Search

Ionic liquids and poly(ionic liquid)s act as bulk and/or passivation agents when used as additives in methylammonium-free lead perovskites, leading to devices showing enhanced power conversion efficiencies, reduced hysteresis and improved stability.

A new straightforward synthetic strategy has been elaborated to achieve star-shaped triazatrinaphthylene and, for the first time, triazatrianthrylene derivatives. Their solution- and solid-state properties were thoroughly characterized by cyclic voltammetry, UV-vis absorption spectroscopy, X-ray diffraction, and density functional theory calculations. Original hexagonal molecular arrangements were found in the crystal phase, which opens a new pathway for designing materials with improved three-dimensional charge-transport properties.

In this study, novel ZnO/ZnWO4 nanocatalysts were synthesized for the removal of organic compounds under ultraviolet (UV) and visible-light irradiation. ZnO was prepared by a homogenous precipitation process followed by an impregnation technique for the formation of ZnO/ZnWO4 photocatalysts with different percentages of tungsten. The resulting photocatalysts formed a mesoporous network of ZnO nanoparticles, with a size of 18 nm, and modified by tungsten, according to X-ray diffraction and N2 sorption analyses. Their morphology and composition were studied by transmission electron microscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. According to optical studies, the absorption edge of the ZnO nanomaterials revealed that the red-shift with augmented tungsten concentration resulted in a decrease in the forbidden energy gap (Eg) from 3.25 eV to 2.95 eV. Therefore, the ZnO/ZnWO4 compound absorbed light in the visible-light region, which probably indicates that the developed photocatalysts may be active in this region. The presence of surface hydroxyl groups was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, and these hydroxyl groups play a significant role in the photocatalytic activity of the compounds by catching the formed holes in the valence band under irradiation to create the hydroxyl radical, thus improving the photocatalytic property. Zn–ZnW0.2 showed the best photodegradation of rhodamine B (RhB), with a rate constant Kapp = 0.095 min−1 (98.5% degradation) and Kapp = 0.04 min−1 (91% degradation) after 30 and 60 min of irradiation under UV and visible light, respectively. This improvement was rationalized by the effective separation of photogenerated electron–hole (e−/h+) pairs due to the formation of a heterojunction structure between ZnWO4 (ECB = +0.165 eV; EVB = 2.885 eV) and ZnO (ECB = −0.365 eV; EVB = 3.115 eV). In addition, results confirmed that holes (h+) and ˙OH radicals are the major reactive species involved in the photodegradation of RhB dye. A possible reaction mechanism was proposed for explaining the photodegradation of RhB over the ZnO/ZnWO4 photocatalyst. The Zn–ZnW0.2 photocatalyst retained its high photodegradation rate and good photostability over four consecutive cycles with no changes in its morphology.

Due to their outstanding electrochemical properties, electrical conductivity, flexibility, and low-cost, carbon materials open up new opportunities for the design of compact devices with a wide variety of potential applications. Biomass renewable resources for carbon material preparation have attracted huge attention in the last few years due to their widespread availability, low-cost processability and high-performance of the resulting porous carbons for sustainable technological applications. For example, the porosity and morphology of carbon materials, which can be tuned by different activation methods, govern the ion diffusion rate during supercapacitor charge/discharge processes. On the other hand, carbon electrodes have been applied as electrodes for dye-sensitized and perovskite solar cells, thanks to their low fabrication cost, compact structure, and optimized interfaces, which play a key role in the charge collection and stability of the devices. Moreover, due to the possibility of using carbon electrodes for storage and conversion devices, efficient methods to harvest and store energy in one single device are crucial for technological advancement and the energy transition process. This contribution aims to review the advances made in the use of carbon materials obtained from biomass sources as electrodes for storage and energy conversion devices, and the future application of shared and/or distinct carbon electrodes for the development of integrated power packs including supercapacitors and dye-sensitized or perovskite solar cells. The storage properties of supercapacitors are discussed in terms of the textural characteristics of biomass-derived activated carbons while the photovoltaic parameters of solar cells based on bio-sourced carbons are compared with those of devices using conventional metal-based electrodes. Finally, special emphasis is placed on the energy conversion–storage efficiencies of solar cell-supercapacitor integrated devices.

A theoretical study on four organic dyes based on bis(4-hexyloxy)triphenylamine as donor and electron acceptor cyanoacrylic acid with a donor–π–acceptor structure (D–π–(D–A–)–A) using DFT/DFT (TD-DFT)/6-31G(d,p) having a difference of π spacer was designed. The theoretical study of the structural, electronic and optical properties of these dyes (D1, D4) suggests that these materials would be excellent sensitizers as a candidate for the production of dye solar cells, due to the efficient photoinduced electron transfer and strong absorption as well as the electronic properties (HOMO, LUMO, Egap) low band gap, The improved light-harvesting efficiency and free energy change of electron injection (ΔGinject), of new designed sensitizers revealed that these materials would be excellent sensitizers. This theoretical designing paves the way for experimentalists to synthesize more efficient sensitizers for solar cells.

