Construction,Flexibility And Strengthening Mechanism Of Cellulose Composite Carbon Aerogels

Carbon aerogels with remarkable properties（e.g.,ultralow density,excellent conductivity,and chemical stability）have exhibited various advantages in many applications such as energy storage,catalysis,adsorption and separation,and pressure sensing.Especially,compressible carbon aerogels are attracting increasing attention due to their desirable electrical and mechanical properties,as well as chemical and thermal stability.Utilizing the essential flexibility of specific structural units,such as graphene,CNTs,elastic polymer,and other flexible materials,is a prevailing approach to fabricate compressible carbon aerogels.Wearable pressure-and strain-sensing electronics have attracted great attention in various applications,such as flexible displays,wearable devices,and electronic skins.However,it remains challenge to construct flexible carbon materials from biomass.This thesis used renewable cellulose as the main raw material and prepared a series of electrode materials with high electrochemical performance and carbon aerogels with high compressibility,fatigue resistance,and high sensitivity.We provide an effective method and ideal materials for werable devices using biomass-based carbons.Specific research contents are as follows:1.Using cellulose as carbon precursor to prepare a hierarchical porous carbon aerogel as a substrate for in-situ polymerizing conductive polymer polypyrrole（PPy）.The hierarchical porous architecture not only enabled an efficient penetration and uniform loading of PPy throughout the carbon network,but also ensured a rapid transfer of electrolytes and a high accessibility of PPy.Specifically,macropores can not only guarantee the efficient infiltration of conductive polymer into the interior surfaces,but also reduce the diffusion distance of electrolyte ions and make pseudocapacitive active sites of PPy highly available to electrolyte ions;mesopores provided low-resistant channels for the ions;microporous channels enhanced capacitance by providing more surface area.The as-prepared hybrid showd a high specific capacitance of 387.6 F g^-1(0.5 A g^-1in 1.0 M H₂SO₄)and excellent cycling stability（92.6%capacitance retention after 10000 cycles）.This work provides an effective method to sustainably fabricate porous composite electrodes from renewable cellulose for supercapacitors.2.Enhancing the interaction among reduced graphene oxide（r GO）by using cellulose nanocrystal（CNC）.We prepared a CNC/r GO carbon aerogel with integrated performances by designing wave-shape lammelar structures.CNC and low-molecular weight carbon precursors enhanced interaction among r GO layers and thus produced an ultralight,flexible,and stable structure.The as-prepared carbon aerogel displayd an attractive compressibility,which could undergo an extreme strain of 99%,and elasticity（100%height retention after 10000 cycles at30%compression strain）,as well as stable strain-current response（>10000 cycles）.Particularly,the carbon aerogel is ultra-sensitive for detecting tiny change in strain（0.012%）and pressure（0.25 Pa）,which are the lowest detection limits for compressible carbon materials reported in literature.Moreover,the carbon aerogel exhibited repeatable bendable performance and could detect an ultra-low bending angle of 0.052°.The performances enabled the carbon aerogel a promising candidate for wearable devices.3.Using CNC as a nano support to connect MXene nanosheets into carbon aerogels with lamellar structures.The prepared aerogel possessed not only ultrahigh mechanical performances but also linear sensitivity.The interaction between MXene and CNC resulted in stable wave-shape lamellar architecture that can undergo an extreme high compression strain of 95%and long-term compression（10000 cycles,at 50%strain）.It also displayed both extremely high sensitivity(114.6 k Pa^-1)and wide linear range（50 Pa-10 k Pa）that are at the first line of carbon aerogels.In addition,the aerogel could detect a tiny pressure change（1.0Pa）.These advantages allow the carbon aerogel have application in wearable piezoresistive devices for detecting biosignals.4.Proposing a facile,effective,and sustainable route to fabricate a highly compressible carbon aerogel from renewable CNC and konjac glucomannan（KGM）.In this work,CNC served as structural unit,and KGM linked CNC into continuous and oriented aligning layers with wavy shape.The interactions between CNC and KGM gave rise to a lightweight yet highly compressible carbon aerogel.Due to these structural features,the as-prepared carbon aerogel showed ultrahigh structural stability and outstanding mechanical performances.Specifically,it maintained 100%original height and 90.6%original stress after 10000 cyclic compression test at 50%compression strain.It could even undergo a high compression strain of 90%for 1000 cycles,with height retention of 90%and stress retention of 80%,which was superior to graphene or CNT based carbon aerogels.Additionally,the carbon aerogel exhibited linear sensitivity and was assembled into a high-performance sensor to accurately detect human biosignals.