References of "Cloots, Rudi"
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See detailMesoporous amorphous tungsten oxide electrochromic films: a Raman analysis of their good switching behavior
Chatzikyriakou, Dafni ULg; Krins, Natacha ULg; Gilbert, Bernard ULg et al

in Electrochimica Acta (in press)

The intercalation and de-intercalation of lithium cations in electrochromic tungsten oxide thin films are significantly influenced by their structural and surface characteristics. In this study, we ... [more ▼]

The intercalation and de-intercalation of lithium cations in electrochromic tungsten oxide thin films are significantly influenced by their structural and surface characteristics. In this study, we prepared two types of amorphous films via the sol-gel technique: one dense and one mesoporous in order to compare their response upon lithium intercalation and de-intercalation. According to chronoamperometric measurements, Li+ intercalates/de-intercalates faster in the mesoporous film (24s/6s) than in the dense film (48s/10s). The electrochemical measurements (cyclic voltammetry and chronoamperometry) also showed worse reversibility for the dense film compared to the mesoporous film, giving rise to important Li+ trapping and remaining coloration of the film. Raman analysis showed that the mesoporous film provides more accessible and various W-O surface bonds for Li+ intercalation. On the contrary, in the first electrochemical insertion and de-insertion in the dense film, Li+ selectively reacts with a few surface W-O bonds and preferentially intercalates into pre-existing crystallites to form stable irreversible LixWO3 bronze. [less ▲]

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See detailEffect of the RE (RE = Eu, Er) doping on the structural and textural properties of mesoporous TiO2 thin films obtained by evaporation induced self-assembly method
Borlaf, Mario; Caes, Sébastien ULg; Dewalque, Jennifer ULg et al

in Thin Solid Films (2014), 558

Polymeric sol–gel route has been used for the preparation of TiO2 and RE2O3–TiO2 (RE = Eu, Er) mesoporous thin films by evaporation induced self-assembly method using Si (100) as a substrate. The ... [more ▼]

Polymeric sol–gel route has been used for the preparation of TiO2 and RE2O3–TiO2 (RE = Eu, Er) mesoporous thin films by evaporation induced self-assembly method using Si (100) as a substrate. The influence of the relative humidity (RH) on the preparation of the film has been studied being necessary to work under 40% RH in order to obtain homogeneous and transparent thin films. The films were annealed at different temperatures until 900 °C/1 h and the anatase crystallization and its crystal size evolution were followed by low angle X-ray diffraction. Neither the anatase–rutile transition nor the formation of other compounds was observed in the studied temperature range. Ellipsoporosimetry studies demonstrated that the thickness of the thin films did not change after calcination at 500 °C, the porosity was constant until 700 °C, the pore size increased and the specific surface area decreased with temperature. Moreover, the effect of the doping with Er3 + and Eu3 + was studied and a clear inhibition of the crystal growth and the sintering process was detected (by transmission electron and atomic force microscopy) when the doped films are compared with the undoped ones. Finally, Eu3 + and Er3 + f–f transitions were detected by PL measurements. [less ▲]

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See detailSpray-drying synthesis of Na2FePO4F/carbon powders for lithium-ion batteries
Brisbois, Magali ULg; Krins, Natacha ULg; Hermann, Raphael et al

in Materials Letters (2014), 130

Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple ... [more ▼]

Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple and easily up-scalable technique of spray-drying. An aqueous solution containing citric acid as a carbon source was sprayed in a pilot-scale spray-dryer. Heat treatment at 600°C in argon for 12 hours was found appropriate to obtain single-phase Na2FePO4F; only 1.8% of Fe (III) were detected by iron-57 Mössbauer spectroscopy. When cycled against lithium, the discharge capacity reached 110 mAh g-1 at C/15 rate. (C) 2014 Elsevier B.V. All rights reserved. [less ▲]

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See detailYBa2Cu3O7-δ thick films for magnetic shielding: Electrophoretic deposition from butanol-based suspension
Closset, Raphaël ULg; Kumar, Devendra; Wera, Laurent ULg et al

in Materials Letters (2014), 119

Multilayered YBa2Cu3O7-δ (YBCO) thick films were coated on silver substrates by electrophoretic deposition (EPD) followed by heat treatment. A butanol-based YBCO suspension is used instead of the common ... [more ▼]