One of the biggest global challenges for our societies is to provide natural resources to the rapidly expanding population while maintaining sustainable and ecologically friendly products. The increasing public concern about toxic insecticides has resulted in the rapid development of alternative techniques based on natural infochemicals (ICs). ICs (e.g., pheromones, allelochemicals, volatile organic compounds) are secondary metabolites produced by plants and animals and used as information vectors governing their interactions. Such chemical language is the primary focus of chemical ecology, where behavior-modifying chemicals are used as tools for green pest management. The success of ecological programs highly depends on several factors, including the amount of ICs that enclose the crop, the range of their diffusion, and the uniformity of their application, which makes precise detection and quantification of ICs essential for efficient and profitable pest control. However, the sensing of such molecules remains challenging, and the number of devices able to detect ICs in air is so far limited. In this review, we will present the advances in sensing of ICs including biochemical sensors mimicking the olfactory system, chemical sensors, and sensor arrays (e-noses). We will also present several mathematical models used in integrated pest management to describe how ICs diffuse in the ambient air and how the structure of the odor plume affects the pest dynamics.

International audience; For practical applications, flexible solid-state dye-sensitized solar cells (ss-DSSCs) with high photovoltaic per-formance and stability are paramount. A novel iodine (I2)-free polysiloxane based highly conductive poly(ionic liquid), which acts as the lone charge transfer intermediate, is used for the first time as an electrolyte in flexible 1D TiO2 nanotube photoanodes (TiO2 NT) based ss-DSSCs. The I2-free polymer electrolyte plasticized with ethylene carbonate (EC) leads to a higher power conversion efficiency in DSSCs involving TiO2 NTs than the I2- based polymer electrolyte, mainly due to improved Voc and Jsc. Apart from overcoming the visible light ab-sorption loss, this I2-free polymer electrolyte also reduces the charge recombination and thus leads to higher electron lifetime in DSSCs. The I2-free DSSCs also displayed long-term stability measured under ambient and accelerated stability testing. The improvement is also due to the effective pore infiltration into the large pores of TiO2 NT structure in ss-DSSCs.

International audience; An efficient metal-free formulation of a hole transport material (HTM) based on an ionic liquid polymer is developed for n-i-p perovskite solar cells (PSCs), to address reproducibility issues related to the use of complex dopant mixtures based on lithium salts and cobalt coordination complexes. The conductivity of the HTM is thus significantly improved by 4 orders of magnitude, up to 1.9 x 10-3 S.cm-1, using poly(1-butyl-3-vinylimidazolium bis(trifluoromethylsulfonyl)imide) (PVBI-TFSI) as dopant. Introduced in the FTO/c-TiO2/mp-TiO2/K0.05(MA0.15FA0.85)0.95PbI2.55Br0.45/HTM/Au PSC configuration, PVBI-TFSI-HTM formulation shows power conver-sion efficiency as high as 20.3 %, versus 18.4 % for the standard lithium salt-HTM formulation, with considerably re-duced hysteresis and excellent reproducibility. Mechanistic investigations suggest that PVBI-TFSI acts as a source of protons promoting the HTM oxidation.

A highly selective chemisensor for 2-nitrophenol detection was fabricated using ZnO/RuO2 nanoparticles (NPs) synthesized by impregnation method. The as-synthesized NPs were characterized through UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDS), FTIR and X-ray diffraction (XRD). A glassy carbon electrode was modified with as-synthesized ZnO/RuO2 nanoparticles and utilized as a chemical sensor for the detection of 2-nitrophenol. The fabricated sensor exhibited excellent sensitivity (18.20 μA μM−1 cm−2), good reproducibility, short response time (8.0 s.), the lowest detection limit (52.20 ± 2.60 pM) and long-term stability in aqueous phase without interference effects. Finally, the fabricated sensor was validated as a 2-NP probe in various environmental water samples at room conditions.

International audience; We report on the potential of tuning poly(9-vinylcarbazole) (PVK) properties through functionalization for an application as hole transport material (HTM) for perovskite solar cells (PSCs). The synthesized PVK-based polymers were substituted with moieties of interest to improve the solubility, the charge transport properties, or to tune energy levels. Bis(4-methoxyphenyl)amine moieties were found to improve the hole mobility and to increase the HOMO level of the PVK. Therefore, PSCs employing PVK-[N(PhOCH3)2]2 as HTM exhibited a best PCE of 16.7%. Compared to spiro-OMeTAD, first studies have shown that PVK-[N(PhOCH3)2]2 could extend PSC lifetime.

