Host-guest interactions promoted formation of Fe-N4 active site toward efficient oxygen reduction reaction catalysis

Fe N C is the most promising material to replace the noble metal catalyst for cathodic oxygen reduction reaction in proton exchange membrane fuel cells (PEMFCs). However, the practical performance of Fe N C catalyst is significantly limited by its low active site (Fe-N 4 ) density. Herein, we propose to promote the formation of Fe-N 4 active sites in Fe N C catalyst by strengthening the interaction of N precursors and Fe precursors during the carbonization synthesis. In our approach, ionic liquid (IL, [EMIM][NTf 2 ]) with high nitrogen content and good thermal stability is caged in the pores of Fe-ZIF-8 through the host–guest interactions. These interactions are critical for the preservation of Fe and N species and formation of active sites during the synthesis. The optimal catalyst developed with this approach (Fe 0.05 N C/10) has a high density of accessible Fe-N 4 sites (1.88*10 19 sites g −1 ). Therefore, in both acidic and alkaline media, Fe 0.05 N C/10 showed excellent ORR activity comparable to commercial Pt/C catalyst. Moreover, PEMFC performance with a peak power density of 300 mW cm −2 was demonstrated with Fe 0.05 N C/10 under H 2 /O 2 conditions. The synthetic approach reported herein may be used for tailoring of advanced catalyst with high intrinsic activity.