Multilayered YBa2Cu3O7-δ (YBCO) thick films were coated on silver substrates by electrophoretic deposition (EPD) followed by heat treatment. A butanol-based YBCO suspension is used instead of the common acetone-iodine combination. Tests with several dispersing agents reveal that a branched polyethyleneimine (PEI) dispersant develops large positive surface charge on suspended YBCO particles. As a demonstration of the performance of this new suspension formulation, a 12-layer 100 μm-thick YBCO coating was deposited on an Ag tube. The superconducting transition is sharp with onset critical temperature at 92 K. The sample can shield a magnetic field of ~1.3 mT at 77 K, i.e., the best value so far for an YBCO coating on a metallic substrate. © 2013 Elsevier B.V. [less ▲]

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See detailMesoporous Lithium Vanadium Oxide as Thin Film Electrode for Lithium-Ion Batteries: Comparison between Direct Synthesis of LiV2O5 and Electrochemical Lithium Intercalation in V2O5
Caes, Sébastien ULg; Arrebola, Jose Carlos; Krins, Natacha ULg et al

in Journal of Materials Chemistry A (2014), 2

Research in the field of lithium-ion batteries favours electrode materials with high surface area. In this context, this paper is dedicated to mesoporous thin films (MTFs) and compares the electrochemical ... [more ▼]

Research in the field of lithium-ion batteries favours electrode materials with high surface area. In this context, this paper is dedicated to mesoporous thin films (MTFs) and compares the electrochemical performance of g-LiV2O5 MTFs with post-synthesis electrochemical lithium intercalation in a-V2O5 MTFs. Formation of vanadium oxide MTFs by soft-chemistry is notoriously difficult. However, it is shown that wormlike vanadium oxide (V–O) and lithium vanadium oxide (Li–V–O) MTFs can be obtained on silicon substrates by a direct sol–gel soft-templating route (evaporation-induced micelle assembly) using a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) structuring agent. Heat treatment for 1 minute at 400 C (Li–V–O system) or 30 minutes at 350 C (V–O system) leads to the crystallization of g-LiV2O5 or a-V2O5, respectively. These calcination conditions ensure the degradation of the structuring agent while preventing the collapse of the mesostructure, yielding MTFs with pore size diameter in the 30–35 nm range. Using the same set of synthesis conditions, films can be deposited on conductive glass substrates for electrochemical investigation: the a-V2O5 films display better specific capacities, while the cyclability is good for both compositions, even at a current density as high as 30 C-rate. [less ▲]

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See detailStability of templated and nanoparticles dye-sensitized solar cells : photovoltaic and electrochemical investigation of degradation mechanisms at the photoelectrode interface
Dewalque, Jennifer ULg; Nguyen, Ngoc Duy ULg; Colson, Pierre ULg et al

in Electrochimica Acta (2014), 115(1), 478-486

A key issue in the commercialization of dye-sensitized solar cells is to maintain high efficiency and long lifetime. As reported in the literature, dye-sensitized solar cells are stable under visible ... [more ▼]

A key issue in the commercialization of dye-sensitized solar cells is to maintain high efficiency and long lifetime. As reported in the literature, dye-sensitized solar cells are stable under visible light soaking but thermal stress and UV exposure lead to efficiency degradation. However, all the stability studies published so far have been performed on cells whose TiO2 electrodes were prepared by tape casting or screen printing of nanoparticle pastes/inks. The present study concerns cells based on highly porous templated TiO2 electrodes, whose larger surface area could enhance the negative effects of thermal stress, light soaking and UV exposure. The long-term stability of these cells is compared with a classical nanoparticle-based cell using current-voltage measurements (I-V curves) and electrochemical impedance spectroscopy. Due to their higher active interface, templated cells are more sensitive than nanoparticle cells to UV illumination, although this can be easily solved in both cases by the use of a UV filter. The templated cells are as stable as the nanoparticle cells under visible light soaking (UV filtered). However, we showed that templated cells are more stable under thermal stress. Moreover, as evidenced by electrochemical impedance spectroscopy, templated cells show lower transfer resistance, as well as lower recombination resistance compared to nanoparticle cells. The crystallite connectivity promoted by the templating route seems to favor the electron transfers inside the porous layer. Using templated films in dye-sensitized solar cells is therefore really promising because higher conversion efficiencies are reached without promoting cell degradation. [less ▲]

