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

电化学反应强烈依赖于电化学双电层的结构和组成。然而，细节，例如，在表面上的吸附离子的过量浓度，它们的水合作用或溶剂结构是难以获得的，这样的信息只为少数系统所知。我们计划测量双电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，我们获得了有关离子的信息，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，我们表明，对于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，其取决于电位，与电化学系统的电流-电位关系平行。由此，我们确定了电化学诱导的吸附过程。我们达到的灵敏度与新开发的量热计是足以检测热效应后，双层充电，也就是说，在没有电化学电荷转移反应。在这个新的计画中，我们计划首先研究热效应对特定与非特异性离子在Au表面吸附的影响。然后，我们将测量Pt表面上OH-和H-吸附的熵作为电势的函数。我们将确定这些吸附层的稳定的熵的贡献，并希望找到线索的重组的溶剂在界面上。然后，我们研究了非共价键合的阴离子OH覆盖的Pt电极上的反应熵，并将我们的结果与Markovic等人提出的模型进行比较。

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.