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La1-xSrxCoyFe1-yO3 (LSCF) and LSCF-gadolinia-doped ceria (LSCF-GDC) composites are used as solid oxide fuel cell (SOFC) cathodes. In the present study, to maximize the LSCF/gas and LSCF/GDC interfacial area and thus enhance the performance, we fabricated both single-phase LSCF and composite LSCF-GDC thin-film electrodes using a facile and cost-effective polymeric precursor technique. This method involves molecular level mixing of cations in solution form and results in average particle sizes of ca. 72 nm and 60 nm upon annealing at 700 °C, respectively. For LSCF, electrochemical impedance spectroscopy measurements indicate very low electrode polarization resistances of ca. 0.6 Ω cm2 per electrode at 600 °C. However, the addition of GDC results in poorer electrochemical activity but better microstructural and electrochemical stability, all at 600 °C. Surface analysis revealed that Fe surface segregation occurs in the single-phase LSCF, while predominantly Co segregation is observed at the LSCF-GDC composite electrode surface.

With the purpose of investigating the reactivity of Fe carbide as an active phase in Fischer-Tropsch catalysis, we studied the formation of a well-defined Fe carbide surface structure resulting from carbon exposure of an Fe film on Au(111). Using two different sources of carbon (C), namely atomic carbon and ethylene gas, we used synchrotron X-ray photoelectron spectroscopy (XPS) to show that a 6 ML Fe film readily converts into a well-defined and thermodynamically stable carbide phase. Scanning tunneling microscopy (STM) showed that the surface of the Fe carbide film is crystalline and is dominated by Fe(110)-like facets perturbed into a (2 × 2) periodic structure due to insertion of C in the interstitial sites. The reactivity of the carbide film toward CO, H 2 , and O 2 was furthermore probed by XPS under vacuum conditions. While the pristine Fe carbide surface was unreactive toward hydrogen gas at 500 K, we interestingly found that CO dissociation from a preadsorbed monolayer of CO takes place already at low temperature. This observation points to an intrinsic activity of the Fe carbide phase where additional carbon originating from CO can be placed in the Fe carbide surface. The catalytic significance of the model catalyst surface presented here is that it can be seen as a stable Fe carbide phase with intrinsically vacant sites for additional C insertion at elevated pressure, and we propose that such additional C may act as active species in C-C coupling reactions during FTS. The studies pave the way for a better understanding of FTS processes on Fe-based catalysts on the basis of a well-defined model surface.

A series of thin Pt-Co films with different metal ratios were deposited by using the sequential cosputtering directly on a commercial hydrophobic carbon paper substrate at room temperature and in ultra-high vacuum (UHV) conditions. Their electrocatalytic properties toward the oxygen reduction reaction were investigated in 0.5 M $H_2 SO_4$ solution by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV) on rotating disc electrode (RDE). The results showed that Pt particles, deposited by dc-magnetron gun, surround the large Co-clusters deposited by rf-magnetron gun. In addition, the increase of Co content led to an increase in the electrochemical active surface area $(EASA) from 23.75 m_2 /gPt to 47.54 m_2 /gPt for pure Pt and Pt:Co (1:3),$ respectively, which corresponded the improvement of the utilization of Pt by a factor of 1.91. This improvement indicated that the sequential magnetron cosputtering was one of the essential technique to deposit homogeneous metal clusters with desirable size on the gas diffusion layer by adjustment plasma parameters.

International audience; Strategies have been tailored to enhance electro-active material capacities and the cycle lives of sodium-ion batteries. Amongst the available electrode materials, metal–organic framework derived anode materials have begun to stand out because of their versatile compositions, structures, and textures, leading to high specific surface areas and more active electrochemical reaction sites. Herein, Ni-MOF is first prepared from a bio-available organic linker, namely gallic acid, in a benign solvent (water). Then a nickel sulfide/carbon (NiS/C) composite is synthesized via concurrent sulfuration and carbonization under nitrogen flow at 600 °C. Carbon-encapsulated NiS particles are formed, in which the carbon framework both prevents the volume expansion of NiS during discharge and also gives rise to higher conductivity. The resulting NiS/C composite is tested as a potential anode material for sodium-ion batteries and it delivered a capacity of around 208 mA h g−1 at a current density of 1475 mA g−1 after 500 charge/discharge cycles. The Na+-ion diffusion rate is calculated through Warburg impedance analysis, and values of 1.8 × 10−16 and 3.5 × 10−15 S cm−1 are obtained initially and after cell operations are terminated, respectively.

