Electrochemical Lithiation Cycles of Gold Anodes Observed by In Situ High-Energy X‑ray Diffraction

Significant developments of Li-ion batteries will be necessary to cope with the growing demands in electromobility or home storage of (sustainable) electrical energy. A detailed knowledge on the microscopic processes during battery cycling will be increasingly crucial for improvements. Involved phase changes at ambient temperature often involve metastable intermediate states, making both experimental observation and theoretical prediction of process pathways difficult. Here we describe an in situ high energy X-ray diffraction study following the initial alloying and dealloying of Li with an Au thin-film model anode using ionic liquid electrolyte. Six different crystalline alloy phases were observed to be involved in the cyclic phase transitions. Apart from the highest lithiated phase determined in this study, Li₃Au, none of the observed phases could be related to known, thermodynamically stable Li–Au phases. Structural search calculations following the minima hopping method (MHM) allowed the assignment of these phases to distinct metastable Au–Li alloy unit cells

Impact of Structural Differences in Galactocerebrosides on the Behavior of 2D Monolayers

The molecular interactions of three biologically important galactocerebrosides have been studied in monolayers formed at the soft air/water interface as 2D model membranes. Highly surface-sensitive techniques as GIXD (grazing incidence X-ray diffraction), IRRAS (infrared reflection–absorption spectroscopy), and BAM (Brewster angle microscopy) have been used. The study reveals that small differences in the chemical structure have a relevant impact on the physical–chemical properties and intermolecular interactions. The presence of a 2-d-hydroxyl group in the fatty acid favored for <b>GalCer C24:0 (2-OH)</b> monolayers a higher hydration state of the headgroup at low lateral pressures (<25 mN/m) and a higher condensation effect above 30 mN/m. An opposite behavior was recorded for <b>GalCer C24:0</b> and <b>GalCer C24:1</b>, for which the intermolecular interactions are defined by the weakly hydrated but strong H-bonded interconnected head groups. Additionally, the 15-<i>cis</i>-double bond in the fatty acid chain (nervonic acid) of <b>GalCer C24:1</b> stabilized the LE phase but did not disturb the packing parameters of the LC phase as compared with the saturated compound <b>GalCer C24:0</b>

Chemical and Structural In-Situ Characterization of Model Electrocatalysts by Combined Infrared Spectroscopy and Surface X‑ray Diffraction

New diagnostic approaches are needed to drive progress in the field of electrocatalysis and address the challenges of developing electrocatalytic materials with superior activity, selectivity, and stability. To this end, we developed a versatile experimental setup that combines two complementary in-situ techniques for the simultaneous chemical and structural analysis of planar electrodes under electrochemical conditions: high-energy surface X-ray diffraction (HE-SXRD) and infrared reflection absorption spectroscopy (IRRAS). We tested the potential of the experimental setup by performing a model study in which we investigated the oxidation of preadsorbed CO on a Pt(111) surface as well as the oxidation of the Pt(111) electrode itself. In a single experiment, we were able to identify the adsorbates, their potential dependent adsorption geometries, the effect of the adsorbates on the surface morphology, and the structural evolution of Pt(111) during surface electro-oxidation. In a broader perspective, the combined setup has a high application potential in the field of energy conversion and storage