ROBL-II provides four different experimental stations to investigate actinide and other alpha- and beta-emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub-p.p.m. range. The XES station with its five bent-crystal analyzer, Johann-type setup with Rowland circles of 1.0 and 0.5 m radii provides high-energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six-circle heavy duty goniometer of XRD-1 is equipped for both high-resolution powder diffraction as well as surface-sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X-ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD-2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.
Co oxides and oxyhydroxides
have been studied extensively in the
past as promising electrocatalysts for the oxygen evolution reaction
(OER) in neutral to alkaline media. Earlier studies showed the formation
of an ultrathin CoO
x
(OH)
y
skin layer on Co
3
O
4
at potentials
above 1.15 V vs reversible hydrogen electrode (RHE), but the precise
influence of this skin layer on the OER reactivity is still under
debate. We present here a systematic study of epitaxial spinel-type
Co
3
O
4
films with defined (111) orientation,
prepared on different substrates by electrodeposition or physical
vapor deposition. The OER overpotential of these samples may vary
up to 120 mV, corresponding to two orders of magnitude differences
in current density, which cannot be accounted for by differences in
the electrochemically active surface area. We demonstrate by a careful
analysis of
operando
surface X-ray diffraction measurements
that these differences are clearly correlated with the average thickness
of the skin layer. The OER reactivity increases with the amount of
formed skin layer, indicating that the entire three-dimensional skin
layer is an OER-active interphase. Furthermore, a scaling relationship
between the reaction centers in the skin layer and the OER activity
is established. It suggests that two lattice sites are involved in
the OER mechanism.
The aggregation of nanoparticles is a key step in the formation of solid phases and a controlling factor for the behavior of suspended nanoparticles in solution. Using a charged mineral surface [muscovite (001)], we apply the surface X-ray diffraction techniques crystal truncation rod (CTR) measurements and resonant anomalous X-ray reflectivity (RAXR) to investigate the aggregation process of Zr nanoparticles at the sub-nanometer scale. The aggregation process was studied as a function of ionic strength (0, 1, 10, and 100 mM NaCl), and the interfacial particles were characterized by CTR/RAXR and AFM. The observations are consistent with an aggregation process that follows a multistep mechanism, which starts with the 3D aggregation of primary building units to form nanosheets. These sheets continue to grow through addition of building units to their reactive edges at higher ionic strength. Once the size and concentration of aggregates are sufficient, "faceto-face" stacking of nanosheets becomes the preferred aggregation mechanism as this minimizes the electrostatic repulsion of the charge that accumulates along nanosheet edges.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.