Electrocatalytic CO2 reduction in membrane electrode assembly (MEA) electrolyzers is a promising approach to producing carbon-neutral chemicals and fuels at commercially relevant rates. However, short-duration stability owing to cathode flooding...
The
theoretical design of effective metal electrocatalysts for
energy conversion and storage devices relies greatly on supposed unilateral
effects of catalysts structure on electrocatalyzed reactions. Here,
by using high-energy X-ray diffraction from the new Extremely Brilliant
Source of the European Synchrotron Radiation Facility (ESRF-EBS) on
device-relevant Pd and Pt nanocatalysts during cyclic voltammetry
experiments in liquid electrolytes, we reveal the near ubiquitous
feedback from various electrochemical processes on nanocatalyst strain.
Beyond challenging and extending the current understanding of practical
nanocatalysts behavior in electrochemical environment, the reported
electrochemical strain provides experimental access to nanocatalysts
absorption and adsorption trends (i.e., reactivity and stability descriptors) operando. The ease and power in monitoring such key catalyst
properties at new and future beamlines is foreseen to provide a discovery
platform toward the study of nanocatalysts encompassing a large variety
of applications, from model environments to the device level.
X-ray
photoemission electron microscopy (XPEEM), with its excellent
spatial resolution, is a well-suited technique for elucidating the
complex electrode–electrolyte interface reactions in Li-ion
batteries. It provides element-specific contrast images that allows
the study of the surface morphology and the identification of the
various components of the composite electrode. It also enables the
acquisition of local X-ray absorption spectra (XAS) on single particles
of the electrode, such as the C and O K-edges to track the stability
of carbonate-based electrolytes, F K-edge to study the electrolyte
salt and binder stability, and the transition metal L-edges to gain
insights into the oxidation/reduction processes of positive and negative
active materials. Here we discuss the optimal measurement conditions
for XPEEM studies of Li-ion battery systems, including (i) electrode
preparation through mechanical pressing to reduce surface roughness
for improved spatial resolution; (ii) corrections of the XAS spectra
at the C K-edge to remove the carbon signal contribution originating
from the X-ray optics; and (iii) procedures for minimizing the effect
of beam damage. Examples from our recent work are provided to demonstrate
the strength of XPEEM to solve challenging interface reaction mechanisms
via post mortem measurements. Finally, we present
a first XPEEM cell dedicated to operando/in situ experiments
in all-solid-state batteries. Representative measurements were carried
out on a graphite electrode cycled with LiI-incorporated sulfide-based
electrolyte. This measurement demonstrates the strong competitive
reactions between the lithiated graphite surface and the Li2O formation caused by the reaction of the intercalated lithium with
the residual oxygen in the vacuum chamber. Moreover, we show the versatility
of the operando XPEEM cell to investigate other active materials,
for example, Li4Ti5O12.
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