Low-temperature electrodeposition approach leading to robust mesoscopic anatase TiO2 films

Anatase TiO2, a wide bandgap semiconductor, likely the most worldwide studied inorganic material for many practical applications, offers unequal characteristics for applications in photocatalysis and sun energy conversion. However, the lack of controllable, cost-effective methods for scalable fabrication of homogeneous thin films of anatase TiO2 at low temperatures (ie. < 100 °C) renders up-to-date deposition processes unsuited to flexible plastic supports or to smart textile fibres, thus limiting these wearable and easy-to-integrate emerging technologies. Here, we present a very versatile template-free method for producing robust mesoporous films of nanocrystalline anatase TiO2 at temperatures of/or below 80 °C. The individual assembly of the mesoscopic particles forming ever-demonstrated high optical quality beads of TiO2 affords, with this simple methodology, efficient light capture and confinement into the photo-anode, which in flexible dye-sensitized solar cell technology translates into a remarkable power conversion efficiency of 7.2% under A.M.1.5G conditions

Electrodeposition of TiO2 Using Ionic Liquids

International audienceWe report on the electrodeposition of TiO2 upon transparent conducting oxide (ITO) by using a milder electrochemical bath based on room-temperature ionic liquids (1-ethyl-3-methyl imidazolium-bis(trifluoromethylsulfonyl)imide)) and titanium butoxide as a soluble precursor. By taking advantage of oxygen reduction which proceeds about 500 mV before titanium +IV reduction, wellcrystallized thin films of anatase TiO2 are tailored under potentiostatic control at −1.5 V (vs. AgCl/Ag) / 100◦C followed by a rapid post-annealing treatment at 500◦C in air

Exceptional activity of mesoporous beta-MnO2 in the catalytic thermal sensitization of ammonium perchlorate

Mesoporous beta-MnO2 has been prepared, characterized and demonstrated to possess excellent catalytic activity in the thermal decomposition of ammonium perchlorate. The observed unprecedentedly low decomposition temperatures, fast reaction rates and enhanced heat releases in the catalysed formulations make mesoporous beta-MnO2 promising as a high-performing ballistic modifier in AP-based composite solid rocket propellants

Glycerol-plasticized agarose separator suppressing dendritic growth in Li metal battery

International audienceThe growth of dendrite is the major limitation to the development of the Li-metal battery. To solve it, we disclose the preparation and performances of separator (MAGly) with a complete “green” formulation using biosourced and sustainable compounds: agarose as biopolymer along with glycerol as plasticizing agent. The natural biopolymer films are non-porous in nature and possess high elasticity with high stiffness along a wide temperature range (−35 to 180 °C), able to prevent the perpendicular dendritic Li growth. Moreover, they provide high Li+ ionic conductivity, which was evident from electrochemical symmetrical battery tests resulted in efficient plating/stripping of Li metal, without dendrite formation. Preliminary tests in Li battery, with LiFePO4 as positive electrode show very satisfying performance regarding the same test with the commercial Celgard® separator. Furthermore, the application of this new sustainable separator can be extended to post Li-metal system as demonstrated by the electrochemical tests realized with K+/K

Design of Laccase–Metal Organic Framework-Based Bioelectrodes for Biocatalytic Oxygen Reduction Reaction.

International audienceLaccase in combination with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator is a well-known bioelectrocatalyst for the 4-electron oxygen reduction reactions (ORR). The present work deals with the first exploitation of mesoporous iron(III) trimesate-based metal organic frameworks (MOF) MIL-100(Fe) (MIL stands for materials from Institut Lavoisier) as a new and efficient immobilization matrix of laccase for the building up of biocathodes for ORR. First, the immobilization of ABTS in the pores of the MOF was studied by combining micro-Raman spectroscopy, X-ray powder diffraction (XRPD), and N2 porosimetry. The ABTS-MIL-100(Fe)-based modified electrode presents excellent properties in terms of charge transfer kinetics and ionic conductivity as well as a very stable and reproducible electrochemical response, showing that MIL-100(Fe) provides a suitable and stabilizing microenvironment for electroactive ABTS molecules. In a second step, laccase was further immobilized on the MIL-100(Fe)-ABTS matrix. The Lac-ABTS-MIL-100(Fe)-CIE bioelectrode presents a high electrocatalytic current density of oxygen reduction and a reproducible electrochemical response characterized by a high stability over a long period of time (3 weeks). These results constitute a significant advance in the field of laccase-based bioelectrocatalysts for ORR. According to our work, it appears that the high catalytic efficiency of Lac-ABTS-MIL-100(Fe) for ORR may result from a synergy of chemical and catalytic properties of MIL-100(Fe) and laccase

