Atomic-scale Design Of 2-D MgH₂ Materials For Gas Adsorption And Catalysis Based On First-principles

Two-dimensional hydrides,as a new class of two-dimensional materials,have shown excellent performance in catalysis and sensing and received attention from domestic and foreign researchers in recent years.Two-dimensional MgH₂ has a large specific surface area,and at the same time,the two constituent elements of Mg and H are light in weight,widely distributed,and harmless to the human body and the environment,which makes its potential application range wider.With the trend of material design at home and abroad increasingly entering the micro level,based on first-principles quantum theory and computational methods,this thesis studied the gas adsorption,sensing and electrocatalytic properties of two-dimensional MgH₂ in depth,and theoretical analysis and atomic-scale design of the potential applications of twodimensional MgH₂ were carried out based on energy,atomic and electronic structure.The main research contents and results of this thesis are as follows:（1）Theoretical study of two-dimensional MgH₂ for adsorption of haze-causing gases.We designed pristine MgH₂,MgH₂ with H atom vacancy and MgH₂ doped with metal atoms to study their adsorption for CO,NO,NO2 and SO2（haze-causing gases）.The results show that the pristine MgH₂ cannot produce stable adsorption for the four haze-causing gases,but by introducing H atom vacancy on the surface of the pristine MgH₂,a stronger binding effect occurs between the substrate and the gas:the adsorption energy is significantly reduced,the adsorption distance is also greatly reduced.At the same time,the results of electronic structure calculations also prove that MgH₂ with H atom vacancy can be more sensitive and stable to the adsorption of haze-causing gases.MgH₂ doped with single metal atoms such as Ti,V,Cr,Mo can also produce stable adsorption of haze-causing gases,and the adsorption performance of different metal atoms is different for various gases.When designing materials,specific MgH₂ doping elements should be selected based on the type of adsorbed gas and comprehensive calculation results.（2）First-principles study on adsorption of volatile organic compounds（VOCs）by twodimensional MgH₂.By applying different degrees of strain engineering on the two-dimensional MgH₂ surface,the effects on the structure of MgH₂ and the adsorption properties of MgH₂for two types of VOCs,HCHO and CH3COCH3,were analyzed.The results show that when 1%5%tensile strain and compressive strain are applied to the two-dimensional MgH₂ surface,the geometric and electronic structures of MgH₂ change to some extent.In terms of adsorption properties,the adsorption energies of MgH₂ for HCHO and CH3COCH3 decreased with the increase of tensile strain when different tensile strains were applied.When different compressive strains are applied,the most stable adsorption of MgH₂ to HCHO and CH3COCH3 also comes from 5%compressive strain,and the electronic band gaps also change accordingly.The above conclusion show strain engineering can be applied on the surface of two-dimensional MgH₂ to adjust adsorption performance,and the strain engineering can be applied to the adsorption detection of VOCs such as HCHO and CH3COCH3.（3）Theoretical design of electrocatalytic ammonia synthesis on single-atom doped twodimensional MgH₂.After introducing transition metal single-atom on the surface of twodimensional MgH₂,the calculation results show that MgH₂ doped with Sc,Ti,V,Mo singleatom respectively can stably adsorb N2,and the adsorption configurations are "end-on"configurations.Based on the "end-on" adsorption configuration,we analyzed the two electrocatalytic ammonia synthesis reaction paths of distal and alternating.After comparison,it was found that in the four kinds of single-atom doped MgH₂,the overpotentials of the reactions carried out on the surfaces of Ti-MgH₂ and V-MgH₂ are relatively low,which are 0.57 V and 0.50 V,respectively.The lower overpotentials indicate the application potential of the twodimensional MgH₂ in the field of electrocatalytic ammonia synthesis.At the same time,after comparing with the HER competition reaction on the surface of different MgH₂ substrates,it can be seen that the four substrate has a higher priority for the adsorption of N2,which indicates that the single-atom doped MgH₂ material maintains a high reaction efficiency for nitrogen reduction reaction（NRR）.