Electrocatalysis and transport in nanoporous gold

在这个子项目中，我们将研究纳米多孔金的形态和表面组成如何影响电催化反应和内部质量传递条件。在执行潜在程序或在高温下储存期间，纳米多孔金的韧带变粗。在使用过程中，这改变了质量运输条件和可用表面积。粗化过程的时间过程受纳米孔材料表面吸附物的影响。这类添加剂对材料的催化活性有影响。在这个子项目中，我们研究了在电化学电位程序和温度等不同实验条件下粗化过程的时间过程。重点研究了利用电化学方法测定纳米孔金的内表面积和有效扩散系数。这些方法适用于不从电化学电池中取出样品的情况。结果将与使用扫描电子显微镜的选定测量相关联。此外，我们还研究了特殊吸附阴离子的加入和通过欠电位沉积形成的外来金属单层如何改变粗化过程的动力学。在第二种方法中，我们使用扫描电化学显微镜的表面询问模式和互补的非原位光谱技术（主要是x射线光电子能谱（XPS））研究表面氧化物和表面结合反应中间体的数量。然后，我们将研究通过欠电位沉积获得的单层外来金属如何改变表面氧化物和反应中间体的数量，作为施加电位的函数。在此基础上，我们希望设计出有效修饰纳米多孔金作为甲醇氧化反应电催化剂的方法，该反应已被选为模型反应。将电催化实验结果与甲醇在液相和气相中被分子氧氧化的结果进行比较。

In this sub-project we will investigate how morphology and surface composition of nanoporous gold influences electrocatalytic reactions and internal mass transport conditions. During the execution of potential programme or during storage at elevated temperatures the ligaments of nanoporous gold coarsen. This changes mass transport condition and available surface area during the use. The time course of the coarsening process can be influenced by adsorbates at the surface of the nanoporous material. Such adlayers have an influence on the catalytic activity of the material.In this sub-project we investigate which time course the coarsening process flows under different experimental conditions such as electrochemical potential programs and temperature. We focus on the electrochemical methods to determine the internal surface area and the effective diffusion coefficient inside the nanoporous gold. These methods are applicable without removal of the sample from the electrochemical cell. The results will be correlated to selected measurements using scanning electron microscopy. Furthermore, we investigate how the addition of specifically adsorbing anions and the formation of monolayers of foreign metals by under-potential deposition will change the kinetics of the coarsening process.In a second approach we study the amount of surface oxides and surface-bound reaction intermediates using the surface interrogation mode of scanning electrochemical microscopy and complementary ex-situ spectroscopic techniques, mainly x-ray photoelectron spectroscopy (XPS). We will then study, how monolayer of foreign metal obtained by under-potential deposition will change the amount of surface oxides and reaction intermediates as a function of applied potential.From the thus obtained insights we would like to devise ways for effective modification of nanoporous gold as electrocatalyst for methanol oxidation reaction that has been selected as the model reaction. The results of the electrocatalytic experiments will be compared to the oxidation of methanol by molecular oxygen in liquid phase and in gas phase.