Research On Hydrogen-Sensing Properties Control Of Tin Oxide Nanowires And Their Sensor Performance

As one of the most potential new energy,hydrogen(H₂)energy has the characteristics of high energy density and zero-emission.Hydrogen,which is the core pillar of global energy transformation,has been applied in the fields of fuel cell and power generation.On the other hand,H₂ is a colorless,odorless and flammable gas.The safety issues caused by H₂ leakage are highly valued.Therefore,it is urgent to fabricate H₂ sensors with high sensitivity and low power consumption.Tin oxide(Sn O₂),with good thermal stability and electrical conductivity,has broad application prospects in the field of H₂ detection.However,the problems of high operating temperature and low sensitivity detection at low operating temperature are still existing.The low-dimensional Sn O₂ colloidal nanowires have become an ideal material for fabricating highly sensitive and low-power consumption H₂ sensor because of the large specific surface area,high activity and solution processability.In order to analyze the adsorption behavior of H₂ on the surface of Sn O₂ based on the gas-sensing mechanism model of semiconductor metal oxides,the adsorption model was built by Materials Studio,and the first-principles calculation based on the density functional theory(DFT)using VASP software package was conducted.Based on the above model,in this paper,Sn O₂ nanowires(about 2 nm in diameter),which were synthesized via a solvothermal process,were drop-coated onto the alumina substrates at room temperature.An in-situ annealing treatment at 350 ^oC was conducted to achieve the porous network of Sn O₂nanowires,accompanied by the removal of organic ligands coated on the surface.This treatment improves the active area and electron transport of materials.Typically,the sensor had a response of 13 toward 40 ppm H₂ at 250 ^oC,with the response/recovery time being13/15 s,respectively.To further improve the sensing properties of the sensor,we continued to optimize the adsorption model of H₂ on the(110)crystal face of Sn O₂.Because of the unique catalytic activities of palladium(Pd),the H₂-sensing mechanism of the Pd-doped Sn O₂ was investigated in detail.Compared to the pristine Sn O₂-based model,the Pd-doped Sn O₂ model had higher adsorption energy and the amount of Bader charge transfer was almost ten times greater than before.H₂ molecules adsorbed on the surface of Sn O₂ as a donor-like surface state,resulting in significant n-type doping behavior.Therefore,according to the optimized model,we fabricated the Pd-doped Sn O₂gas sensors based on tunable physicochemical properties of colloidal nanowires.After Pd doping,the operating temperature of the sensor has been reduced from 250 ^oC to 150 ^oC,with the response/recover time significantly shorten from 13 s/15 s to 6 s/3 s upon 40 ppm H₂,respectively.Our work revealed the enhanced H₂-sensing mechanism of Pd-doped Sn O₂ from the perspective of a theoretical calculation,providing theoretical guidance for the synthesis of H₂-sensitive materials and the design of the H₂ sensors.