Post-synthetic Chemical Fixation of Fe2+ in MOF to Prepare Fe2 N-Embedded N-Doped Graphene Nanoribbons for Superior Oxygen Reduction Reaction.

The construction of efficient non-precious metal electrocatalysts for oxygen reduction reaction (ORR) with controlled structures and active sites is of fundamental importance for the wide utilization of hydrogen fuel cells. Herein, we report a controllable chemical fixation strategy that enables the simultaneous optimization in both of local and external structure of the Fe-N-C catalyst. The post-synthetic single-atomic chemical fixation of Fe2+ ions in coordinated-free bi-pyridine sites combined with the carbonation afford a Fe2N-embedded N-doped graphene nanoribbon (Fe2N/NGNRs) with dispersing Fe2N nanoparticles embedded in NGNR. When used as ORR electrocatalyst, Fe2N/NGNR exhibits a half-wave potential of 0.87 V and 0.79 V vs. RHE in alkaline and acid medium, respectively, comparable to commercial Pt/C (20 wt%) catalysts. The prominent ORR activity of Fe2N/NGNR is verified an H2-O2 fuel cell which displayed a peak power density of 307.7 mW/cm2 when using the Fe2N/NGNR as the catalyst in the cathode electrode.