Ab initio analysis of sulfur tolerance of Ni, Cu, and Ni-Cu alloys for solid oxide fuel cells

Interactions between sulfur and Ni1-xCux (x = 0.00, 0.25, 0.50, 0.75, and 1.00) were examined by a first-principles analysis based on density functional theory (DFT) calculations to provide a scientific basis for intelligent design of sulfur-tolerant anode materials for solid oxide fuel cells (SOFCs). Examination of slab models with three and five atomic layers for Ni and Cu (111) surfaces indicates that sulfur species may adsorb on four types of sites: atop, bridge, hcp hollow, and fcc hollow, among which the fcc-hollow centers are the most energetically favorable. The adsorption energy of sulfur on Ni is approximately 20% higher than that on Cu for both unrelaxed and relaxed five-layer surface models, which is qualitatively in good agreement with experimental observations. Using two active sites at three-fold hollow sites, the adsorption energy for sulfur on Ni1-xCux is predicted as a function of the alloy composition. Alloying Ni with Cu improves sulfur tolerance, however not to the degree of pure Cu. (c) 2006 Published by Elsevier.