1. In situ techniques for characterization of layered double hydroxide-based oxygen evolution catalystsAndraž Mavrič, Matjaž Valant, 2023, review article Abstract: Functional layered double hydroxide (LDH) usually contains different cationic substitutes to increase the activity of the oxygen evolution reaction (OER). The intrinsic OER activity of LDH materials is connected with the chemical composition and dispersion of metal cations substitutions in the matrix phase. The potential induced phase transitions, in particular hydroxide-to-oxyhydroxide transitions, are a predisposition for the high OER activity of LDH materials and can be followed by coupling the electrochemical experiments with spectroscopic techniques. The understanding of LDH catalysts under electrochemical conditions also allows an understanding of the behavior of OER catalysts based on transition metals, metal-chalcogenides, -pnictides, -carbides, and metal–organic frameworks. The surfaces of those materials are intrinsically poor OER catalysts. However, they act as precursors to catalysts, which are oxidized into a metal (oxy)hydroxide. This review summarizes the use of in situ techniques for the characterization of LDH-based OER electrocatalysts and presents the influence of these techniques on the understanding of potential induced phase transitions, identification of active sites, and reaction mechanisms.
Keywords: oxygen evolution reaction, layered double hydroxide, in-situ characterization
Published in RUNG: 14.07.2023; Views: 2422; Downloads: 16
 Full text (5,05 MB)
This document has many files! More... |
2. CO[sub]2 activation over nanoshaped CeO[sub]2 decorated with nickel for low-temperature methane dry reformingKristijan Lorber, Janez Zavašnik, Iztok Arčon, Matej Huš, Janvit Teržan, Blaž Likozar, Petar Djinović, original scientific article Abstract: Dry reforming of methane (DRM) is a promising way to
convert methane and carbon dioxide into H2 and CO (syngas). CeO2
nanorods, nanocubes, and nanospheres were decorated with 1−4 wt % Ni.
The materials were structurally characterized using TEM and in situ
XANES/EXAFS. The CO2 activation was analyzed by DFT and
temperature-programmed techniques combined with MS-DRIFTS. Synthesized CeO2 morphologies expose {111} and {100} terminating facets,
varying the strength of the CO2 interaction and redox properties, which
influence the CO2 activation. Temperature-programmed CO2 DRIFTS
analysis revealed that under hydrogen-lean conditions mono- and bidentate
carbonates are hydrogenated to formate intermediates, which decompose
to H2O and CO. In excess hydrogen, methane is the preferred reaction
product. The CeO2 cubes favor the formation of a polydentate carbonate
species, which is an inert spectator during DRM at 500 °C. Polydentate covers a considerable fraction of ceria’s surface, resulting in
less-abundant surface sites for CO2 dissociation
Keywords: surface carbonates, in situ characterization, Ni XANES, Ni EXAFS, spectator species, CeO2 nanoshapes, CO2 activation
Published in RUNG: 13.07.2022; Views: 2518; Downloads: 0
This document has many files! More... |
3. STUDY OF ATMOSPHERIC AEROSOL PROPERTIES IN THE VIPAVA VALLEYLonglong Wang, doctoral dissertation Abstract: The aim of the dissertation was to study aerosol loading distributions and properties over the Vipava valley, a representative hot-spot for complex mixtures of different aerosol types of both anthropogenic and natural origin.
An infrared Mie and a two-wavelength polarization Raman lidar systems
were used as main detection tools. The polarization Raman lidar, which
provides the capability to extract the extinction coefficient, backscatter coefficients, depolarization ratio, backscatter Ångström exponent, lidar ratio and
water vapor mixing ratio profiles, was itself designed, built and calibrated as
a part of this thesis. Lidar data, combined with in-situ measurements, was
used to determine detailed information on different aerosol types. Vertical
profiles of aerosol mass concentration were extracted from the Mie lidar data
taken in April 2016, where the in-situ measurements of aerosol size distribution and number concentration as well as aerosol absorption coefficient and black carbon mass concentration were used to estimate the mass extinction efficiency (MEE). Aerosol morphology and chemical composition determined by SEM-EDX on sampled particles were used for the identification
of primary aerosol types. Two cases with different atmospheric conditions
(long range mineral dust transport and local biomass burning) and different
expected the dominant presence of specific aerosol types (mineral dust and
soot) were investigated in more detail. They revealed significantly different
aerosol properties and distributions within the valley, affecting radiative heat
exchange.
A more detailed investigation of aerosol properties throughout the troposphere in different atmospheric conditions was made possible by the two-wavelength polarization Raman lidar system, deployed in Ajdovščina (town
of Vipava valley) from September 2017. Using its aerosol identification capabilities, based on particle depolarization ratio and lidar ratio measurements,
it was possible to identify predominant aerosol types in the observed atmospheric structures, for example in different atmospheric layers in the case of
the stratified atmosphere. Primary anthropogenic aerosols within the valley were found to be mainly emitted from two sources: individual domestic
heating systems, which mostly use biomass fuel and traffic. Natural aerosols,
transported over large distances, such as mineral dust and sea salt, were observed both above and entering into the planetary boundary layer. Backscatter contribution of each aerosol type was separated and the corresponding
extinction contribution was derived from lidar observations.
Keywords: Vipava valley, aerosol distribution, aerosol characterization, lidar
remote sensing, in-situ measurements, aerosol loading.
Published in RUNG: 23.10.2018; Views: 8567; Downloads: 164
Full text (29,39 MB) |
