Evolution Of Elements In Asphaltene-based Porous Carbon During Nitrogen-doping Process

Nitrogen-doped porous carbons have shown attractive application prospect in the field of energy storage, catalysis, separation because of its unique mechanical, optical and electronic properties. Study on the surface functional groups changes of nitrogen-doped porous carbon during pyrolysis will be significant for incorporating nitrogen into carbon materials purposefully. In this paper, Nitrogen-doped carbons with different heat treatment temperature were synthesized by using asphaltene as carbon source and MS as nitrogen source. And on this basis nitrogen-doped porous carbons were synthesized by CO2 activation. The effects of preoxidation treatment on its pore-structure, surface chemical properties and the electrochemical performance were discussed. The main research contents and results are briefly summarized as shown below:(1) Study on the surface functional groups changes of nitrogen-doped porous carbon during pyrolysisNitrogen-doped carbons (AOM-Ts) were successfully synthesized by selected AO which was obtained by pre-oxidation from asphaltene(A) as carbon source and MS as nitrogen source, mixing and grinding them physically, and then put them into the center of an electrie furnace quartz tube, subjecting to heat treatment at different pyrolysis temperatures from room temperature to the desired temperature under the protection of nitrogen. For comparison, the referential samples (AM-Ts) prepared were following the same procedure, and the only difference between the two groups was that the latter used the asphaltene as carbon source. The results showed that the AO holds the the char yield up to 63.75% at 800 ?, generating carbonyl groups and showing better thermal stability, and the oxygen content is significantly higher than that of asphaltene. The oxygen containing functional groups in AO can act as active sites for the reaction of the -NH2 groups in MS during the process of heat treatment. When the pyrolysis temperature aboves 500 ?, the content of nitrogen and oxygen in AOM-T is higher than that of AM-T. In terms of sample AOM-T, the nitrogen functional groups mainly exist in the form of N-5 and N-6 heated below 500 ?; When the pyrolysis temperature rises to 600 ?, N-Q groups emerge except for N-5 and N-6 groups; With the temperature continues to rise to 700 ?, the newly generated N-X groups appear. With the increase of heat treatment temperature, the contents of N-5 basically remain unchanged, the contents of N-6 gradually decrease, and the contents of N-X and N-Q increase. However, the form of oxygen containing functional groups have little changed, all existing in the form of O-? and O-? type, and the contents of O-? are greater than that of O-?.(2) Effect of precursor preoxidation teatment on the structure and properties of the Nitrogen-doped porous carbonNitrogen-doped porous carbons (AMP-t/AOMP-t) were synthesized by CO2 activation, using asphaltene/preoxidation asphaltene as carbon precursor, MS as nitrogen source. The influence of preoxidation treatment on its pore-structure, surface chemical properties and the electrochemical performance was investigated. Results showed that the nitrogen content, the specific surface area, total entrance value and the sum contents of N-6 and N-5 of the AOMP-4 become increased, the AOMP-4 has a specific surface area of 986 m2g-1, nitrogen content of 4.85 wt.% and total entrance value of 0.61cm3g-1 and it also gets the the maximal specific capacitance of 197 F g-1 at 100 mAg-1 and specific capacitance of 136 F g-1 at 10 Ag-1 in 6 M aqueous solution of KOH. The capacitance retention retains about 90% of the initial capacitance after 5,000 cycles at a current density of 1 Ag-1.