Dual zeolitic imidazolate frameworks derived cobalt- and nitrogen-doped carbon nanotube-grafted flower- and leaf-like hierarchical porous carbon electrocatalysts for oxygen reduction.

Cobalt- and nitrogen-doped carbon nanotube-grafted flower- and leaf-like hierarchical porous carbon materials (Co,N/FLC@CNT) are prepared by growth of zeolitic imidazolate framework-67 (ZIF-67) on flower- and leaf-like zinc-ZIF (FL-Zn-ZIF) followed by thermal treatment without additional carbon source. This hierarchically porous structure can expose active sites efficiently and is also favorable for electrolyte permeation and O₂ diffusion. Furthermore, the self-generation of CNTs can improve electron conduction. Co,N/FLC@CNT has high contents of pydinic- and graphitic-N and large electrochemical active surface area (463 cm²). The Co,N/FLC@CNT presents excellent ORR activity in terms of high limiting current density (5.6 mA cm⁻²) and half-wave potential (0.82 V), which is almost the same as commercial Pt/C. The H₂O₂ yield of Co,N/FLC@CNT for ORR is 11.3%, which is close to that of Pt/C (8.0%). The ORR on Co,N/FLC@CNT proceeds via 4e⁻ path. Co,N/FLC@CNT presents better stability and methanol-tolerant ability than Pt/C. [ABSTRACT FROM AUTHOR]