Interfacial Design For Property Regulation Of Chitosan-based Carbon Aerogel

In the last decade,the rapid development of flexible wearable electronics has created a great demand for flexible conductive materials.Porous carbon aerogels are conductive aerogels with ultra-low density and chemical stability,which show great application prospects in many fields,such as energy storage,catalysis,adsorption,separation,and so on.However,conventional carbon aerogels are mostly hard or brittle,making it difficult to apply to flexible devices.Current flexible aerogels are mainly made of polymers,one-dimensional and/or two-dimensional nano-conductive materials.The challenge of these kind of aerogels is that they are hard to achieve both electrical conductivity and high fatigue resistance.Under the theme of"carbon neutrality"today,it is of great significance to develop green and sustainable methods to prepare interconnected structural monoliths.Chitosan,a kind of biomass material prepared from shrimp and crab shells,is the only widely existing natural polycationic basic polysaccharide at present,which shows attractive biocompatibility and degradability.Herein,through the utilization of chitosan’s special physical and chemical properties,the microstructure of chitosan-based carbon aerogel and the interfacial interaction between chitosan polymer and nanomaterial are designed.The rational design increased electrochemical and mechanical properties of chitosan-based carbon aerogels,as well as achieving the compressibility and elasticity of biomass-based carbon aerogel.This work provides important theories and methods for the construction of composite carbon aerogels and biomass-based lightweight porous materials.It also promotes the application of biomass-based carbon aerogel in electrochemical energy storage devices,wearable sensors and other cutting-edge fields.The research contents are as follows:1.Construction of chitosan based composite carbon aerogel with synergistic action of double electric layer capacitor and pseudocapacitor for energy storage application.The large specific surface area and pore volume of porous carbon aerogels provide abundant sites for interfacial reactions,electron storage,and active site dispersion,etc.,which make them suitable for energy storage.This work prepared a chitosan-based self-crosslinking hydrogel by using abundant amine groups in chitosan chains.A nitrogen-self-doped carbon aerogel was fabricated after freeze-drying the hydrogel with a following carbonization process,without any physical or chemical activation.The structure exhibited hierarchical porous structure,which not only allowed the efficient infiltration and uniform coating of polyaniline（PANI）in the inner network but also permitted a rapid penetration and desorption of electrolytes.Due to short diffusion pathway,uniformly coating of PANI,and high accessibility of PANI to electrolytes,the composite electrode had a very high supercapacitance of 373 F g^–1(1.0 A g^–1)and excellent rate capability(275 F g^–1,10 A g^–1)in a three-electrode system.The symmetric supercapacitor also showed a supercapacitance of high up to 285 F g^–1(0.5 A g^–1),and a very high energy density of 22.2 Wh kg^–1.Furthermore,the composite also presented a good cycling stability,and the capacitance retention rate is80%after 5000 cycles.2.By using the electrostatic interaction between chitosan polycations and negatively charged two-dimensional transition metal carbides and carbonitride nanomaterials（MXenes）,combined with ice-templated method and carbonization process,chitosan-derived carbon was epitaxially welded to MXene nanosheets,and light-weight carbon aerogels with aligned layered structures were successfully fabricated.Due to the connecting effect,the lamellas are flexible,highly compressible and elastic as well as structurally stable.These features allow the aerogel to withstand extremely high compression strain up to 99%,and retains 76.8%of its original stress after 10 cycles.It can also go through long-term compression up to 150000cycles,and after 10000 and 150000 cycles,its height was maintained as high as 97%and91.6%,and the stress reduction was 18%and 32%,respectively.Moreover,the aerogels can be repeated bending.The mechanical properties and its electrical conductivity make this composite carbon aerogel a promising candidate in flexible wearable devices and provide idea for designing novel composite materials from various 2D nanosheets.3.In order to explore the role that interfacial interactions play on the mechanical properties of the compressible and elastic aerogels,and how they affect the breakage and slippage between the structural units under compression conditions,Fe³⁺that can coordinate with chitosan polymer is introduced into the systems.Through interface design,the problem of a large number of structural defects in the material sheet was significantly solves,leading to sheet structures with a high degree of integration.The well-formed lamellas realized effective stress transfer through the aerogel during compression process.Different from the structural collapse of the control sample under large-strain compression,the carbon aerogel with coordination can withstand up to 99%compressive strain and spring back to the original height after the external force was released.And it only showed 5%permanent set after50000 compression cycles at 50%compressive strain.Furthermore,due to the introduction of fire-retardant components of montmorillonite,the aerogel exhibited thermal stability,which can maintain its compressibility and elasticity in flames.4.The regular lamellar structure enables the material to have the performance as strain/stress sensors.In order to explore their sensing application and improve the environmental friendliness of the materials,an all-biomass-based compressible elastic conductive material was prepared.Chitosan was used as a renewable carbon source,and cellulose nanocrystal was used as structural reinforcement materials;coordination effect was introduced to strengthen the structure.The material can withstand 95%compression strain and retain 82%of its original height after 10 compression cycles.It retained 94%of the height and 72%of the stress after 50000 cyclic compressions at 50%strain,exhibiting a stable structure.Taking advantage of its mechanical properties and unique wavy sheet structure,we used the material to construct a wearable piezoresistive sensor with an ultra-wide linear range of 0-18 k Pa.The sensitivity was 27.2 k Pa^-1.The sensitivity remained stable after 1000 cycles at 50%strain.As for tiny stress detection,the carbon aerogel exhibited ultra-high sensitivity of 103.5 k Pa^-1,and the detection limit was as low as 1.0 Pa,which enabled it to stably and clearly record biological signals such as human pulse.It could slao detect changes in bending angle.The scalability of the method and the attractive properties of the aerogels paving its way for the preparation of biomass-based green carbon materials,especially for chitosan polymer-based materials.