纳米纤维素/碳纳米管碳气凝胶的制备及其电化学性能

Preparation and electrochemical performance of nanocellulose/carbon nanotube carbon aerogel

纳米纤维素作为一种绿色无污染、来源广泛的生物质材料,在超级电容器电极材料领域具有极大的应用潜力,但其本身导电性能差,严重影响了其应用效果。笔者以硫酸盐漂白木浆为原料,采用2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)氧化法制得了表面富含羧基(1.5506 mmol/g)的具有较高长径比的纳米纤维素(CNF)纤丝,并将纳米纤维素悬浮液作为多壁碳纳米管(MWCNT)的良好分散剂配置CNFs/MWCNTs悬浮液,将所得悬浮液经冷冻干燥和高温碳化制得CNFs/MWCNTs碳气凝胶,并结合热重曲线、拉曼光谱和扫描电镜等进行分析。结果表明:添加MWCNT后,气凝胶前驱体的热稳定性有明显的提高,在相同碳化条件下,CNFs/MWCNTs碳气凝胶的石墨化程度优于CNFs碳气凝胶。利用三电极体系,对比添加MWCNT前后碳气凝胶的电化学性能,发现添加MWCNT后的碳气凝胶工作电压从0.4 V提高到0.6 V,内阻由1.06900Ω降低到0.97531Ω,其比电容在电流密度为1 A/g的条件下由172.45 F/g增加到238.89 F/g。经过1500次循环后其比电容保持率由55.6%提高到85.4%,库伦效率维持在99.95%。该纳米纤维素/碳纳米管碳气凝胶是一种较为良好的超级电容器电极材料。

As a green and pollution-free biomass material with a wide range of sources,nanocellulose has great application potential in the field of supercapacitor electrode materials,but its poor conductivity seriously has limited the application.As a carbon-based material with high conductivity and low internal resistance,carbon nanotubes can be compounded with nanocellulose as a reinforced phase,and carbon electrode materials with the advantages of both can be prepared.Using sulfate bleached wood pulp as a raw material,the 2,2,6,6-tetramethylpiperidine-1-oxygen radical(TEMPO)oxidation method was used to prepare nanocellulose(CNF)filaments rich in carboxyl groups with high aspect ratio.Using the combination of the infrared spectroscopy and conductivity titration,the carboxyl group content of nanocellulose surface carboxyl group was measured to be 1.5506 mmol/g.The X-ray diffraction pattern and thermogravimetric analysis curve were used to characterize the nanocellulose,and the results showed that,compared with the natural cellulose,the nanocellulose prepared by the TEMPO oxidation method retained the basic crystal form of cellulose,and its thermal degradation rate was lower and the residual carbon content was higher,which had the potential to prepare carbon materials.Through the ultraviolet absorbance and transmittance analysis of nanocellulose suspension and CNFs/MWCNTs suspension,it was shown that the nanocellulose suspension was a good dispersant of multi-walled carbon nanotubes(MWCNT),and CNFs/MWCNTs aerogels were prepared by freeze-drying of the resulting suspension as precursors of CNFs/MWCNTs carbon aerogels.The morphology of the precursors was observed by the scanning electron microscopy and their thermal stability was analyzed.The residual carbon content of aerogel precursors was higher,and the thermal stability was significantly improved.CNFs/MWCNTs aerogels were prepared by the high-temperature carbonization,which were analyzed using the combination of thermogravimetric curves,Raman spectroscopy and scanning electron microscopy.Under the same carbonization conditions,the graphitization degree of CNFs/MWCNTs carbon aerogels was better than that of CNFs carbon aerogels.Using the three-electrode system,comparing the electrochemical performance of carbon aerogels before and after MWCNT,it was found that the wor-king voltage of carbon aerogels after the MWCNT addition increased from 0.4 to 0.6 V,the internal resistance decreased from 1.06900 to 0.97531Ω,and its specific capacitance increased from 172.45 to 238.89 F/g at a current density of 1 A/g.After 1500 cycles,the specific capacitance retention rate increased from 55.6%to 85.4%,and the coulombic efficiency remained at 99.95%.The CNFs/MWCNTs carbon aerogels have higher working voltage,lower internal resistance,higher specific capacitance,and more stable capacitance retention rate,which is a relatively well-behaved supercapacitor electrode material.