Density Functional Theory Study for Ni Diffusion on Ni(111) Surface under Solid Oxide Fuel Cell Operating Condition

Understanding the sintering mechanism of Ni in a solid oxide fuel cell (SOFC) anode is one of the important issues to discuss the long-term durability of SOFC performance. The sintering behavior of Ni is affected not only by the operating temperature but also by the gas composition in the anode chamber. We analyzed the surface diffusion of a Ni adatom and Ni complexes on the Ni(111) surface under the operating temperature and gas compositions in the anode by using density functional theory. The Ni adatom, Ni-H and Ni-S complexes, which can be formed by H₂ and H₂S in anode gas, were considered as diffusion species on the Ni surface. It is theoretically confirmed that the formation of a NiS complex influences the sintering behavior of Ni depending on the temperature and the impurity H₂S concentration in the fuel. Our calculated results are compared with the experimental observation on Ni sintering under various temperatures and H₂S concentrations to find a good agreement. We clearly showed the important effect of gas composition in the anode on the sintering properties of Ni in the SOFC anode.