Nitrogen doped hard carbons are synthesized from chitosan via hydrothermal carbonization (HTC) followed by further carbonization process at different temperatures (500, 750, 1000 degrees C). Those carbons are investigated as sodium ion battery anode materials. Latter, under HTC conditions, SnO2 nanoparticles are incorporated with carbon source to obtain SnO2/C composite. The influence of binders (carboxymethyl cellulose (CMC) and poly (vinylidene fluoride) (PVDF)) on the cyclic performance are investigated in which better cycling performances are achieved with PVDF. Indeed, electrochemical impedance spectroscopy test results reveal that the electrode prepared with PVDF has lower charge transfer resistance than that of CMC binder. Sodium ion diffusion coefficient values in the presence of CMC and PVDF are calculated from the Nyquist plot to be 4.35 x 10(-11) and 3.06 x 10(-10) cm(2)/s after 50 cycles, respectively.

The electrical and NO2 sensing properties of a series of porphyrin derivatives (PPC12, PPC16, ZnPPC12) were studied within wide temperature range from 293 to 423 K under the N2 gas flow and in the frequency range from 1 kHz to 1 MHz for ac electrical measurements. The dc conductivities and the activation energies were found to be in the range of 10−13−10−12 S cm−1 at the room temperature and 0.46–1.03 eV respectively. The increased C number in the alkyl chain and addition of metal ion to the porphyrin causes a decrease in the conductivity. The ac conductivity was well represented by the power law form Aω s. The s parameter depending on temperature was varied 0.79–1.2. The conduction mechanism for all porphyrins could be related to small polaron tunneling (SPT) model. As an application, the NO2 sensing properties of ZnPPC12 were investigated depending on temperature.

In this study, unsupported platinum and platinum–cobalt ultra-thin catalyst layers with varying metal loadings were prepared by a sequential magnetron sputtering technique. The deposited catalyst layers were characterized using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), X-ray diffraction, cyclic voltammetry, and rotating disk electrode methods. Ultra-low Pt loadings, in the range of 6–22 µg cm−2, were used to examine the kinetic properties of the deposited catalyst layers. The results revealed that the highest electrochemically active surface area, 89.7 m2 g−1, was obtained for Pt:Co (1:3) nanocatalyst with an optimum Pt loading of 10 µg cm−2. The XPS and UPS results indicated that the catalyst layers prepared at elevated temperatures contained a high degree of Pt–Co interaction. It was seen that the incorporation of Co atoms into the Pt lattice improved the oxygen reduction reaction (ORR) activity of the catalysts at certain Pt:Co concentrations and sputtering temperatures. Among all catalyst layers, the highest mass and specific current density values (793.08 A $${\text{g}}_{\text{Pt}}^{ - 1}$$ and 1163.18 µA cm−2, respectively) were obtained from the electrode with 10 µg cm−2 Pt loading prepared at 300 °C. Although the introduction of Co atoms in the catalyst layer did not result in a systematic enhancement in the ORR performance, the Pt:Co (1:1) composition deposited at 300 °C had the highest ORR performance with a mass activity of 571.17 A $${\text{g}}_{\text{Pt}}^{ - 1}$$ and a specific activity of 835.59 µA cm−2 among the all Co-containing catalysts. Our results indicated that heat treatment, surface structure, and composition have profound effects on the performance of the catalyst layers.

Pure and bimetallic Co–Pt clusters were grown on TiO2(110) and studied by scanning tunneling microscopy (STM). Despite the lower mobility of Co atoms on TiO2 compared to Pt, STM experiments demonstrate that exclusively bimetallic clusters can be deposited through either order of deposition, provided that deposition of the first metal results in a sufficient density of seed clusters to nucleate all of the metal atoms from the second deposition. Bimetallic clusters of varying compositions were prepared by depositing different Co:Pt ratios at room temperature with a fixed total coverage of 0.25 ML. The average cluster heights decrease with increasing Co fraction since the higher Co coverage results in a greater number of nucleation sites. After heating to 800 K, the pure Pt clusters exhibit the greatest increase in average cluster height; however, both Pt and Co clusters become encapsulated with titania upon annealing to 800 K, which is also the onset temperature for Co desorption. Low energy ion scattering ...

