High-Throughput Synthesis and Characterization of PGM-Free Oxygen Reduction Reaction Electrocatalysts

Unprecedented 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 cathode catalysts.1,2 For example, electrocatalytic activities approaching those of platinum have been obtained for classes of catalysts derived from iron salts and metal-organic frameworks and iron salts and carbon-nitrogen-containing polymers such as polyaniline and cyanamide.3-6 With further improvements in these materials and electrodes based on these materials, especially in hydrogen-air performance and long-term performance durability, these materials will become viable for numerous applications including automotive propulsion power. For the general class of pyrolyzed iron-carbon-nitrogen PGM-free materials, it has been determined that variables such as the metal salt, polymer, metal to polymer ratio, as well as the temperature and atmosphere in which the composites are pyrolyzed are important in determining the activity and activity stability of the resulting catalysts.1,2 Changing these variables and testing their effect on the resulting catalyst properties is a very time-consuming process and only a limited portion of the 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-polyaniline and iron- zeolitic imidazolate framework-derived ORR electrocatalysts. The robotic systems in Argonne's High-Throughput Research Laboratory have been utilized to synthesize numerous (forty to forty-five) compositions in these two material systems. A multi-channel flow double electrode (m-CFDE) cell was designed and constructed for the simultaneous screening the ORR activity of multiple samples using an aqueous hydrodynamic technique. Unlike commercially-available m-CFDE's, this cell was designed with removable electrode plugs facilitating the quick change of catalyst on the glassy carbon electrode and also replacement of damaged electrodes. The results from the m-CFDE cell were validated against those obtained using the standard rotating disk electrode technique. The high-throughput structural characterization of the materials using techniques such as X-ray diffraction and X-ray absorption spectroscopy and correlation of the phase and atomic structure will be described. The high-throughput testing of these materials in a 25-electrode array fuel cell from NuVant Systems Inc. will also be described. In addition, the use of in situmulti-sample X-ray absorption spectroscopy to determine the atomic structure of the materials during the pyrolysis step of preparation will be described. Acknowledgements 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). 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 under Contract No. DE-AC02-06CH11357. 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. References M. Lefevre, E. Proietti, F. Jaouen, and J.-P. Dodelet, Science, 324 (2009) 71-74. H. Chung, G. Wu, D. Higgins, P. Zamani, Z. Chen, P. Zelenay "Heat-Treated Non-precious Metal Catalysts for Oxygen Reduction " for Electrochemistry of N4 Macrocyclic Metal Complexes, Volume 1: Energy, Editors: J. H. Zagal, F. Bedioui, Springer, 2016. E. Proietti, F. Jaouen, M. Lefevre, N. Larouche, J. Tian, J. Herranz, and J.-P. Dodelet, Nature Comm., 416 (2011) 1-9. H. Barkholtz, L. Chong, Z. Kaiser, T. Xu, and D.-J. Liu, Catalysts, 5 (2015) 955-965. H. Zhang, H. Osgood, X. Xie, Y. Shao, and G. Wu, Nano Energy, 31 (2017) 331-350. H.T. Chung, D.A. Cullen, D. Higgins, B.T. Sneed, K.L. More, and P. Zelenay, 2016 PRiME Meeting, Honolulu, Hawaii, October 2-7, 2016.