Density Functional Theory Study Of The Adsorption And Dissociation Of H₂S On Cu （100） Surface

In the corrosive environment containing H2S, metals will be corroded in diversity offorms, which results in the equipment to rupture, leak and even explode. The corrosion bringslots of economic losses and lead to major accidents. However, the microscopic reactionprocess of H2S corrosion, and various of corrosion mechanisms need to be unraveled. Thetheoretical study of H2S molecules in the microscopic behavior on metal surface is of greatsignificance to explore the corrosion mechanism and reduce the corrosion phenomenon. Inthis thesis, using periodic density functional theory, the adsorption and dissociation of H2Smolecular on the Cu (100) surface were studied, and the influence of water solvent on theadsorption and dissociation of H2S was also explored. Including:Through the simulation and analysis of the adsorption of H2S, H/HS and H/H/S on theCu (100) surface, we found that H, S and HS tended to be adsorbed on the hollow site of thesurface, while H2S tended to be adsorbed on the top site of the surface. The electronatmosphere of S s, p orbital in adsorbates mixed with Cu d orbital, which formed the S-Cucovalent bond. The adsorption of H2S and HS could make the S-H bond activate. The order ofthe adsorption energy is H/H/S co-adsorption> H/HS co-adsorption> H2S adsorption,indicating that H2S adsorbed on the Cu (100) tended to dissociate.Two elementary reactions of H2S dissociation (H2Sâ†'H+HS and HS+Hâ†'S+2H)were studied by transition state theory. The results showed that the process of these twoelementary reactions were similar. H atom departed from S atom in the effect of Cu surface.The dissociation products were adsorbed on the Cu surface alone, lowering the total energy ofthe system. The barriers of the two elementary reactions were both very low, and the S atomadsorbed on the surface facilitated the further formation of corrosion products. What’s more,in the dissociation process, H-Cu bond receive the electrons released from the cleavage of H-S bond. And, the adsorption of decomposition product reduces the system energy, whichmade the reactions take place smoothly.On the basis of the above resluts, the influence of water solvent on the adsorption anddissociation of H2S was studied by the conductor-like screening model. The results showedthat the solvent effect could promote the adsorption of H2S and the products, and had slightinfluence on the structures. What’s more, the barriers and heat of the reactions was similar tothose in vacuum, so the Conductor-like Screening Model (COSMO) didn’t promote thedissociation of H2S. Then, the microscopic behaviors of H in water solvent on the surfacewere studied. The results showed that H could be adsorbed on and in Cu (100) because of thesmall radius. The migration of H was easy, creating conditions for the metal destruction byhydrogen molecules. The migration of H atom on and in Cu (100) was one of the reasons whythe water solvent promoted the corrosion.