Deuterium Tracer Experiments Prove the Thiophenic Hydrogen Involvement During the Initial Step of Thiophene Hydrodesulfurization

We reassess literature data and demonstrate that the intermolecular hydrogen transfer occur likely during the primary catalytic interaction between thiophene molecules, rendering it the credible thiophene hydrodesulfurization (HDS) pathway. Deuterium tracer experiments prove that thiophenic hydrogen plays a part in direct C-S cleavage, in the initial step of thiophene HDS. Hypothetical surface intermediates for thiophene exchange do not precede, i.e. do not form prior to the surface intermediates for thiophene HDS. Therefore the established thiophene exchange/HDS scheme and the sequence of events are not the viable concepts. Since the deuterium data also indicate that C4H5S(a)—radicals are not formed this means there are no common surface or reaction intermediates for the thiophene exchange and HDS and both reactions proceed parallel. Graphical Abstrac

Highly porous activated glassy carbon film sandwich structure for electrochemical energy storage in ultracapacitor applications: Study of the porous film structure and gradient

Glassy carbon plates were thermochemically gas phase oxidized to obtain monolithic sandwichlike electrode assemblies with high surface area porous films for electrochemical energy storage applications. Film thicknesses were varied by variation of oxidation parameters time, temperature, and oxygen concentration and measured with electron microscopy. The mass density of the porous carbon film material was estimated by fitting a geometrical model to experimental gravimetric data. Optical Raman spectroscopy line scans suggest that the porosity has a gradient between the surface and the film/bulk interface, which is supported by pore-size distribution data obtained from small-angle x-ray scattering (SAXS) on slightly oxidized and fully oxidized samples. Detailed inspection of the power law behavior of SAXS data suggests that the internal surface area of well-oxidized glassy carbon (GC) is compact and extends over the entire probed volume and thus has optimal pore connectivity. This effect goes along with pore enlargement and a relative decrease of internal surface area per volume. Slightly oxidized carbon has no pore space with a compact, high connectivity internal surface area. The corresponding SAXS power law and the x-ray density suggest that this high volumetric surface area must be interpreted as a result of surface roughness, rather than true geometric or volumetric surface area. In consequence, is this surface area of limited use for electrochemical energy storage

Fe-resonant valence band photoemission and oxygen NEXAFS study on La1-xSrxFe0.75Ni0.25O3-{\delta}

Iron resonant valance band photoemission spectra of Sr substituted LaFe0.75Ni0.25 O3-{\delta} have been recorded across the Fe 2p - 3d absorption threshold to obtain Fe specific spectral information on the 3d projected partial density of states. Comparison with La1-xSrxFeO3 resonant VB PES literature data suggests that substitution of Fe by Ni forms electron holes which are mainly O 2p character. Substitution of La by Sr increases the hole concentration to an extent that the eg structure vanishes. The variation of the eg and t2g structures is paralleled by the changes in the electrical conductivity

Effect of lattice volume and strain on the conductivity of BaCeY-oxide ceramic proton conductors

In-situ electrochemical impedance spectroscopy was used to study the effect of lattice volume and strain on the proton conductivity of the yttrium-doped barium cerate proton conductor by applying the hydrostatic pressure up to 1.25 GPa. An increase from 0.62 eV to 0.73 eV in the activation energy of the bulk conductivity was found with increasing pressure during a unit cell volume change of 0.7%, confirming a previously suggested correlation between lattice volume and proton diffusivity in the crystal lattice. One strategy worth trying in the future development of the ceramic proton conductors could be to expand the lattice and potentially lower the activation energy under tensile strain

An electron hole doping and soft x-ray spectroscopy study on La1-xSrxFe0.75Ni0.25O3-{\delta}

