultra-small angle X-ray scattering (USAXS) was used to measure the agglomerate size distribution during the ink drying. A small environmental chamber was used to examine drying phenomena of high solid-content inks and dispersions to determine structural evolution during ink drying. The effects of ionomer concentration, catalyst concentration, and solvent composition on the microstructure of the catalyst inks and electrode are correlated with the MEA performance and operando diagnostic data. The goal of these studies is to guide the MEA fabrication process to optimize MEA performance and durability.

References

[1] I. V. Zenyuk, N. Englund, G. Bender, A. Z. Weber and M. Ulsh, J. Power Sources 332 (2016), 372–382.

[2] M.Wang, J.Park, S. Kabir, K. C. Neyerlin, N. Kariuki, H. Lv, V. R. Stamenkovic, D. J. Myers, M. Ulsh, and S. A. Mauger, ACS Applied Energy Materials 2 (2019), 6417-6427

Acknowledgements

Argonne National Laboratory is managed for the U.S Department of Energy (DOE) by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357. This work was authored in part by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. DOE under Contract No. DE-AC36-08GO28308. This research used the resources of the Advanced Photon Source (APS), a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This research is conducted under the auspices of the Million Mile Fuel Cell Truck (M2FCT) Consortium (https://millionmilefuelcelltruck.org), which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office.