Calculation And Mechanism Of Gas Adsorption Behavior On Tungsten Oxide Surface

Tungsten oxide is a kind of metal oxide gas-sensitive material with great potential for research and development,which has been widely used in the detection of a variety of gas molecules.The detection accuracy and sensitivity of tungsten oxide are the main bottlenecks restricting its applications.The gas-sensitive optimization techniques based on element doping and oxygen vacancy tuning have been widely used in experiments.However,the selection of the doped element usually relies on trial and error.Moreover,the surface of the doped element and the surface with the oxygen vacancy after adsorption usually have complex structure and electron distribution characteristics,which affects the detection accuracy and sensitivity of the tungsten oxide system.At present,there is a lack of systematic and comprehensive theoretical analysis and universal rule guidance for the sensing mechanism and gas-sensitive regulation mechanism with the consideration of tungsten oxide surface type,doping element type,oxygen vacancy concentration and distribution.Therefore,it is crucial to systematically study the influence rules of tungsten oxide surface types and surface modification methods on its adsorption performance,and to reveal the microscopic mechanisms of gas adsorption considering the effects of surface structure,doping element,and oxygen vacancy.This is of great significance for the design and development of high-performance tungsten oxide gas-sensitive materials.Aiming at studying the influence mechanisms of tungsten oxide surface characteristics and doping elements on the adsorption properties,a thermodynamic adsorption model is constructed based on first principles,which can introduce key factors such as gas type,surface type,doping element,ambient temperature and gas partial pressure.Taking typical flammable and explosive hydrogen as an example,the influence of different doping elements and adsorption sites on the gas-sensitive performance of tungsten oxide system is predicted,and the optimal doping element Ir conducive to the adsorption of hydrogen atom is proposed.The gas-sensitivity enhancement mechanism is elucidated by the valence band center theory,which discloses that surface and subsurface Ir doping reducing the distance between the d-band and p-band centers and the Fermi levels.This provides a reliable theoretical support for the design and development of high-performance gas-sensitive materials.A variety of surface adsorption models with oxygen vacancies at different positions and concentrations are constructed to study the adsorption performance of tungsten oxide material with oxygen vacancy.The effects of oxygen vacancy types on the hydrogen atom adsorption properties of（1 1 0）_WO3surfaces are systematically investigated.The results show that the hydrogen adsorption performance of（1 1 0）_WO3surface can be improved effectively by regulating the oxygen vacancies with the symmetric distribution mode on the top layer surface.The calculations reveal the modification mechanism of oxygen vacancies to enhance the reduction of tungsten atoms.On this basis,the thermodynamic calculation realizes the accurate simulation of gas adsorption and desorption behavior of tungsten oxide material under actual working conditions.The temperature programmed desorption experiments and the predicted results have a high consistency.Therefore,the calculations can provide a new strategy for the development of high-performance gas-sensitive materials.Aiming at the detection of the typical toxic carbon monoxide using the tungsten oxide system,the carbon monoxide adsorption model of various tungsten oxide surfaces is constructed,and the diversity of adsorption mechanism of different tungsten oxide surfaces is predicted.Combined with thermodynamic calculations,the adsorption mechanism of carbon monoxide→carbon dioxide by tungsten oxide for carbon monoxide detection is revealed.It predicts that the optimal temperature of carbon monoxide gas-sensitive detection is 540 K under actual working conditions.The calculation of the reaction transition state shows that the carbon monoxide surface adsorption reaction process includes two stages:adsorption and escape.It provides a reliable guide and a new theoretical analysis method for the design of metal oxide gas-sensitive materials.