Ionic-Liquid-Modified Electrocatalysts: From Surface Science to Spectroelectrochemistry

离子液体(ILS)独特的物理化学性质激发了催化领域新概念的发展，如离子液体层固体催化剂(SCILL)。在这种方法中，IL被用作设计者修饰剂来提高选择性。这一概念被成功地应用于多相催化，最近又被转移到电催化。尽管电化学SCILLS具有很大的潜力，但到目前为止，IL诱导的选择性提高的机理还没有得到深入的研究。本项目旨在从分子水平上深入了解IL修饰的电催化。我们将遵循一种独特的方法，将超高真空(UHV)中的表面科学与原位光谱电化学相结合。特高压表面科学和电化学将(I)使用相同的原子定义的模型表面，(Ii)使用相同的模型反应，以及(Iii)使用密切相关的实验方法。在超高真空中，我们将通过红外反射吸收光谱和结合分子束方法的程序升温脱附/反应来鉴定表面中间体。在电化学条件下，电化学红外反射吸收光谱和差示电化学质谱结合循环伏安法可获得相同的信息。将通过实验和理论方面的合作伙伴网络获得更多信息。我们确定了三个日益复杂的原型模型反应：(1)CO的氧化，(2)甲醇的氧化，(3)烯丙醇/丙烯醛的氧化/还原。这些模型反应可在超高真空研究和电化学中获得，显示出明显的结构依赖性、电子效应和系综效应。它们是确定IL诱导的反应机制、能量学和微动力学变化的分子起源的完美测试案例。我们将从简单的单晶(铂，钯)开始，发展到由金属纳米粒子(铂，钯)在有序氧化物薄膜(Co3O4(111)/Ir(100))上组成的复杂模型催化剂。相同的模型表面将在表面科学和电化学中使用。这将有可能使用一种新的实验系统，允许超高压制备和直接转移到光谱电化学池。在模型催化剂上，我们将通过物理气相沉积的方法沉积咪唑类离子液体，通过取代来调节离子液体的性质(配位强度、极性等)。利用超高压模型催化剂的结构多样性，我们将以前所未有的详细程度获得对电化学SCILL的机械洞察。

The unique physicochemical properties of ionic liquids (ILs) have inspired the development of new concepts in catalysis, such as the Solid Catalyst with Ionic Liquid Layer (SCILL). In this approach the IL is employed as a designer modifier to enhance the selectivity. The concept is successfully applied in heterogeneous catalysis and, recently, was transferred to electro¬catalysis. In spite of the great potential of electrochemical SCILLs the mechanism of IL-induced selectivity enhancement has remained unexplored up to date. This project aims at an in-depth understanding of IL-modified electrocatalysis at the molecular level. We will follow a unique approach that couples surface science in ultrahigh vacuum (UHV) to in-situ spectroelectro¬chemistry. UHV surface science and electrochemistry will be linked (i) using the same atomically-defined model surfaces, (ii) using the same model reactions, and (iii) using closely related experimental methods. In UHV we will identify the surface intermediates by infrared reflection absorption spectroscopy and the products by temperature programmed desorption/reaction in combination with molecular beam methods. Under electrochemical conditions equivalent information is obtained from electrochemical infrared reflection absorption spectroscopy and differential electrochemical mass spectrometry combined with cyclic voltammetry. Additional information will be available through a network of cooperation partners in experiment and theory. We identified three prototypic model reactions of increasing complexity: (1) the oxidation of CO, (2) the oxidation of methanol (3) the oxidation/reduction of allyl alcohol/acrolein. These model reactions, accessible in UHV studies and in electrochemistry, show pronounced structure dependencies, electronic effects and ensemble effects. They are perfect test cases to identify the molecular origins of IL-induced changes in the reaction mechanism, energetics and microkinetics. Starting from simple single crystals (Pt, Pd) we will proceed to complex model catalysts consisting of metallic nanoparticles (Pt, Pd) on ordered oxide films (Co3O4(111)/Ir(100)). Identical model surfaces will be employed in surface science and in electrochemistry. This will be possible using a new experimental system that allows UHV preparation and direct transfer to the spectroelectrochemical cell. On the model catalysts, we will deposit imidazolium based ILs by physical vapor deposition, tuning the properties of the IL by substitution (coordination strength, polarity, etc.). Taking advantage of the structural diversity of UHV-born model catalysts we will obtain mechanistic insights into electrochemical SCILLs at an unprecedented level of detail.