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

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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.