DFT Study On Methane Dehydrogenation And Carbon Deposition Resistance On Cu/Ni-SOFC Anode Surfac

Solid oxide fuel cell（SOFC）has been widely concerned for its high efficiency,low emission and high fuel flexibility.At present,the problem of carbon deposition in nickel-based anode materials has been one of the key technologies to be solved urgently when using hydrocarbon fuel in solid oxide fuel cells（SOFC）,and doping other elements is one of the effective ways.In order to improve the performance of"carbon deposition resistance",Cu was doped on the surface of Ni-based catalyst and oxidized to form Cu O/Ni interface.The microscopic mechanism of methane dehydrogenation and carbon deposition on the surface/interface after doping was deeply studied and discussed,which provided relevant data support for solving the practical problem of carbon deposition in Ni-based anode materials.Starting from the surface with the lowest energy crystal plane on the Ni surface,a Ni（111）surface and five different Ni/Cu_x（111）surfaces with different Cu doping levels（x=1,4,5,8,9）were established.Using density functional theory（DFT）based on quantum chemistry,the adsorption energy,optimal adsorption site,kinetics,and reaction heat of important substances in methane,methane dissociation,carbon formation,and decarbonization processes were calculated and analyzed for each surface.Combined with literature reports,it was found that Cu would be partially oxidized into Cu O during the catalytic process,resulting in partial alloy de-alloying on the surface under the conditions of methane dehydrogenation and decarbonization pathways,forming a Cu O-loaded Ni（111）（Cu O/Ni（111））interface.Therefore,a Cu O/Ni（111）interface model was established,and the effect of Coulomb force on the model was optimized by the DFT+U method.Furthermore,the removal of surface carbon and the activity of sequential methane dehydrogenation reactions on the interface were further explored.The calculation results showed that:（1）Cu doping Ni base surface significantly reduced the adsorption capacity of pure Ni base surface to each species;（2）On all surfaces,the dissociation of CH to C and H is a rate-control step in the process of methane dehydrogenation;（3）Compared with pure Ni（111）surface,except Ni/Cu₈（111）surface,the introduction of Cu into Ni surface increases the energy barrier during the whole process of methane dissociation,weakens the catalytic activity of Ni catalyst to a certain extent,and inhibits the direct deposition of coke on the surface.（4）The oxidation and hydroxylation of CH molecules should be given priority in the carbon removal pathway on the surface of Cu/Ni bimetallic catalysts,while the direct formation of C should be avoided.（5）The formation of Cu O changes the rate control step of methane dehydrogenation on Ni-based surface,which becomes the conversion process from CH₄to CH₃+H.（6）The production of Cu O will further reduce the catalytic activity of sequential dehydrogenation of methane and increase the energy barrier of each reaction;（7）The best carbon deposition resistance pathway at the Cu O/Ni（111）interface is CH+OH→CHOH,the rate-limiting energy barrier is 1.26e V,and the reaction heat is-1.66e V.In summary,all the results indicate that the introduction of Cu atoms to the surface of the Ni-based catalyst will sacrifice the surface dehydrogenation of methane,but significantly improve the coke resistance of the catalyst.