| By coupling piezoelectric and gas sensing characteristics of ZnO,the room-temperature self-powered gas sensor has been firstly realized by our team in 2013.The output of the device acts not only as a power source,but also as a response signal to test gas in new gas sensor.The new gas sensor has important promoting effect for the development of gas sensor.However,the initial self-powered gas sensor based on ZnO is mainly focused on strong reducibility gas sensing,such as H2S and H2.Its sensing performance in low reducing gas,such as ethanol,is relatively poor.Noble metal(Pt,Pb and Au)modification has been applied in low reducing gas sensing,and better results have been obtained.However,its cost is too high,and its performance can been further enhanced.UV illumination is introduced to enhance the performance of room-temperature self-powered ethanol sensor in this work.Specific studies are as follows:(1)UV-assisted room-temperature self-powered ethanol sensor based on ZnO nanowire arrays.Firstly,ZnO nanowire arrays were synthesized via a wet-chemical route.Secondly,high transparent device was fabrication by using ITO glass as electrode and the new test system was designed.Finally,the ethanol sensing experiment was conducted.Under the assistance of UV illumination,the piezoelectric output of ZnO NWs acts not only as a power source,but also as a response signal to ethanol gas at room temperature by combining their piezoelectric,photoelectric and gas sensing characteristics.Upon exposure to 700 ppm ethanol at room temperature under 67.5 mW/cm2 UV illumination,the piezoelectric output voltage of ZnO NWs(under 34 N compressive forces)decreases from 0.80 V(in air)to 0.12 V and the response is up to 85.Negative-charged chemisorbed oxygen ions can be formed through the adsorbed oxygen molecules on the surface of ZnO NWs capturing free electrons from the conduction band of ZnO.When the device is placed in the dark.the chemisorbed oxygen ion is thermally stable at room temperature and difficult to remove from the surface of ZnO NWs due to the large adsorption energy.Under UV illumination,photo-generated electrons can combine with oxygen molecules in air,which can form additional photo-induced oxygen ions.The photo-induced oxygen ions are weakly bounded to ZnO NWs and can be easily removed.The room-temperature reaction between the photo-induced oxygen ions and ethanol molecules increases the carrier density in ZnO NWs,resulting in a strong piezoelectric screening effect and very low piezoelectric output.(2)Room-temperature self-powered H2S sensor based on CdS nanorod arrays.Room-temperature self-powered H2S gas sensor based on CdS nanorod arrays.Firstly,CdS nanorod arrays were synthesized via a hydrothermal method.Secondly,the device was fabrication by using as-prepared CdS nanorod arrays.Finally,H2S gas sensing experiment was conducted.The piezoelectric output of CdS NRs acts not only as a power source,but also as a response signal to H2S gas at room temperature by combining their piezoelectric and gas sensing characteristics.Upon exposure to 600 ppm H2S gas at room temperature,the piezoelectric output voltage of CdS NRs(under 34 N compressive forces)decreases from 0.32 V(in air)to 0.12 V and the response is up to 62.5.The device structure with good flexibility can be driven by tiny mechanical energy in our living environment.And the test results show that the device has practical applications in room-temperature detection of H2S.CdS is a metal sulfide,which cannot react with H2S molecule.However,ZnO is a metal oxide,which can react with H2S molecule.Hence,the performance of the self-powered H2S gas sensor based on CdS is better than that based on ZnO.This is also a highlight of the work. |
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