Room-Temperature Synthesis of High Surface Area Anatase TiO2 Exhibiting a Complete Lithium Insertion Solid Solution

International audienceThe synthesis of highly divided anatase TiO2 nanoparticles displaying 300 m(2) g(-1) surface area is achieved by following a two-step synthetic process at room temperature. The particles exhibit a needle-like morphology composed of self-assembled 4 nm nanoparticles. The crystallization process from amorphous TiO2.1.6H(2)O to oriented aggregation of anatase TiO2 proceeds according to a slow solid dehydration process takingplace in a large range of pH in deionized water (1 < pH < 12) or alternatively when including a low amount of NH4F(aq) in solution. Driven by their high surface area enhancing the chemical/electrochemical reactivity, it is reported in the case of the anatase TiO2 that a modification in the lithium insertion mechanism is no longer attributable to a two-phase reaction between the two-end members Li epsilon TiO2 and Li0.5 +/- TiO2 when downsizing the particle size, but instead through a complete solid solution all along the composition range

Room-Temperature Synthesis of Iron-Doped Anatase TiO2 for Lithium-Ion Batteries and Photocatalysis

International audienceIron-doped nanocrystalline particles of anatase TiO2 have been successfully synthesized using a complete room-temperature synthetic approach, leading to particles of high surface area (280 m2/g) and a narrowed band gap of 2.3 eV. These particles were introduced for photocatalysis under white light in standard conditions (AM1. 5G) and in lithium-ion batteries to reveal in these two aspects the pros and cons of the doping effect

Design of metal organic framework–enzyme based bioelectrodes as a novel and highly sensitive biosensing platform

International audienceNanocomposites combining the mesoporous iron(III) trimesate MIL-100(Fe) (MIL: Matériaux Institut Lavoisier) and platinum nanoparticles (Pt-NPs) have been used as immobilization matrices of glucose oxidase (GOx). Due to the physico-chemical properties of Pt-NPs (electroactivity) and MIL-100(Fe) (high specific surface area and pore volume, biocompatibility), the resulting GOx–MIL-100(Fe)–PtNP bioelectrode exhibits excellent electrocatalytic performances for glucose detection. This novel glucose biosensor presents a high sensitivity of 71 mA M−1 cm−2 under optimum conditions and a low limit of detection of 5 μM with low response time (&lt;5 s). In contrast, substitution of iron by chromium or aluminum in MIL-100 leads to a much lower sensitivity and higher response time values, suggesting that the iron centres of MIL-100(Fe) may be involved in a synergistic effect which indeed enhances the catalytic oxidation of glucose and biosensor activity. Thus, this work extends the scope of MOF nanoparticles with engineered cores and surface to the field of highly sensitive, durable glucose biosensors

Room-Temperature Synthesis of Iron-Doped Anatase TiO₂ for Lithium-Ion Batteries and Photocatalysis

Iron-doped nanocrystalline particles of anatase TiO₂ (denoted <i>x</i>% Fe-TiO₂, with <i>x</i> the nominal [Fe] atom % in solution) have been successfully synthesized at room temperature by a controlled two-step process. Hydrolysis of titanium isopropoxide is first achieved to precipitate Ti­(OH)₄ species. A fine control of the pH allows one to maintain (i) soluble iron species and (ii) a sluggish solubility of Ti­(OH)₄ to promote a dissolution and condensation of titanium clusters incorporating iron, leading to the precipitation of iron-doped anatase TiO₂. The pH does then influence both the nature and crystallinity of the final phase. After 2 months of aging at pH = 2, well-dispersed nanocrystalline iron-doped TiO₂ particles have been achieved, leading to 5–6 nm particle size and offering a high surface area of ca. 280 m²/g. This dissolution/recrystallization process allows the incorporation of a dopant concentration of up to 7.7 atom %; the successful incorporation of iron in the structure is demonstrated by X-ray diffraction, high-resolution transmission electron microscopy, and Mössbauer spectroscopy. This entails optical-band-gap narrowing from 3.05 to 2.30 eV. The pros and cons effects of doping on the electrochemical properties of TiO₂ versus lithium are herein discussed. We reveal that doping improves the power rate capability of the electrode but, in turn, deserves the electrolyte stability, leading to early formation of SEI. Finally, we highlight a beneficial effect of low iron introduction into the anatase lattice for photocatalytic applications under standard AM1.5G visible-light illumination