Sol-Gel Assisted Synthesis of Encased Polymer Electrolyte Fuel Cell Cathode Catalysts

Abstract

State-of-the-art polymer electrolyte fuel cell (PEFC) cathode catalyst layers (CCLs) are composites of proton-conducting perfluorosulfonic acid (PFSA) ionomer and platinum alloy catalyst particles. The PFSA is in the form of agglomerates dispersed throughout the CCL and also as a thin film coating the carbon support and platinum alloy particle surface.1 The thin PFSA film on the catalyst surface has been shown to both decrease oxygen reduction reaction (ORR) activity and cause high oxygen transport resistance.2-4 Such ionomer-catalyst surface interactions can negatively affect both PEFC performance and durability. This talk will describe an approach to addressing the issues of ionomer poisoning of ORR activity, local oxygen transport resistance, and the lack of PEFC cathode performance durability by encasing Pt and Pt alloy catalyst particles in the cavity of a 3D porous inorganic framework. Platinum (Pt) and platinum alloys (PtxMy) encased in 3D porous inorganic nanocrystal catalysts have been prepared by a sol-gel process combined with chemical reduction. Catalysts with 5, 10 and 20 Pt/PtxMy wt% have been prepared and their ORR activity has been evaluated using the thin-film rotating disk electrode (TF-RDE) technique. The platinum content in the encased catalysts has been determined using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence (XRF). The morphology, crystal structure, and spatial distributed of the metal nanoparticles have been characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and energy-dispersive X-ray spectroscopy, respectively. References C. Cetinbas, R. K. Ahluwalia, N. N. Kariuki, and D.J. Myers, J. Electrochem. Soc., 165(13), F1051 (2018).Kongkanand and M. F. Mathias, J. Phys. Chem. Lett., 7, 1127 (2016).Subbaraman, D. Strmcnik, A. P. Paulikas, V. R. Stamenkovic, and N. M. Markovic, Chemphyschem, 11, 2825 (2010).Subbaraman, D. Strmcnik, V. Stamenkovic, and N. M. Markovic, J. Phys. Chem. C, 114 8414 (2010). Acknowledgements This work was supported by the United States Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office. Argonne is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC.