Constructing Models For The Surface Stability And Adsorption Of Metallics

Metallics,including metals and alloys such as transition metals(TMs),singleatom alloys(SAAs),binary alloys(BAs),near-surface alloys(NSAs),and high-entropy alloys(HEAs),are widely applicable to heterogeneous catalysis,energy storage,gas sensors,molecular electronics,biomedicine,corrosion-resistance engineering,and so on.Generally,surface stability(determined by surface energy and ejection energy)and surface adsorption(determined by adsorption energy)together control the practical application of metallics.Therefore,the identification of determinants of surface stability and adsorption and the further development of effective prediction models are crucial for designing advanced metallics.However,the diverse composition and possible chemical disorder of metallics particularly alloys generate great challenges to understanding their surface properties.Therefore,the current studies of surface stability and adsorption mainly focus on TMs,nanoparticles,and partial simple-alloy systems but not on complex alloys.Moreover,the models on simple metallics are still limited by the low prediction accuracy,ambiguous physical picture,and hardly-determined parameters,prohibiting the prediction of surface stability and adsorption and the establishment of the correlation between these two properties.In this thesis,based on the intrinsic properties of materials,the surface stability and adsorption of metallics have been systematically studied and the models of surface energy,ejection energy,and adsorption energy in dissolution are established.The detailed contents are as follows:Firstly,based on the scheme of bond breaking,we propose the intrinsic model of surface energy(corresponding to the average surface stability).This model demonstrates that the surface energy is determined by the period number and group number of bulk atoms and the valence-electron number,electronegativity and coordination number of surface atoms,which is predictive for various systems covering elemental crystals in both solid and liquid phases,intermetallics,Mg-based SAAs,IIIV semiconductor compounds,transition-metal carbides,and transitional-metal nitrides.We find that the material-dependent property of surface energy is mainly governed by the electronic properties of bulk and surface atoms,while the electronic and geometric characteristics together control the anisotropy of surface energy.Furthermore,our model establishes a quantitative relationship between surface energy and adsorption energy and reveals the origin of the material-dependent error of first-principles methods in calculating surface energy and adsorption energy.Secondly,we study the determinants of ejection energy of surface atoms,corresponding to the surface-site stability of metallics.By introducing the electronic and geometric gradients of surface sites to characterize the alloying and dissolution effects,a predictive model has been built to quantitatively determine the ejection energy of TMs,SAAs,BAs,NSAs,and HEAs.Our model uncovers the electronic and geometric determinants of the surface-site stability,indicating that the ejection-energy trends of surface atoms are mainly determined by the bond-breaking effect(corresponding to the coupling between the cohesive energy and the geometric gradient)and alloying effect(corresponding to the electronic gradient).The former plays a consistent and dominant role in determining the ejection energy of different TMs and alloys,while the latter becomes increasingly important as the alloying proceeds.This model reveals the differences and connections between the bonding characteristics of different alloys,rationalizes the physical origin of the good corrosion resistance of(100)terrace found by experiments,and helps design advanced alloys with optimal surface stability.Finally,we study the surface adsorption in dissolution,identifying that the cohesive properties of surface sites play an increasingly important role in determining the adsorption energy with the dissolution going on,while the alloying effects of adsorption energy can be quantified by the electronic gradient of active centers.Accordingly,the cohesive energy and electronic gradient of the surface sites have been proposed as powerful descriptors for understanding the surface adsorption and reaction of metallics and established a predictive model to determine the adsorption energy of TMs,NSAs,BAs,and HEAs in dissolution.This model unveils a novel physical picture of surface adsorption on TMs and alloys in dissolution,demonstrating that the d-band upper-edge gradient,d-band width,and s-band depth together control the trends of adsorption energy on alloys.Furthermore,this model can effectively capture the surface-active quantities including the reaction energy,activation energy,and catalytic activity,which is helpful for designing advanced alloy catalysts.Overall,this thesis has established effective descriptors and predictive models in determining the surface stability and adsorption of metallics.Our models reveal the novel physical picture of surface stability and adsorption and clarify the differences and connections between these two properties,which provide the theoretical foundation for developing advanced metallics.