Covalent organic frameworks (COFs) possessing a well-defined structure and abundant functional groups are prospective pseudocapacitive electrode materials. However, their intrinsic poor electrical conductivity and stacking problems usually impede the utilization of their active sites. Herein, we conduct an in situ growth of polyimide COFs (donated as NTDA COFs) enriched with carbonyl groups on multiwalled carbon nanotubes (MWCNTs). An impressive capacitance of 467 F g–1 at 1 A g–1 is achieved for the as-prepared NTDA/MWCNTs composite, significantly surpassing both the pure MWCNTs (60.3 F g–1) and NTDA COFs (284.4 F g–1). No decay of capacitance is observed after 10,000 cycles at 10 A g–1. The assembled device NTDA/MWCNTs//activated carbon reaches a high energy density of 17 Wh kg–1 at 750 W kg–1 while keeping superior charging/discharging stability of 89.5% after cycling for 19,000 times at 10 A g–1. In situ Fourier transform infrared (in situ FT-IR) tests together with the exploration of electrode kinetics show that the boosted capacitance of NTDA/MWCNTs is mainly donated by the redox reactions of carbonyl groups on NTDA COFs, which is largely activated by MWCNTs.
Graphical Change from none to one hundred percent just by a simple calcination : Directly using graphene to support gold nanoparticles gives no catalytic activity. But if the graphene support just undergoes a very simple thermal treatment for removing some oxygen-containing groups on it, a full conversion can be obtained within only half hour. Graphene is a promising support material for gold (Au) catalysts and its surface functional groups may play important roles in Au catalysis. By using alcohol oxidation with molecular oxygen as the probe, this work reveals that the oxygen-containing groups on the graphene support significantly affect the Au catalysis. The carbonyl groups can totally deactivate the catalysts. Just by thermally treating the graphene at suitable conditions to remove the carbonyl groups, the catalytic performance of the Au catalysts can be greatly improved. Even a full conversion can be obtained in a very short reaction time (just 0.5 h), when the oxygen content of the graphene support decreases from the initial 6.67% to 2.58% with the almost disappearance of C═O groups. The mechanism is also analyzed. Despite poisoning the present catalytic reaction, the Au-support interaction elucidated in this work may be beneficial to some other catalytic reactions with different reaction mechanism. Thus, this work helps to enhance the catalytic activity of graphene-supported Au catalysts, according to the applied catalytic reactions.
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