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See detailPore-filling of Spiro-OMeTAD determined by Rutherford backscattering spectrometry in templated TiO2 photoelectrodes
Dewalque, Jennifer ULg; Colson, Pierre ULg; Thalluri, Venkata Visveswara Gopala Kris ULg et al

in Organic Electronics (2014), 15

Liquid-state dye-sensitized solar cells can suffer from electrolyte evaporation and leakage. Therefore solid-state hole transporting materials are investigated as alternative electrolyte materials ... [more ▼]

Liquid-state dye-sensitized solar cells can suffer from electrolyte evaporation and leakage. Therefore solid-state hole transporting materials are investigated as alternative electrolyte materials. However, in solid-state dye-sensitized solar cells, optimal TiO2 films thickness is limited to a few microns allowing the adsorption of only a low quantity of photoactive dye and thus leading to poor light harvesting and low conversion efficiency. In order to overcome this limitation, high surface area templated films are investigated as alternative to nanocrystalline films prepared by doctor-blade or screen-printing. Moreover, templating is expected to improve the pore accessibility what would promote the solid electrolyte penetration inside the porous network, making possible efficient charge transfers. In this study, films prepared from different structuring agents are discussed in terms of microstructural properties (porosity, crystallinity) as well as impact on the dye loading and Spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) solid electrolyte filling. We first report Rutherford backscattering spectrometry as an innovative non-destructive tool to characterize the hole transporting materials infiltration. Templated films show dye loading more than two times higher than nanocrystalline films prepared by doctor-blade or screen-printing and solid electrolyte infiltration up to 88%. [less ▲]

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See detailLow temperature crystallization of yttrium orthoferrite by organic acid-assisted sol-gel synthesis
Stevens, Frédéric ULg; Cloots, Rudi ULg; Poelman, D. et al

in Materials Letters (2014), 114

Yttrium orthoferrite (YFeO3) is a promising material for visible light photocatalytic applications due to its band gap of 2.2-2.6 eV. However, during the synthesis of YFeO3, unwanted composition can be ... [more ▼]

Yttrium orthoferrite (YFeO3) is a promising material for visible light photocatalytic applications due to its band gap of 2.2-2.6 eV. However, during the synthesis of YFeO3, unwanted composition can be obtained and the crystallization requires temperatures as high as 850 C. Powders of YFeO3 were prepared using a sol-gel method with and without organic acids (citric acid, tartaric acid, malonic acid and oxalic acid) used as organic modifiers. The band gap of these powders was measured by diffuse reflection spectroscopy, and the crystallinity and crystalline phase content were characterized by X-ray diffraction. Organic acids allow a higher purity and facilitate crystallization. This work aims to produce YFeO3 powders at the lowest possible temperature. Citric acid was found to be the best additive: it reduces the crystallization temperature below 450 C. This opens new perspectives such as the deposition of crystalline YFeO3 thin films onto conductive glass for water-splitting applications. © 2013 Elsevier B.V. [less ▲]

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See detailAC vs. DC electrophoretic deposition of hydroxyapatite on titanium
Ozhukil Kollath, Vinayaraj ULg; Chen, Qiang; Closset, Raphaël ULg et al

in Journal of the European Ceramic Society (2013), 33(13-14), 27152721

In this study, electrophoretic deposition (EPD) of hydroxyapatite (HA) powder on titanium plate was performed using butanol as solvent under direct current (DC) and alternating current (AC) fields. The ... [more ▼]

In this study, electrophoretic deposition (EPD) of hydroxyapatite (HA) powder on titanium plate was performed using butanol as solvent under direct current (DC) and alternating current (AC) fields. The zeta potential of the suspensions was measured to define their stability and the charge on the particles. Coating thickness was varied by adjusting the voltage and time of deposition. Surface morphology and cross section thickness were studied using scanning electron microscopy and image analysis software. Surface crack density was calculated from the micrographs. The results showed that the samples of similar thickness have higher grain density when coated using AC as compared to DC EPD. This facile but novel test proves the capability of AC-EPD to attain denser and uniform HA coatings from non-aqueous medium. [less ▲]

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See detailTiO2 templated films used as photoelectrode for solid-state DSSC applications: study of the pore filling by Rutherford Backscattering Spectroscopy
Dewalque, Jennifer ULg; Colson, Pierre ULg; Thalluri, Venkata Visveswara Gopala Kris ULg et al

Poster (2013, September)

