Structure Control And Electrochemical Performance Of Bamboo Lignin-based Flexible Carbon Nanofiber

Carbon nanofibers have excellent flexibility,a large specific surface area,high mechanical strength,and good chemical stability,making them suitable as supercapacitor electrode materials.Lignin has the potential to be used in the production of flexible carbon nanofibers.Research and development of lignin-based flexible carbon nanofibers with excellent performance and regulating their structure and properties are the focus of scientific research.In this study,bamboo lignin was used as raw material to prepare flexible carbon nanofiber by electrospinning,pre-oxidation,and carbonization.The structure was optimized by adjusting the parameters,and the effects on the flexibility,microstructure,thermal stability,microcrystalline structure,surface functional groups,surface element composition,and electrochemical properties of the materials were studied.The relationship among the parameters,structure,and properties was established to reveal its regulatory mechanism.The main results were listed as follows:（1）The molecular weight of PVP at the optimal preparation technology of bamboo lignin-based flexible nanofiber membrane was 1260000.It was mixed at 5:5 to form a 23 wt%spinning precursor,and the spinning voltage was 24 kv,with 14 cm spinning distance,0.026ml/min injection speed,and 100 r/min rotating speed of the receiving roller.The PVP and bamboo lignin were physically combined mainly.According to the pyrolysis characteristics of bamboo lignin-based flexible nanofiber membrane,the pre-oxidation temperature of bamboo lignin-based flexible nanofiber should be lower than 250℃,the carbonization temperature should be higher than 550℃,and the optimized heating rate for carbonization was 5℃/min.（2）The preparation of bamboo lignin-based carbon nanofiber was divided into two steps,pre-oxidation and carbonization.The temperature was increased from room temperature to150℃with 0.5℃/min and maintained for 1 hour in the pre-oxidation process;then,the temperature was increased from 150℃to 250℃with 0.5℃/min and maintained for 1.0 hour.In the carbonization process,the carbonization temperature was 800℃,and the carbonization time was 1 hour.The bamboo lignin-based carbon nanofiber membrane was not flexible,and the carbon structure was amorphous,with the surface had C=C and C=N groups.Among them,the C-type was mainly composed of C-C and C=C,and the N-type was mainly composed of pyridine N and graphitized N.The O element was mainly existing in the oxygen-containing hydroxyl group in the bamboo lignin.The bamboo lignin-based carbon nanofibers have good thermal stability,and the cyclic voltammetry and constant current charge-discharge were 97.30F/g and 108.95 F/g,respectively.（3）The Fe-doped bamboo lignin-based flexible carbon nanofiber’s optimum parameters were doping of 5%K₂Fe O₄,the carbonization temperature of 800℃,and the carbonization time of 1 hour.The Fe-doped bamboo lignin-based flexible carbon nanofibers have an excellent fiber shape and uniform element distribution,with surface loading the Fe₂O₃particles.Under the scan rate of 5 m V/s and current density of 0.5 A/g,the specific capacitance was122.65 F/g and 129.9 F/g,respectively.（4）The optimum parameters of the C-Fe doping bamboo lignin-based flexible carbon nanofiber were the doping ratio 5%Fe+0.4%CB,the carbonization temperature at 800℃,and the carbonization time at 1.0h.The carbon black（CB）had no significant effect on the microcrystalline structure,surface functional groups,and chemical composition of the bamboo lignin-based flexible carbon nanofiber,but the thermal stability was improved.The material has good flexibility,low graphitization degree,and more defects and disordered structure were included in the fiber structure.It had well flexibility,and the surface elements were evenly distributed.Under the scan rate of 5 m V/s and current density of 0.5 A/g,the cyclic voltammetry and constant current specific capacitance values were 198.39 F/g and 231.2 F/g,respectively.