MIL‐101‐Derived Mesoporous Carbon Supporting Highly Exposed Fe Single‐Atom Sites as Efficient Oxygen Reduction Reaction Catalysts

Abstract Fe single‐atom catalysts (Fe SACs) with atomic FeN x active sites are very promising alternatives to platinum‐based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal–organic frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF‐derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeN x active sites. Herein, NH 2 ‐MIL‐101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N‐doped carbon supports (denoted herein as NC‐MIL101‐T) with a well‐defined mesoporous structure at different pyrolysis temperatures. The NC‐MIL101‐T supports are then impregnated with a Fe(II)‐phenanthroline complex, and heated again to yield Fe SAC‐MIL101‐T catalysts rich in accessible FeN x single atom sites. The best performing Fe SAC‐MIL101‐1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half‐wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc–air batteries (a near maximum theoretical energy density of 984.2 Wh kg Zn −1 ) and solid‐state zinc–air batteries (a peak power density of 50.6 mW cm −2 and a specific capacity of 724.0 mAh kg Zn −1 ).