In this work, un-doped and carbon (C) doped TiO2 nanotubes were fabricated and their hydrogen sensing properties were investigated. A Ti foil was anodized in an aqueous hydrofluoric acid (HF) electrolyte (0.5 wt%) at room temperature to form TiO2 nanotube arrays. C-doped TiO2 nanotubes were obtained through two methods; a chemical process and thermal acetylene (C2H2) treatment. In the chemical method, a Ti foil was anodized ‘in-situ’ in aqueous solution of 0.5 wt% polyvinyl alcohol (PVA)+0.5 wt% HF. In the heat treatment method, a Ti foil was anodized in an aqueous (HF) electrolyte (0.5 wt%) to obtain TiO2 nanotubes, and then C-doped TiO2 nanotubes were obtained by heating as-prepared nanotubes at 500 °C in a quartz tube under a continuous N2 and C2H2 flux (1:1). The obtained un-doped and C-doped TiO2 nanotubes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The H2 sensing properties of the nanotubes exposed to 5000 ppm H2 were investigated at 100 °C. C-doped TiO2 nanotubes showed a lower response to H2 than the undoped TiO2 nanotubes.

Polycrystalline quaternary Co2MnAl1−x Sn x films with x=0.25, 0.5, 0.75, 1 were prepared at room temperature using magnetron sputtering technique on SiO2 substrates and post-annealed at various temperatures. We investigated the crystal structures, magnetic properties, and magnetic damping constants (α) of the prepared films. Out-of-plane angular dependences of the resonance field and the linewidth of the ferromagnetic resonance spectra were measured and analyzed using the Landau–Lifshitz–Gilbert equation to determine the magnetic properties and damping constant. Co2MnAl0.75Sn0.25 and Co2MnSn films had A2 ordered crystal structure while Co2MnAl0.25Sn0.75 and Co2MnAl0.5Sn0.5 films had A2 ordering up to 400 °C and 300 °C annealing temperature, respectively, and they had B2 ordering for the remaining temperatures. Also the crystal structure deteriorated at 600 °C for all of the film systems. The saturation magnetization, M S , of films increased with annealing temperature till 400 °C except Co2MnAl0.5Sn0.5 in which M S increased till 500 °C, which is consistent with the structural analysis. The effective magnetization was obtained from the FMR spectra and it was found that it decreased with increasing Sn-concentration and reached a minimum value at Co2MnAl0.25Sn0.75 composition. Lastly, Co2MnAl1−x Sn x films annealed at 500 °C showed the best crystal ordering. The lowest α value was 0.008 and obtained from Co2MnAl0.5Sn0.5 films annealed at 500 °C.

Columnar liquid crystal porphyrin compounds have been deposited onto the gold pads of quartz crystal microbalances (QMBs). The sensitivities of the resulting sensors have been measured with respect to volatile organic compounds (VOCs) and have been found to be of interest for future applications. The results show a strong influence of the length of the side alkyl chains, furthermore the thermal history of the coated film also affects the measured properties. The partition coefficients of the coatings have been calculated from the sensor responses.

A series of thin Pt films were deposited by dc magnetron sputtering directly on a commercial hydrophobic carbon paper substrate having a thin microporous Vulcan-XC72 layer or upon a thin Ti sublayer sputtered on the top of the microporous carbon film. The electrocatalytic properties of the sputtered Pt films toward the oxygen reduction reaction were investigated in 0.5 M H2SO4 solution and in a hydrogen PEM fuel cell. The catalyst with ultralow Pt loading of 22 mu g cm(-2) deposited on a 33 angstrom thick Ti sublayer is robust, mechanically stable, possesses highly developed surface area and improved catalytic efficiency. Its performance as a MEA cathode in a single hydrogen PEM fuel cell (577 mA cm(-2) at 0.4 V cell voltages and a maximum power of 0.954W) proved to be much superior compared to that of MEA with the same cathode Pt loading but without Ti sublayer (173 mA cm(-2) at 0.4 V, 0.231W, respectively). (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.