| Increased energy needs urgently require the development of energy storage devices.For the unique excellent performance,supercapacitors become one of the most promising energy storage devices.Electric double layer capacitor(EDLC)is a type of supercapacitor.The performance of EDLC greatly depends on the properties of the electrode materials.In this paper,porous carbon materials were prepared from the co-thermal dissolution soluble portions of Zhaotong lignite and different biomass,and the carbon precursors were analyzed by mass spectrometry.By acquiring the molecular composition of carbon precursors and the morphology of porous carbon materials,the relationship between the molecular composition of carbon precursors and the properties of the materials was established.First,the material preparation conditions were optimized.A one-step carbonization activation method was used to prepare porous carbon materials using Zhaotong lignite thermal dissolution soluble portion as the carbon precursor,Nano-ZnO as the templating agent,and KOH as the activator.The effects of activation temperature,activation time,templating agent and alkali-to-carbon ratio are discussed in details.By comparing the electrochemical properties of materials prepared under different conditions,the optimal conditions were finally determined to be an alkali-to-carbon ratio of 3:1,a template ratio of 3:1,an activation temperature of 700 ~oC,an activation time of 2 h,a carbonization temperature of 300 ~oC,and a carbonization time of 30 min.Under the optimal conditions,the specific capacitance of the obtained carbon material reached 299 F/g.Second,carbon precursor was further optimized.The material was prepared by using the co-thermal dissolution soluble portions of Zhaotong lignite and biomass(rice husk,rice stalk and wheat straw)at different mass ratios.At the same time,the carbon precursors were analyzed by mass spectrometry.For the thermal dissolution soluble portion of lignite and rice husk(RH),the specific capacitance was 352 F/g when the ratio of RH reached 3/4.Meanwhile,the soluble portion mainly consisted of ester compounds and phenolic compounds.As the proportion of RH increases,the number of compounds with high carbon number and high degree of unsaturation decreases,and the relative content of nitrogen-containing compounds in the soluble portion increases.The co-thermal dissolution soluble portions of rice straw(RS)and lignite were also used as the carbon precursors.When the ratio of RS is 1/4,the specific capacitance was as high as 355 F/g.After 10,000 cycles,the retention rate was as high as 75.3%.Oxygen-containing compounds account for a large proportion of soluble portions compounds and are mainly esters.A high content of esters may be due to the esterification reaction during the thermal disslolution process.Besides oxygen-containing compounds,the presence of nitrogen-containing compounds has an obvious effect on the electrochemical properties of porous carbon materials.When the co-thermal dissolution soluble portions of wheat straw(WS)and lignite was used as the carbon precursor,the best specific capacitance was 384 F/g with a ratio of WS at 1/4.In a two-electrode system,the capacitance retention rate was 98.2%after 10,000 cycles.The existence of N-containing compounds also affected the material properties.Nitrogen-containing compounds in the form of intracyclic nitrogen ware not easily volatile during the carbonization process and inlined to remain in the materials.From the above results,it can be further concluded that the content of ester compounds in the soluble portions is the highest,and the stable presence of the ester compounds is helpful for the deposition rate of carbon elements.After the addition of biomass,the content of nitrogen-containing compounds in the soluble portion increases,and the presence of nitrogen-containing compounds can improve the electrochemical performance of electrode materials.The paper has 46 figures,22 tables and 110 references. |
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