Correlating Fe source with Fe-N-C active site construction: Guidance for rational design of high-performance ORR catalyst

Abstract

Pyrolyzed Fe-NX/C materials derived from Fe-doped ZIF-8 are recently emerged as promising alternatives to noble metal platinum-based catalysts towards oxygen reduction reaction (ORR) and elucidating the dependacne of Fe source on the active site structure and final ORR performance is highly desirbale for further development of these materials. Here, we designed and synthesized a series of Fe-N-C catalysts using ZIF-8 and various iron salts (Fe(acac)3, FeCl3, Fe(NO3)3) as precusors. We found that the iron precursors, mainly the molecular size, hydrolysis extent, do play a major role in determining the final morphology of Fe, namely forming the Fe-Nx coordination or Fe3C nanoparticles, as well as the site density, therefore, significantly affecting the ORR activity. Among the three iron sources, Fe(acac)3 is most advantageous to the preferential formation of single-atom Fe-Nx active sites and the derived catalyst demonstrated best ORR performance.