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PengXiang Hou1 Jin-Cheng Li1 Chang Liu1 Hui-Ming Cheng1

1, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning, China

The oxygen reduction reaction (ORR) is the most important processes in a wide range of renewable energy technologies, such as in fuel cells and metal–air batteries.1 Fe-N-C has emerged as a promising noble-metal-free catalyst for the ORR, however, to achieve a catalytic activity comparable to that of Pt in acidic medium remains a great challenge.2 Here we develop a simple and scalable atomic isolation technique to synthesize a porous Fe-N-C catalyst with a high concentration of N-coordinated single Fe atoms by pyrrole polymerization on carbon nanotubes (CNTs), followed by Fe3+ and Zn2+ ion adsorption, and finally one-step pyrolysis.3 Additional acid leaching and a second treatment are not required. During the pyrolysis, Fe atoms are uniformly dispersed with and spatially isolated by Zn atoms and directly convert to N-coordinated single Fe atoms, instead of large inactive Fe particles. Furthermore, pores are formed along with the volatilization of the isolation Zn atoms, and these are greatly beneficial to ORR activity. As a result, the obtained porous carbon composite catalyst exhibits excellent ORR performance with a half-wave potential value of 0.82 V in an acidic medium, 20 mV more positive than that of Pt/C with a “standard” loading of 0.1 mg cm-2 and only 20 mV more negative than that of Pt/C with the same loading of 0.3 mg cm-2. The technique can be generalized to other carbon supports, including carbon black, graphene oxide, and flexible films of single-wall CNTs or carbon cloth. The obtained flexible composite films show even better ORR performance with 40-60 mV more positive onset potentials than Pt/C loaded on carbon cloth. Considering the low-cost and simplicity of this fabrication process, these high-efficiency, robust catalysts with a high concentration of single Fe atom sites are promising candidates to substitute for noble Pt-based catalysts in fuel cells.
References
1. J.C. Li, P.X. Hou, S.Y. Zhao, C. Liu, D.M. Tang, M. Cheng, F. Zhang, H.M. Cheng. A 3D Bi-Functional Porous N-Doped Carbon Microtube Sponge Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions, Energy Environ. Sci., 9, 3079 (2016).
2. J.C. Li, P.X. Hou, C. Shi, S.Y. Zhao, D.M. Tang, M. Cheng, C. Liu, H.M. Cheng. Hierarchically Porous Fe-N-Doped Carbon Nanotubes as Efficient Electrocatalyst for Oxygen Reduction, Carbon, 109, 632 (2016).
3. J.C. Li, Z.Q. Yang, D.M. Tang, L.L. Zhang, P.X. Hou, S.Y. Zhao, C. Liu, M. Cheng, G.X. Li, F. Zhang, H.M. Cheng. N-doped carbon nanotubes containing a high concentration of single iron atoms for efficient oxygen reduction, NPG Asia Mater., under publication.

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