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The hydrogen production from photo-electrocatalytic water splitting attracts extensive attention as a direct way to convert solar energy into chemical fuels. In this work, innovative photo-anodes composed of TiO2 which has a preferable growth orientation [2 1 1] conjugated with PEDOT as bi-layers are prepared by a dry process strategy, combining oxidative and metalorganic chemical vapor deposition (CVD). Pure anatase, dendritic TiO2 films of variable thickness are obtained at 500 °C by varying the deposition time. Increase of films thickness from 474 to 2133 nm results in morphologies that evolve from dense and angular structures to isolated and nanostructured tree-like columns with a concomitant decrease of the charge transfer resistance due to the enhancement of active facets of anatase structure. The PEDOT/TiO2 bi-layer with an overall thickness of 1350 nm and a 50 nm thick upper-PEDOT layer exhibits the highest photocurrent response (0.26 mA cm−2 at 1.8 V/RHE), a fast photocurrent response under illumination, and the best hydrogen yield up to 4.1 µmol cm-2h−1 with electronic conductivity being three order of magnitude higher than pristine TiO2

International audience; Cost-effective, active and stable electrocatalysts are crucial for hydrogen production via electrocatalytic water splitting. Here, we describe the preparation of novel nanofibers (NF) made of Ni/Gd2O3/NiO heterostructures by electrospinning. The fabricated materials showed high electrocatalytic performance for hydrogen evolution reaction (HER) with onset potential values of 89 mV, which are very close to those of platinum (Pt). NiO chemical and electronic properties were successfully optimized in Ni/Gd2O3/NiO coaxial heterostructures; NiO NFs doped with Gd3+ significantly enhanced its electrical conductivity and promoted HER reaction kinetics. These NFs offer the distinct advantages of long-term durability and readiness for hydrogen production via HER, and also better performance than benchmark Pt catalysts. The successful fabrication of these metal oxide NFs and nanostructures may represent a new approach for the rational synthesis of efficient HER catalysts.

International audience; Designing efficient electrode materials for electrochemical water splitting is the most critical challenge for next-generation hydrogen fuel production. This study describes the development of free-standing nitrogen-doped carbon nanofiber (N-CNF) electrodes that incorporated cobalt/cobalt oxide (Co/ CoOx) nanoparticles (NPs) and were decorated with palladium NPs (Pd NPs). These free-standing electrodes displayed high electrocatalytic activity during electrochemical water splitting, and were fabricated in three steps: (i) solution electrospinning of polyacrylonitrile (PAN)/cobalt acetate nanofiber mats; (ii) PAN/cobalt acetate nanofiber mat peroxidation and stabilization in air atmosphere followed by pyrolysis (carbonation) in nitrogen atmosphere; and (iii) decoration of the electrode surface with 5 and 10 nm Pd NPs by controlled atomic layer deposition (ALD) (100 and 200 cycles, respectively). The N-CNF-Co/CoOx-Pd electrode performance was tested in simultaneous hydrogen/oxygen evolution reactions (HER/OER) with an alkaline electrolyte solution (1 M KOH). The electrodes were as electroactive as Pt and IrO2 (reference electrodes) for overall electrochemical water splitting. The most efficient electrode displayed very interesting overpotential (100 mV and 160 mV @ j = 10 mA cm-2 for HER and OER, respectively), Tafel slope (33 and 113 mV dec-1), and exchange current density (1.15 and 22.4 mA cm-2) values. Interestingly, electrodes with the smallest Pd NP size (5 nm/100 ALD cycles) showed higher electrocatalytic activity for HER and OER than electrodes coated with bigger particles (10 nm/200 ALD cycles) and the reference Pt electrode. The effect of Co/CoOx NP encapsulation in the graphitic layers of N-CNFs and coating with Pd NPs on the electrode electrocatalytic activity are discussed in detail.

Plasma polymerized organosilicon thin films were deposited in a MW-PECVD using hexadimethylsiloxane (HMDSO) as a precursor. Thin films were synthetized with different plasma conditions ranging from soft (low plasma energy) to hard (high plasma energy) ones. Quantitative 29Si solid state NMR and FTIR spectroscopy were used to characterize the bulk composition. X-ray photoelectron spectroscopy (XPS) coupled with Density Functional Theory (DFT) calculations were used to determine the surface chemical composition. In addition, water contact angle (WCA) measurements were performed in order to complete the surface characterization. The bulk and the surface of the plasma polymerized HMDSO (PP-HMDSO) showed a complex chemical composition. The four main environments M, D, T and Q were present in the films. An additional environment Si(CH2)(CH3)3 denoted S was detected in the PP-HMDSO films. The chemical composition comparison showed a difference between the bulk and the surface of the films. Under soft plasma conditions, a high amount of SiOC3 termination was present in the bulk of the films. While, the SiO2C2 chains were highly present on the surface. On the other hand, under hard plasma conditions, the number of the SiOC3 termination increased on the surface and decreased in the bulk. Under soft plasma conditions, the PP-HMDSO structure was close to PDMS, while under hard plasma conditions, the PDMS similarity was lost.

