Fe–N–C materials exhibit excellent activity and stability for oxygen reduction reaction (ORR), as one of the most promising candidates to replace commercial Pt/C catalysts. However, it is challenging to unravel features of the superior ORR activity originating from Fe–N–C materials. In this work, the electronic and geometric structures of the isolated Fe–N–C sites and their correlations with the ORR performance are investigated by varying the secondary thermal activation temperature of a rationally designed NC‐supported Fe single‐atom catalyst (SAC). The systematic analyses demonstrate the significant role of coordinated atoms of SA and metallic Fe nanoparticles (NPs) in altering the electronic structure of isolated Fe–N–C sites. Meanwhile, strong interaction between isolated Fe–N–C sites and adjacent Fe NPs can change the geometric structure of isolated Fe–N–C sites. Theoretical calculations reveal that optimal regulation of the electronic and geometric structure of isolated Fe–N–C sites by the co‐existence of Fe NPs narrows the energy barriers of the rate‐limiting steps of ORR, resulting in outstanding ORR performance. This work not only provides the fundamental understanding of the underlying structure–activity relationship, but also sheds light on designing efficient Fe–N–C catalysts.

Recently, novel core-shell MOF@COF hybrids display excellent performance in various fields because of their inherited advantages from their parent MOFs and/or COFs. However, it is still a grand challenge to adjust the morphology of MOFs and/or COFs for consequent performance improvement. Herein, a Ti-MOF@TpTt hybrid coated with ultra-thin COF nanobelt, which is different from the fibrillar-like parent COF, is successfully synthesized through a sequential growth strategy. The as-obtained Pd decorated Ti-MOF@TpTt catalyst exhibits much higher photocatalytic performance than those of Ti-MOF, TpTt-COF, and Ti-MOF@TpTt hybrids with fibrillar-like COF shell for the photocatalytic cascade reactions of ammonia borane (AB) hydrolysis and nitroarenes hydrogenation. These can be attributed to its high BET surface area, core-shell structure, and type II heterojunction, which offers more accessible active sites and improves the separation efficiency of photo-generated carriers. Finally, the possible mechanisms of the cascade reaction are also proposed to well explain the improved performance of this photocatalytic system. This work presents a constructive route for designing core-shell MOF@COF hybrids with controllable morphology adjustment of COF shell, leading to the improved photocatalytic ability to broaden the applications of MOF/COF hybrid materials.

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