The Effect of Dispersion-Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe-N-C Platinum Group Metal-Free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells
Authors: Mauger Scott A , Khandavalli Sunilkumar , Iyer Radhika , Park Jaehyung , Osmieri Luigi , Cetinbas Firat , Myers Deborah J. , Ulsh Michael , Neyerlin Kenneth C. 
Published: December 2020

The microstructure of platinum-group-metal-free (PGM-free) catalyst layers is known significantly impact mass and proton transport and is critical for optimization of PGM-free fuel cells.1 It is known that catalyst ink formulation can influence interactions between catalyst and ionomer which in turn influence the catalyst layer microstructure. In this talk, we present an investigation of catalyst inks consisting of Fe-N-C catalysts and Nafion ionomer to understand how the ratio of H2O and 1-propanol (nPA) influences ink microstructure. Steady-shear and dynamic-oscillatory-shear rheology, in combination with x-ray scattering, were used to study the interparticle interactions and the agglomerated structure of the inks. In the absence of ionomer, the inks were significantly agglomerated, approaching a gel-like microstructure. Increasing H2O% was found to increase agglomeration due to hydrophobic nature of the catalysts. Addition of ionomer was found to initially stabilize catalysts against agglomeration for all H2O%. However, at high ionomer concentrations (I/C > 0.35) interesting differences were observed based on H2O%. The nPA-rich inks were found to remain predominantly stable while ionomer appears to flocculate H2O-rich inks. Finally, the ink microstructure is compared with catalyst layer microstructure, which shows a direct correlation. This work shows that the controlling the ink microstructure is critical to designing optimized catalyst layers.

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. The submitted manuscript was created, in part, by UChicago Argonne, LLC, Operator of Argonne National Laboratory, Argonne, U.S. Department of Energy Office of Science laboratory, operated under Contract No. DE-AC02- 06CH11357. This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory, also under Contract No. DE-AC02-06CH11357. Funding provided as part of the Electrocatalyst Consortium (ElectroCAT), an Energy Materials Network Consortium funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

(1) Wang, G.; Osmieri, L.; Star, A. G.; Pfeilsticker, J.; Neyerlin, K. C. Elucidating the Role of Ionomer in the Performance of Platinum Group Metal-Free Catalyst Layer via in Situ Electrochemical Diagnostics. Journal of The Electrochemical Society
2020, 167 (4), 044519. https://doi.org/10.1149/1945-7111/ab7aa1.