TiON and TiO2 were grafted onto the surfaces of mesoporous silica MCM-41 by plasma enhanced chemical vapour deposition (PECVD). The results of small-angle X-ray diffraction (SAXRD), X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and nitrogen physisorption revealed that the mesoporous structure of MCM-41 was retained and the pore size reduced from 2.46 nm to 2.19 nm and 2.18 nm after grafting of amorphous TiO2 and TiON, respectively. In consequence, the pore volume and BET surface area decreased. These results indicate the deposition of TiO2 and TiON particles on the surface of MCM-41, leading to partial blockage of its pores. The grafted materials were found to be effective adsorbents for methylene blue dye. The results of batch adsorption experiments at pH 7 demonstrated that TiON@mSiO2 nanocomposite showed the highest adsorption capacity in comparison with MCM-41 and TiO2@mSiO2, which is due to its highly negative zeta potential at neutral conditions. The equilibrium adsorption process fits well with the Langmuir isotherm model and the calculated maximum adsorbed quantity qmax was found to be 129 mg/g. The pseudo-second order model best represents the adsorption kinetics data. Accordingly, the TiON@mSiO2 nanocomposite can be used for the purification of wastewater from toxic organic dyes such as methylene blue.

In this work, we provide new insights into the design of Ti@TiO2photocatalyst with enhanced photothermal activity in the process of glycerol reforming. Ti@TiO2nanoparticles have been obtained by sonohydrothermal treatment of titanium metal nanoparticles in pure water. Variation of sonohydrothermal temperature allows controlling nanocrystalline TiO2shell on Ti0surface. At 100 < T < 150°C formation of TiO2NPs occurs mostly by crystallization of Ti(IV) amorphous species and oxidation of titanium suboxide Ti3O presented at the surface of Ti0nanoparticles. At T > 150°C, TiO2is also formed by oxidation of Ti0with overheated water. Kinetic study highlights the importance of TiO2nanocrystalline shell for H2generation. Electrochemical impedance spectroscopy points out more efficient electron transfer for Ti@TiO2nanoparticles in correlation with photocatalytic data. The apparent activation energy, Ea= (25–31) ± 5 kJ·mol−1, assumes that photothermal effect arises from diffusion of glycerol oxidation intermediates or from water dynamics at the surface of catalyst. Under the heating, photocatalytic H2emission is observed even in pure water.

International audience; Due to their polymorphism, TiO 2 films are quintessential components of state-ofthe-art functional materials and devices for various applications from dynamic random access memory to solar water splitting. However, contrary to other semiconductors/dielectric materials, the relationship between structural/morphological and electrical properties at the nano and microscales remains unclear. In this context, the morphological characteristics of TiO 2 films obtained by metalorganic chemical vapor deposition (MOCVD) and plasma-enhanced chemical vapor deposition (PECVD), the latter including nitrogen doping, are investigated and they are linked to their in-and out-plane electrical properties. A transition from dense to tree-like columnar morphology is observed for the MOCVD films with increasing deposition temperature. It results in the decrease in grain size and the increase in porosity and disorder, and subsequently, it leads to the decrease in lateral carrier mobility. The increase in nitrogen amount in the PECVD films enhances the disorder in their pillar-like columnar morphology along with a slight increase in density. A similar behavior is observed for the out-plane current between the low temperature MOCVD films and the undoped PECVD ones. The pillar-like structure of the latter presents a lower in-plane resistivity than the low temperature MOCVD films, whereas the out-plane resistivity is lower. The treelike columnar structure exhibits poor in-and out-plane conductivity properties, whereas pillar-like and dense TiO 2 exhibits similar in-and out-plane conductivities even if their morphologies are noticeably different.

The facile synthesis and design of noble metal-free efficient catalysts to accelerate the sluggish kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge for electrolytic water splitting. In that context, the preparation of efficient catalysts with superior catalytic activity from cheap raw materials on a large scale is crucial. Briefly, Ni/NiO/TiO2/rGO is designed using the environmental-friendly and easily up-scalable PECVD technique. This trinary composite presents significance in regulating the crystalline structure, composition and electronic properties towards superior HER and OER activity in acidic solution as bifunctional electrocatalysts for efficient water splitting. Together with the promising long-term stability and durability, Ni/NiO/TiO2/rGO displays excellent electrocatalytic activity towards HER with η10 of 130 mv vs RHE and a Tafel slope of 40 mV/dec.

Photoelectrochemical cells (PEC) are promising devices for hydrogen production via sunlight energy. One of the important challenges in this area is to design photoactive electrodes able to absorb visible light. A good photoelectrochemical behavior depends on the presence of surface active sites to photogenerate current at the lower possible potential for water splitting. Recent investigations in this field are focusing on perovskite materials such as CaCu3Ti4O12 (CCTO) as visible light active electrode due its outstanding structure in which CCTO encloses in its structure a visible light absorbance component (CuO). The presence CuO on the material surface is mainly responsible for trapping electrons. Therefore, CCTO photoelectrocatalysts were prepared using different amounts of graphene oxide (GO) in this work. Physico-chemical characterizations showed that the oxidation of GO at high temperatures lead to the reduction of Ti4+ to Ti3+ and Cu2+ to Cu+, causing a segregation of copper on grain boundaries regions as revealed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman characterizations. Electrochemical performance and materials resistivity are measured in dark and under visible light irradiation. CCTO prepared using 3% of GO showed 50% higher photocurrent generation and hydrogen generation rate than pure phase of CCTO.

