Competitive Anion/Water and Cation/Water Interactions at Electrified Copper/Electrolyte Interfaces Probed by in Situ X-ray Diffraction
Competitive Anion/Water and Cation/Water Interactions at Electrified Copper/Electrolyte Interfaces Probed by in Situ X-ray Diffraction
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DOI：
10.1021/jp301709z
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发表时间：
2012-05-24
影响因子：
3.7
通讯作者：
Broekmann, Peter
中科院分区：
文献类型：
--
作者：
Keller, Hubert;Saracino, Martino;Broekmann, Peter
采用原位表面x射线衍射（SXRD）方法研究了铜/电解质界面的完整三维结构。在10 mM HCI中，氯离子在高电位下化学吸附在Cu（100）上，形成p(1 X 1)-Cl层：这种阴离子化学吸附层作为近表面液体电解质中水分子和水合氢离子横向有序的结构模板。这种界面几何结构的证据主要来自于沿（10L）层棒的表面敏感x射线衍射数据的强度分布。沿（10L）棒的特征振荡强度分布是由化学吸附氯离子的阴离子内亥姆霍兹层（IHL）和阳离子外亥姆霍兹层（OHL）组成的中心双层体系造成的。后者在本案例中由优先填充其下氯晶格的4倍中空位点的水合氢离子构成。IHL和OHL被一个额外的界面水层隔开。IHL和OHL中的阴离子和阳离子争夺这些水种，作为其溶剂化壳的一部分。氯/水/水合氢离子双分子层可以被认为是一个典型的模型系统，其中阴离子和阳离子在耦合双分子层系统中共享界面水作为其溶剂化壳的一部分。在这方面，Cl-/水/水合氢离子双分子层与先前研究的Cl-/水/K+体系有很大的不同，在前者中，界面水被明确地分配到OHL中碱金属阳离子的溶剂化壳层。在OHL中缺乏强溶剂化的碱金属阳离子导致水和水合氢离子的面内和面外交换动力学增加，这表现在各向同性的原子位移参数中，Cl-/水/水合氢离子的原子位移参数明显高于Cl-/水/K+体系。将我们的研究结果与其他最先进的SXRD研究结果进行全面比较，强烈表明部分溶剂化阳离子在阴离子修饰的金属电极表面上的吸附必须被认为是一种特定的阳离子吸附现象，因为形成的双层体系的特定结构以及所涉及的界面动力学显然取决于结构形成中阴离子和阳离子的化学性质。
The full 3D structure of a copper/electrolyte interface is studied by means of in situ surface X-ray diffraction (SXRD) methods. Chloride anions chemisorb on Cu(100) in 10 mM HCI at high potentials under formation of a p(1 X 1)-Cl adlayer: This anionic chemisorption layer serves as a structural template for the lateral ordering of water molecules and hydronium cations in the near-surface liquid electrolyte. Evidence for this interfacial geometry is mainly derived from the intensity distribution of surface-sensitive X-ray diffraction data along the (10L)-adlayer rod. The characteristic oscillating intensity distribution along the (10L) rod is due to a centered bilayer system consisting of the anionic inner Helmholtz layer (IHL) of chemisorbed chloride and the cationic outer Helmholtz layer (OHL). The latter is constituted in the present case by hydronium cations that preferentially populate 4-fold hollow sites of the underlying chloride lattice. IHL and OHL are separated by an extra interfacial water layer. Anions and cations in the IHL and OHL compete for these water species as part of their solvation shell. The Cl/water/hydronium bilayer can be considered as a prototypical model system where the anions and cations in the coupled bilayer system are sharing the interfacial water as part of their solvation shell. In this respect, the Cl-/water/hydronium bilayer considerably differs from the previously studied Cl-/water/K+ system where the interfacial water was clearly assigned to the solvation shell of the alkali metal cation in the OHL. The absence of strongly solvated alkali metal cations in the OHL leads to an increase in the in-plane and out-of-plane exchange dynamics of water and hydronium cations as manifested by an isotropic atomic displacement parameter that is notably higher for the Cl-/water/hydronium than for the more static Cl-/water/K+ system. A comprehensive comparison of our results with other state-of-the-art SXRD studies strongly suggests that the adsorption of partly solvated cations on-top of an anion-modified metal electrode surface has to be considered as a specific cation adsorption phenomenon since the particular structure of the formed bilayer system as well as the involved interfacial dynamics clearly depend on the chemical nature of the anions and cations involved in the structure formation.