The present work deals with the synthesis of multichromophores which strongly absorb the solar spectrum to functionalize the nanoparticle oxide semiconductor used in the hybrid cells. At first, we developed a material that forms a chromophore triphenodioxazine. We obtained some triphenodioxazines with high yields up to 70 percent. On the other hand, we have carried out many tests such as UV-Visible, Cyclic voltammetry for our molecules to check their electronic and optical properties. The results confirmed that these chromophores meet the criteria for use in photovoltaic cells. Finally, we have successfully realized photovoltaic cells with triphenodioxazine. The findings were very interesting since the photovoltaic conversion efficiencies ranged from 4.30% to 6.30%. The new synthesis strategy of these chromophores opens a way for the development of organic materials used for photovoltaics.

Increased levels of nitrate (NO3-) in the environment can be detrimental to human health. Herein, we report a robust, cost-effective, and scalable, hybrid material-based colorimetric/luminescent sensor technology for rapid, selective, sensitive, and interference-free in situ NO3- detection. These hybrid materials are based on a square-planar platinum(II) salt [Pt(tpy)Cl]PF6 (tpy = 2,2';6',2″-terpyridine) supported on mesoporous silica. The platinum salt undergoes a vivid change in color and luminescence upon exposure to aqueous NO3- anions at pH ≤ 0 caused by substitution of the PF6- anions by aqueous NO3-. This change in photophysics of the platinum salt is induced by a rearrangement of its crystal lattice that leads to an extended Pt···Pt···Pt interaction, along with a concomitant change in its electronic structure. Furthermore, incorporating the material into mesoporous silica enhances the surface area and increases the detection sensitivity. A NO3- detection limit of 0.05 mM (3.1 ppm) is achieved, which is sufficiently lower than the ambient water quality limit of 0.16 mM (10 ppm) set by the United States Environmental Protection Agency. The colorimetric/luminescence of the hybrid material is highly selective to aqueous NO3- anions in the presence of other interfering anions, suggesting that this material is a promising candidate for the rapid NO3- detection and quantification in practical samples without separation, concentration, or other pretreatment steps.

Stimuli responsive composites consisting of inorganic or organometallic coordination substrates supported on porous platforms that integrate and improve the key features of both the substrate and platform, open the doorway to advanced multifunctional materials. This work presents a new class of stimuli responsive multifunctional materials based on platinum(II) terpyridyl luminophores@silica composites. Presented here is how the intercalation of Pt(II) salts with a planar architecture and sterically permitting terpyridyl ligands within meso or microporous silica support impacts Pt(II) spectroscopies. The photophysics and luminescence properties of square-planar Pt(II) salts are dictated by their intermolecular, non-covalent Pt⋯Pt interactions between the individual Pt(II) units; a feature that has been explored in designing stimuli responsive materials. This work explores a novel methodology where the electronic structure and luminescence behavior of such salts are systematically varied through their intercalation within rigid silica frameworks. The intercalation of Pt(II) complexes with varied degrees of non-covalent Pt⋯Pt interactions in the virgin form within meso-macroporous silica supports generates materials that show marked variation in their electronic structure and luminescence behavior compared to their virgin salts. Further, the spectroscopies show a systematic dependance on the mean pore size of the silica support. The X-ray powder diffraction and microscopy studies reveal these behaviors to be related to the perturbations in their long-range structural order, that gets reflected in their microcrystalline dimensions and particle morphologies.

International audience; Facet-engineered monoclinic scheelite BiVO4 particles decorated with various cocatalysts were successfully synthesized by selective sunlight photodeposition of metal or metal oxy(hydroxide) nanoparticles onto the facets of truncated bipyramidal BiVO4 monoclinic crystals coexposing {010} and {110} facets. X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning Auger microscopy revealed that metallic silver (Ag) and cobalt (oxy)hydroxide (CoOx(OH)y) particles were selectively deposited onto the {010} and {110} facets, respectively, regardless of the cocatalyst amount. By contrast, the nickel (oxy)hydroxide (NiOx(OH)y) photodeposition depends on the nickel precursor amount with an unprecedented selectivity for 0.1 wt % NiOx(OH)y/BiVO4 with a preferential deposition onto the {010} facets and the edges between the {110} facets. Moreover, these noble metal-free heterostructures led to remarkable photocatalytic properties for rhodamine B photodecomposition and sacrificial water oxidation reactions. For instance, 0.2 wt % CoOx(OH)y/BiVO4 led to one of the highest oxygen evolution rates, i.e., 1538 μmol h–1 g–1, ever described which is ten times higher than that found for bare BiVO4. The selective deposition of cobalt (oxy)hydroxide species onto the more electron-deficient facet of truncated bipyramidal monoclinic BiVO4 particles favors photogenerated charge carrier separation and therefore plays a key role for efficient photochemical oxygen evolution.

Facet-engineered monoclinic scheelite BiVO

Carbon from biomass as an active material for supercapacitor electrodes has attracted much interest due to its environmental soundness, abundance, and porous nature. In this context, activated carbon prepared from coconut shells

International audience; By using 1,2-propanediol instead of the classic polyol solvent, ethylene glycol, ultra-long silver nanowires are obtained in only 1 h. These nanowires lead to transparent electrodes with a sheet resistance of 5 Ohms per sq at a transparency of 94%, one of the highest figures of merit for nanowire electrodes ever reported.

