| Solid oxide fuel cells(SOFCs)are expected to be a key technology in future power sources.Compared with other kinds of fuel cells technology and transformation devices,SOFCs obtain many desirable advantages,such as the use of solid electrolytes,the lack of moving parts,ability to circumvent precious metal use,high efficiency,environmental-friendly and fuel flexibility.However,a major shortcoming in the practical application of SOFC is easily poisoned by compounds presenting in the feed stream which dissociate and contain H2 S gas,and then decompose into sulfur atom.The strongly adsorbed sulfur atom hinder the active sites and leading to the sulfur poisoning of catalyst's anode,what is more,influencing the long-term stability and activity of the catalyst's anode.The unfavorable deactivation of catalyst becomes the main obstacle with respect to the commercialization of SOFC.The effects of Ni-based dope with IB group dopants on the S poisoning characteristics are analyzed by the means of the first-principles approaches based on the density functional theory(DFT)and the ab initio atomistic thermodynamics method combining the electronic structure results with the thermodynamics data(considering the influence of temperature and the partial pressure).In addition,the effects of electric field on the sulfur poisoning properties are studied for the Ni/Cu system with different Cu concentrations.The goals of these investigations are to find the mechanisms of alloying Ni with ?B group elements in enhancing the sulfur-tolerance ability and search for an optimal catalyst to decline sulfur poisoning.The work performed and results reached are shown below:1.The poisoning effects of S atom on the(1 0 0),(1 1 0)and(1 1 1)metal surfaces of pure Ni and Ni-based doped with IB(coinage)metals(Cu,Ag,Au)are systematically studied.It is found that introducing IB doping metals into Ni surface can keep the d-band center from the Fermi level and weaken the adsorption of S on the(1 0 0)and(1 1 0)surfaces,and the S tolerance ability increases in the order of Ni,Cu/Ni,Ag/Ni and Au/Ni.However,on the(1 1 1)surface,the S tolerance ability increases in the order of Ag/Ni(or Cu/Ni),Ni,and Au/Ni.With increasing the coverage of the IB metal dopants,it is obviously that not only Au,but Cu and Ag can increase its S tolerance.We therefore propose that alloying Ni with IB metals can increase its S tolerance and the Au dopant has more pronounced effects in enhancing the resistance to sulfur poisoning of the Ni anode as compared with the pure Ni and the Ag-or,Cu-doped Ni materials.2.The effects of sulfur poisoning on the(1 0 0),(1 1 0)and(1 1 1)surfaces of pure Ni and Cu/Ni alloy are studied in consideration of the effect of electric field and the Cu concentration.For pure Ni,the(1 1 1)surface is more resistance to sulfur,while the(1 0 0)surface forms the most stable S adsorption.When the Cu concentration increase to 50% on the surface Ni layer,the(1 1 0)surface becomes the most vulnerable surface to the sulfur poisoning.And the Ni surface with a copper skin has the strongest sulfur tolerance ability as compared with the pure Ni and Cu/Ni surface with lower concentration of Cu dopants.Beside,under the electric field of 1.0 V/?,the sulfur adsorption and phase transition temperature can be further declined.Therefore,we can assert that a copper skin can improve the anti-sulfur poison of the Ni anode under high electric field. |
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