(588d) “Smart MEA” Approach: Design of Catalyst Layer

Authors: 
Serov, A., University of New Mexico
Stariha, S., University of New Mexico
Workman, M., University of New Mexico
Artyushkova, K., University of New Mexico
Atanassov, P., University of New Mexico

It is well known that clean energy sources are currently in high demand. Different type of fuel cells, such as proton exchange membrane (PEMFCs) or anion-exchange membrane fuel cells (AEMFC) are a potential solution. At the moment, the technologies use platinum-based catalysts with a high loading of the catalyst, which are expensive and contribute to ~40% of the total cost of a PEMFC.(1) For the decades, considerable investment was involved into the examination of the non-platinum group metal (non-PGM) catalysts. One rapidly developing class of non-PGM catalysts for oxygen reduction reaction (ORR) are materials based on transition metal-carbon-nitrogen networks (M-N-C).(2)  Those materials include Fe, Co or Mn precursors and nitrogen-containing organic precursors (either polymeric or low molecular weight ones). It is widely recognized that nitrogen species of M-N-Cs play a crucial role in the ORR mechanism. It has been suggested that the nitrogen stabilizes the attachment of the transition metals to the underlying carbon support creating the ORR active sites.(2-4) UNM group have examined a number of different organic precursors in our previous research. They include different combinations of transition metals with: tetramethoxy phenylporphyrin)(6),poly(ethyleneimine) (7), 4-aminoantipyrine(1), and carbendazim(8).

Composition of the catalyst from both chemical speciation and morphology (porosity, roughness, texture) plays crucial role in the interaction between those materials and ionomers (both proton and anion-exchange types). It also should be mentioned that the pore structure is critical to the transport of oxygen to active sites and removal of water (in order to prevent flooding). The variations of the pore-structure induced by the chemical changes introduced during fuel cell operation has to be understood in order to design non-PGM electrocatalysts with durability similar to DOE recommended. In present work, our group will discuss the focused ion beam/scanning electron microscopy (FIB-SEM) sectioning to obtain a visual 3D representation of catalyst layer morphology.

These 3D images will be used to generate detailed estimates of the evolution of structural parameters such as: specific surface area, total porosity, connectivity of pores, and others as a result of durability studies.

References

1.         M. H. Robson et al. Electrochim. Acta 90, 656-665 (2013).

2.         F. Jaouen  et al. Energy Environ. Sci. 4, 114-130 (2011).

3.         S. Kattel et al. Phys Chem Chem Phys 16, 13800-13806 (2014).

4.         U. I. Kramm et al. J. Am. Chem. Soc. 136, 978-985 (2014).

5.         U. Tylus et al. J. Phys. Chem. C 118, 8999-9008 (2014).

6.         K. Artyushkova et al.. Journal of Power Sources 226, 112-121 (2013).

7.         A. Serov et al.. Applied Catalysis B: Environmental 127, 300-306 (2012).

8.         A. Serov et al.. Adv. Energy Mater. 4, 7 (2014).