Metal-Organic Framework-Derived Graphene Mesh: a Robust Scaffold for Highly Exposed Fe-N 4 Active Sites toward an Excellent Oxygen Reduction Catalyst in Acid Media.

This study demonstrates a special ultrathin N-doped graphene nanomesh (NGM) as a robust scaffold for highly exposed Fe-N 4 active sites. Significantly, the pore sizes of the NGM can be elaborately regulated by adjusting the thermal exfoliation conditions to simultaneously disperse and anchor Fe-N 4 moieties, ultimately leading to highly loaded Fe single-atom catalysts (SA-Fe-NGM) and a highly exposed morphology. The SA-Fe-NGM is found to deliver a superior oxygen reduction reaction (ORR) activity in acidic media (half-wave potential = 0.83 V vs RHE) and a high power density of 634 mW cm -2 in the H 2 /O 2 fuel cell test. First-principles calculations further elucidate the possible catalytic mechanism for ORR based on the identified Fe-N 4 active sites and the pore size distribution analysis. This work provides a novel strategy for constructing highly exposed transition metals and nitrogen co-doped carbon materials (M-N-C) catalysts for extended electrocatalytic and energy storage applications.