(Invited) Platinum Group Metal-Free Oxygen Reduction Reaction Electrocatalysts from Fe-N-C Family: Activity, Durability and Manufacturability (2017)

PEM fuel cells have been recognized as one of the most promising candidates for motive and stationary power source. Among the PGM-free catalysts known today, Fe-N-C catalysts (especially made by high temperature pyrolysis) are considered the most viable candidates for platinum substitution from cathode side of fuel cell. There are several ways for synthesis of highly active M-N-C electrocatalysts which involved dispersion of organic N-C precursor and metal salts on support (carbon, MOF or silica), followed by high temperature pyrolysis and post pyrolysis treatments. Among them imidazole-based materials have been the most promising. In this talk we will describe GPGM-free catalysts materials derived from imidazoles using 3 different synthesis methods. The INRS team has developed a MOF-based Fe/N/C catalyst (synthesized using FeAc+Phen+ZIF-8 precursors) with catalyst initial mass activity of 10.6 mA/mg at 0.9 V and maximum initial performance (0.91 W/cm 2 ) [1]. The long term stability of the catalyst was also evaluated and compared with the best literature value (LANL catalyst, which was measured at 0.4 V and 80 o C) [2]. As shown earlier by the Mukerjee group at NEU, encapsulation of Fe chelates within the confines of a MOF as a part of wet chemical synthesis results in formation of highly active and durable M-N-C electrocatalysts [3]. This presentation will provide synthetic, mechanistic and steady state polarization results measured both at a PEM and PAFC single cell. Some aspects of durability and immunity towards anions will also be presented. The UNM team used Sacrificial Support Method (SSM) for preparation of highly active electrocatalysts derived from different imidazole precursors. The influence of imidazole precursors, SSM synthetic parameters (number of post treatments, duration of treatment, heat treatment temperature etc) on the final activity of ORR electrocatalysts was studied in Rotating Ring Disc Electrode as well as in Membrane Electrode Assembly set ups [4-5]. Pajarito Powder performed an extensive R&amp;D on scaling up of the Fe-N-C catalysts made from imidazole MOFs. Such parameters, which will influence the catalyst activity and durability as heat treatment temperature, post treatment conditions, catalyst layer fabrication in MEA were optimized for the materials on the level of 25-50g per batch. It was shown that VariPore ™ allows to reproducibly synthesize commercial amount of ORR PGM-free catalysts with improved activity matching smaller lab scale batches and improve the durability of imidazole-derived catalysts [6]. [1] E. Proietti, F. Jaouen, M. lefèvre, N. Larouche, J. Tian, J. Herranz, J. P. Dodelet “Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells”, Nature Communications 2 (2011) 416. [2] G. Wu, K.L. More,C.M. Johnston, P. Zelenay "High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt" Science 332 (2011) 443-447. [3] K. Strickland, E. Miner, Q. Jia, U. Tylus, N. Ramaswamy, W. Liang, M.-T. Sougrati, F. Jaouen. S. Mukerjee "Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination" Nature Comm. 6, Article number: 7343 (2015) [4] D. Sebastian, A. Serov, K. Artyushkova, J. Gordon, P. Atanassov, A. S. Arico, V. Baglio "High Performance and Cost‐Effective Direct Methanol Fuel Cells: Fe‐N‐C Methanol‐Tolerant Oxygen Reduction Reaction Catalysts" ChemSusChem 9 (15) (2016) 1986-1995. [5] D. Sebastian, A. Serov, K. Artyushkova, P. Atanassov, A. S. Arico, V. Baglio "Performance, methanol tolerance and stability of Fe-aminobenzimidazole derived catalyst for direct methanol fuel cells", J. Power Sources 319 (2016), 235–246. [6] A. Serov, M. J. Workman, K. Artyushkova, P. Atanassov, G. McCool, S. McKinney, H. Romero, B. Halevi, T. Stephenson "Highly stable precious metal-free cathode catalyst for fuel cell application", J. Power Sources 327 (2016) 557-564.