Covalent organic polymer-derived carbon nanotube-twined carbon nanospheres for efficient oxygen electroreduction and capacitance storage

Three-dimensional (3D) porphyrin-based covalent organic frameworks (COFs) supporting on carbon nanotubes (CNTs) were prepared by one-pot polymerization method. After annealing the prepared COF@CNT composites, CNT-twined nitrogen-doped carbon nanospheres (N-C@CNTs) were formed. N-C@CNTs-800 prepared at 800 degrees C demonstrated the efficient electrocatalytic performance for oxygen reduction reaction (ORR). The ORR half-wave potential of N-C@CNTs-800 reached about 0.87 V in KOH and 0.73 V in HClO4, comparable with the best non-precious metal catalysts (NPMCs). Moreover, the specific electric double-layer capacitance of N-C@CNTs-800 was about 250 F g(-1), larger than many similar carbons reported previously. The special structure of COF precursors consisting of the flexible triangular pyramid-shaped tris(4-formylphenyl)amine and the rigid porphyrin units was favorable for the exposure of active N species on carbon surface, and also facilitated the fabrication of CNT-twined nitrogen-doped carbon nanospheres. The used CNTs clearly contributed to the enhanced graphitization degree and abundant porosities of the carbonized N-C@CNTs. Thermal conversion of COF@CNT composites provided a simple synthesis strategy for preparing robust carbon electrode materials for oxygen electroreduction and capacitance storage.