Heterojunction Enhanced Piezo-Gas Sensing Performances Of ZnO Nanocomposite Through Modulating Surface Energy Band Structures

Self-powered gas sensor is the latest achievement of ZnO nanogenerator application in gas sensing fields.The self-powered gas sensor is presented by coupling the piezoelectric and gas sensing characteristics,and the piezoelectric output generated by ZnO nanowires acts as both the power source and the sensing signal.In this work,by constructing heterojunctions on ZnO nanowire surface,we have greatly enhanced the piezo-gas-sensing performances and developed the application fields and application environment for self-powered gas sensor.In addition,we have also investigated several novel machenisms of heterojunction enhanced piezo-gas-sensing.These results can stimulate a research trend of self-powered gas sensor.This study is mainly shown as follews:(1)High room-temperature H2 sensing performance has been realized from SnO2/ZnO nanoarray nanogenerator.Without any external electricity power source,the portable device can be driven by human motion,in which the piezoelectric output can actively act as both the power source and H2 sensing signal.Upon exposure to 800 ppm H2 at room temperature,the piezoelectric output voltage of the device under the same applied deformation decreases from 0.80 V(in dry air)to 0.14 V,and the sensitivity is up to 471.4.The detection limit is?10 ppm H2,and the selectivity against H2 at room temperature is very high.The excellent room-temperature H2 sensing performance can be attributed to the coupling of the piezoelectric screening effect of ZnO nanowires and the conversion of SnO2/ZnO heterojunctions.(2)High sensitivity,selectivity and reliability have been achieved from ZnSnO3/ZnO nanowire piezo-nanogenerator as self-powered gas sensor for detecting liquefied petroleum gas(LPG)at room temperature.After being exposed to 8000 ppm LPG,the output piezo-voltage of ZnSnO3/ZnO NWs under compressive deformation is 0.089 V,much smaller than that in air ambience(0.533 V).The sensitivity against 8000 ppm LPG is up to 83.23,and the low limit of detection is 600 ppm.The ZnSnO3/ZnO nanowire self-powered gas sensor has good selectivity for LPG.After two months,the decline of the sensing performance is less than 69%.Such piezo-LPG sensing at room temperature can be ascribed to the new piezo-surface coupling effect of ZnSnO3/ZnO nanocomposites.The practical application of the device driven by human motion has also been simply demonstrated.This work provides a novel approach to fabricate LPG sensors and promotes the development of self-powered sensing system.(3)Room-temperature self-powered H2S sensing with high response and selectivity has been realized from Cu-ZnO nanowires.Upon exposure to 1000 ppm H2S at room temperature,the piezoelectric output voltage of the device(5 at.%Cu-ZnO)under compressive force decreases from 0.552(in dry air)to 0.049 V,and the response is up to 1045,over 8 times larger than that of undoped ZnO nanowires.The selectivity against H2S is also very high at room temperature.The enhanced room-temperature H2S sensing performance can be attributed to the coupling of the piezoelectric screening effect of ZnO nanowires and the synergistic effect of Cu dopant.This study can stimulate a research trend of designing new gas sensor for detecting toxic gases at room temperature.