High Coverage Water Aggregation and Dissociation on Fe(100): A Computational Analysis

详细信息    查看全文

• 作者：Shaoli Liu ; Xinxin Tian ; Tao Wang ; Xiaodong Wen ; Yong-Wang Li ; Jianguo Wang ; Haijun Jiao
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：November 13, 2014
• 年：2014
• 卷：118
• 期：45
• 页码：26139-26154
• 全文大小：926K
• ISSN：1932-7455

文摘

Water adsorption and dissociation on the Fe(100) surface at different coverages have been calculated using density functional theory methods and ab initio thermodynamics. For the adsorption of (H₂O)_n clusters on the (3 脳 4) Fe(100) surface, the adsorption energy is contributed by direct H₂O鈥揊e interaction and hydrogen bonding. For n = 1鈥?, direct H₂O鈥揊e interaction is dominant, and hydrogen bonding becomes more important for n = 4鈥?. For n = 6鈥? and 12, structurally different adsorption configurations have very close energies. Monomeric H₂O dissociation is more favored on the clean Fe(100) surface than that on H₂O or OH precovered surfaces. O-assisted H₂O dissociation is favorable kinetically (O + H₂O = 2OH), and further OH dissociation is roughly thermo-neutral. With the increase of surface O coverage (nO, n = 2鈥?), further H₂O dissociation has similar potential energy surfaces, and H₂ formation from surface adsorbed H atoms becomes easy, while the desorption energy is close to zero for n = 7. The calculated thermal desorption temperatures of H₂O and H₂ on clean surface agree well with the available experiment data. The characteristic desorption temperatures of H₂O and H₂ coincided at 310 K are controlled by the kinetics of disproportionation (2OH 鈫?O + H₂O) and dissociation (2OH 鈫?2O + H₂) of surface OH groups. The dispersion corrections (PBE-D2) overestimate slightly the adsorption energies and temperatures of H₂O and H₂ on iron surface. At 0.5 ML coverage (6 脳 OH), the adsorbed OH groups at the bridge sites do not share surface iron atoms and form two well-ordered parallel lines, and each OH group acting as donor and acceptor forms hydrogen bonding with the adjacent OH groups, in agreement with the experimentally observed surface structures. At 1 ML coverage of OH (12 脳 OH) and O (12 脳 O), the adsorbed OH groups at the bridge sites share surface iron atoms and form four well-ordered parallel lines; and the adsorbed O atoms are located at the hollow sites. Energetic analysis reveals that 1 ML OH coverage is accessible both kinetically and thermodynamically, while the formation of 1 ML O coverage is hindered kinetically since the OH dissociation barrier increases strongly with the increase of O pro-covered coverage. All these results provide insights into water-involved reactions catalyzed by iron and broaden our fundamental understanding into water interaction with metal surfaces.