Liquid-state dye-sensitized solar cells can suffer from electrolyte evaporation and leakage. Therefore solid-state hole transporting materials are investigated as alternative electrolyte materials ... [more ▼]

Liquid-state dye-sensitized solar cells can suffer from electrolyte evaporation and leakage. Therefore solid-state hole transporting materials are investigated as alternative electrolyte materials. However, in solid-state dye-sensitized solar cells, optimal TiO2 films thickness is limited to a few microns allowing the adsorption of only a low quantity of photoactive dye and thus leading to poor light harvesting and low conversion efficiency. In order to overcome this limitation, high surface area templated films are investigated as alternative to nanocrystalline films prepared by doctor-blade or screen-printing. Moreover, templating is expected to improve the pore accessibility what would promote the solid electrolyte penetration inside the porous network, making possible efficient charge transfers. In this study, films prepared from different structuring agents are discussed in terms of microstructural properties (porosity, crystallinity) as well as effect on the dye loading and Spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) solid electrolyte filling. 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. Besides, we have implemented Rutherford backscattering spectrometry (RBS) as an innovative non-destructive tool to characterize the hole transporting materials infiltration. Templated films show dye loading more than two times higher than nanocrystalline films prepared by doctor-blade or screen-printing and solid electrolyte infiltration up to 88%. [less ▲]

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See detailNanosphere Lithography: A Powerful Method for the Controlled Manufacturing of Nanomaterials
Colson, Pierre ULg; Henrist, Catherine ULg; Cloots, Rudi ULg

in Journal of Nanomaterials (2013)

The never-ending race towards miniaturization of devices induced an intense research in the manufacturing processes of the components of those devices. However, the complexity of the process combined with ... [more ▼]

The never-ending race towards miniaturization of devices induced an intense research in the manufacturing processes of the components of those devices. However, the complexity of the process combined with high equipment costs makes the conventional lithographic techniques unfavorable for many researchers. Through years, nanosphere lithography (NSL) attracted growing interest due to its compatibility with wafer-scale processes as well as its potential to manufacture a wide variety of homogeneous one-, two-, or three-dimensional nanostructures. This method combines the advantages of both top-down and bottom-up approaches and is based on a two-step process: (1) the preparation of a colloidal crystal mask (CCM) made of nanospheres and (2) the deposition of the desired material through the mask. The mask is then removed and the layer keeps the ordered patterning of the mask interstices. Many groups have been working to improve the quality of the CCMs. Throughout this review, we compare the major deposition techniques to manufacture the CCMs (focusing on 2D polystyrene nanospheres lattices), with respect to their advantages and drawbacks. In traditional NSL, the pattern is usually limited to triangular structures. However, new strategies have been developed to build up more complex architectures and will also be discussed. [less ▲]

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See detailHigh Performance DSSC Based on Semiconducting Oxides Prepared Through Soft Chemistry Processes
Dewalque, Jennifer ULg; Schrijnemakers, Audrey ULg; Thalluri, Venkata Visveswara Gopala Kris ULg et al

Conference (2013, July)

DSSCs have been reported by O’Regan and Grätzel in the early nineties as a very promising alternative to conventional photovoltaic silicon devices. Main benefits of these cells are their low cost as well ... [more ▼]

DSSCs have been reported by O’Regan and Grätzel in the early nineties as a very promising alternative to conventional photovoltaic silicon devices. Main benefits of these cells are their low cost as well as their mild manufacturing process. In most of the specific literature, DSSCs are made of TiO2 films prepared by doctor-blade or screen-printing of anatase nanoparticles paste. However, due to the random organization of the nanoparticles, pore accessibility by the dye and electrolyte could be incomplete. Moreover, some anatase crystallites could suffer from a lack of connectivity, leading to electron transfer issues. The strategy adopted by our group to improve photovoltaic efficiencies involves a templating-assisted process allowing the preparation of highly porous layers with well-ordered and accessible pores as well as improved crystallites connectivity. The main goal is to increase the film surface area and to perfectly control the mesostructure in order to maximize the adsorption of active dye and the electrolyte infiltration inside the porous network. This talk especially focuses on the templating-assisted synthesis of TiO2 and ZnO semiconducting layers used as photoelectrode in DSSCs. Besides, due to the surface area improvement as well as the perfect control of the pore organization and the pore size, the templating strategy can be an effective solution to overcome light harvesting and solid electrolyte filling limitations encountered in solid-state DSSCs. Special effort is paid to the tuning of the TiO2 and ZnO semiconducting layers mesostructure in order to match with solid-state DSSC applications. [less ▲]