Three new dyes encompassing the organometallic [Ru(dppe)2] (dppe = 1,2-bis(diphenylphosphino)ethane) fragment were designed and prepared for application in dye-sensitized solar cells. Introduction of the strong electron-withdrawing benzothiadiazole (BTD) unit as an additional acceptor in the attracting ligand led to original D−[M]−A−π−A′ architectures. In particular the use of a thienyl-BTD motif led to a narrow bandgap sensitizer with deep-green coloration. The dye afforded 5.2% power conversion efficiency in TiO2-based DSSC device in the presence of the iodine/iodide couple as redox mediator. A joint experimental and theoretical study of the new dyes is reported.

Polycrystalline anatase thin films, (001)- and (101)-oriented anatase TiO 2 single crystals and (001)- and (110)-oriented rutile TiO 2 single crystals with various surface treatments were studied by photoelectron spectroscopy to obtain their surface potentials. Regardless of orientations and polymorph, a huge variation of the Fermi level and work function was achieved by varying the surface condition. The most strongly oxidized surfaces are obtained after oxygen plasma treatment with a Fermi level ∼2.6 eV above the valence band maximum and ionization potentials of up to 9.5 eV (work function 7.9 eV). All other treated anatase surfaces exhibit an ionization potential independent of surface condition of 7.96 ± 0.15 eV. The Fermi level positions and the work functions vary by up to 1 eV. The ionization potential of rutile is ∼0.56 eV lower than that of anatase in good agreement with recent band alignment studies.

Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan–French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.

TiO2 electrodes were modified with different WO3 loadings and photoelectrochemical characterization revealed an increase in photocurrent density and decrease in interface charge transfer resistance with increasing amount of WO3. A decrease in green PL was observed with WO3 addition indicating more mobility of charges and therefore less probability of recombination. A series of TiO2 photoanodes modified by WO3 were designed with different geometrical configurations for dye-sensitized solar cell (DSSC) applications, WO3 was introduced successively in the screen-printed paste, as an undercoat and in the TiCl4 pretreatment bath. The results indicated a decrease in photovoltaic performance of all devices modified by WO3 compared to TiO2 reference cell. The highest conversion efficiency of the modified cells was observed for the configuration of WO3 introduced into the TiCl4 pretreatment bath. In this case, the optimized contact between the coupled semiconductors improved the charge transfer, also the direct contact of WO3 with the FTO substrate decreased the loss of electrons by confinement and recombination.

Undoped and Zn-doped SnO2 nanocrystals were prepared using a straightforward polyol method and the influence of the doping on the structural, textural, and optical properties was carefully studied. X-ray diffraction (XRD) patterns revealed after annealing the formation of cassiterite, i.e. rutile-like, tetragonal SnO2 crystallites and the absence of any crystalline zinc phase whatever the doping concentration. However, the average crystallite size decreased from 9 to 6.5 nm when the doping concentration increased from 0 to 10 at%, respectively. Furthermore, Transmission Electron Microscopy (TEM) and N2 sorption porosimetry showed that all samples prepared were made of an aggregated network of almost spherical nanoparticles, the size of which decreased when increasing the doping concentration up to 10 at%. The presence of SnO2 and zinc oxide species was assessed by EDX (Energy Dispersive X-ray spectroscopy) analysis. According to UV–visible absorption measurements, this decrease in nanoparticle size was accompanied by a decrease in the band gap value from 3.50 eV for undoped SnO2 to 3.17 eV for 10 at% Zn-doped SnO2. The photocatalytic properties of undoped and Zn-doped SnO2 nanoparticles were evaluated by studying the photodecomposition of methylene blue (MB) and methyl orange (MO) as organic pollutant models. The 10 at% Zn-doped SnO2 nanoparticles showed the highest photocatalytic activity for both MB and MO decomposition and led to an almost complete discoloration of MB solutions, i.e. 98%, after irradiation of 120 min and to an apparent MB degradation constant rate reaching 0.058 min−1.

Nanometric V-doped particles with vanadium concentration varying from 0 to 10% were prepared using the polyol method. The influence of the doping on the textural, structural and optical properties was studied by various methods of characterization. X-ray diffraction (XRD) patterns disclose that nanocrystallites of cassiterite, i.e. rutile-like tetragonal structure SnO2 and the absence of a new vanadium phase in the XRD pattern in the different concentration of doping were formed after annealing, the ordinary crystallite size decreased from 20.6 to 12.3 when the doping concentration increased from 0 to 10%, respectively. Moreover, the N2 sorption porosimetry and transmission electron microscopic show that all samples synthesized were constituted of an aggregated network of almost spherical nanoparticles, which sizes changed with the altitude in the doping concentration to 10%. In accordance with UV–visible absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.25 eV, for undoped SnO2, to 2.75 eV, for SnO2 doped at 10%. On the other part, the photocatalytic activity of undoped and V-doped SnO2 nanoparticles was studied using methylene blue (MB) as model organic pollutants. The SnO2 nanoparticles doped at 10% of vanadium disclosed that the discoloration of MB reached 97.4% after irradiation of 120 min, with an apparent constant rate of the degradation reaching 0.035 min−1 for MB degradation that was about 2.5 times more than that of pure SnO2 (0.014 min−1).

