Water-hydroxyl phases on an open metal surface: breaking the ice rules
Water-hydroxyl phases on an open metal surface: breaking the ice rules
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DOI：
10.1039/c1sc00355k
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发表时间：
2012-01-01
期刊：
影响因子：
8.4
通讯作者：
Hodgson, Andrew
中科院分区：
文献类型：
--
作者：
Forster, Matthew;Raval, Rasmita;Hodgson, Andrew
羟基是许多表面催化氧化还原反应中的关键反应中间体，然而建立水/羟基在金属表面上吸附的相图仍然是界面化学的一个相当大的挑战。虽然在紧密堆积的金属表面上形成的结构已被广泛讨论，但反应性更强的开放金属表面上的相图很复杂，并且氢键结构在很大程度上尚不清楚。基于扫描隧道显微镜和密度泛函理论计算，我们报道了水/羟基在Cu（110）上的相图，对形成的复杂氢键结构提供了完整的分子描述。随着温度的降低和水/羟基比的增加，观察到三种不同的相：纯OH二聚体，延长的1H（2）O：1 OH链，沿着紧密堆积的Cu行排列，最后是扭曲的二维六方c（2 x 2）2 H（2）O：1 OH网络。这些相都不遵守常规的“冰规则”，相反，它们的结构可以基于羟基的弱H捐赠来理解，这有利于由水捐赠到羟基和羟基吸附位点之间的竞争主导的H键合结构。羟基在1D链结构中的Cu桥位点中结合，但在2D网络中被置换到顶部位点，以便以其优选的顶部结合几何形状容纳水。因此，可以简单地通过改变表面温度和水含量来调节羟基的吸附位点和稳定性，从而对开放金属模板如何影响形成的水/羟基结构和羟基的活性提供了新的见解。
Hydroxyl is a key reaction intermediate in many surface catalyzed redox reactions, yet establishing the phase diagram for water/hydroxyl adsorption on metal surfaces remains a considerable challenge for interfacial chemistry. While the structures formed on close packed metal surfaces have been discussed widely, the phase diagram on more reactive, open metal surfaces, is complex and the H-bonding structures are largely unknown. Based on scanning tunnelling microscopy and density functional theory calculations, we report the phase diagram for water/hydroxyl on Cu(110), providing a complete molecular description of the complex hydrogen bonding structures formed. Three distinct phases are observed as the temperature is decreased and the water/hydroxyl ratio increased: pure OH dimers, extended 1H(2)O:1OH chains, aligned along the close-packed Cu rows, and finally a distorted 2D hexagonal c(2 x 2) 2H(2)O:1OH network. None of these phases obey the conventional `ice rules', instead their structures can be understood based on weak H donation by hydroxyl, which favours H-bonding structures dominated by water donation to hydroxyl, and competition between hydroxyl adsorption sites. Hydroxyl binds in the Cu bridge site in the 1D chain structures, but is displaced to the atop site in the 2D network in order to accommodate water in its preferred atop binding geometry. The adsorption site and stability of hydroxyl can therefore be tuned simply by changing the surface temperature and water content, giving a new insight as to how the open metal template influences the water/hydroxyl structures formed and the activity of hydroxyl.