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See detailStudies on the Influence of Different Grain-sized Titania Scattering Layers for Dye Sensitized Solar Cells
Thalluri, Venkata Visveswara Gopala Kris ULg; Henrist, Catherine ULg; Vertruyen, Bénédicte ULg et al

Poster (2013, July)

The efficiencies of dye sensitized solar cells (DSCs) are boosted up to 12% by NIR light harvesting dyes and with the usage of scattering layer in the device preparation.The importance of Titania ... [more ▼]

The efficiencies of dye sensitized solar cells (DSCs) are boosted up to 12% by NIR light harvesting dyes and with the usage of scattering layer in the device preparation.The importance of Titania scattering layers was studied as a part of this work. These scattering layers were prepared from two different grain-sizes (100 nm & 500 nm) for SQ2-NIR and N3-UV/Vis DSCs. The 100 nm grain-sized Titania paste was commercially supplied and 500 nm grain-sized Titania paste was prepared according to literature. The morphological and structural properties of these bigger grain-sized Titania layers were deliberated by using and Scanning Electron Microscope (SEM) and X-Ray diffraction (XRD) measurements. The influence of these bigger grain-sized Titania scattering layers in SQ2-NIR and N3-UV/Vis DSCs were expounded by using various electro-optical characterization techniques such as light I-V, electrochemical impedance spectroscopy (EIS) shown in Figure 1 and external quantum efficiency (EQE) measurements. The importance of understanding the influence of these bigger grain-sized scattering Titania layers could pave a way for future design and optimizing of DSCs for increasing the amount of light harvesting. [less ▲]

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See detailTiO2 templated films used as photoelectrode for solid-state DSSC applications: study of the pore filling by Rutherford Backscattering Spectroscopy
Dewalque, Jennifer ULg; Colson, Pierre ULg; Thalluri, Venkata Visveswara Gopala Kris ULg et al

Poster (2013, July)

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. However, in solid-state DSSCs, TiO2 films thickness is limited to few µm allowing the adsorption of only a low quantity of photoactive dye and thus leading to a poor light harvesting and low conversion efficiencies. In order to overcome this limitation, templated-assisted dip-coating techniques are used to obtain thin films with high surface area. Moreover, templating is expected to improve the pore accessibility what would promote the solid electrolyte penetration inside the porous network, making possible efficient charge transfers. In this study, films prepared from different structuring agents are discussed in terms of microstructure properties (porosity, crystallinity) and impact on the dye loading and solid electrolyte filling. As-obtained templated films have been compared to nanocrystalline films prepared by doctor blade or screen printing as reference. 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. Solid electrolyte infiltration has been extensively investigated by Rutherford Backscattering Spectroscopy (RBS). Finally, templated films were evaluated as photoelectrode in solid-state DSSCs and compared to nanoparticles layers. [less ▲]

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See detailSystematic processing of β – tricalcium phosphate for efficient protein loading and in vitro analysis of antigen uptake
Ozhukil Kollath, Vinayaraj ULg; De Geest, Bruno; Mullens, Steven et al

in Advanced Engineering Materials (2013), 15(4), 295-301

Microparticulate calcium phosphate (CaP) powders are promising drug carriers because of their biocompatibility and degradability under physiological conditions. The adsorption capability of CaP ... [more ▼]

Microparticulate calcium phosphate (CaP) powders are promising drug carriers because of their biocompatibility and degradability under physiological conditions. The adsorption capability of CaP microparticles makes them interesting candidates, within the inorganic carrier materials, for delivering protein antigens to professional antigen presenting cells (APC) for vaccination purpose. However, in order to bind and deliver a sufficient amount of protein, the challenge is to effectively increase the binding capacity of this material. In this study, b-tricalcium phosphate (b-TCP) powder is engineered to obtain microparticles with increased protein loading, using bovine serum albumin as a model antigen. The decrease in particle size and increase in specific surface area of carrier is shown to strongly affect protein adsorption. Finally, we demonstrate that the processed b-TCP is capable of delivering its protein payload in vitro to dendritic cells, which are professional APCs and the target cell population for microparticulate vaccines. [less ▲]

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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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