We describe the construction and discuss the performance of a novel combined ultrahigh vacuum (UHV)-electrochemistry set-up, allowing the controlled preparation and structural characterization of complex nanostructured electrode surfaces by high resolution scanning tunnelling microscopy (STM) under UHV conditions on the one hand and, after electrode transfer under clean conditions, electrochemical measurements under continuous, controlled electrolyte mass transport conditions on the other. Electrochemical measurements can be coupled with online product detection, either using an additional collector electrode or by differential electrochemical mass spectrometry (DEMS). The potential of the set-up will be illustrated in two electrocatalytic reactions on complex, but structurally well-defined bimetallic electrode surfaces, O reduction on PtAg/Pt(111) monolayer surface alloys and bulk CO oxidation on Pt monolayer island modified Ru(0001) electrodes. We will particularly demonstrate the importance of structural characterization after the electrochemical measurements for identifying structural modifications induced by the electrochemical environment and thus avoiding misleading conclusions about the structure-activity relationships.

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We report results of a combined experimental and computational model study on the interaction of the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI) with a Mg thin film model electrode grown on a Ru(0001) substrate, which aims at a fundamental understanding of the solid electrolyte interphase formation at the electrode–electrolyte interface in postlithium batteries. Scanning tunneling microscopy, x-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy were employed for the characterization of the Mg thin film model electrode, revealing oxygen-free and atomically flat Mg films. Room temperature XPS measurements after vapor deposition of a (sub)monolayer of BMP-TFSI on the Mg film revealed the formation of a “contact layer” on Mg(0001), created by the reactive decomposition of the IL. In agreement with computationally determined core level binding energies of stable reaction products (dispersion corrected density functional theory calculations), we identified mainly inorganic MgF2-, MgO-, and MgS-like surface compounds, but also other more complex (Mg2+-free) F-, O-, and/or S-containing “TFSI-like” and carbon-containing adsorbed species. The deposition of higher IL amounts (up to 6 monolayers) results in the overgrowth of the direct “contact layer” by molecularly adsorbed BMP-TFSI. Heating of the adsorbate covered surface to around 470 K leads to desorption of multilayer BMP-TFSI and the partial desorption and transformation of adsorbed (Mg2+-free) “TFSI-like” decomposition products on the Mg substrate into MgF2-, MgO-, and MgS species or the respective adsorbed Fad, Oad, and Sad species.