Skip to main content

Ionic Liquid Interface Dynamcis

Periodic Reporting for period 3 - ILID (Ionic Liquid Interface Dynamcis)

Reporting period: 2019-10-01 to 2021-03-31

The aim of the project is to take the ground-breaking step from our present knowledge of static properties to the understanding and control of dynamical processes at ionic liquid interfaces. Ionic liquids (ILs) are chosen as model systems for liquids in general for two reasons: First, their structural diversity allows their properties to be tailored over a wide range, and second, they can be studied using the extremely powerful methods of surface science in ultra-high vacuum due to their low vapor pressure. Such studies cannot be performed for conventional liquids, since they evaporate.

ILs are not only relevant from a fundamental point of view, but also for a variety of applications. In catalysis, two new concepts have been put forward: Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL). In both, a high surface area solid substrate is covered with a thin IL film, which contains a dissolved metal complex for SILP, or which modifies active sites at the support for SCILL. For these and other applications, a fundamental understanding of the dynamical processes at the gas/IL and/or IL/support interfaces is strongly needed, but does not exist. Equally important, but even more challenging, is the investigation of the dynamics of chemical reactions in ILs, also under electrochemical conditions.

Therefore, the applicant proposes a multi-method approach with new and unique setups to follow these dynamical processes in real time, that is, while they occur. Towards this goal, four key topics will be addressed: (A) How do gases pass through the gas/liquid interface? (B) How does the liquid/solid interface form? (C) Real-time studies of reactions in ILs, and (D) Real-time studies of electrochemical processes in ILs. The achieved insight will then enable to control the processes at the molecular level by tailoring the properties of the ILs. This promises a breakthrough not only for ILs, but for liquid interfaces in general.
The project runs very smooth and is on track. Four key topics have been described in the proposal, all of which are followed successfully.

Topic A “How do gases pass through the gas/liquid interface?” required to build a new ultrahigh vacuum-based molecular beam setup which allows for studying the interaction of gases with ionic liquid surfaces. The setup was planned, ordered and built together within the first 12 months of the project and is in operation since October 1, 2017. We already obtained novel and interesting data concerning the sticking/uptake of CO2 in an amine-containing ionic liquid. The performance of the new apparatus is better than expected. In particular, the XPS option, which was not planned originally, proves to be extremely helpful.

Topic B “How does the liquid/solid interface form?” addresses the fundamental understanding of adsorption and wetting behaviour of ionic liquids on different surfaces. Here, already very interesting results have been obtained. Particular highlights are the detailed insights in the growth behaviour and in exchange processes of cation and anions at the ionic liquid/support interface. The latter can be traced back to a collaborative effect of minimizing surface tension and maximizing the interaction strength at the ionic liquid/support interface. We also performed necessary complementary studies of the surface composition and enrichment effect in bulk ionic liquid mixtures, which serve as reference for the thin films but are also interesting in themselves.

Topic C “Real-time studies of reactions in ionic liquids” also runs very successful. In particular, we studied surface-induced changes in the thermochromic transformation of an ionic liquid cobalt thiocyanate complex, and the reactions of a polyhalide ionic liquid with copper, silver, and gold.

Topic D “Real-time studies of electrochemical processes in ionic liquids” is the most challenging part of project. As planned, we have developed a task-specific sample holder allowing for in situ studies in an electrochemical cell, and first successful measurements have been performed. In particular, we could show that using a two electrode setup with two identical electrodes information on the bias-dependent arrangement of anions and cations can be deduced. Various ionic liquids with different cations (aromatic, nonaromatic) and anions (small and large) were studied.

Altogether 10 papers have been published until March31, 2019. Several are in preparation.
For all for Topics, we have performed either novel experimental developments or achieved novel scientific results. For Topic A, we built up a worldwide unique experimental setup to study the dynamic interaction of a molecular beam with a liquid IL surface. In Topic B, we have followed the dynamic exchange processes of cations and anions at the ionic liquid/solid interface for the first time and deduced a molecular level understanding of the ongoing processes. In Topic C we performed unique elementally resolved in situ studies of thermochromic transitions, and of the dissolution of metals in ionic liquids using surface science methods. In Topic D, we developed a new and unique sample holder for in situ XPS under electrochemical conditions.
Until the end of the project, we hope to obtain a detailed molecular level understanding of all elementary steps relevant for the interface dynamics of ionic liquids in Topics A-D.