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See detailLong term stability of TiO2 templated multilayer films used as high efficiency photoelectrode in liquid DSSCs
Dewalque, Jennifer ULg; Nguyen, Ngoc Duy ULg; Henrist, Catherine ULg et al

Poster (2013, March)

To our knowledge, the stability results reported in the literature only concern cells made from classical doctor-bladed or screen-printed nanoparticles films. This study focuses on the comparison of the ... [more ▼]

To our knowledge, the stability results reported in the literature only concern cells made from classical doctor-bladed or screen-printed nanoparticles films. This study focuses on the comparison of the long-term stability of these cells with DSSCs working with templated mesoporous films. Indeed, the increased surface area of templated films could lead to a faster degradation of the resulting cells. In accordance with IEC:1646:1996 standard tests, light soaking test at 45°C has been applied to determine the cells stability under prolonged illumination. Moreover, thermal stress in the dark has been applied. Unfortunately, due to the sealing material heat resistance, thermal stress test was only performed at 45°C. [less ▲]

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See detailHierarchical Porous TiO2 thin films by soft and dual templating: A quantitative approach of specific surface and porosity
Henrist, Catherine ULg; Cloots, Rudi ULg; Colson, Pierre ULg et al

Poster (2013, March)

Hierarchical porous structures, with different pore sizes, constitute an important field of research for many applications. However, increasing the pore size results in the decrease of specific surface ... [more ▼]

Hierarchical porous structures, with different pore sizes, constitute an important field of research for many applications. However, increasing the pore size results in the decrease of specific surface. There is a need to quantify and predict the resulting porosity and specific surface. We have prepared hierarchical porous TiO2 thin films either by surfactant templating (soft) or dual surfactant/microspheres templating (soft/hard). They all show narrow, bimodal distribution of pores. Soft templating route leads to very thin films showing high specific surface and bimodal porosity with diameters of 10 nm and 54 nm. Dual templating route combines a Pluronic surfactant-based precursor solution with polystyrene (PS) microspheres (diam. 250 nm) in a one-pot simple process. This gives thicker films with a bimodal distribution of pores (8 nm and 165-200 nm). The dye loading of hierarchical films is compared to pure Pluronic-templated TiO2 films and shows a relative decrease of 29% for Single Templating (ST) and 43% for Dual Templating (DT-250). Finally, a geometrical model is proposed and validated for each system, based on the agreement between calculated specific surfaces and experimental dye loading with N719 dye. [less ▲]

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See detailLithium transition metal (Ti, Nb, V) oxide mesoporous thin films: contrasting results when attempting direct synthesis by evaporation-induced self assembly
Caes, Sébastien ULg; Malherbe, Cédric ULg; Krins, Natacha ULg et al

in Microporous and Mesoporous Materials (2013), 172

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution ... [more ▼]

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H2O/TM ~10 (TM = Ti,Nb,V) and the common Pluronic structuring agent P123 (EO20-PO70-EO20). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350°C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions. [less ▲]

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See detailMorphological and opto-electrical properties of solution deposited Platinum counter electrode for low cost dye sensitized solar cells
Thalluri, Venkata Visveswara Gopala Kris ULg; Décultot, Marc ULg; Henrist, Catherine ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15

Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative ... [more ▼]

Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative cheaper catalyst materials did not yet yield to equivalent efficiencies. In this work, we tried to understand how to reduce the amount of deposited Pt-material and simultaneously to deliver higher DSC performances. We systematically compared the properties of Pt-counter electrodes prepared by simple solution deposition methods such as spray-coating, dip-coating, brushing with reference to the Pt-electrodes prepared by sputtering onto fluorine doped-tin oxides (FTOs). The morphological and structural characterizations of the deposited Pt-layers were performed by atomic force microscopy (AFM) and scanning electron microscope (SEM). The composition of Pt-material was quantified by using SEM electron dispersive x-ray (EDX) mapping measurements are further compared with optical transmission measurements. Also contact angle and sheet resistance measurements were performed. By taking Pt-layers composition, morphology and structural factors into account 9.16% efficient N3 dye based DSCs were assembled. The DSCs were subjected to various opto-electrical characterization techniques like current-voltage (I-V), external quantum efficiency (EQE), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and transient photo voltage (TPV) measurements. The obtained experimental data suggest that the Pt counter electrodes prepared by solution deposition methods can also reach to high DSC device performances with a consumption of very less amount of Pt material compared with sputtered Pt-layers. This process also proves that higher DSC performances are not limited to the usage of sputtered Pt-layer as counter electrode. [less ▲]

