Abstract
While improved activity was recently reported for bimetallic iron-metal-nitrogen-carbon (FeMNC) catalysts for the oxygen reduction reaction (ORR) in acid medium, the nature of active sites and interactions between the two metals are poorly understood. Here, FeSnNC and FeCoNC catalysts were structurally and catalytically compared to their parent FeNC and SnNC catalysts. While CO cryo-chemisorption revealed a twice lower site density of M-Nx sites for FeSnNC and FeCoNC relative to FeNC and SnNC, the mass activity of both bimetallic catalysts is 50-100% higher than that of FeNC due to a larger turnover frequency in the bimetallic catalysts. Electron microscopy and X-ray absorption spectroscopy identified the coexistence of Fe-Nx and Sn-Nx or Co-Nx sites, while no evidence was found for binuclear Fe-M-Nx sites. 57Fe Mössbauer spectroscopy revealed that the bimetallic catalysts feature a higher D1/D2 ratio of the spectral signatures assigned to two distinct Fe-Nx sites, relative to the FeNC parent catalyst. Thus, the addition of the secondary metal favored the formation of D1 sites, associated with the higher turnover frequency.
| Original language | English |
|---|---|
| Pages (from-to) | 14737-14747 |
| Number of pages | 11 |
| Journal | Journal of the American Chemical Society |
| Volume | 145 |
| Issue number | 27 |
| DOIs | |
| State | Published - Jul 12 2023 |
Funding
The authors would like to acknowledge Dr. Sören Dresp, Dr. Shuang Li, Dr. Huan Wang and Dr. Tobias Reier for assistance with RRDE, XPS, nitrogen physisorption and CO pulse chemisorption experiments. We also thank Prof. Ulrike I. Kramm for help with Mössbauer spectroscopy measurements. Aberration-corrected STEM-EELS was conducted at the Center for Nanophase Materials Sciences, which is a US Department of Energy Office of Science User Facility, at Oak Ridge National Laboratory. This project received partial financial support by the Graduate School of Excellence Energy Science and Engineering (GRC1070). The research leading to some of these results has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 779366. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation program, Hydrogen Europe and Hydrogen Europe research. A.Z. and A.K. acknowledge support from the French ANR project ANR-19-CE05-0006 (SPECTROSCOPE) and Synchrotron SOLEIL (Gif-sur Yvette, France) for provision of synchrotron radiation facilities at beamline SAMBA (proposal number 20201432). F.L., M.P., and P.S. acknowledge financial support by the Bundesministerium für Bildung und Forschung (BMBF) under The German Israeli Battery and Fuel Cell program, FKZ 03XP0251.