Ni supported on yttrium-stabilized zirconium oxide catalysts have been prepared by electroless plating method. Structure, electronic and chemical state of Ni as a function of Ni content (1, 7 and 12 wt%) have been characterized combining X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction (H2-TPR) and BET. The catalytic activity for the CO2 methanation was studied in the 250–500 °C temperature range, finding the highest CO2 conversion and CH4 selectivity for the catalyst with the largest Ni loading. A dependence of activity and CH4 selectivity on Ni crystallites size was highlighted
Expanding the activity
of wide bandgap semiconductors from the
UV into the visible range has become a central goal for their application
in green solar photocatalysis. The hybrid plasmonic/semiconductor
system, based on silver nanoparticles (Ag NPs) embedded in a film
of CeO
2
, is an example of a functional material developed
with this aim. In this work, we take advantage of the chemical sensitivity
of free electron laser (FEL) time-resolved soft X-ray absorption spectroscopy
(TRXAS) to investigate the electron transfer process from the Ag NPs
to the CeO
2
film generated by the NPs plasmonic resonance
photoexcitation. Ultrafast changes (<200 fs) of the Ce N
4,5
absorption edge allowed us to conclude that the excited Ag NPs transfer
electrons to the Ce atoms of the CeO
2
film through a highly
efficient electron-based mechanism. These results demonstrate the
potential of FEL-based TRXAS measurements for the characterization
of energy transfer in novel hybrid plasmonic/semiconductor materials.
Hematite (α-Fe2O3) is an earth-abundant
indirect n-type semiconductor displaying a band gap of about 2.2 eV,
useful for collecting a large fraction of visible photons, with frontier
energy levels suitably aligned for carrying out the photoelectrochemical
water oxidation reaction under basic conditions. The modification
of hematite mesoporous thin-film photoanodes with Ti(IV), as well
as their functionalization with an oxygen-evolving catalyst, leads
to a 6-fold increase in photocurrent density with respect to the unmodified
electrode. In order to provide a detailed understanding of this behavior,
we report a study of Ti-containing phases within the mesoporous film
structure. Using X-ray absorption fine structure and high-resolution
transmission electron microscopy coupled with electron energy loss
spectroscopy, we find that Ti(IV) ions are incorporated within ilmenite
(FeTiO3) near-surface layers, thus modifying the semiconductor–electrolyte
interface. To the best of our knowledge, this is the first time that
an FeTiO3/α-Fe2O3 composite
is used in a photoelectrochemical setup for water oxidation. In fact,
previous studies of Ti(IV)-modified hematite photoanodes reported
the formation of pseudobrookite (Fe2TiO5) at
the surface. By means of transient absorption spectroscopy, transient
photocurrent experiments, and electrochemical impedance spectroscopy,
we show that the formation of the Fe2O3/FeTiO3 interface passivates deep traps at the surface and induces
a large density of donor levels, resulting in a strong depletion field
that separates electron and holes, favoring hole injection in the
electrolyte. Our results provide the identification of a phase coexistence
with enhanced photoelectrochemical performance, allowing for the rational
design of new photoanodes with improved kinetics.
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.