International audience; The most critical challenge in hydrogen fuel production is to develop efficient, eco-friendly, lowcost electrocatalysts for water splitting. In this study, self-supported carbon nanofiber (CNF) electrodes decorated with nickel/nickel oxide (Ni/NiO) and palladium (Pd) nanoparticles (NPs) were prepared by combining electrospinning, peroxidation, and thermal carbonation with atomic layer deposition (ALD), and then employed for hydrogen evolution and oxygen evolution reactions (HER/OER). The best CNF-Ni/NiO-Pd electrode displayed the lowest overpotential (63 mV and 1.6 V at j = 10 mA cm-2), a remarkably small Tafel slope (72 and 272 mV dec-1), and consequent exchange current density (1.15 and 22.4 mA cm-2) during HER and OER, respectively. The high chemical stability and improved electrocatalytic performance of the prepared electrodes can be explained by CNF functionalization via Ni/NiO NP encapsulation, the formation of graphitic layers that cover and protect the Ni/NiO NPs from corrosion, and ALD of Pd NPs at the surface of the selfsupported CNF-Ni/NiO electrodes.

International audience; Asymmetric and nanostructured polystyrene-block-poly(2-vinyl pyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO or SVEO, S:V:EO ≈ 56:34:10, M ∼ 79.5 kg.mol–1 and Đ ∼ 1.05) thick films blended with 20 wt % of a short PS homopolymer (hPS, M ∼ 10.5 kg.mol–1 and Đ ∼ 1.09) were achieved by combining the non-solvent induced phase separation (NIPS) process with a solvent vapor annealing (SVA) treatment. Here, the NIPS step allows for the formation of a highly-permeable sponge-like substructure topped by a dense thin layer exhibiting poorly-ordered nanopores while the subsequent SVA treatment enables to reconstruct the material top surface into a porous monolayer of well-ordered hexagonal perforated lamellae (HPL). This optimized film architecture generated by NIPS-SVA showed a mean water permeability of 860 L h–1 m–2 bar–1, which is roughly twice time higher than the flux measured through NIPS made PS-b-P2VP-b-PEO/hPS materials having poorly-ordered nanopores. The post-SVA treatment also revealed as a powerful tool to tailor the thickness of the nanostructure formed within the blended material since monoliths entirely composed of a HPL phase were produced by increasing the time of exposure to a chloroform stream. The water flux of such PS-b-P2VP-b-PEO/hPS monoliths was found to be an order of magnitude lower than that of their asymmetric film homologues.

International audience; Nickel titanate on reduced graphene oxide (NiTiO3/rGO) were elaborated by facile microwave ignition method. The prepared nanomaterials were controlled using different ratios of GO to NiTiO3. The synthesized photo catalysts were characterized by X-Ray Diffraction (XRD), Raman Spectroscopy, Infrared Spectroscopy, Transmission Electron Microscopy (TEM), and UV-Reflectance Spectroscopy. The results demonstrate that photocatalytic performance of the photocatalysts for hydrogen generation increases up to 8383 mu mol/(h.g) with increasing graphene content up to 5%). However, further increase in graphene content above this optimum level has decreased the performance of photocatalyst. The enhanced photocatalytic performance for hydrogen evolution is attributed to extension of its absorption edge to the visible light region, directly related to retard recombination of electron-hole pairs due to synergistic effects of NiTiO3 and graphene which leads to more efficient utilization of the solar energy.

International audience; Photocatalytic water splitting into hydrogen is considered as one of the key solutions to the current demand for eco-responsible energy. To improve the efficiency and sustainability of this process, the development of a TiO2-based photoanode by adding bio-sourced surfactants to the sol–gel preparation method has been considered. Three different polymeric biosurfactants (GB, GC, and BIO) have been tested, giving rise to three different materials being structurally and morphologically characterized by XRD, Rietveld refinement, BET, SEM, AFM, and XPS, which was completed by light absorption, photocatalytic (Pilkington test), electronic (EIS and C-AFM), and photoelectrochemical (cyclic voltammetry) measurements. Correlations between the structure/morphology of materials and their functional properties have been established. One specific surfactant has been proven as the most suitable to lead to materials with optimized photoelectrochemical performance in direct relation with their photocatalytic properties essentially controlled by their specific surface area.

International audience; Green H-2 production by solar water splitting relies entirely on the intrinsic properties of the photocatalyst. In this study the impact of these intrinsic properties on the photocatalytic activity of anatase TiO2, the quintessential component of state of the art photocatalytic systems was explored at the nanoscale. The exploration involved a holistic microstructural and optical characterization of fully crystallized anatase thin films synthetized by metalorganic chemical vapor deposition. A combination of electron microscopy, spectroscopic ellipsometry, and infrared spectroscopy revealed that when the deposition temperature increased, the morphology evolved from dense to porous and columnar nanostructures. Interestingly, the columns with a complex, tree-like nanostructure photogenerated 18 times more H-2 than the densest sample. This result shows that the beneficial effect of the morphological nano-complexification and crystallographic diversification of the exchange facets on the photocatalytic performance outweighs the detrimental aspects inherent to this evolution, namely the drop of the charge carrier transport and the increase of residual stress.

