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 O-2 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 cm(2)). 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.