氢和硫原子在Pd、Au和Cu及PdAu、PdCu合金(111)表面吸附的密度泛函研究

用密度泛函理论研究了氢和硫原子在金属Pd、Au、Cu以及合金PdM3、Pd2M2 和Pd3M(111)表面的吸附(M=Au, Cu), 得到了覆盖率为0.25时最稳定的吸附位、结合能以及吸附前后表面的驰豫情况. 结果表明, 氢和硫均与Pd形成最稳定的吸附, Cu次之, Au的吸附最弱, 其在三种纯金属(111)表面的最稳定吸附位均为fcc位. 由于PdAu合金具有较大的晶格常数, Pd3Au 合金吸附氢的结合能甚至较纯Pd更大, 除此之外, 氢和硫在PdM合金表面的吸附基本随M组分的增加而减弱, 而最稳定的吸附位随金属种类和组成变化而变化. 根据计算得到的吸附结合能, 发现与PdCu合金相比, PdAu合金在Au含量较低(约25%, 摩尔分数)时, 氢和硫吸附的结合能下降较慢, 而Au含量较高(跃50%)时, 结合能迅速下降, 这表明含金量为25%-50%的PdAu合金有可能在保持相近透氢性能的同时, 比PdCu合金具有更好的抗硫毒性.

DFT Study on Hydrogen and Sulfur Adsorption on (111) Surface of Pd, Cu, Au, and PdAu, PdCu Alloys

The gradient corrected density functional theory (DFT) calculations were presented on the adsorption of both hydrogen and sulfur on pure Pd(111), Cu(111) and Au(111) surfaces, as well as on PdM3(111), Pd2M2(111), and Pd3M(111) surfaces. The most favorable adsorption sites, binding energies and the relaxation during adsorption were obtained with a coverage of 0.25. The Pd surface exhibited the strongest adsorption of both hydrogen and sulfur atoms. Cu was the next and Au had the weakest affinity with them. The binding energies of adsorption of hydrogen and sulfur on PdM alloys decreased with the increase of the concentration of metal M, except Pd3Au, in which case, the adsorption of hydrogen on Pd3Au (111) surface was even stronger than that on pure Pd, due to the larger lattice constant. According to the values of binding energy, it was found that the binding energies of both hydrogen and sulfur on PdAu decreased slower than that on PdCu, when the concentration of Au was lower than 25% (molar fraction). However, they decreased quickly when the concentration of Au exceeded 50%. PdAu alloy with 25%-50% Au was a promising candidate to resist sulfur and also with high performance in hydrogen permeation.