Atomic Co-N4 and Co nanoparticles confined in COF@ZIF-67 derived core-shell carbon frameworks: bifunctional non-precious metal catalysts toward the ORR and HER

Constructing heterostructures of covalent organic frameworks (COFs) and metal organic frameworks (MOFs) has gained great attention for various applications due to their well-defined skeletons, ordered porosity and designable functions. Herein, the core-shell structured carbon frameworks, which contain high density active sites of uniform Co nanoparticles and atomic Co-N-4, were realized by direct pyrolysis of TP-BPY-COF@ZIF-67. The thin COF-shell not only prevented the collapse and aggregation of ZIF-67 but also promoted the formation of mesopores for mass transport, and enhanced the graphitization degree for conductivity. The resultant COF@ZIF(800) exhibited bifunctional catalytic performance for the ORR and HER, in which the half-wave potential for ORR was 0.85 V in 0.1 M KOH and the over-potential for HER was 0.16 V at 10 mA cm(-2) in 1 M KOH were achieved. This work sheds light on exploring COFs and MOFs in electrochemical energy storage and conversion systems.