Ni与钇稳定的氧化锆(111)表面相互作用以及界面活性的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 系统研究了Ni原子在钇稳定的氧化锆(YSZ)(111)和富氧的YSZ(YSZ+O)(111)表面不同位置的吸附, 以及CO和O₂分子在Ni₁(单个镍原子)/YSZ和Ni₁/YSZ+O表面吸附的几何与电子结构特征. 结果表明: 1) 单个Ni原子倾向于吸附在O原子周围, 几乎不吸附在Y原子周围, 且Ni原子在氧空位上吸附最稳定; 2)和YSZ相比, 单个Ni原子在YSZ+O表面易发生氧化现象, Ni原子失去1.06 e电子, 被氧化成了Ni⁺, 吸附能力更强; 3)被氧化的Ni催化活性大幅下降, 大大减弱了表面对O₂和CO等燃料气体的吸附作用.

The first-principles study on the interaction of Ni with the yttria-stabilized zirconia and the activity of the interface

Solid oxide fuel cell (SOFC) is expected to be a crucial technology in future power generation due to its advantages of high efficiency, fuel adaptability, all-solid state, modular assembly, and low pollution. The Ni/YSZ (yttrium-stabilized zirconia) cermet is the most popular anode material in SOFCs. However, a major problem is that it can be easily oxidized, thus resulting in the decline of long-term stability and activity as an anode catalyst. A better performance of the Ni/YSZ cermet can be obtained by improving its microstructure as well as the Ni distribution in it. Interactions between Ni and the yttria-stabilized zirconia (YSZ) (111) or oxygen-enriched YSZ(111) (YSZ+O) surface are studied in terms of the first-principles method based on the density functional theory with particular focus put on the activity of the Ni atom at the interface. The geometric and electronic structures of CO and O₂ on the Ni₁ (the single Ni atom)/YSZ and Ni₁/YSZ+O surfaces are also studied. It is found that the Ni atom tends to be adsorbed to O sites and away from the Y atoms on both the surfaces. The most favorable adsorption site is the oxygen vacancy, which has an adsorption energy of 2.85 eV. Compared with YSZ, the single Ni atom loses 1.06 electrons and is oxidized as Ni⁺ on YSZ+O, which produces a strong interaction between the Ni atom and YSZ+O. Strong adsorption is mainly attributed to the interaction between Ni 3d and O_u 2p orbitals. And the oxidation of Ni can lead to the decrease of electrocatalytic activity of the Ni catalyst. The d-band DOS (density of states) peaks of the Ni₁/YSZ+O are lower than that of the Ni₁/YSZ, and the corresponding d-band centers are shifted away from the Fermi level to lower energy with the ε_d value of -3.69 eV; therefore the CO and O₂ adsorption is weakened. While the adsorption energy for CO on the Ni₁/YSZ+O (0.42 eV) is much lower than that on the Ni₁/YSZ surface (1.78 eV). In addition, the adsorbed CO gains 0.07 electrons, less than those on the Ni₁/YSZ surface (0.34 e). The adsorption energy of O₂ on Ni₁/YSZ+O also decreases (0.34 eV) and gains fewer electrons (0.24 e) as compared with the corresponding values (2.57 eV, 1.15 eV) on Ni₁/YSZ. Results would improve our understanding on the mechanism of oxidation of Ni on the Ni/YSZ anode of SOFCs and would be of great importance for designing highly active catalysts used for fuel cells.