利用纳米合金中低配位原子活性设计高效水催化剂的第一性原理研究

Based on the energy shortage and heavy haze in China, the interaction of sunlight with metal nanoparticles deposited TiO2 to split water and produce hydrogen is a subject of great significance and challenge, in which one of the key steps is to find the efficient metal catalyst. In the reaction of ammonia synthesis by photocatalysis, Ranjit et al. found that the ammonia yield depended on the bond strength between the deposited metal and the hydrogen atom, suggesting that we can ignore the role of TiO2. We can deposit the metals (with strong interaction with water by calculations) on TiO2, and then test whether the efficient hydrogen production correspondent to strong interaction between metal and water, which can enhance the research efficiency. In our previous studies, the applicant found that water can be split on ruthenium clusters, and the active center usually located around the atoms with low coordinated atoms. In view of the superior of the alloy synergetic catalysis and the stronger activation of the atoms with low coordinated degree, this subject adopts first-principles calculations to study three aspects: first, analyzing the relationship between the stabilities and the alloy compound and finding the stable nanoalloy structure with low coordinated atoms; second, the modulation mechanism of the low coordinated atoms on the enhanced adsorption and reaction barrier of nanoalloy to split water; third, based on the theory of the first two steps, predicting the compounds and the geometric structures of the other nanoalloy catalyst that can efficiently split water, and calculating the water splitting barrier to verify it. This subject may contribute theoretical support to design efficient catalyst for water splitting.

在我国能源短缺和雾霾严重的背景下，太阳能作用在金属颗粒沉积的TiO2上分解水制取氢气的课题有重要意义且极具挑战，其中关键一环是找到高效金属催化剂。Ranjit等人在光催化合成氨中发现氨气产率取决于在TiO2上沉积的金属与氢原子成键强弱，启发我们可以抛开衬底作用，先找到与水分子作用较强的金属，再将其沉积到TiO2上来验证高产氢效率是否对应金属和水的强相互作用，从而提高研发效率。前期研究中，申请人发现水分子可在钌团簇上分解，团簇的活性中心往往在配位数少的原子附近。鉴于纳米合金催化性能优越及低配位原子活性较强，本项目采用第一性原理计算方法，研究3个问题。包括：1）分析团簇稳定性与合金成分的关系，找到具有低配位数原子的稳定纳米合金结构；2）低配位原子对水吸附和分解作用增强的物理机制；3）预测高效分解水的纳米合金的成分和结构，计算水分解势垒验证之。本项目有望为设计高效水催化剂提供理论支持。

在我国能源短缺和雾霾严重的背景下，太阳能作用在金属颗粒沉积的TiO2上分解水制取氢气的课题有重要意义且极具挑战，其中关键一环是找到高效金属催化剂。我们用第一性原理以及高斯计算了水分子在Run (n = 2−14)团簇上吸附的能量以及动力学性质。研究发现了团簇比Ru块体吸附和分解水的性能更好，由于其分解势垒小于吸附能。我们解释了显著的奇偶震荡可以通过几何效应解释，低配位的原子贡献了最低未占据轨道，可以俘获水分子的孤对电子。我们进一步研究了研究合金效应对PtRun-1 (n=2-14) 和H2O-PtRun-1(n=2-14)体系的几何构型、稳定性及吸附水特性的影响。 结果表明：铂原子替代钌原子的能量较低，容易与钌团簇形成合金，铂原子喜欢占据配位数较低位置。 相对于纯钌团簇，合金效应很大程度上提高了水分子在PtRun团簇上的吸附能。 考虑范德瓦尔斯力后，水分子在PtRu7 上的吸附能增大，分解势垒降低，水分子可以在PtRu7 上分解。 铂钌合金也适合做分解水制取氢气的催化剂。研究结果为研究分解水分子的高效催化剂提供了新思路。