| AVS 64th International Symposium & Exhibition | |
| Applied Surface Science Division | Thursday Sessions |
| Session AS+BI+SA+SS-ThM |
| Session: | Spectroscopy of the Changing Surface |
| Presenter: | Michael Dzara, Colorado School of Mines |
| Authors: | M.J. Dzara, Colorado School of Mines K. Artyushkova, University of New Mexico C. Ngo, Colorado School of Mines M.B. Strand, Colorado School of Mines J. Hagen, Colorado School of Mines S. Pylypenko, Colorado School of Mines |
| Correspondent: | Click to Email |
Producing inexpensive polymer electrolyte membrane fuel cells requires significant reduction in the amount of platinum group metal (PGM) oxygen reduction reaction (ORR) catalyst used. High surface area iron- and nitrogen-functionalized carbon (Fe-N-C) materials are a promising PGM-free replacement. These catalysts are very heterogeneous, leading to difficulties in discerning contributions from various potential active sites and identifying the most active species.1 Techniques such as scanning transmission electron microscopy (STEM), energy dispersive x-ray spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS) provide structural and chemical information that can be correlated to ORR activity measured with electrochemical methods. Ambient pressure XPS (AP-XPS) and x-ray absorption spectroscopy (XAS) conducted in a humidified O2 environment, at an elevated temperature, and with applied potential offer opportunities to study materials under in situ conditions to determine adsorbates, intermediates, and products during ORR steps.2,3
In this work, model Fe-N-C catalysts are studied along with reference nitrogen-doped carbon (N-C) materials. Development of model catalyst materials with controlled morphology and speciation can simplify the elucidation of active sites. Micro-porous N-C nanospheres with high graphitic content were synthesized by a solvothermal treatment of resorcinol, formaldehyde, and ethylenediamine, and a subsequent pyrolysis in N2.4 Incorporation of Fe into the N-C nanospheres was carried out by wet-impregnation of various Fe precursors followed by a second N2 pyrolysis. By varying synthetic parameters, a set of N-C and Fe-N-C nanospheres with diverse compositions and properties were produced. Differences in composition and structure were evaluated using STEM-EDS and XPS, demonstrating control over N and Fe quantity and speciation. Select N-C and Fe-N-C nanospheres were then characterized with in situ AP-XPS, and in the case of Fe-N-C nanospheres, in situ XAS. By understanding the ORR on these model Fe-N-C nanospheres, synthesis-property-performance conclusions are drawn, guiding the development of highly active Fe-N-C catalysts.
1 A. Serov, K. Artyushkova, E. Niangar, C. Wang, N. Dale, F. Jaouen, M.-T. Sougrati, Q. Jia, S. Mukerjee, and P. Atanassov, Nano Energy 16, 293 (2015).
2 K. Artyushkova, I. Matanovic, B. Halevi, and P. Atanassov, J. Phys. Chem. C 121, 2836 (2017).
3 Q. Jia, N. Ramaswamy, H. Hafiz, U. Tylus, K. Strickland, G. Wu, B. Barbiellini, A. Bansil, E.F. Holby, P. Zelenay, and S. Mukerjee, ACS Nano 9, 12496 (2015).
4 N.P. Wickramaratne, J. Xu, M. Wang, L. Zhu, L. Dai, and M. Jaroniec, Chem. Mater. 26, 2820 (2014).