BN/GdxTi(1-x)O(4-x)/2 nanofibers were elaborated via electrospinning technique. The properties of the prepared nanofibers were controlled using different ratios of gadolinium. All the prepared nanofibers exhibit the tetragonal structure of anatase TiO2 phase. An increase in the unit cell volume and a decrease in the crystallite size were observed with increasing the doping amount of Gd3+ as revealed by Rietveld refinement analysis. The defect in TiO2 lattice was observed by Raman. The Gd3+ incorporation inside TiO2 lattice, which is accompanied by the creation of Ti-O-Gd bond, was characterized by the X-ray photoelectron spectra. Scanning electron microscopy demonstrates that the average diameter of BN/GdxTi(1-x)O(4-x)/2 nanofibers decreased by 0.1 μm in comparison to nanofibers without doping. The d-spacing raised by 0.01 nm after doping as demonstrated by high-resolution transmission electron microscopy. The distribution of BN and Gd3+ was homogenous and uniform on nanofibers as depicted by EDX. The incorporation of many impurity levels between valence band and conduction band enhanced absorptivity under visible light as revealed by UV–vis spectrophotometry. Moreover, the surface area of nanofibers was improved by 5 times after Gd3+ doping as demonstrated by BET which is favorable for the increase of photocatalytic activity. The electrons transfer rate (recorded by the electrochemical impedance spectroscopy analysis) was improved by gadolinium doping as well. The photocatalytic results indicate that the BN/GdxTi(1-x)O(4-x)/2 nanofibers improve hydrogen production up to 192,602 ± 1500 μmole/g during 6 h under visible light. The BN/GdxTi(1-x)O(4-x)/2 nanofibers produced 7 times more hydrogen than nanofibers without BN. This improvement could be attributed to the e−/h+ stability that reached 63.69 ms average time before recombination due to the beneficial effect of BN nanosheets.

Communication orale invitée; International audience

Communication orale invitée; International audience

International audience; Previously optimized anatase and nitrogen-doped anatase TiO2 coatings have been grown by low-frequency plasma-enhanced chemical vapor deposition (PECVD) on different kinds of substrates at low plasma power (64W) and high plasma power (100W) for photo-electrochemical studies. Nitrogen-doped TiO2 layers exhibit better photoactivity and also higher electronic conductivity under UV and visible irradiations than non-doped materials. The main reason is that nitrogen introduction induces TiO2 band gap tailoring towards higher wavelengths. In addition, films prepared at low plasma power present a typical photo-material' behavior (whose activity depends directly on the presence of light) while layers synthesized at higher plasma power contain an initial conductive phase giving them an activity that exists in the dark yet and can be slightly enhanced by illumination. Such conclusions are prominent in the field of photo-anodic thin films; indeed PECVD could constitute a promising approach for tailoring the efficiency of photo-electrochemical cells for hydrogen production under solar light.

In the published version of the manuscript, some of the values in Table 2 did not match the headings: 1) In the Table 2 heading, units of the 2nd order reaction rate constant, [Formula presented], were indicated to be m/s. However, the values of [Formula presented] provided in the Table were in units of L/(s m²).2) In the Table 2 heading, units of the reactive flux, [Formula presented], were indicated to be m/s. However, the values of [Formula presented] provided in the Table were in units of L/min (i.e. were not normalized by the membrane surface area).3) Values of [Formula presented] for the 5 layer LBL membrane need to be corrected:– Test #1: (8.90±2.10)·10⁻⁴ L/(s m²) should be changed to (9.65±1.76)·10⁻⁴ L/(s m²). After units conversions, the correct value is (11.61±2.12) 10⁻⁶ m/s.– Test #2: (8.66±0.27)·10⁻⁴ L/(s m²) should be changed to (8.65±0.28)·10⁻⁴ L/(s m²). After units conversions, the correct value is (10.41±0.34) 10⁻⁶ m/s.– Test #3: (6.74±0.27)·10⁻⁴ L/(s m²) should be changed to (6.79±0.37)·10⁻⁴ L/(s m²). After units conversions, the correct value is (8.17±0.45) 10⁻⁶ m/s.The revised Table 2 with correct values of [Formula presented] and [Formula presented] in units of m/s is attached below. In addition, the last sentence on page 345 of the published manuscript contained a typo, wherein [Formula presented] was assigned the value of 8.0·10⁻⁶±1.5·10⁻⁶ m/s instead of the correct value of 7.9·10⁻⁶±0.8·10⁻⁶ m/s. (Note that Table 2 in the published manuscript contains the correct value). Thus, the sentence should read as follows: “The normalized 1st order reaction rate constants are (7.9±0.8)·10⁻⁶ m/s and (6.0±0.0)·10⁻⁶ m/s for P25 and PECVD-generated catalysts, respectively.” The authors would like to apologize for these errors. http://dx.doi.org/10.1016/j.memsci.2016.04.050.

