Design And Investigation Of Self-powered Ammonia Sensors Based On Triboelectric Nanogenerator

With the development of Internet of Things,it is necessary to provide large quantities of batteries to maintain independent and continuous operation of sensor nodes in the sensor network,which needs periodical replacement and maintenance.Besides,the problems of bulky power supply system and continuous energy consumption are not neglectable.From this perspective,developing self-powered sensors that can be directly driven by environmental sustainable energy is helpful to get rid of the dependence on additional power supplies.Combing triboelectrification with electrostatic induction,triboelectric nanogenerator(TENG)can effectively harvest various renewable clean energies and then convert them into electricity,which opens up a new way for building self-powered sensing system without external power supplies.As one of the typical toxic and harmful gases generated in the process of industrial and agricultural development,ammonia(NH₃)can cause serious air pollution and threaten human health.Meanwhile,exhaled NH₃ is a typical biomarker for noninvasive disease diagnosis.In summary,it is of significant research value for environmental protection and health monitoring to develop TENG-based self-powered NH₃ sensors through combining NH₃sensing technology with self-powered technology.At present,the research of self-powered gas sensors is immature,and some properties like sensitivity and detection limit should be further improved.Meanwhile,the development of flexible electronics technology will gradually expand the application of self-powered gas sensors in the field of wearable health monitoring.In view of the above research status and development trend,this work systematically investigated the self-powered NH₃ sensors based on TENG from the following three aspects:the optimization of composite sensing films,the design of functional structure and the exploration of gas sensing mechanism coupling gas adsorption with electrostatic induction.The main contents of this dissertation are summarized as follows:1.Highly sensitive self-powered sensors were prepared based on the load resistance matching effect of TENG.By using Ti:sapphire femtosecond laser treatment,the surface of PTFE film was etched to enhance the output performance of TENG.The output voltage and current of the TENG are 1.93 times and 3.02 times higher than that of the untreated PTFE film,respectively.Meanwhile,polyaniline-multiwalled carbon nanotubes(PANI-MWCNTs)composite sensing film was grown on flexible polyimide(PI)substrate by in-situ polymerization self-assembly method.The characterization results showed that PANI-MWCNTs composite film possessed better spatial-staggered nanofiber structure.Meanwhile,the strong?-?conjugation between PANI and MWCNTs enhanced the electron delocalization and improved the gas sensing response of the NH₃ sensor.Compared with the PANI film-based sensor,PANI-MWCNTs composite film-based sensor presented better gas sensing response toward 1–100 ppm NH₃ and shorter response/recovery times.Furthermore,the PANI-MWCNTs sensor showed good selectivity,repeatability,long-term stability,bending resistance,and the detection limit can reach to 0.01 ppm.2.High performance,room temperature NH₃-sensing composite film was prepared based on the new member of two dimensional transition metal carbonitrides(MXene)family named niobium carbide(Nb₂CT_x),which improved the gas sensing performance of the self-powered NH₃ sensor under moisture environment.Ultrathin Nb₂CT_xnanosheets were prepared by hydrofluoric acid(HF)etching and tetrapropylammonium hydroxide(TPAOH)intercalation process,and the gas sensing properties of the Nb₂CT_xnanosheets were studied.For comparison,the NH₃ sensing properties of the Nb₂CT_x/PANI composite film were studied by spraying Nb₂CT_x nanosheets on the surface of PANI synthesized by in-situ polymerization method,and the effects of Nb₂CT_x deposition amount on the gas sensing properties of the composite film were explored.The results showed that Nb₂CT_x nanosheets were dispersed on the surface of PANI nanofibers,and close contact interfaces were formed between them via intermolecular hydrogen bonding.Then,the Nb₂CT_x/PANI composite film-based NH₃sensor was driven by a facile PTFE/Nylon-based TENG.Test results showed that the Nb₂CT_x/PANI composite film-based NH₃ sensor exhibited excellent gas sensing properties toward 1–100 ppm NH₃ at room temperature and high relative humidity(RH)environment(87.1%RH)with good linear response,selectivity,repeatability,and long-term stability.Compared with pure PANI-based sensor,strong influence of high humidity on the sensing response of the Nb₂CT_x/PANI sensor was greatly reduced.In addition,the gas sensing mechanism of Nb₂CT_x/PANI composite film was analyzed in detail.3.An integrated self-powered triboelectric gas sensor with good NH₃ detection ability was prepared.Cerium-doped zinc oxide(Ce-Zn O)film with good NH₃ sensing capability and triboelectric properties was synthesized via hydrothermal method and spraying method.Meanwhile,as another triboelectric film,polydimethylsiloxane(PDMS)with surface microstructure was prepared by patterned-template method.The Ce-doping concentration effectively adjusted the grain size,morphology and band gap of Zn O,which was helpful to improve the room-temperature gas sensing properties of the composite sensing film.The gas-sensing performances presented that the response of the Ce-Zn O sensor based on the optimized Ce doption concentration(0.004 M)toward 10 ppm NH₃ is 3.3 times higher than that of Zn O sensor under moisture environment,and the sensitivity is about 20.13%ppm^-1.Furthermore,the NH₃ sensing mechanism of the integrated triboelectric gas sensor was deeply analyzed by establishing the gas sensing model based on the coupling effect of NH₃ adsorption and electrostatic induction.In addition,the Ce-Zn O based triboelectric NH₃ sensor can be directly driven by the fluctuating stress from the chest during human breathing process,which provided a new idea for constructing wearable respiratory NH₃ and breathing patterns monitoring system driven by respiratory stress.4.Utilizing the expansion/contraction stress of balloon during the respiration process,an integrated TENG was designed for converting respiration flow kinetic energy to electricity.Ce-Zn O-PANI composite film that acted as gas sensing layer,triboelectric layer,and electrode was prepared by adding Ce-Zn O nanoparticles into the in-situ polymerization process of PANI.To meet the requirement of simulated breathing test,a real-time/simulated self-powered respiration system for gas sensing measurement was built with flow limiting valve,flowmeter and other components.Under the fixed flow rate(5 L/min),the output voltage of the two test systems showed good consistency.On this basis,the response characteristics of the triboelectric gas sensor toward 0.1–25ppm NH₃ were measured by simulated respiration system.Furthermore,the respiration flow rate(2–6 L/min),frequency,and breathing patterns(fast,slow and deep breathing)could be detected by the real-time respiration test system.Finally,the NH₃-sensing mechanism of the triboelectric gas sensor was further analyzed.