Gas Sensing And Electrochemical Properties Of Porous Silicon Composites

Nowadays,traditional ceramic gas sensors are increasingly unable to meet people's needs.Looking for new room temperature gas sensitive materials will be the focus of current research.Porous silicon material can show good room temperature gas sensitive characteristics,high specific surface area,high activity,etc.It is gradually becoming a new development direction in the field of gas sensing.It is found that the gas sensitive properties of porous silicon materials have much room for improvement,especially in selectivity and stability.At the same time,porous silicon has great application value in the field of supercapacitor energy storage due to its special microstructure.Based on this background,the porous silicon-based composites were prepared by composite technology,and the gas sensitive and electrochemical properties of the composites were investigated.Porous silicon was prepared by providing square wave current with a self-designed circuit control device.The microstructure of porous silicon prepared by constant current etching method and square wave current etching method was characterized by scanning electron microscopy(SEM).It was found that the porous silicon prepared by square wave current etching method is smoother and more orderly,and the pore size distribution is concentrated in 1-1.5?m.The porosity test shows that the porosity of porous silicon prepared by square wave current corrosion method is slightly higher,which lays a foundation for subsequent experiments.The cuprous oxide/porous silicon(Cu₂O/PS)composites were prepared by electrochemical deposition with controlling deposition time.The morphology and structure of the Cu₂O/PS composite were characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).The gas sensitive property of the composite was tested by using a static gas sensitive testing system designed by ourselves.The electrochemical performance of the composite was tested by the electrochemical workstation.The specific surface area of the samples was characterized by BET test.The experimental results show that the Cu₂O grains grow preferentially along the(111)and(200)crystal planes in the pore wall and surface of porous silicon,and aggregate into coral-like grains with the increase of deposition time.The Cu₂O/PS composite with deposition time of 60 min shows better gas sensitivity selectivity to NH₃ at room temperature.It can continuously and stably respond and recover.When the concentration of NH₃ is 50 ppm,the gas-sensitive response of the composite is 3.78,and the response/recovery time is 67/30 s.When the charging current is 0.01 m A,the specific capacity of the composite sample deposited for 90 min is 1149 m F/g,which is about 26 times that of porous silicon.At the same time,the specific surface area of the Cu₂O/PS composite increases with the increase of deposition time,and decreases after reaching a certain peak value,which is consistent with the change trend of the electrochemical test analysis results.The nickel/porous silicon(Ni/PS)composite was prepared by phosphorous-free electroless plating technology.The morphology and structure of the Ni/PS composites were analyzed.The gas sensitive properties,electrochemical properties and specific surface area of the Ni/PS composites were tested.The experimental results show that the nickel particles grow in the direction of(111)preferentially on the surface of porous silicon and in the hole,and are villous.With the increase of plating time,the nickel particles cluster into fluff balls,which disorderly overlay on the surface of porous silicon.They finally form a dense nano nickel film layer.At room temperature,the Ni/PS composites with different plating time show good gas sensitivity to NH₃.The Ni/PS composite with plating time of 180 min has a gas sensitive response of 5.54 to 50 ppm NH₃,and has strong stability.It responds/recovers quickly in gas sensitivity tests.The composites exhibit good electron transport ability and charge storage ability,which can increase with the increase of plating time.When the charge current is 0.01 m A,the specific capacity of the composite with plating time of 240 min is 2388.3 m F/g,which is about 58times that of porous silicon.The specific surface area of the Ni/PS composite sample increases with the increase of time,which accords with the changing trend of electrochemical test results.