A combined computational and experimental study has been performed to investigate the best carbazole dyes for iodide- and cobalt-based DSSCs. TDDFT calculations have been implemented to figure out the electronic properties of three kinds of carbazole dyes, namely SD4, JM1 and JM2. These carbazole dyes have similar structures and their main difference lies on the position of their alkyl chain substituent. The calculated absorbance-spectra of the three dyes in the UV–visible range are in good agreement with the experimental results. The HOMO–LUMO analysis reveals that the SD4 dye has a better charge separation and a LUMO position slightly higher compared to the others. Calculations have been carried out to quantify the intramolecular charge-transfer (ICT). The result shows that JM2 has the highest q CT but unfortunately accompanied by a short d CT which indicates that the opportunity of electron recombination is high in JM2. The computational results also indicate that SD4 is the most promising candidate as a sensitizer in DSSC compared to JM1 and JM2. These results are in agreement with our experimental test using iodide-based electrolyte. On the other hand, the experiments show that JM2, which has two hexyl chains located in the edge of molecule, has the best performance when coupled with cobalt-based electrolyte.

A highly selective chemisensor for 2-nitrophenol detection was fabricated using ZnO/RuO

International audience; The development of NiO-based molecular photocathodes is attracting growing interest in thefield of dye-sensitized photoelectrochemical cells (DS-PEC) for efficient conversion of sunlightinto fuel. For this purpose different strategies are developed to assemble the molecularcomponents together in order to build functional devices. Here, an original dye-catalystsupramolecular assembly was designed and obtained via axial coordination of a cobalt-basedH2-evolving catalyst, i.e. a cobaloxime complex, to a pyridyl-functionalized rutheniumdiacetylide photosensitizer. The new supramolecular assembly was successfully employed forthe construction of efficient NiO-based photocathodes for solar hydrogen production. We reporta joint experimental and theoretical study of the new photocatalytic system, includingelectrochemical and XPS analyses. Photo-electrochemical generation of H2 under pertinentaqueous conditions eventually led to a faradaic efficiency of 27 %

Earth-abundant NiO/anatase TiO2 heteronanostructures were prepared by a straightforward one-pot sol–gel synthetic route followed by a suitable thermal post-treatment. The resulting 0.1–4 wt% NiO-decorated anatase TiO2 nanoparticles were characterized by X-ray diffraction, electron microscopy, Raman and UV-visible spectroscopy and N2 sorption analysis, and showed both nanocrystallinity and mesoporosity. The careful determination of the energy band alignment diagram by a suitable combination of XPS/UPS and absorption spectroscopy data revealed significant band bending at the interface of the p–n NiO/anatase TiO2 heterojunction nanoparticles. Furthermore, these heterojunction photocatalysts exhibited an improved photocatalytic activity in H2 production by methanol photoreforming compared to pure anatase TiO2 and commercial P25. Thus, an average H2 production rate of 2693 μmol h−1 g−1 was obtained for the heterojunction of a 1 wt% NiO/anatase photocatalyst, which is one of the most efficient NiO/anatase TiO2 systems ever reported. An enhanced dissociation efficiency of the photogenerated electron–hole pairs resulting from an internal electric field developed at the interface of the NiO/anatase TiO2 p–n heterojunctions is suggested to be the reason of this enhanced photocatalytic activity.

Using the polyol method and a thermal post-treatment, nanoporous tin dioxide (SnO2) were prepared at different hydrolysis ratio (h = n (H2O)/n (Sn)). The influence of the hydrolysis ratio on the structural, textural, optical and electrical properties of SnO2 nanopowders was investigated by employing a set of various techniques including Fourier Transform Infra-Red spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), Energy Dispersive X-ray spectroscopy (EDX), Scanning Electron Microscopy (SEM), Nitrogen Sorption Porosimetry and Impedance Spectroscopy. FTIR and EDX studies revealed that SnO2 species were obtained. Nanocrystallites of cassiterite, i.e. rutile-like tetragonal SnO2 structure, were formed after annealing in air at 700 °C and the average crystallite size increased from 12.8 to 29.1 when the hydrolysis ratio rose from 17 to 24. Moreover, TEM, SEM, and N2 sorption porosimetry investigations indicated that the sample prepared for h = 17 was composed of an aggregated network of almost spherical nanoparticles, the morphology and sizes of which changed with the increase in the hydrolysis ratio to h = 24 and the mesoporosity of which was found to be linked to the interparticle space. Moreover, this increase in mean nanoparticle size was accompanied by a decrease in the band gap value from 3.4 eV (h = 17) to 3.16 eV (h = 24). Finally, bulk conductivity dependence with temperature was found to follow an Arrhenius law for samples annealed at 700 °C with an activation energy of 0.65 eV for h = 17, 0.69 eV for h = 20 and 0.71 eV for h = 24 that is typical of SnO2 nanopowders.

