Microcalorimetric investigations of anion and cation adsorption at well-ordered Au and Pt surfaces - On the influence of hydration and solvent structure on the entropy of formation of the electrochemical double layer

电化学反应强烈地依赖于电化学双层的结构和组成。然而，诸如吸附离子的表面过量浓度、它们的水合作用或溶剂结构等细节很难获得，而且只有少数体系知道这些信息。我们计划测量双层充电时的热量作为电势的函数。由此我们确定了充电过程的反应熵。与电荷平衡一起，我们获得了离子的信息，这些离子参与了充电过程，它们的水合作用，它们的表面过量浓度和伴随的溶剂水的重组。在项目的前一阶段，我们展示了Ag和Cu在Au（111）上的欠电位沉积，我们可以测量沉积过程的反应熵，依赖于电位，平行于电化学系统的电流-电位关系。由此我们确定了电化学诱导的吸附过程。我们用新开发的量热计达到的灵敏度足以检测双层充电时的热效应，即在没有电化学电荷转移反应的情况下。在新项目中，我们计划首先研究热对Au表面上特定和非特定离子吸附的影响。然后我们将测量OH-和h -吸附在Pt表面的熵作为电位的函数。我们将确定熵对这些层稳定化的贡献，并希望在界面处找到溶剂重组的线索。然后，我们研究了oh覆盖Pt电极上非共价结合阴离子的反应熵，并将我们的结果与Markovic等人针对这些系统提出的模型进行了比较。

Electrochemical reactions are strongly dependent on the structure and composition of the electrochemical double layer. However, details, e.g. on the surface excess concentration of the adsorbed ions, their hydration or on the solvent structure are difficult to obtain and such information known only for few systems. We plan to measure the heat upon charging of the double layer as a function of the potential. From this we determine the reaction entropy of the charging process. Together with the charge balance, we obtain information on the ions, which are involved in the charging process, their hydration, their surface excess concentrations and accompanying restructuring of the solvent water. In the previous phase of the project we showed for Ag and Cu underpotential deposition on Au(111) that we can measure the reaction entropy of the deposition process dependent on the potential, in parallel to the current-potential-relation of the electrochemical system. From this we identified the electrochemically induced adsorption processes. The sensitivity we reached with the newly developed calorimeter is sufficient to detect heat effects upon double layer charging, that is, in the absence of electrochemical charge transfer reactions. In the new project, we plan first to investigate the heat effects upon specific and non-specific ion adsorption on Au surfaces. Then we will measure the entropy of OH- and H-adsorption on Pt surfaces as a function of the potential. We will determine the entropic contribution to the stabilization of these adlayers and hope to find hints on the restructuring of the solvent at the interface. We then study the reaction entropy of non-covalently bound anions on OH-covered Pt electrodes and compare our results with the model proposed by Markovic et al. for those systems.