Cao Yilin, Chen Zhao-Xu
Institute of Theoretical and Computational Chemistry, Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, PR China.
Phys Chem Chem Phys. 2007 Feb 14;9(6):739-46. doi: 10.1039/b610691a. Epub 2006 Dec 19.
To explore the effect of surface contaminants on water chemistry at metallic surfaces, adsorption and decomposition of water monomers on clean and X/Pd(111)(X = C, N and O) surfaces are investigated based on density functional theory calculations. It is revealed that H(2)O binds to Pd(111) surface primarily through the mixing of its 1b(1) with the Pd 4d(z(2)) state. A charge accumulation between the oxygen atom of water and the bound Pd atom is calculated, which is found to be relevant to the H(2)O-Pd interaction. Water adsorption results in a reduction of surface work function and the polarization of the X 2p states. The O-H bond scission of H(2)O on the clean Pd(111) is an energy unfavorable process. In the case of X-assisted O-H bond breaking on X/Pd(111) surfaces, however, the reaction barrier tends to be lower than that on the clean surface and decreases from C/Pd(111) to O/Pd(111). In particular, water decomposition is found to become feasible on O/Pd(111), in agreement with the experimental observations. The calculated barrier is demonstrated to be correlated linearly with the density of X 2p states at the Fermi level. A thorough energy analysis demonstrates that the following geometrical and electronic factors favor the barrier reduction on X/Pd(111) with respect to water decomposition on clean Pd(111): (i) the less deformed structure of water in TS; (ii) the decreased bonding competition between the fragments OH and H. The remarkable decrease of the barrier on O/Pd(111) is revealed to be due to the largest stabilization of the split H atom and the least deformation of water in the TS.
为了探究表面污染物对金属表面水化学的影响，基于密度泛函理论计算，研究了水单体在清洁的和X/Pd(111)(X = C、N和O)表面上的吸附和分解。结果表明，H₂O主要通过其1b₁与Pd 4d(z²)态的混合与Pd(111)表面结合。计算得出水的氧原子与结合的Pd原子之间存在电荷积累，发现这与H₂O-Pd相互作用有关。水的吸附导致表面功函数降低以及X 2p态的极化。H₂O在清洁的Pd(111)上的O-H键断裂是一个能量不利的过程。然而，在X/Pd(111)表面上X辅助的O-H键断裂的情况下，反应势垒往往低于清洁表面上的反应势垒，并且从C/Pd(111)到O/Pd(111)逐渐降低。特别地，发现水在O/Pd(111)上的分解变得可行，这与实验观察结果一致。计算得出的势垒与费米能级处X 2p态的密度呈线性相关。全面的能量分析表明，以下几何和电子因素有利于相对于清洁Pd(111)表面上的水分解降低X/Pd(111)表面上的势垒：(i)过渡态中水分子结构变形较小；(ii)片段OH和H之间的键合竞争减弱。O/Pd(111)表面上势垒的显著降低被发现是由于分裂的H原子的最大稳定性和过渡态中水分子的最小变形。