Nanocrystalline mesoporous pure and vanadium-doped (0–10 at%) SnO2 nanopowders were prepared by the polyol route. Compositional, textural and structural properties of pure and V-doped SnO2 nanopowders were thoroughly characterized by FTIR, XRD, TEM, DTA/TGA/MS, N2 sorption porosimetry and UV–visible Diffuse Reflectance Spectroscopy. According to XRD patterns, undoped and V-doped SnO2 materials exhibited the typical rutile-type tetragonal structure of SnO2 with average crystallite sizes ranging from 8.8 to 5.4 nm when the vanadium content was increased up to 10 at%. As shown by UV–visible Diffuse Reflectance Spectroscopy, this decrease in particle size was accompanied by a decrease of the band gap energy value from 3.36 eV for pure SnO2 down to 2.2 eV for 10 at% V-doped SnO2. Moreover, both FTIR and EDX analyses assessed the presence of SnO2 and vanadium oxide species the amount of which increasing with the doping content. Finally, the nanopowders prepared were composed of a mesoporous network of aggregated nanoparticles with BET specific areas increasing from 46.6 ± 1.5 to 61.7 ± 2 m2 g−1 when the vanadium concentration was varied from 0 to 10 at%. The V-doped nanopowders prepared by the polyol method therefore showed all the required textural and structural features to be used as visible photocatalysts or active layer in gas sensors.

The formation of heterostructures has proven to be a viable way to achieve high photoelectrochemical water splitting efficiencies with BiVO4 based photoanodes. Especially, cobalt and nickel based oxides are suitable low cost contact materials. However, the exact role of these contact materials is not yet completely understood because of the difficulty to individually quantify the effects of surface passivation, charge carrier separation and catalysis on the efficiency of a heterostructure. In this study, we used photoelectron spectroscopy in combination with in situ thin film deposition to obtain direct information on the interface structure between polycrystalline BiVO4 and NiO, CoOx and Sn-doped In2O3 (ITO). Strong upwards band bending was observed for the BiVO4/NiO and BiVO4/CoOx interfaces without observing chemical changes in BiVO4, while limited band bending and reduction of Bi and V was observed while forming the BiVO4/ITO interface. Thus, the tunability of the Fermi level position within BiVO4 seems to be limited to a certain range. The feasibility of high upwards band bending through junctions with high work function (WF) compounds demonstrate that nickel oxide and cobalt oxide are able to enhance the charge carrier separation in BiVO4. Similar studies could help to identify whether new photoelectrode materials and their heterostructures would be suitable for photoelectrochemical water splitting.

International audience; Facet-engineered anatase TiO2 with NiO nanoparticles heterocontacts were successfully prepared by selective photodeposition of NiO nanoparticles onto the {101} facet of the top-truncated bipyramidal TiO2 anatase nanocrystals coexposed with {001} and {101} facets. The morphology and electronic properties of the resulting 0.1–10 wt % NiO-decorated TiO2 were investigated by X-ray diffraction, high-resolution electron microscopy, N2 sorption analysis, and UV–vis spectroscopy. Furthermore, a careful determination of the energy band alignment diagram was conducted by a model experiment using XPS and UPS to verify charge separation at the interface of the NiO−TiO2 heterostructure. The model experiment was performed by stepwise deposition of NiO onto oriented TiO2 substrates and in-situ photoelectron spectroscopy measurements without breaking vacuum. Core levels showed shifts of 0.58 eV toward lower binding energies, meaning an upward band bending in TiO2 at the NiO–TiO2 interface. Furthermore, 0.1 wt % NiO–TiO2 exhibited 50% higher activities than the pure TiO2 for methylene blue (MB) photodecomposition under UV irradiation. This enhanced photocatalytic activity of NiO–TiO2 nanocomposites was related to the internal electric field developed at the p–n NiO−TiO2 heterojunction, leading to vectorial charge separation. Finally, mechanistic studies conducted in the presence of carrier or radical scavengers revealed that holes dominantly contributed to the photocatalytic reactions in the case of NiO–TiO2 photocatalysts while electrons played the main role in photocatalysis for the pure TiO2 materials.