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See detailDifferences in the structural and magnetic properties of nanosized barium hexaferrite powders prepared by single and double microemulsion techniques
Koutzarova, T.; Kolev, S.; Ghelev, Ch et al

in Journal of Alloys & Compounds (2013), 579

Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was ... [more ▼]

Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was explored of the type of microemulsion technique on the microstructure and on the magnetic properties of the barium hexaferrite powders. The average particle size of the barium hexaferrite powders was in the range from 110 nm to 442 nm depending on the method and conditions of synthesis. The particles with size below 150 nm had irregular shapes between spherical and platehexagonal; the bigger ones had an almost perfect hexagonal shape. The powders obtained by single microemulsion had better magnetic characteristics (saturation magnetization of 65.12 emu/g and coercivity field of 3.6 × 105 A/m) than those obtained by double microemulsion. © 2013 Elsevier B.V. All rights reserved. [less ▲]

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See detailTiO2 templated multilayer films used as high efficiency photoelectrode in liquid or solid DSSCs
Dewalque, Jennifer ULg; Cloots, Rudi ULg; Mathis, François ULg et al

Conference (2012, April 10)

Mesoporous anatase thin films are very promising materials to act as electrode in dye-sensitized solar cells. Randomly oriented nanocrystalline TiO2 particles are usually used to prepare photoelectrodes ... [more ▼]

Mesoporous anatase thin films are very promising materials to act as electrode in dye-sensitized solar cells. Randomly oriented nanocrystalline TiO2 particles are usually used to prepare photoelectrodes with a thickness of 10-15 µm. Templated-assisted dip-coating techniques are used to obtain thin films with ordered porosity. However, monolayer films prepared by dip-coating from a solution suffer from a low quantity of active material with a limited surface area, leading to poor photovoltaic performances. Therefore a multilayer deposition process is needed to increase the film thickness along with surface area. Multilayer dip-coating procedures have already been reported but are usually characterized by a lack of linearity in the evolution of parameters (roughness, surface area, PV performances) as the number of layer increases. In this study, we investigate a dip-coating-based multilayer deposition technique delaying these limitations. First, the influence of the template on the film organization and porosity is studied in terms of long-range order, percentage of porosity, pore size, surface area and pores connectivity. Different techniques such as transmission electron microscopy (TEM), atmospheric poroellipsometry (AEP) and UV-visible absorption spectroscopy (UV-vis.) have been used to describe the microstructural features of the films. The film exhibiting the highest dye loading was selected and its thickness gradually increased up to 4 µm. Finally, the photovoltaic performances of the thick films (1 to 4 µm) have been evaluated in combination with the N719 dye and a liquid electrolyte and show excellent efficiency (6.1%) when compared to values reported in the literature. Such mesostructured films were compared in terms of photovoltaic performance with TiO2 nanoparticles films, generally used in DSSC. Films were further evaluated by Rutherford Backscattering Spectrometry (RBS) as high performance photoelectrode in solid-state DSSCs, in combination with Z907 dye and Spiro-OMeTAD as solid electrolyte. [less ▲]

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See detailRutherford backscattering analysis of porous thin TiO2 films
Mayer, Matej; von Toussaint, Udo; Dewalque, Jennifer ULg et al

in Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2012), 273

The additional energy spread due to sample porosity was implemented in the SIMNRA simulation code, version 6.60 and higher. Deviations of the path length and energy loss distributions from the ones ... [more ▼]

The additional energy spread due to sample porosity was implemented in the SIMNRA simulation code, version 6.60 and higher. Deviations of the path length and energy loss distributions from the ones expected from a Poisson distribution of the number of traversed pores are taken into account. These deviations are due to the interaction of pores at higher pore concentrations by overlap or blocking. The skewnesses of the energy distributions are approximated by two-piece normal distributions with identical first three moments. Propagation of porosity-induced energy spread in thick layers is taken into account. Calculated results are compared to experimental data obtained with thin TiO2 mesoporous films measured by Rutherford backscattering (RBS),transmission electron microscopy (TEM), and atmospheric poroellipsometry. [less ▲]

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See detailMagnetic properties of nanosized MgFe2O4 powders prepared by auto-combustion
Ghelev, Ch; Koutzarova, T.; Kolev, S. et al

in Journal of Physics: Conference Series (2012), 356(1), 012048

Targets were prepared to be used for magnetron sputtering and laser ablation and their microstructural and magnetic properties were investigated. The base material was nanosized MgFe2O4 powder produced by ... [more ▼]

