Preparation Of Carbon Nanotube/Tannic Acid-Based Composite Gel And Its Sensing And Energy Storage Performance

With the development of the times,future electronic devices are developing in the direction of miniaturization,light weight,flexibility and portability.As an important branch of flexible electronic devices,flexible/wearable sensing and energy storage devices have great mechanical flexibility and have great potential in the fields of personalized health monitoring,human motion energy conversion and storage,etc.Among them,flexible sensors can convert various external stimulus signals into detectable electrical signals,and have the advantages of fast response time,high sensitivity,and long service life.Flexible energy storage devices have the advantages of fast charging and discharging,and high cycle life.Due to their excellent physical and chemical properties,carbon nanotubes have attracted much attention in the fields of flexible sensing,energy storage,adsorption and catalysis.The introduction of carbon nanotubes provides feasibility for improving the electrical conductivity of flexible sensing and energy storage devices,enhancing the device sensitivity and their sensing/storage performance.In this study,carbon nanotubes（SWCNTs）and tannic acid（TA）were composited to prepare carbon nanotubes and tannic acid（SWCNT/TA）composite gels,and their sensing and energy storage properties were explored.In addition,by introducing different metal ions into the SWCNT/TA composite gel to construct a metal-phenol network,the effect of metal ions on the sensing performance of the composite gel was explored,and its application in flexible sensing devices was explored.The main research contents are summarized as follows:（1）SWCNT/TA composite aerogels and hydrogels were prepared by hydrothermal treatment and one-step hydrothermal method with carbon nanotubes acidified by nitric acid as skeleton and tannic acid as dispersant.Its microstructure and mechanical properties were characterized,and its sensing and electrochemical properties were explored.The mechanical strength of SWCNT/TA aerogel increases with the increase of carbon nanotube concentration and tannic acid concentration,and the maximum compressive strength can reach 28 k Pa.When the concentration of carbon nanotubes and tannic acid are both 3 mg m L^-1,the as-prepared SWCNT/TA_3:3aerogel has a wide linear range of 0.014-28 k Pa,its sensitivity can be as high as 432k Pa^-1,and the response time is only 300 ms.The sensing performance of SWCNT/TA_3:3 aerogel is better than most of the carbon nanotube-based composites reported in the literature.In addition,the SWCNT/TA_3:3 hydrogel was used as the electrode material of supercapacitor,and the specific capacitance value was 164.37 F g^-1 at the current density of 1 A g^-1,which was still 164.37 F g^-1 at the current density of 20 A g^-1.It can maintain a specific capacitance as high as 134.2 F g^-1,showing excellent rate performance,and still maintains a rate performance of 70.5%after10,000 cycles of charge and discharge at a current density of 20 A g^-1,indicating that SWCNT/TA_3:3 Hydrogels can be used in the field of supercapacitor energy storage.（2）In order to explore the effect of metal ions on the sensing performance of the gel,the SWCNT/TA composite hydrogel was immersed in Mg Cl₂ or Al Cl₃ solution,and the metal-phenol network was introduced through the chelation of metal ions and tannic acid.Mg²⁺/SWCNT/TA and Al³⁺/SWCNT/TA hydrogels were obtained,and further freeze-dried to obtain the corresponding aerogels.Characterize its microstructure and mechanical properties,and test its sensing properties.Studies have shown that with the introduction of Mg²⁺and Al³⁺,the electrical conductivity of metal ions/carbon nanotubes/tannic acid composite aerogels is significantly better than that of carbon nanotubes/tannic acid composite aerogels without metal salts.Amorphous short fibers appeared in its micromorphological structure.Due to the different binding ability of tannic acid to different metal ions,more amorphous short fibers appeared in Mg²⁺/SWCNT/TA_1:1 than in Al³⁺/SWCNT/TA_1:1.At the same time,the introduction of metal salts weakens the mechanical properties of aerogels.Under the same pressure,Mg²⁺/SWCNT/TA_1:1 and Al³⁺/SWCNT/TA_1:1 have larger deformation amounts than SWCNT/TA_1:1.The emergence of metal ions/carbon nanotubes/tannic acid composite aerogels has improved the sensing performance.The as-prepared Mg²⁺/SWCNT/TA_1:1exhibits the best sensing performance when the concentration of carbon nanotubes and tannic acid is 1 mg m L^-1,and its sensitivity is as high as 13662 k Pa-1 in the pressure load range of 0.014-1.05 k Pa,the change of external pressure stimuli has a fast response（200 ms）and recovery ability（200 ms）,and its sensing performance far exceeds that of carbon nanotube-based composites of the same pressure sensing type.On this basis,a series of flexible sensor devices were prepared,and their practical applications were explored,in touch display,human movement and physical health monitoring,perception of subtle facial expression changes caused by emotional changes,voice recognition and subtle Strain or vibration monitoring has great potential.