Operando x-Ray Absorption Spectroscopy Investigation of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction

Abstract

Oxygen reduction reaction (ORR) plays a key role in the development of fuel cell technology, and great efforts have been made to reduce the amount of platinum, required to speed up this sluggish reaction, or, even more desirable, to use efficient electrocatalysts based on earth-abundant metals. To date, numerous single-atom catalysts in the form of metal-doped carbon-nitrogen materials (MNC) have proved to be a promising alternative to ORR Pt-based materials. [1-3]In this study we employed advanced spectroscopic techniques, namely Mössbauer spectroscopy and operando X-ray absorption (XAS) spectroscopy, to understand the structural and electronic factors underlying an increase in the catalytic turn over frequency (TOF) of bimetallic FeSnNC and FeCoNC catalysts, relative to the parent FeNC materials. In particular, 57Fe Mössbauer spectroscopy identified a larger ratio of D1/D2 species in both bimetallic catalysts, supporting a larger ratio of Fe(III)-Nx/Fe(II)-Nx sites. The combination of extended X-ray absorption fine structure (EXAFS) modeling, and the analysis of operando X-ray absorption near-edge spectroscopy (XANES) spectra revealed a disordered carbon structure around FeNx active sites, and variations in the iron oxidation state that can be linked to the enhanced intrinsic catalytic reactivity (TOF). This talk is therefore intended to draw attention to the potential of the XAS technique, especially when applied to in-situ/operando studies in the field of electrocatalysis. References F. Luo, A. Roy, L. Silvioli, D.A. Cullen, A. Zitolo, M.T. Sougrati, I.C. Oguz, T. Mineva, D. Teschner, S. Wagner, J. Wen, F. Dionigi, U.I. Kramm, J. Rossmeisl, F. Jaouen and P. Strasser. P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction. Nature Materials 2020, 19, 1215-1223A. Zitolo, N. Ranjbar, T. Mineva, J. Li, Q. Jia, S. Stamatin, G.F. Harrington, S.M. Lyth, P. Krtil, S. Mukerjee, E. Fonda, F. Jaouen. Identification of catalytic sites in cobalt-nitrogen-carbon materials for the oxygen reduction reaction. Nature Communications 2017, 8(1), 957A. Zitolo, V. Goellner, V. Armel, M. T. Sougrati, T. Mineva, L. Stievano, E. Fonda, F. Jaouen. Identification of catalytic sites for oxygen reduction in iron and nitrogen doped graphene materials. Nature Materials 2015, 14, 937-942