Targets were prepared to be used for magnetron sputtering and laser ablation and their microstructural and magnetic properties were investigated. The base material was nanosized MgFe2O4 powder produced by citrate auto-combustion synthesis. The auto-combusted powders were annealed at temperatures in the range 600 - 1000°C in air to study the effect of temperature on thofe formation MgFe2O4. The saturation magnetization Ms was 24.30 emu/g at room temperature. © Published under licence by IOP Publishing Ltd. [less ▲]

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See detailNanosphere Lithography and Hydrothermal Growth : How to Increase Surface Area and Control Reversible Wetting Properties of ZnO Nanowire Arrays ?
Colson, Pierre ULg; Schrijnemakers, Audrey ULg; Vertruyen, Bénédicte ULg et al

in Journal of Materials Chemistry (2012), 22(33), 17086-17093

Due to their large surface-area-to-volume ratio as well as their interesting intrinsic optical and electronic properties, ZnO 1D nanostructures are part of the few dominant materials for nanotechnology ... [more ▼]

Due to their large surface-area-to-volume ratio as well as their interesting intrinsic optical and electronic properties, ZnO 1D nanostructures are part of the few dominant materials for nanotechnology. In this article, we compare two different routes of using the nanosphere lithography for the manufacturing of well-aligned, density-controlled ZnO nanowires by low-temperature hydrothermal growth. The first route uses the colloidal mask as a template for the patterned growth of the nanowires, while in the second route, the nanospheres act as a mask to pattern the seed layer. SEM and XRD characterizations are performed on samples manufactured by both routes and evidence patterned well-aligned nanowires with high c-axis texturing in the first synthetic route. Oriented growth is less pronounced in the second route, as well as the ability to adsorb dye. However, for the first route the dye loading measurements reveal that the amount of N-719 adsorbed is higher than on unpatterned ZnO nanowires films, highlighting an increased interface area. Reversible hydrophobicity to superhydrophilicity transition was observed and intelligently controlled by alternation of UV illumination and dark storage. This promising synthetic route opens exciting perspectives for the production of ZnO nanowire arrays with tunable density, wetting properties and enhanced adsorption properties. [less ▲]

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See detailMicrostructural evolution of a TiO2 mesoporous single layer film under calcination: Effect of stabilization and repeated thermal treatments on the film crystallization and surface area
Dewalque, Jennifer ULg; Cloots, Rudi ULg; Dubreuil, Olivier et al

in Thin Solid Films (2012), 520

This study quantifies the highest perturbation encountered by the first layer of a TiO2 12 layers-mesoporous coating, which is submitted to a multistep calcination process. Besides, we propose an ... [more ▼]

This study quantifies the highest perturbation encountered by the first layer of a TiO2 12 layers-mesoporous coating, which is submitted to a multistep calcination process. Besides, we propose an alternative thermal treatment in order to limit the degradation induced by repeated calcinations. This paper reports and compares the modifications in film thickness, surface area, anatase crystallite size and global crystallinity of films obtained from different thermal treatments. It defines the maximum crystal size compatible with the preservation of the mesoarchitecture initially induced by templating. Differences in microporosity and rate of crystallization are also discussed. [less ▲]

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See detailDense La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for IT-SOFC's: Sintering study and electrochemical characterization
Traina, Karl ULg; Henrist, Catherine ULg; Vertruyen, Bénédicte ULg et al

in Journal of Alloys & Compounds (2011), 509(5), 1493-1500

This paper presents the sintering behaviour of a La0.9Sr0.1Ga0.8Mg0.2O2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by ... [more ▼]

This paper presents the sintering behaviour of a La0.9Sr0.1Ga0.8Mg0.2O2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by calcination at 1200 ◦C during 1 h. This synthesis method gives great uniformity of the powder and allows shaping into compacts without requiring a grinding step. The grain size distribution (between 0.5 and 4 m) favours a good sintering behaviour: open porosity disappear at 1400 ◦C and relative densities over 99% can be achieved after 6 h at 1450 ◦C. The same powder can also be sintered into a thin disc of ∼100 mthickness. The characterization of the dense material by impedance spectroscopy shows that the activation energies below and above 600 ◦C are 1.0 eV and 0.7 eV, respectively. The conductivity at 800 ◦C is ∼0.11 S cm−1. Special attention is devoted to the temperature range between 200 ◦C and 400 ◦C, where the intragrain and intergrain contributions can be distinguished. The analysis of the parameters describing the intragrain constant phase element in the equivalent circuit suggests that, above 325 ◦C, the system evolves from a distribution of relaxation time to only one relaxation time. The analysis of the data by the complexes permittivity show that ionic oxide conduction mechanism would occur in two steps. In the first, an oxygen vacancy would be released and, in the second, the migration of the ionic oxide would take place in the material. [less ▲]