The conductivity of the electron hole and polaron conductor La1-xSrxFe0.75Ni0.25O3-{\delta}, a potential cathode material for intermediate temperature solid oxide fuel cells, was studied for 0 <x < 1 and for temperatures 300 K <T < 1250 K. In LaSrFe-oxide, an ABO3 type perovskite, A-site substitu-tion of the trivalent La3+ by the divalent Sr2+ causes oxidation of Fe3+ towards Fe4+, which forms conducting electron holes. Here we have in addition a B-site substitution by Ni. The compound for x = 0.5 is identified as the one with the highest conductivity ({\sigma} ~ 678 S/cm) and lowest activation energy for polaron conductivity (Ep = 39 meV). The evolution of the electronic structure was monitored by soft x-ray Fe and oxygen K-edge spectroscopy. Homogeneous trend for the oxida-tion state of the Fe was observed. The variation of the ambient temperature conductivity and activation energy with relative Sr content (x) shows a correlation with the ratio of (eg/eg+t2g) in Fe L3 edge up to x=0.5. The hole doping process is reflected by an almost linear trend by the variation of the pre-peaks of the oxygen K-edge soft x-ray absorption spectra

The effect of solvent and electric field on the size distribution of iron oxide microdots: Exploitation of self-assembly strategies for photoelectrodes

An increasing number of technologies benefit from or require patterned surfaces on a micro- and nanoscale. Methods developed to structure polymer films can be adapted to fabricate low-cost patterned ceramics using nonlithographic techniques, for example, dewetting and phase separation in thin films. In this paper we describe a simple patterning process that does not require a template and is able to produce Fe2O3 microdots with a spatial periodicity. Our method involves the dewetting of a silicon substrate by a thin metal oxide precursor film, in which the liquid film breaks up because of fluctuations in the film thickness induced by solvent evaporation or an external applied electric field. The patterning is followed by a thermal treatment at 550 °C to produce crystalline Fe2O3 microdots with a diameter range of 200 nm to 3 μ

The effect of annealing temperature on the structural, optical, and electrical properties of CdS films

Cadmium sulfide (CdS) photocatalyst films were grown on glass by chemical bath deposition (pH 9.4, 70 °C) and then annealed in nitrogen from 423 K to 823 K in steps of 100 K. The XRD crystallite size increases in a sigmoidal manner from 60 nm to 100 nm while the optical band gap energy decreases from 2.42 eV to 2.28 eV. This trend is paralleled by the decreasing Urbach energy, but only up to 623 K, where it increases again. This is the temperature where the Cd effectively surpasses the phase transformation from cubic to hexagonal, and the activation energy for electronic transport drops by a factor of nearly tw

Protons in lattice confinement: Static pressure on the Y-substituted, hydrated BaZrO3 ceramic proton conductor decreases proton mobility

Yttrium substituted BaZrO3, with nominal composition BaZr0.9Y0.1O3, a ceramic proton conductor, was subject to impedance spectroscopy for temperatures 300 K < T < 715 K at mechanical pressures 1 GPa < p < 2 GPa. The activation energies Ea of bulk and grain boundary conductivity from two perovskites synthesized by solid-state reaction and sol-gel method were determined under high pressures. At high temperature, the bulk activation energy increases with pressure by 5% for sol-gel derived sample and by 40% for solid-state derived sample. For the sample prepared by solid-state reaction, there is a large gap of 0.17 eV between the activation energy at 1.0 GPa and > 1.2 GPa. The grain boundary activation energy is around a factor two times as that of the bulk, and it reaches a maximum at 1.25 - 1.5 GPa, and then decrease as the pressure increases, indicating higher proton mobility in the grain boundaries at higher pressure. Since this effect is not reversible, it is suggested that the grain boundary resistance decreases as a result of pressure induced sintering. The steady increase of the bulk resistivity upon pressurizing suggests that the proton mobility depends on the space available in the lattice. In return, an expanded lattice with a/a0 > 1 should thus have a lower activation energy, suggesting that thin films expansive tensile strain could have a larger proton conductivity with desirable properties for applications

High temperature oxygen NEXAFS valence band spectra and conductivity of LaFe3/4Ni1/4O3 from 300 K to 773 K

LaFe3/4Ni1/4O3 was subjected to oxygen near edge x-ray absorption fine structure (NEXAFS) spectroscopy for 300 K < T < 773 K. The spectra show in the pre-edge a small hole doped peak originating from Ni substitution. The relative spectral weight of this transition to the weight of the hybridized O(2p) - Fe(3d) transitions scales with T and has a maximum at around 600 K. The characteristic energies of the thermal activated spectral intensity and conductivity suggest that the concentration of charge transferred electrons from O(2p) to Ni(3d) increases and that the pre-edges account in part for the polaron activated transport