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This study examines the effect of pretreatment and doping to enhance the ORR activity of multiwalled carbon nanotubes (MWCNTs). Melamine and thio-urea are chosen as precursors for mono and co-doping, respectively. A series of samples with pristine and pretreated CNTs are prepared and characterized physicochemically by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) and electrochemically by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The obtained results show that co-doping is an effective way for improving ORR activity, due to the synergistic effect of N and S for changing the charge and spin density, respectively. Moreover, thio-urea favors the proportion of pyridinic and graphitic nitrogen configurations within doped samples. As a consequence, our synthesis method gives samples with superior ORR activity. The maximum ORR activity is obtained for NS-OX-CNTs which shows an over potential of 0.95 V vs RHE at 0.1 mA/cm2, which is comparable to Pt/C (0.98 V vs RHE). The electron transfer number (n) is calculated as 3.9 at 0.4 V which suggests that the ORR proceeds through a dominant 4 e− path. These comparable half-cell results to that of Pt/C pave the way for further testing as cathode materials for anion exchange membrane fuel cells (AEMFC). Graphical abstract

In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. With proper water management, the achievable power output in AEMFCs is comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies.

Activation is commonly used to improve the surface and porosity of different kinds of carbon nanomaterials: activated carbon, carbon nanotubes, graphene, and carbon black. In this study, both physical and chemical activations are applied to graphene oxide by using CO2 and KOH-based approaches, respectively. The structural and the chemical properties of the prepared activated graphene are deeply characterized by means of scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and nitrogen adsorption. Temperature activation is shown to be a key parameter leading to enhanced CO2 adsorption capacity of the graphene oxide-based materials. The specific surface area is increased from 219.3 m2 g−1 for starting graphene oxide to 762.5 and 1060.5 m2 g−1 after physical and chemical activation, respectively. The performance of CO2 adsorption is gradually enhanced with the activation temperature for both approaches: for the best performances of a factor of 6.5 and 9 for physical and chemical activation, respectively. The measured CO2 capacities are of 27.2 mg g−1 and 38.9 mg g−1 for the physically and chemically activated graphene, respectively, at 25 °C and 1 bar.

With the gradual rise in atmospheric carbon dioxide brought about by human activities and industry effluents, research has now been geared toward carbon capture and storage. To achieve high carbon dioxide adsorption capacity, development of nanomaterials with optimized properties has been attracting growing interest for more than ten years already. Such multi-parameter investigations require a complex and rigorous analysis in order to compare the different developed adsorbents and improve their performances. In this review, we propose a state-of-the-art approach related to the four most studied nanostructured adsorbents for carbon dioxide capture: graphene, carbon nanotubes, zeolite, and metal organic frameworks. The capture processes and the nanomaterials of interest were described as well as the modifications applied to improve the efficiency of carbon dioxide capture. The present unprecedented analysis allows to correlate the nanomaterial properties, especially surface area and pore volume, to the CO2 adsorption capacity. The results reveal that contrary the popular belief, the CO2 capture improvement is not solely liable on the high surface area and the high pore volume of the nanosorbents. This outcome may be useful in the course of improvement of nanostructured materials for CO2 capture for future technologies.

International audience; Functionalization on the carbon material of PEM fuel cells providing them an ionic conductivity, has been thought as a promising way to improve the catalyst activity. Pt/Vulcan catalysts grafted with polystyrene sulfonate (PSSA) groups from 5 to 20 wt.% have been prepared. Owing to the ion-exchange properties of the PSSA grafted on carbon support, we developed less-Nafion electrodes, with only 0.25 or 0.50 mg cm− 2 Nafion loading. The effect of PSSA graft ratio and the Nafion amount was studied in a single cell at 30 °C by polarization curves and impedance measurements. It was found that 5 and 10 wt.% PSSA with 0.50 mg cm− 2 Nafion allow high efficiency, however lower than 10 wt.% grafted Pt/C with 0.25 mg cm− 2 Nafion only. The performance of the various electrodes could be correlated to the overall amount of sulfonate introduced: highest yields were obtained with an overall sulfonate concentration near 0.7–0.8 μmol cm− 2.

Chemical vapor deposition (CVD) reaction from metal particles to produce graphene has seldom been reported so far. In this paper, the CVD growth of graphene was conducted under ambient pressure without a dedicated stage for reduction treatment. Interestingly, copper nanoparticles supported on MgO prepared by simple impregnation were able to efficiently catalyze graphene. Quantification of the prepared graphene was carefully conducted. For the optimized conditions, 1000 °C for 30 min, high content of graphene (up to 27 at.%) could be produced. Our method shows high efficiency and growth rate of graphene, produced at much lower cost compared to the existing methods.

Half-cell is an ex situ device generally used in fuel cell investigations. The present work is related to half-cell investigations of a particular catalyst for polymer electrolyte membrane (PEM) fuel cells, namely Pt/Vulcan catalyst grafted with 5 wt.% polystyrene sulfonate (PSSA). It was found that the behavior of the half-cell to be immersed in a sulfuric solution was influenced by the hot-pressing conditions in the preparation process: optimum hot-pressing conditions had to be searched for improved, reliable performance of half cells. A stable Nafion® membrane interface on the catalytic layer (CL) was obtained at 135 °C, 40 bars for 6 min. Otherwise, owing to the ion-exchange properties of the PSSA graft, electrodes were prepared with lower amounts of Nafion® and the effect of Nafion® introduction in the preparation was discussed: test electrodes mounted in half-cell had either 0.25 or 0.50 mg cm−2 Nafion® dispersed in CL, or with 0.50 mg cm−2 deposited on CL surface. Their performances for oxygen reduction reaction (ORR) were studied using linear voltammetry (LV) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry was used for determination of the electrochemical surface area (ECSA) of each electrode. It has been shown that fresh electrodes with 0.50 mg cm−2 Nafion® dispersed in CL exhibit promoted behavior in ORR. However, the GDE prepared with Nafion® deposition on CL surface exhibits the best resistance to ageing tests performed by potential cycling between 0 and 1.2 V/NHE, as revealed by ECSA measurements.

