Preparation Of Biomass Fruit Shell Cellulose Nanofibers And Carbon Materials And Their Application In Supercapacitors

The excessive consumption of non-renewable energy such as fossil energy and environmental pollution make it urgent to develop new green renewable materials and energy storage equipment.Flexible supercapacitors have become a research hotspot due to their excellent electrochemical performance and mechanical flexibility.Cellulose nanofibers have excellent properties such as high reactivity,high mechanical strength and degradability.Combining the advantages of cellulose nanofibers and electroactive materials,it is of great significance to construct cellulose nanofibers flexible electrode with excellent electrochemical properties and apply them in flexible supercapacitors.Agricultural and forestry waste wood fiber biomass is rich in carbon,clean and renewable,and can be used as an excellent raw material for preparing energy storage materials.In this paper,cellulose nanofibers and nitrogen-doped porous carbon materials were prepared with walnut shells and Amygdalus Pedunculata Pall shells as raw materials.Cellulose nanofibers and nitrogen-doped carbon materials were used as flexible substrates and electroactive materials to construct carbon aerogel flexible electrode,and the relationship between the structure and properties of the materials was systematically studied.The research results provide a theoretical basis for the design and development of biomass based energy storage materials,and provide a new idea for the high value conversion and utilization of biomass,which is of great significance for alleviating energy shortage and environmental pollution.The specific research contents are as follows:（1）Preparation and properties research of 3D network structure cellulose nanofibers.The cellulose was extracted and purified by chemical method from walnut shells and Amygdalus Pedunculata Pall shells,and cellulose nanofibers were prepared after mechanical treatment and TEMPO oxidation.The morphology,crystallinity,mechanical strength and other properties of cellulose nanofibers were studied systematically.The results showed that the two kinds of cellulose nanofibers had three-dimensional network structure,high crystallinity and rich surface charge.The walnut shell cellulose nanofibers prepared under the condition of ball milling time of 4 h and adding 7.1 g Na Cl O had the highest aspect ratio,higher crystallinity（82.04%）and the highest tensile strength（238.15MPa）,which was superior to the Amygdalus Pedunculata Pall shell cellulose nanofibers.Thus,walnut shell cellulose nanofibers could be used as a flexible substrate for supercapacitors.（2）Construction of cellulose nanofibers carbon aerogel and its application in flexible supercapacitor.Nitrogen doped walnut shell based carbon materials were prepared by chemical crosslinking and KOH activation methods using walnut shell as carbon source andγ-polyglutamic acid as nitrogen source.The obtained carbon materials displayed excellent electrochemical properties(specific capacitance of 341.0 F g^-1 at current density of 0.5 A g^-1),which can be used as an electroactive material.Carbon aerogel with 3D network structure was constructed by self-assembly of cellulose nanofibers,nitrogen-doped carbon material and graphene.The effects of different proportions on the morphology,electrical conductivity,compressive strength and electrochemical properties of the carbon aerogel were systematically investigated.The constructed electrode exhibited high conductivity(0.04 S cm^-1),compressive stress（30.8 k Pa）and the specific capacitance could achieve 164.4 F g^-1 at the current density of 0.5 A g^-1.The results show that the cellulose nanofibers of biomass shell has certain development potential in flexible supercapacitor.