Towards the direct instrumental identification of active electrocatalytic sites using scanning tunneling microscopy

如果不开发新的信息丰富但同时又负担得起的研究工具、方法和程序，就不可能对复杂的自然物体有更深入的了解。探索和建模的原始而强大的方法很可能仍然是控制材料科学进步的支柱。在这个项目中，我们提出了一种利用电化学扫描隧道显微镜对多相电催化剂表面所谓的活性位点进行实验鉴定的方法。该项目利用的基本思想是，在反应条件下，与非活性位点相比，定义与液体电解质接触的催化活性位点上的隧道势垒的参数是不同的，重要的是，随着时间的推移（例如，由于接近反应物和/或离开产物）而变化。因此，在电位控制下，在尖端和样品之间测量的隧道电流也应该以不同的方式随时间变化，从而揭示局部过程。通过比较隧道电流作为时间的函数和不同表面位置的尖端到表面距离，有可能阐明催化中心的位置。我们的初步结果支持这一基本观点。具有准周期性表面结构和极低表面迁移率的低指数和高指数单晶电极、纳米结构系统以及对未来可持续能源供应重要的催化反应将分别用于该项目中作为模型对象和反应。量子化学计算将用于（合作）清楚地揭示该方法的潜在物理基础，以支持有关局部催化活性的实验数据的定量解释，并迭代改进该方法。

A deeper understanding of complex objects of nature is not achievable without the development of new informative but at the same time affordable research tools, methodologies and procedures. Original and powerful approaches for probing and modeling will most likely remain pillars controlling the advances in materials science. In this project, we propose an approach for experimental identification of so-called active sites at the surface of heterogeneous electrocatalysts using electrochemical scanning tunneling microscopy. The project utilizes the basic idea that under reaction conditions the parameters defining the tunneling barrier over the catalytically active site in contact with liquid electrolytes will be different, and, importantly, vary with time (e.g. due to approaching reactants and/or departing products), compared to those over the inactive sites. Therefore, the tunneling current measured between the tip and the sample under potential control should also change with time in a different way revealing local processes. By comparing the tunneling current as a function of time and tip-to-surface distance over different surface sites, it would be possible to elucidate the location of the catalytic centers. Our preliminary results support this basic idea. Low-index and high-index single crystal electrodes with quasi-periodic surface structures and very low surface mobility of atoms, nanostructured systems, as well as catalytic reactions important for future sustainable energy provision will be used in this project as model objects and reactions, respectively. Quantum chemistry calculations will be used (in collaboration) to clearly reveal the underlying physical foundations of the method, to support the quantitative interpretation of the experimental data regarding the local catalytic activity, and to iteratively improve the methodology.