Activity and Composition of Fe-Based Oxygen Reduction Reaction Electrocatalysts Synthesized and Characterized Using High-Throughput Approaches

Abstract

Incredible progress has been made over the past decade in increasing both the oxygen reduction reaction (ORR) activity and durability of platinum group metal-free (PGM-free) polymer electrolyte fuel cell (PEFC) cathode catalysts. The class of catalysts demonstrating the highest ORR activities are those typically denoted as “Fe-N-C” and synthesized by heat treating iron salts and zinc-based zeolitic imidazolate frameworks (ZIFs) and/or phenanthroline, as carbon and nitrogen sources, or by heat treating iron-substituted ZIFs. For this class of PGM-free materials, it has been determined that variables such as the metal and carbon-nitrogen macrocycle content, as well as the temperature and atmosphere in which the composites are heat treated are important in determining the activity and activity stability of the resulting catalysts.1-4 Changing these variables and testing their effect on the resulting catalyst properties is a time-consuming process and only a limited portion of the composite composition and temperature space have been explored for this broad class of materials. This presentation will describe the development and application of high-throughput methodology to explore the effects of these parameters on the activity and fuel cell performance of iron-carbon-nitrogen ORR electrocatalysts with a variety of transition metal dopants. A multi-channel flow double electrode (m-CFDE) cell was designed and constructed for the simultaneous screening the ORR activity of multiple materials using an aqueous hydrodynamic technique. The structural characterization of the materials using X-ray absorption spectroscopy (XAS) and correlation of the atomic structure with ORR activity will be described, as will the high-throughput testing and optimization of the electrode composition using a 25-electrode array fuel cell. The use of in situ XAS to determine the atomic structure of the materials during heat treatment of the precursors will be presented, as well as operando characterization of the cathode catalyst layer during fuel cell operation. References Wang, H. Zhang, H. Lin, S. Gupta, C. Wang, Z. Tao, H. Fu, T. Wang, J. Zheng, G. Wu, and X. Li, Nano Energy, 25 (2016) 110.Zhang, S. Hwang, M. Wang, Z. Feng, S. Karakalos, L. Luo, Z. Qiao, X. Xie, C. Wang, D. Su, Y. Shao, and G. Wu, J. Am. Chem. Soc., 139 (2017) 14143-14149.Proietti, F. Jaouen, M. Lefevre, N. Larouche, J. Tian, J. Herranz, and J.-P. Dodelet, Nature Comm. 2 (2011) 1.Zitolo, V. Goellner, V. Armel, M.-T. Sougrati, T. Mineva, L. Stievano, E. Fonda, and F. Jaouen, Nature Materials, 14 (2015) 937. This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.