International audience; This article describes a cell architecture that achieves enhanced light harvesting with less dye quantity while simultaneously improving the performance of the polysiloxane-based solid-state dye-sensitized solar cells (DSSCs). We report the synthesis of bimodal mesoporous anatase TiO2 films by a dual templating approach, combining a block-copolymer template (Pluronic P123) and polystyrene nanospheres (PS) as soft and hard templates, respectively. The AFM and TEM analysis of TiO2 films revealed a mixture of mesoporous and macroporous morphology in which dual porosity is generated by combustion of soft and hard templates. The size of the macropores was varied by employing PS beads with different diameters (62, 130 and 250 nm). The influence of the macropore size on the dye loading and pore infiltration is the main purpose of this article. The bimodal porosity leads to increased light scattering due to enhanced optical path length, and better pore infiltration of the polysiloxane electrolyte is achieved. The amount of dye uptake by the dual films is lower than that of soft films because the large pore size reduces the total surface area. The optimum bimodal structure was obtained when combining P123 surfactant and the 130 nm PS beads leading to the lowest charge transfer resistance and a high efficiency for DSSCs is reported with both liquid and polymer electrolytes. Even if the dye uptake was lower, the photovoltaic performance has been maintained and improved in some devices. The open circuit voltage and fill factor were improved, owing to a successful joining of different effects i.e. increased light harvesting, facile electrolyte penetration and reduced charge recombination.

International audience; In this article, we discuss the effect of the polysiloxane-based poly(ionic liquid) (PIL) electrolytes viscosity on the infiltration into mesoporous and bimodal TiO2 thin films with different thickness, and consequently on the DSSC performance. The mesoporous films contain small mesopores of 8–10 nm, resulted from the use of Pluronic P123 surfactant (SOFT), resulting in high surface area. The DUAL (soft/hard) templated films have unique bimodal porous structures comprising 8–10 nm mesopores and 60–70 nm macropores resulted from the use of P123 and 130 nm polystyrene beads, which encouraged the electrolyte pore infiltration and light harvesting. Electrochemical impedance spectroscopy confirms the lower charge transfer resistance of the DUAL templated TiO2 films as opposed to SOFT TiO2 electrodes which corresponds to higher DSSC efficiency, despite having lower dye adsorption thanks to the improved PIL electrolyte infiltration within larger pores. The addition of ionic liquids to PIL significantly lowers the viscosity, increases the ionic conductivity and I3− diffusion rate, resulting in noticeable improvement in photovoltaic performance in both SOFT and DUAL templated photoanodes for all the observed thickness.

International audience; NiO/(101)-anatase-TiO2 heterostructure nanoparticles were synthesized by depositing NiO onto the (101) facet of anatase crystals via the supercritical fluid chemical deposition (SFCD) route. Thorough characterization experiments performed by various techniques (XRD, UV-Vis DRS, N2 sorption, HR-TEM, EDX, and XPS) indicate that the SFCD method allowed a good dispersion of NiO onto the TiO2 nanoparticles for NiO amounts below 2 wt%. Compared to pure TiO2, the 0.1–1 wt% NiO–TiO2 nanocomposites showed enhanced photocatalytic properties for methylene blue (MB) and methyl orange (MO) decomposition under UV light irradiation, the 0.25 wt% NiO–TiO2 system leading to the highest efficiencies. The photocatalytic properties were then rationalized in terms of the acidic properties and electronic structures of the NiO–TiO2 nanocomposites. This higher photocatalytic activity was mainly related to the heterocontact at the interface of the NiO–TiO2 crystallites and to the enhanced reaction rates at the NiOx surface.

The photocatalytic (PC) performance of titanium dioxide (TiO2) nanoparticles strongly depends on their specific surface, the presence of crystal defects, their crystal phase, and the exposed crystal facets. In order to understand which of these factors contributes most significantly to the PC activity of TiO2 colloids, all of them have to be individually analyzed. This study entails the synthesis of five anatase nanocrystal samples. By maintaining the same reactant ratios as well as hydrothermal sol–gel synthesis route and only varying the autoclaving time or temperature, different crystallite sizes are obtained under comparable experimental conditions. A decrease in PC performance with increase in specific surface area is found. Such an unexpected counterintuitive result establishes the basis for a better understanding of the crucial factors that ultimately determine the PC activity. These are investigated by studying nanocrystals bulk and surface structure and morphology using a selection of complementary analysis methods (X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), X-ray diffraction (XRD)…). It is found that a change in the nanocrystal morphology from an equilibrium state truncated tetragonal bipyramid to a more elongated rod-like structure accompanied by an increase in oxygen vacancies is responsible for an augmented PC activity of the TiO2 nanocrystals.

