State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
Langmuir. 2013 Jun 11;29(23):7025-37. doi: 10.1021/la4014812. Epub 2013 May 28.
Water adsorption and decomposition on stoichiometrically perfect and oxygen vacancy containing ZnGa2O4 (100), (110), and (111) surfaces were investigated through periodic density functional theory (DFT) calculations. The results demonstrated that water adsorption and decomposition are surface-structure-sensitive processes. On a stoichiometrically perfect surface, the most stable molecular adsorption that could take place involved the generation of hydrogen bonds. For dissociative adsorption, the adsorption energy of the (111) surface was more than 4 times the energies of the other two surfaces, indicating it to be the best surface for water decomposition. A detailed comparison of these three surfaces showed that the primary reason for this observation was the special electronic state of the (111) surface. When water dissociated on the (111) surface, the special Ga3c-4s and 4p hybridization states at the Fermi level had an obvious downshift to the lower energies. This large energy gain greatly promoted the dissociation of water. Because the generation of O(3c) vacancy defects on the (100) and (110) surfaces could increase the stability of the dissociative adsorption states with few changes to the energy barrier, this type of defect would make the decomposition of water molecules more favorable. However, for the (111) surface, the generation of vacancy defects could decrease the stability of the dissociative adsorption states and significantly increase their energy barriers. Therefore, the decomposition of water molecules on the oxygen vacancy defective (111) surface would be less favorable than the perfect (111) surface. These findings on the decomposition of H2O on the ZnGa2O4 surfaces can be used toward the synthesis of water-splitting catalysts.
通过周期性密度泛函理论（DFT）计算，研究了化学计量完美和含氧空位的 ZnGa2O4（100）、（110）和（111）表面上水的吸附和解吸。结果表明，水的吸附和解吸是表面结构敏感的过程。在化学计量完美的表面上，最稳定的分子吸附涉及氢键的生成。对于离解吸附，（111）表面的吸附能超过其他两个表面的吸附能的 4 倍，表明它是水分解的最佳表面。对这三个表面的详细比较表明，观察到的这种情况的主要原因是（111）表面的特殊电子态。当水在（111）表面分解时，费米能级处的特殊 Ga3c-4s 和 4p 杂化态明显向下移动到较低的能量。这种大的能量增益极大地促进了水的解离。由于在（100）和（110）表面上生成 O(3c)空位缺陷可以在能量势垒变化不大的情况下增加离解吸附态的稳定性，这种缺陷会使水分子的分解更有利。然而，对于（111）表面，空位缺陷的生成会降低离解吸附态的稳定性并显著增加其能量势垒。因此，水分子在含氧空位缺陷的（111）表面上的分解不如完美（111）表面有利。这些关于 ZnGa2O4 表面上水分解的发现可用于水分解催化剂的合成。