In the highly competitive market of fuel cells, proton exchange membrane fuel cells operating in the range 80–150 °C seem quite promising. One of the main hurdles for emergence of such a technology is the development of phosphonic acid-based membranes characterized by high conductivity and stability beyond 80 °C. In this work, new polymer blend membranes mixing a fluorinated polymer (poly(VDF-co-CTFE)) and a phosphonated polymer (poly(CTFE-alt-DEVEP)) have been prepared at low cost. High proton conductivity (40 mS m−1 at 80 °C, 100% HR) and good thermal stability, directly related to the specific structuration of membranes, have been demonstrated. Due to cross-linking effect, argon plasma treatment of blend membranes has enabled to improve their thermal stability and fuel retention without altering their morphology, chemical composition and proton conductivity. Plasma-treated blend membranes appear as good candidates for PEMFC, as shown by preliminary fuel cell tests.

International audience; Photoelectrochemical water splitting under visible light has attracted attention for renewable hydrogen production. Despite prevalent investigations, many challenges still hindered an efficient energy conversion, such as enhancing the reaction efficiency in visible light. Thus controlling the photoelectrode materials is an essential step in designing new materials for water splitting. CaCu3Ti4O12 (CCTO) has received great attention as photocatalyst under solar light due to its combined band gap as result of the presence in its structure of TiO2 active in UV light and CuO active under visible light. In this work, a cubic CCTO with different amount of exfoliated hexagonal boron nitride has been synthesized. The produced materials were fully characterized. Physico-chemical characterizations demonstrate that bore and nitrogen co-doped CCTO causes an increase in grain boundaries thickness, and thus leads to shift peaks in XRD and Raman spectra. UV–Vis diffuse reflectance spectroscopy showed a decrease of the bang gap value after adding boron nitride nanosheets into CCTO. The electrochemical performance and the resistivity of the obtained materials were performed using electrochemical impedance spectroscopy in dark and under visible light exposition. The onset potential recorded for CCTO with 3% of boron nitride nanosheets (Eg = 2.9), is around 0.5 V and the current generation is 16 times more than pure phase of CCTO. This work shows that CCTO with 3% of boron nitride nanosheets can be considered as an active photoelectrocatalyst under visible light irradiation for water splitting. Hydrogen production measurements show that the rate of H2 production reached arround 8.1 µmol/h under visible light after adding 3% of BN nanosheets to CCTO which presents 16 times increase in comparison with pure CCTO.

International audience; In this work, we report a novel photocatalyst based on boron and nitrogen co-doped TiO2 rutile (1 1 0) honeycomb structures. The photocatalyst has been prepared by simultaneously oxidizing and doping a Ti-foil substrate at 750 degrees C. The unit cell volume and the crystallite size of grown TiO2 films were measured by Rietveld refinement analysis. The co-doping by boron and nitrogen was achieved simultaneously with the oxidation of the titanium, resulting in a rutile (1 1 0) textured TiO2 film. X-ray photoelectron spectroscopy analysis revealed the presence of Ti-O-N and Ti-O-B-N bonds, and the presence of crystal defects in the lattice was detected and displayed by Raman spectroscopy. The water photo-oxidation properties have been measured as well, and the photocurrent of the B/N co-doped rutile sample prepared reached 270 mu A/cm(2) at 1 V under visible light and was stable in time. The efficient visible light absorption properties of the fabricated nanomaterial were attributed to the presence of oxygen vacancies and the introduction of impurity levels, as well as to synergistic effects between the introduced boron and nitrogen elements. The results presented demonstrate a new route for the preparation of TiO2 based catalysts, and open prospects for the photocatalysis community.

International audience; Among the electrolyte membranes for proton conduction in hydrogen production systems and fuel cells, phosphonic acid-based membranes are promising because of their advantage as good proton conductors in anhydrous medium which allows their use in systems operating at high temperature (80-150 degrees C) which is not the case of sulfonic acid-based ones such as the well-known Nafion (R) commercial membrane. In this study, a plasma polymerization process using a continuous or pulsed glow discharge has been implemented to prepare original Plasma Enhanced Chemical Vapor Deposition (PECVD also called plasma polymerization) phosphonic acid-based membranes using dimethyl allylphosphonate as a single precursor. The structural and proton transport properties of such membranes have been correlated with the plasma parameters in the deposition of films. The membranes prepared by pulsed plasma deposition method exhibit a better proton conductivity than that of membranes prepared by continuous plasma deposition method, in direct relation with their specific structural properties. The optimal plasma membrane, obtained in a pulsed 100 W plasma discharge, has shown specific resistance to proton conduction twice less than Nafion (R) 212 one which is great for the final applications of such membrane.

A PECVD (Plasma-enhanced Chemical Vapor Deposition) process operating at 150 °C has been implemented to prepare micro-columnar porous TiO2 anatase thin films, performing post-annealing at 300 °C for 5 h. Optimized PECVD conditions have enabled us to obtain homogeneous films with thickness equal to 1–2 μm ± 0.2 μm. An anatase seeding interface deposited prior to the PECVD process has enabled us to reduce crystallization time down to 1.5 h. The size of nano-crystals in prepared anatase thin films has been estimated to be 20 nm by applying the Scherrer equation. Besides, the band-gap energy (Eg) of synthesized anatase thin films on quartz was found to be 3.30 eV.