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See detailTiO2 mesoporous thin films studied by Atmospheric Ellipsometric Porosimetry: A case of contamination
Dubreuil, Olivier ULg; Dewalque, Jennifer ULg; Chene, Grégoire ULg et al

in Microporous and Mesoporous Materials (2011), 147

Anatase mesoporous TiO2 thin films are frequently prepared by surfactant templating to control porosity development and Atmospheric Ellipsometric Porosimetry is a reliable and fast technique allowing the ... [more ▼]

Anatase mesoporous TiO2 thin films are frequently prepared by surfactant templating to control porosity development and Atmospheric Ellipsometric Porosimetry is a reliable and fast technique allowing the determination of the porosity of such films. After prolonged exposition to high-vacuum (6×10-6 mbar), the films porosity exhibits a degraded behavior during porosimetric measurements, indicating a vacuum-induced modification. The main effect resulting from such exposition to high-vacuum is a wet- tability modification of the films, resulting in an increase of the hydrophobic character of the TiO2 surface. This evolution induces non-correct results in porosimetric measurements due to the fact that the contact angle parameter needed to calculate the pore size distribution is highly different from the reference films. A surface contamination explains such modifications and a restoration of the films is obtained by using ultraviolet treatment. [less ▲]

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See detailSpray drying: An alternative synthesis method for polycationic oxide compounds
Rivas-Murias, B.; Fagnard, Jean-François ULg; Vanderbemden, Philippe ULg et al

in Journal Of Physics And Chemistry Of Solids (2011), 72(3), 158-163

Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good ... [more ▼]

Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good reproducibility. The possibility of scaling up for production of large quantities with fast processing time is well established by the commercial availability of powders of various compositions. In this paper, we have discussed the advantages and limitations of this method and demonstrated its interest by synthesizing a few polycationic compounds selected for their attractive properties of thermoelectricity [Bi1.68Ca2Co1.69O8, La(0.95)A(0.05)CoO(3) (A = Ca, Sr, Ba)] or magnetoresistance [La(0.70)A(0.30)MnO(3) (A=Sr, Ba)]. We have confirmed the quality of these samples by reporting their structure, magnetic and transport properties. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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See detailCharacterization of surface and porous properties of synthetic hybrid lamellar silica
Toussaint, Gilles ULg; Rodriguez, Miguel Angel; Cloots, Rudi ULg et al

in Journal of Non-Crystalline Solids (2011), 357

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric ... [more ▼]

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications. [less ▲]

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See detailEffect of non-ionic surfactant and acidity on chitosan nanofibers with different molecular weights
Ziani, Khalid; Henrist, Catherine ULg; Jerome, Christine et al

in Carbohydrate Polymers (2011), 83(2), 470-476

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See detailTiO2 multilayer thick films (up to 4 μm) with ordered mesoporosity: Influence of template on the film mesostructure and use as high efficiency photoelectrode in DSSCs
Dewalque, Jennifer ULg; Cloots, Rudi ULg; Mathis, François ULg et al

in Journal of Materials Chemistry (2011), 21(20), 7356-7363

Mesoporous templated anatase thin films are very promising materials to act as photoelectrode in dye-sensitized solar cell. Templated-assisted dip-coating techniques are used to obtain thin films with ... [more ▼]

Mesoporous templated anatase thin films are very promising materials to act as photoelectrode in dye-sensitized solar cell. Templated-assisted dip-coating techniques are used to obtain thin films with ordered porosity. However, monolayer films are very thin and suffer from a low quantity of active material, leading to poor photovoltaic performances. In this paper, a dip-coating-based multilayer deposition technique is reported. First, we have studied the influence of the template on the film organization and porosity in terms of long-range order, percentage of porosity, pore size and pores connectivity. Different techniques such as transmission electron microscopy (TEM), atmospheric poroellipsometry (AEP) and UV-visible absorption spectroscopy (UV-vis.) have been used to describe the microstructural features of the films with a thickness of 1 µm. The film exhibiting the highest dye loading was selected and its thickness gradually increased up to 4 µm. Finally, the photovoltaic performances of the thick films (1 to 4 µm) have been evaluated in combination with the N-719 dye and show excellent efficiency (6.1%) when compared to values reported in the literature. Such mesostructured films are compared in terms of photovoltaic performance with TiO2 nanoparticles films, generally used in DSSC. [less ▲]

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