Voltage Response Self-powered Humidity Sensor Based On Modified Cellulose Material

Humidity sensors are becoming increasingly important in many fields such as environmental monitoring,industrial process control,agricultural production,food storage,aviation and medical science.With the rapid rise and development of electronic wearable textiles,people put forward new requirements for humidity sensor devices.At present,the humidity sensor based on the characteristics of metal oxides,sulfur oxides and graphene materials is widely studied,but there are problems such as complex preparation process,high cost,heavy pollution and so on.Cellulose material is the most abundant polymer material in nature,with high hydrophilicity,renewable,biodegradable,non-toxic,biocompatible and other advantages,is a good substrate for humidity sensors.Therefore,in this paper,two kinds of self-powered humidity sensors with high sensitivity,fast response,good flexibility and no external power supply were prepared by using modified cellulose as humidity sensitive material.In this paper,cellulose filter paper（FP）with high hydrophilicity,high flexibility,porous and pure cotton non-woven fabric（NWF）was selected,and cobalt chloride（CoCl₂）with high hydrophilicity and variable color was used as the modified material.The CoCl₂@FP and CoCl₂@NWF humidity sensitive composite film was prepared by simple"impregnation and drying"method.Thus build CoCl₂@FP and CoCl₂@NWF self-powered humidity sensor.The main research work is as follows:Firstly,CoCl₂/FP composite film with color change and humidity sensitive response was prepared.The results showed that Cl and Co were uniformly distributed on the CoCl₂/FP composite film,and the main physical changes occurred between the filter paper and cobalt chloride.The current response and visible spectrum of CoCl₂/FP composite film were measured.The results show that from low humidity to high humidity,CoCl₂/FP composite film presents a color change from blue to red,and the color change is reversible.In the selectivity test of a variety of volatile solvents,it shows excellent selectivity to humidity.In addition,the CoCl₂/FP composite film sensor has an obvious current response in the range o f RH11%-98%,and the current change is more than 1 000 times.Then,the CoCl₂/FP composite film is prepared into CoCl₂@FP self-powered humidity sensor.The self-powered sensor based on FP has a good humidity response throughout the humidity range（RH11-98%）,due to the capillary structure of the porous cellulose membrane and the highly hydrophilic CoCl₂ material,which facilitates the adsorption and diffusion of water molecules.Notably,the sensor can have an output voltage in excess of 200 m V in high humidity（RH98%）.From low humidity to high humidity,the color changes from blue to red,and this change is reversible.Due to the high flexibility of cellulose fibers,the sensor maintains the output voltage even after 3 000 bends and folds.And,the CoCl₂@FP humidity sensor device has also been successfully applied to human respiratory monitoring and movement frequency tracking,etc.Finally,in order to explore the application effect based on textile materials,the porous NWF was used as the backing material and modified by different concentration of CoCl₂solutions in order to obtain the CoCl₂@NWF composite film with moisture-sensitive properties.The CoCl₂@NWF self-powered humidity sensor obtained by simple pasting not only shows a maximum response value of more than 200 m V output voltage under RH98%,but also a good cyclic performance.In addition,due to the unique characteristics of non-woven materials,the sensor also exhibits excellent resistance to bending and durability.Finally,we also explored the humidity monitoring of this sensor,which showed an excellent response performance to human respiration;thus,indicating that our sensor exhibits great potential in practical applications.So,the uniqueness of this new self-powered wearable humidity sensor technology can open up new application fields for the development of intelligent textiles and personal health products in the future Internet of Things.