Theoretical Investigations On The Design Of Electrocatalysts Based On Two-Dimensional Metal Chalcogenides And Catalytic Mechanism

For a long time,the rapid development of industrialization of human society mainly depends on the massive use of fossil fuels.However,fossil fuels are not renewable,and harmful gases（such as CO,CO₂,NO,SO₂）are produced during the use of fossil fuels,all of which makes us face the crisis of energy exhaustion and environmental pollution.Therefore,the search for clean and renewable energy has become a major issue to be solved urgently in recent years.Electrochemical hydrogen-water conversion（H₂+O₂→H₂O）has always been a research hotspot in the field of sustainable energy technology,which mainly includes hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）in water electrolyzer,as well as oxygen reduction reaction（ORR）in hydrogen fuel cell.Their sluggish kinetics makes it important to develop corresponding high-efficient catalysts.At present,platinum（Pt）-based materials are the best electrocatalysts for HER and ORR,while Ru O₂ or Ir O₂ are the most excellent OER electrocatalysts.However,the scarcity and high cost of these precious metals have seriously hindered their large-scale use.Therefore,in order to realize large-scale commercialization of this energy conversion technology,it is urgent to develop low-cost,durable and efficient electrocatalysts.In recent years,two-dimensional（2D）metal chalcogenides have attracted great attention in the field of electrocatalysis due to their advantages of simple structure,easy access,easy preparation and low price.Based on density functional theory,this thesis takes a series of 2D metal chalcogenides as research objects to perform theoretical research on their structural stability,electrical conductivity and electrocatalytic performance.The main findings are as follows:1.Metal tellurides are expected to be the excellent candidate for high efficiency electrocatalysts,since they can exhibit some fascinating properties,such as high carrier mobility and stability.2D ternary telluride Ni₂Sb Te₂ monolayer is systematically studied in this thesis.It is found that Ni₂Sb Te₂ monolayer has excellent structural stability and electrical conductivity.In particular,due to the multi-component synergism,Ni₂Sb Te₂ monolayer can show good ORR catalytic performance,and the overpotential of the system is as low as 0.33 V,even lower than that of precious metal Pt.In addition,the adsorption capacity of the Ni₂Sb Te₂ monolayer surface for oxygen molecules can be effectively enhanced by doping with Fe or Co atoms.The Ni₂Sb Te₂ monolayers doped with Fe or Co atoms not only maintain their original excellent ORR catalytic activity but also improve selectivity toward the four-electron reduction pathway,effectively suppressing the formation of H₂O₂.2.Compared with Ni₂Sb Te₂,2D ternary telluride Ta Ir Te₄ is a typical topological material with robust topological surface states.In addition to multi-component synergism,it also has the characteristics of strong electron transmission ability and stable surface state,which is conducive to the rapid and stable occurrence of electrocatalytic reactions.There,we investigated the stability and the ORR catalytic performance of Ta Ir Te₄ monolayer with low Ir-loading.It is found that Ta Ir Te₄monolayer can be exfoliated from the bulk phase and is demonstrated to have high stablity and good conductivity.More intriguingly,the adsorbed O₂ molecules on the surface of Ta Ir Te₄ monolayer can be effectively activated and dissociated into two separated O*species through a very small energy barrier as 0.28 e V（even lower than Pt）.When the four-electron（4e）dissociation path of ORR occurs on the Ta Ir Te₄monolayer,a very small overpotential of 0.47 V can be observed,which can be even comparable to the Pt（111）surface.Besides,the 2D Ta Ir Te₄ monolayer can also exhibit high selectivity,and effectively inhibit the formation of by-product H₂O₂.The TI topological states can have an important effect on the excellent ORR catalytic activity of 2D Ta Ir Te₄ monolayer.Undoubtedly,the design of ORR electrocatalysts based on the fascinating topological materials can be a new and effective way to obtain low cost and high efficiency ORR electrocatalyst.3.Generally,Rh-based materials have strong corrosion resistance and good stability,and the research on this kind of materials will be beneficial to promote the practical application of related catalysts.Based on it,the structural stability,electrical conductivity and ORR electrocatalytic properties of three Rh Te monolayers with different configurations（i.e.,r-Rh Te,o-Rh Te and h-Rh Te）were systematically studied.It is revealed that the three Rh Te monolayers have high stability and intrinsic conductivity.Particularly,r-Rh Te monolayer is identified as having good ORR catalytic activity.Mechanism analysis shows that two adjacent positively charged Te atoms on the surface of r-Rh Te monolayer can provide an active site for oxygen adsorption and dissociation.It is confirmed that the ORR reaction occurs on the r-Rh Te monolayer surface along the dissociation pathway with the over-potential of 0.56 V.Moreover,the ORR catalytic activity of r-Rh Te monolayer could be effectively enhanced by the substitution of Cr,Mn and Fe,where very small over-potential was achieved（0.36 V,0.43 V and 0.48 V,respectively）,and even comparable to or lower than the state-of-the-art Pt（111）.Meanwhile,the formation of by-product H₂O₂ is effectively inhibited,exhibiting high selectivity for 4e pathway.4.In addition,the structure and electrocatalytic properties of a series of sulfides containing electron-deficient Ga atoms（i.e.,2D Ga S,Fe Ga₂S₄ and Ni Ga₂S₄ monolayers）are investigated in depth.The computed results reveal that the Ga S,Fe Ga₂S₄ and Ni Ga₂S₄ monolayers can be easily exfoliated from their bulks,which are dynamically,thermodynamically and mechanically stable.The HER and OER electrocatalytic performance can effectively improved through doping Si,Ge,Sn,P,As and Sb.For example,Ge-Ga S、Ge-Ni Ga₂S₄and Ge-Fe Ga₂S₄ can show high HER catalytic performance,while As-Ga S,Sn-Ni Ga₂S₄ and Sn-Fe Ga₂S₄ exhibit excellent OER catalytic performance,even equivalent to Ir O₂ and Ru O₂ systems.In particular,Sn-Ga S,Ge-Fe Ga₂S₄ and Ge-Ni Ga₂S₄ can simultaneously exhibit high-efficiency HER and OER catalytic performance to act as the excellent candidates for bifunctional electrocatalysts.In conclusion,2D metal chalcogenides with abundant sources and diverse properties have a wide application prospect in the field of electrocatalysis.Obviously,these studies based on 2D metal chalcogenide systems can provide excellent candidates for the design of low-cost and efficient ORR,OER and HER catalysts,and as well as provide new ideas and valuable theoretical guidance for the experimental synthesis of related catalysts.