Two different kinds of PECVD anatase-based composite membranes have been successfully prepared by PECVD synthesis (at 150 °C)/post-annealing (at 300 °C) of a titania film deposited on macroporous supports as a top-layer or a skin-coverage. Photocatalytic activity of PECVD anatase films has been proved performing Pilkington test and methylene blue degradation determination in a lab-scale diffusion cell. Measurements of methylene blue degradation and water flow in a pilot-scale dynamic unit have enabled to show the performance of PECVD anatase-based membranes in terms of permeation and photocatalytic properties. Whereas bi-layered membranes present higher photo-degradation ability (up to 2.5 × 10−8 mol s−1 m−2 destroyed methylene blue moles per unit of time and of membrane surface area), skin-covered membranes are characterized by higher water permeance (up to 6800 L h−1 m−2 bar−1). So both kinds of membranes should have an interest as photocatalytic contactors.

Amorphous non-oxide a-SiCxNy:H thin films have been synthesized at 300 or 500 K from an Ar/HMDSN/NH3 gas mixture in a lab-scale microwaves PECVD reactor. These thin films have been characterized by FTIR spectroscopy and spectroscopic ellipsometry coupled with gas adsorption, in order to evidence the influence of PECVD synthesis conditions on the materials composition and microstructure. Deposition at high temperature (500 K) was found to yield more inorganic and more compact films in comparison with those obtained at room temperature. In addition, when considering long term aging at room temperature for more than 1 month, the films synthesized at high temperature were found to be more stable toward oxidation in (humid) air.

Due to their good chemical and thermal inertness, SiCxNy:H films are suitable for a variety of applications in electronic, tribology, optic, photovoltaic and more recently gas separation membranes. For these applications, film evolution can be attractively probed by FTIR spectroscopy. In this work, a systematic quantum mechanical study of the vibrational modes position in the pattern of a-SiC x N y (O):H is presented. Vibrational frequencies of Si C, Si N, C N, Si H, C H and N H moieties have been calculated at DFT/B3LYP level of theory using the 6-311 ++G(3df,3pd) basis set. Characteristic absorption domains have been compared with FTIR data from the literature. In particular, DFT calculations provide guidelines to discriminate Si H from C N stretching bands, which are calculated to lie below and above ~ 2230 cm − 1 , respectively. As an example, the oxidation of a microwave PECVD SiC x N y :H films during ageing was evidenced in this work through the progressive increase of Si O stretching band (~ 1040 cm − 1 ). The simultaneous decay of the band centered at 2170 cm − 1 was attributed to the vanishing of Si H bond upon oxidation. This example illustrates that unambiguous band assignment is required to provide a molecular description of the ageing process, which is in turn required to optimize the material composition and stability. Results of these calculations will be helpful to identify both the chemical moieties and their environment in future investigations on a-SiC x N y :H materials but also on materials containing additional elements such as B- or O-doped SiCN-based systems.

International audience; Zinc ferrite @ titanium dioxide (ZnFe2O4@TiO2) composite nanofibers were elaborated by combining the two different techniques: electrospinning and plasma-enhanced chemical vapor deposition (PECVD). The nanofiber compositions were controlled using different ratios of zinc to iron. Their structural, morphological, and optical properties were analyzed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, BET surface area, Raman spectroscopy, and UV–visible spectrophotometry. The photocatalytic activity has been investigated by the degradation of methylene blue under visible light. The results indicate that the combination of spinel structure with titanium dioxide improves the photodegradation up to 98%. The deposition of TiO2 via PECVD on zinc ferrite enhances the absorption of TiO2 into the visible region and increases the electron–hole separation. In addition, the improved surface area can promote adsorption, desorption, and diffusion of reactants and products, which is favorable to obtain a high photocatalytic activity.

International audience

In the highly competitive market of fuel cells, solid alkaline fuel cells using liquid fuel (such as cheap, non-toxic and non-valorized glycerol) and not requiring noble metal as catalyst seem quite promising. One of the main hurdles for emergence of such a technology is the development of a hydroxide-conducting membrane characterized by both high conductivity and low fuel permeability. Plasma treatments can enable to positively tune the main fuel cell membrane requirements. In this work, commercial ADP-Morgane® fluorinated polymer membranes and a new brand of cross-linked poly(aryl-ether) polymer membranes, named AMELI-32®, both containing quaternary ammonium functionalities, have been modified by argon plasma treatment or triallylamine-based plasma deposit. Under the concomitant etching/cross-linking/oxidation effects inherent to the plasma modification, transport properties (ionic exchange capacity, water uptake, ionic conductivity and fuel retention) of membranes have been improved. Consequently, using plasma modified ADP-Morgane® membrane as electrolyte in a solid alkaline fuel cell operating with glycerol as fuel has allowed increasing the maximum power density by a factor 3 when compared to the untreated membrane.

International audience; A plasma polymerization process using a continuous glow discharge has been implemented for preparing proton conducting membranes from trifluoromethane sulfonic acid and styrene. The chemical and physical structure of plasma membranes has been investigated using FTIR and SEM. The films are homogeneous with a good adhesion on commercial gas diffusion layer (E-Tek®). Their deposition rate can be increased with increasing flow rate and input power. The thermogravimetric analysis under air of plasma polymers has showed a thermal stability up to 140 °C. Compared to the pulsed glow discharge studied in a previous paper, the continuous glow discharge has enabled to enhance the proton conductivity of membranes by a factor 3 (up to 1.7 mS cm−1). Moreover, the low methanol permeability (methanol diffusion coefficient down to 5 × 10−13 m2 s−1) of membranes has been confirmed by this study. In an industrial context, a reactor prototype has been developed to manufacture by plasma processes all active layers of fuel cell cores to be integrated in original compact PEMFC or DMFC.