International audience; Carbon nanotubes (CNTs) are difficult to process, and their assembly in macroscopic materials that allow us to benefit from the exceptional properties of the nanotubes is of crucial interest for applications. The developed CNT processing procedures usually involve additives that remain in the final product and are known to diminish the properties of the CNT-based material. Here, we propose a multistep approach to process single-walled carbon nanotubes (SWNTs) and obtain macroscopic additive-free SWNT materials. High-quality dispersion purified SWNTs is first induced in polar solvent due to their preceding reduction reaction with an alkali metal. The partial debundling process occurring at this stage leads to ramified SWNTs. They can then be self-assembled by attractive intermolecular forces through a controlled destabilization of the dispersions by a simple oxidation. Swollen gels of SWNTs are formed at an air/solvent interface. After freeze-drying, the additive-free SWNT material shows a hierarchical structure with highly interconnected SWNTs. Thanks to the obtained ramification of the SWNTs, these latter are able to well entangle what guarantees the robustness of the obtained additive-free SWNT material. Moreover, this integrated process offers an increase of the accessible surface compared to that of the raw bundled SWNTs. The obtained assembled SWNTs show an improved adsorption capacity.

Nanoparticles of tungsten and tungsten carbide have been prepared using solid-state chemistry methods. After the vapor phase impregnation of a tungsten hexachloride precursor on a carbon support, a temperature-programmed reduction/carburization was performed. Several parameters were investigated and the evolution of obtained samples was followed by XRD and TEM. The optimization of the reaction parameters led to the preparation of W, W2C and WC particles well dispersed on the support. WC phase however could not be obtained alone with less than 10 nm mean size. This could be explained by the carburization mechanism and the carbon diffusion on the support.

International audience; Gold nanoparticles have been generated for the first time within open-cell macrocellular polyHIPE matrices, leading to new hybrid organic–inorganic catalytic supports labelled “Au@polyHIPE”. The overall synthesis can be realized with ease, as it is based on the spontaneous nucleation of gold nanoparticles. These new hybrid organic–inorganic materials have then been tested for heterogeneous catalysis, particularly for eosin Y reduction in the presence of NaBH4. In this reductive media the as-synthesized hybrid catalytic supports “Au@polyHIPE” exhibit a good activity. All the kinetic parameters are discussed in term of internal surface (porosity), external surface (shape), temperature and gold loading revealing a first order reaction.

The stability and rheology of tricaprylin oil-in-water emulsions containing a mixture of surface-active hydrophilic silica nanoparticles and pure nonionic surfactant molecules are reported and compared with those of emulsions stabilized by each emulsifier alone. The importance of the preparation protocol is highlighted. Addition of particles to a surfactant-stabilized emulsion results in the appearance of a small population of large drops due to coalescence, possibly by bridging of adsorbed particles. Addition of surfactant to a particle-stabilized emulsion surprisingly led to increased coalescence too, although the resistance to creaming increased mainly due to an increase in viscosity. Simultaneous emulsification of particles and surfactant led to synergistic stabilization at intermediate concentrations of surfactant; emulsions completely stable to both creaming and coalescence exist at low overall emulsifier concentration. Using the adsorption isotherm of surfactant on particles and the viscosity and optical density of aqueous particle dispersions, we show that the most stable emulsions are formed from dispersions of flocculated, partially hydrophobic particles. From equilibrium contact angle and oil-water interfacial tension measurements, the calculated free energy of adsorption E of a silica particle to the oil-water interface passes through a maximum with respect to surfactant concentration, in line with the emulsion stability optimum. This results from a competition between the influence of particle hydrophobicity and interfacial tension on the magnitude of E.

We present new hybrid organic/inorganic materials dedicated to heterogeneous catalysis. The systems are obtained by the polymerization of a high internal phase reverse emulsion (the so-called polyHIPE porous materials) and have been further functionalized with various organic groups in order to promote the growth of palladium nanoparticles on its surface. Final supports are then tested for their ability to catalyze the Suzuki–Miyaura coupling reaction, and one material exhibits better activity than the well-known Pd@C powder system. Furthermore, the catalytic activities of these materials are close to those obtained with their homogeneous catalysis counterpart. These new supports remain active towards a wide range of substrates associated with Suzuki–Miyaura carbon–carbon coupling reactions.

Microcellular polymer, known as polyHIPE, which is synthesized by polymerization of high internal phase emulsion, has been associated with heterogeneous nucleation. In this issue, we have generated palladium nanoparticles in situ by an impregnation−reduction method. The nanoparticle synthesis is very sensitive to conditions such as temperature, pH, metallic precursor, solvent, and surface chemistry of the support. We have tried to control the particle sizes and dispersion state by a careful choice of the reaction parameters and/or a suitable matrix functionalization. In a catalysis application aspect, we checked the efficiency of our supports via a hydrogenation reaction. Some of our supports offer good activity, even compared to commercial Pd/C, and also a satisfying reusability.

Discrete spheroidal particles of interconnected microcellular foams were synthesised by suspension polymerisation of a high internal phase emulsion. These particles have been surface-grafted with functionalised macromolecular chains by controlled radical polymerisation using a covalently-bond TEMPO initiator.