3 research outputs found
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, Li<sub>3</sub>Au, 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