International audience; A membrane or an electrode binder to be used in a solid alkaline fuel cell (SAFC) needs to (i) be insoluble in both aqueous solutions and the required fuels, and (ii) exhibit an hydroxide ion conductivity. To achieve these goals, two pathways were employed: (i) one consists of the radical copolymerization of diallyldimethylammonium chloride (DADMAC) with chlorotrifluoroethylene (CTFE) while (ii) the other one is based on the counter-ion exchange of a poly(DADMAC) by fluorinated anions. First, the radical copolymerization of CTFE with DADMAC under various experimental conditions was achieved in yields up to 85%, and DADMAC percentages in the copolymers were higher than those in the feed compositions. To obtain insoluble copolymers, high CTFE feed contents ([70 mol %) were required. The other route consisting in the partial replacement of the Cl- counter-ions in the water-soluble poly(DADMAC) by bistrifluoromethanesulfonimide (TFSI-) did confer the starting material insolubility in water while maintaining its conductivity. When the fluorinated poly(DADMAC) was obtained from concentrated solutions of fluorinated surfactant, it was observed that the amount of counter-ions exchanged was difficult to control, which limits optimization. Nevertheless, under diluted conditions, membranes with ion exchange capacity up to 0.7 meq g-1, and conductivities close to 1 mS cm-1 were obtained. Although their conductivities were low, these membranes fulfill the requirements for a SAFC membrane in terms of solubility in DMSO, water insolubility, and thermal stability (Td,10% > 320 °C). When used in a fuel cell, as a binder in the membrane-electrode assembly (MEA), significant improvements were noted (þ50% of the open circuit voltage, þ580% in current density, and þ540% in accessible power).

A complete PECVD process for the plasma polymerization of miniature proton exchange membranes (PEM) is presented. Styrene and trifluoromethane sulfonic acid are used as plasmagen precursors in a capacitive coupled low pressure discharge. The process is monitored by impedance probe measurements to ensure stability and reproducibility. FTIR analyses show that such membranes are mainly made up of a polystyrene-like matrix with grafted sulfonic acid groups, which proportion is tuneable as a function of the plasma parameters. The best results in term of deposition rate, monomer structure retention and PEM performances are obtained under pulsed plasma conditions, enhancing radical processes compared to continuous plasma. Because of their thinness and cross-linked structure, such membranes exhibit a similar proton conduction ability and a methanol permeability reduced by a factor 150 compared to Nafion®. SEM observations show a good compatibility of plasma polymerized membranes whatever the substrate is. Consequently, PECVD process enables their better integration in micro fuel cells compared to conventional spin coating method.

Recent advances in miniaturization technology make polymer electrolyte membrane fuel cells very attractive as power sources for portable devices. Ion-exchange membranes for microscale fuel cells are synthesized by plasma polymerization (using a precursor containing ion-exchange groups) and intensively characterized. Ion-exchange plasma membranes are thin, amorphous, and dense materials with no defects. Spectroscopic analyses reveal a polymer-type matrix containing a rather high concentration of ion-exchange groups. Under the best synthesis conditions, membranes show a satisfying ionic conduction level and a high compatibility with other active layers of fuel cells, making them suitable for insertion in such power-supply devices.

Les procedes plasma ont ete initialement developpes pour la microelectronique dans les annees 50. Ils representent une technologie a la fois propre, produisant peu ou pas d'effluents, et extremement souple dont l'equipement de base permet d'atteindre des objectifs aussi divers que singuliers en termes de proprietes d'usage specifiques. Forts de ces avantages, ils sont aujourd'hui utilises dans de nombreux domaines de la chimie des materiaux, notamment pour la modification ou la synthese de membranes. Selon la nature du gaz precurseur du plasma et par le choix de conditions operatoires adequates, il est possible par de tels procedes, de realiser des traitements de surface (par reticulation, greffage et/ou gravure) en vue de modifier les proprietes de surface (rugosite, adhesion, hydrophobie...) de membranes polymeres, ou d'elaborer des couches minces inorganiques ou hybrides de grandes stabilites chimique et thermique. Cet article presente trois nouveaux procedes plasma developpes en laboratoire et destines a modifier ou synthetiser des membranes «sur mesure »: la modification de surface de membranes par des plasmas de gaz fluores, et l'utilisation du procede en configuration depot pour la preparation de membranes pour la separation de gaz et de vapeurs d'une part, de membranes a conduction ionique pour micro piles a combustible d'autre part.

National audience

International audience; In this work, low frequency PECVD a-SiCxNy:H thin films have been synthesized in the temperature range 25-300 A degrees C from hexamethyldisilazane precursor mixed with ammonia at various concentrations. A relevant correlation has been evidenced between the [N]/[C] atomic ratio in the gaseous phase and in the deposited thin films, allowing both prediction and control of the film microstructure. A simple method based on the analysis of the films FTIR spectra was proposed to determine the value of the [N]/[C] ratio and thus predict or adjust the gas transport properties of the membrane materials. Attractive ideal selectivities alpha*(He/N2) exceeding 90 with He permeance I (He) > 3.10(-7) mol.s(-1).m(-2).Pa-1 were measured at 150 A degrees C for the films prepared at 300 A degrees C with an optimum [N]/[C] atomic ratio in the range 0.1-1.5. These films behave as molecular sieve membranes with a thermally activated transport of helium.

