LAUSR

Abstract Fe-N x -C materials are extensively investigated due to their outstanding performance for oxygen reduction reaction (ORR). However, even though Fe 3 C, pyridinic N, and Fe N coordinations have been widely recognized as active sites for catalyzing the ORR, there is almost no report about the dominating functional groups responsible for the enhancement of ORR performance, especially in acidic media. Here we developed a robust and universal non precious metal catalyst, Fe 3 O 4 nanoparticles (particle size: ∼50 nm) embedded in 3D cross-linking hierarchically porous N-doped carbon (noted as Fe 3 O 4 @HPNC), as a superb ORR performance catalyst in both basic and acidic media. More importantly, in this hybrid there exists no Fe 3 C phase, which makes it easier to identify the prominent group contributing to the enhanced ORR performance. Taking into account that the enhancing factor of the ORR half-wave potential at Fe 3 O 4 -300@HPNC with respect to that at HPNC in acidic media (36.6%) is much higher than that in basic media (7.6%), it could be deduced that the role of the Fe N coordinations for ORR in acidic media is more dominating than that in basic media. Optimized Fe 3 O 4 -300@HPNC exhibits comparable ORR activity in acidic, or even better in basic media, superior stability and MeOH tolerance compared with the commercial Pt/C.