International audience; With the purpose of achieving highly stable and efficient polymer electrolytes for dye-sensitized solar cell (DSSC) applications, a series of new poly(ionic liquids) (PILs), namely, poly(1-N-methylimidazolium-pentylpolydimethylsiloxane)iodide, with different ratios of pentylimidazolium iodide moieties, have been studied and employed to prepare solid-state electrolytes for DSSCs. PILs were further mixed with two types of ionic liquids (ILs), 1-methyl-3-propylimidazolium iodide (MPII) and 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (MPITFSI), and a plasticizer, such as ethylene carbonate (EC), to lower their viscosity and to increase the diffusion coefficient and ionic conductivity. The assembled devices prepared, using the quasi-solid-state electrolytes showed, light-to-electricity conversion efficiencies up to 6% for an active area of 0.2064 cm2. After 250 days, PIL-based cells retained 84% of their initial efficiency. These new findings encourage worldwide practical applications of DSSCs.

Tin dioxide (SnO

International audience; Two metallo-organic dyes were synthesized and used for NiO sensitization in view of their photoelectrochemical applications. The new dyes present an original π-conjugated structure containing the [Ru(dppe)2] metal fragment with a highly delocalized allenylidene ligand on one side and a σ-alkynyl ligand bearing an electron-rich group, i.e. a thiophene or triphenylamine unit, and one or two anchoring functions on the other side. The optoelectronic, electrochemical and photoelectrochemical properties of the dyes were systematically investigated. A broad photoresponse was observed with the absorption maximum at 600 nm. The X-ray crystal structure of one precursor was obtained to elucidate the structural conformation of the organometallic complexes and theoretical calculations were performed in order to address the photophysical properties of the new dyes. These photosensitizers were further implemented in NiO-based photocathodes and tested as photocurrent generators under pertinent aqueous conditions in association with [Co(NH3)5Cl]Cl2 as an irreversible electron acceptor. The dye-sensitized photocathodes provided good photocurrent densities (40 to 60 μA cm(-2)) at neutral pH in phosphate buffer and a high stability was observed for the two dyes.

Clathrate hydrates are crystalline materials made of water molecules forming host cages within which guest molecules are located. The hydrogen bond network ensuring the stability of the host substructure includes ionic defects, having an impact on the physicochemical properties of the systems. In this paper, a new way of introducing these ionic defects is proposed. Type II clathrate hydrates mixing tetrahydrofuran (THF) and perchloric acid guest molecules are synthesized and investigated by means of calorimetric, X-ray diffraction, and Raman scattering measurements together with a computational structure relaxation in the density functional theory approximation. The formation of the mixed clathrate hydrate with perchlorate anion included in the large cage of the cationic host-substructure of the THF type II clathrate hydrate requires the cooling of a (1-α) THF·αHClO4·17H2O solution with α less than 0.125. Above this inherent limitation, a multiphasic regime is observed in the formation of clathrate hydrat...

Photocatalytic activities of mesoporous RuO2/TiO2 heterojunction nanocomposites for organic dye decomposition and H2 production by methanol photoreforming have been studied as a function of the RuO2 loading in the 1 10 wt % range. An optimum RuO2 loading was evidenced for both kinds of reaction, the corresponding nanocomposites showing much higher activities than pure TiO2 and commercial reference P25. Thus, 1 wt % RuO2/TiO2 photocatalyst led to the highest rates for the degradation of cationic (methylene blue) and anionic (methyl orange) dyes under UV light illumination. To get a better understanding of the mechanisms involved, a comprehensive investigation on the photogenerated charge carriers, detected by electron spin resonance (ESR) spectroscopy in the form of O, Ti3+, and O2 trapping centers, was performed. Along with the key role of superoxide paramagnetic species in the photodecomposition of organic dyes, ESR measurements revealed a higher amount of trapped holes in the case of the 1 wt % RuO2/TiO2 photocatalyst that allowed rationalizing the trends observed. On the other hand, a maximum average hydrogen production rate of 618 μmol h1 was reached with 5 wt % RuO2/TiO2 photocatalyst to be compared with 29 μmol h1 found without RuO2. Favorable band bending at the RuO2/TiO2 interface and the key role of photogenerated holes have been proposed to explain the highest activity of the RuO2/TiO2 photocatalysts for hydrogen production. These findings open new avenues for further design of RuO2/TiO2 nanostructures with a fine tuning of the RuO2 nanoparticle distribution in order to reach optimized vectorial charge distribution and enhanced photocatalytic hydrogen production rates.

International audience; We report the electrochemical behavior of a tetracyano triphenodioxazine bearing two triisopropylsilylethynyl moieties (TiPS‐TPDO‐tetraCN) during its reduction studied either in solution or after vacuum evaporation deposition on indium tin oxide (ITO) support. While in dichloromethane, it typically proceeds in two successive monoelectronic reactions, in acetonitrile, the mechanism appears more complex. Fine analysis of the spectroelectrochemical results combined with simulation of the voltammograms with various amount of water suggest the involvement of water and of a restructured dianion in the electrochemical process. In the solid‐state, the formation of the diprotonated compound was demonstrated and the equilibrium diagram of the different species formed as a function of the pH was drawn. The deprotonated form is unstable and decomposes immediately in solution. Its stabilization in solid‐state is attributed to π–π and charge transfer interactions.