International audience; In this work the long-term antibacterial activity of silver doped titania coatings is studied systematically as a function of the titania layer structure (with and without molecular template) and the amount and physical properties of the silver dopant. Silver was incorporated in two different ways into the titania sol–gel films, either by co-deposition, i.e., adding the silver ions directly to the precursor sol of the layer or by post-synthetic impregnation of the mesoporous titania coating. The structure and morphology of the layers were investigated using transmission and scanning electron microscopy, whereas the silver content was determined by Rutherford backscattering spectrometry. Antibacterial properties against Escherichia coli bacteria were studied by colony forming unit assay and agar diffusion method. It was found that directly after preparation, all composite coatings show antibacterial activity both in the dark and under visible light illumination. The antibacterial activity of the co-deposited samples vanished after the first use despite their high and constant remaining silver content (2.597 at%). This type of coating was not effective in agar diffusion tests at all. The antibacterial activity of the impregnated coatings with lower silver contents (0.596 at% and 1.961 at%), however, showed long-lasting antibacterial effect both in the colony forming unit assay and in agar diffusion tests as well. This can be attributed to the fact that the silver content is distributed over the mesoporous network of the titania coating and is effective during the long-term tests.

Sulfonated polystyrene-type membranes were synthesized by plasma polymerization of a mixture of styrene and trifluoromethane sulfonic acid monomers in a low-frequency after-glow discharge plasma reactor. Such a deposition process enables the preservation of the monomers structure, which was confirmed by mass spectrometry analysis. The synthesized plasma-polymerized membranes are dense and uniform with a few microns thickness. Their structure determined by Fourier-transform infra-red spectroscopy and X-ray photoelectron spectroscopy is very rich in sulfonic acid groups (up to 5%) and stable up to 120 °C. Even if their intrinsic proton conductivity is low (10 −1 mS cm −1 ), directly related to their disorganized and highly cross-linked structure, plasma-polymerized membranes present a proton conduction ability similar to Nafion ® because of their low thickness. Due to their highly cross-linked structure, these membranes enable a reduction of the methanol crossover in a factor 10 by comparison with Nafion ® . Thus, the integration of plasma-polymerized films in miniaturized direct methanol fuel cells as proton-exchange membranes seems promising.

Plasma polymerization is a very powerful technique for preparing very thin highly cross-linked polymeric films. As in the case of classical polymers, the gas permeation performances of plasma polymers are strongly related to their chemical composition and structural properties. These properties depend directly on the precursor nature and on the operating conditions of the polymerization process like temperature, monomer flow rate, discharge power, frequency, etc. Previous results obtained by our group show that it is difficult to apply the classical Fick's correlations between the permeability, sorption and diffusion to this type of polymer. In addition, their structure, which is not very well known, is very cross-linked, high disordered and behaves like a complex material with two components: a rubber and an inorganic part. Indeed, these polymers cannot be represented as a regular repeat of monomer units. A mathematical model inspired from the free volume concept and Bondi's contributions group has been proposed for the DEDMS, HMCTSO, HMDSO and OMTSO polymers. This model is based on mesoscopic parameters like the density of the polymer and factor T = number of (Si–C) bonds/number of (Si–O) bonds. The model has displayed good correlations factors for the studied polymers.

The experimental design method was used to investigate the PECVD parameters effects on the properties of plasma polysiloxane membranes synthesized using octamethylcyclotetrasiloxane or hexamethyldisiloxane as monomers. On a wide experimental range and with a minimum number of experiments, the use of such a statistical tool enabled us to set up complete and reliable correlations, in the form of polynomial models connecting the gas transport properties (H2 permeability coefficient, H2/N2 ideal selectivity) and the structural properties (growth rate, density, organic/inorganic nature) of synthesized films with the two most influent synthesis parameters of the PECVD process: the input power (represented by the input voltage) and the monomer flux. The polynomial models enabled us not only to statistically confirm the effects of the PECVD parameters displayed by previous classical experimental studies, but also to model, in the mathematical sense, the evolution of each property of materials taking into account the first and second orders effects of both PECVD synthesis parameters. By the use of a performing statistical tool, we managed to improve the knowledge of relations between synthesis parameters/structure/properties relative to our process.

Grafting of aminosiloxane groups on PVDF supports was performed in a low-frequency plasma deposition process using a tetramethylsilane/ammoniac mixture. The morphology and thickness of plasma-grafted PVDF membranes were characterized by SEM observations; their chemical structure was determined by FTIR analysis, XPS analysis, and contact angle measurements. The membranes anion-exchange capacity for the transport of Cr(VI) was investigated by electroelectrodialysis using a three compartments Kel'F cell. We are able to correlate the plasma grafting parameters with the structure and the electrotransport performances of the synthesized membranes. Starting from 0.10 for the virgin PVDF films, the best Cr(VI) transport number (0.155) is obtained for membranes both rich in substituted amine functions and hydrophobic enough synthesized from an equimolar tetramethylsilane/ammoniac plasma monomers mixture.