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Better understanding the properties of organic aerosols (OA) is attracting increasing attention because of the important role they play in climate change. The viscosity of OA has been shown to rang...

This paper investigates how and under which conditions the lamella of an impacting droplet is punctured by the presence of a small occlusion. Better understanding the conditions which lead to the rupture of the lamella is critical to produce defect free coating layers in the context of spray coating, for example. An analytical model based on surface energy analysis is proposed to obtain the critical thickness below which the liquid layer above the occlusion is unstable and lamella rupture occurs. Furthermore, we have developed a three dimensional multiphase lattice Boltzmann code to confirm the surface energy analysis and study the influence of key parameters like size of the occlusion, impact velocity and wettability of substrate on hole formation. Results show that a hole is more likely to appear as the diameter of the occlusion, the impact velocity, and the hydrophobicity of the surface increase.

International audience; Granular activated carbon (GAC) was synthesized from Silver berry (Elaeagnus Angustifolia L.) seeds using zinc chloride as the activation agent. To optimize the operating parameters, the effects of the time and temperature of carbonization, impregnation ratio, and heating rate on the iodine number and yield of activated carbon were studied. Optimized parameters were impregnation ratio of 1:1, carbonization temperature of 500 degrees C, carbonization time of 1 hour, and heating rate of 5 degrees C/min. The GAC synthesized under optimized conditions was characterized by Nitrogen adsorption-desorption isotherms, SEM, EDX, XRD, FT-IR, Boehm titration, TG-TGA, and TG-IR. It was found that the synthesized GAC has a microporous structure with a BET surface area of 1109 m(2)/g, a micropores volume of 0.317 cm(3)/g, and an average pore diameter of 2.1 nm. The methylene blue (MB) dye was employed as a molecule model to evaluate the porosity and the adsorption capacity of the synthesized GAC. The results showed that the maximum adsorption capacity of MB and the percent portion of the surface area (S-MB/S-BET) were 120.48 mg/g and 30.62%, respectively. The experimental results reveal that the synthesized GAC can be used as a low-cost adsorbent for the removal of small and large environmental pollutants.

International audience; For the first time, an effort has been made to evaluate the charge transport properties of semiconducting natural rubber. Four different ratios of iodine-rubber composites are synthesised and tested for charge transport by current density-voltage characteristics (J-V) and impedance spectroscopy. The optimal doping ratio for best mobility value is identified, and the effect of injection barrier height on mobility is discussed. An attempt has also been made to correlate the density of states (DOS) with mobility and doping ratio. The transport properties of semiconducting natural rubber are compared with one of the most popular p-type material, Poly(3-hexylthio-phene-2,5-diyl) (P3HT) under the same ambience and experimental conditions to demonstrate its potential as a cost-effective and green alternative organic semiconductor.

Hydrogen storage is a promising technology for storage of renewable energy resources. Despite its high energy density potential, the development of hydrogen storage has been impeded, mainly due to its significant cost. Although its cost is governed mainly by electrical energy expense, especially for hydrogen produced with alkaline water electrolysis, it is also driven by the value of the cell tension. The most common means of electrolyzer improvement is the use of an electrocatalyst, which reduces the energy required for electrochemical reaction to take place. Another efficient means of electrolyzer improvement is to use the Computational Fluid Dynamics (CFD)-assisted design that allows the comprehension of the phenomena occurring in the electrolyzer and also the improvement in the electrolyzer’s efficiency. The designed two-phase hydrodynamics model of this study has been compared with the experimental results of velocity profiles measured using Laser Doppler Velocimetry (LDV) method. The simulated results were in good agreement with the experimental data in the literature. Under the good fit with experimental values, it is efficient to introduce a new physical bubble transfer phenomenon description called “bubble diffusion”.

Engaging black and minority-ethnic (BME) individuals in therapy and maintaining a positive therapeutic alliance can be a complex task, especially when challenging a family's core belief system. This study examines how therapists working within a specialist cultural service in London, UK were able to question a family's core cultural belief system whilst building and maintaining a strong therapeutic alliance. Video-assisted semi-structured interviews were carried out with two family members and their two therapists, and analysed using thematic analysis. The findings suggest that core beliefs can be effectively challenged within the context of a strong therapeutic alliance if topics are approached in a sensitive and respectful manner, by trusted therapists who have a degree of knowledge and awareness of their own cultural positioning, as well as an understanding of their clients’ culture. We propose that engaging with culture in this way can strengthen alliance and facilitate positive change.

Owing to the progressive abandoning of the fossil fuels and the increase of atmospheric CO2 concentration, the use of renewable energies is strongly encouraged. The hydrogen economy provides a very interesting scenario. In fact, hydrogen is a valuable energy carrier and can act as a storage medium as well to balance the discontinuity of the renewable sources. In order to exploit the potential of hydrogen it must be made available in adequate quantities and at an affordable price. Both goals can be potentially achieved through the electrochemical water splitting, which is an environmentally friendly process as well as the electrons and water are the only reagents. However, these devices still require a lot of research to reduce costs and increase efficiency. An approach to improve their performance is based on nanostructured electrodes characterized by high electrocatalytic activity. In this work, we show that by using template electrosynthesis it is possible to fabricate Ni nanowires featuring a very high surface area. In particular, we found that water-alkaline electrolyzers with Ni nanowires electrodes covered by different electrocatalyst have good and stable performance at room temperature as well. Besides, the results concern nickel-cobalt nanowires electrodes for both hydrogen and oxygen evolution reaction will be presented and discussed. Finally, preliminary tests concerning the use of Ni foam differently functionalized will be shown. For each electrode, electrochemical and electrocatalytic tests aimed to establishing the performance of the electrolyzers were carried out. Long term amperostatic test carried out in aqueous solution of KOH will be reported as well.

This article presents an exhaustive review of the transport properties necessary for the multiphysics modelling of alkaline water electrolyzer. This article provides experimental data and the correlations needed to calculate thermos-physical properties such as electrical conductivity, density, viscosity, heat capacity, heat and mass transfer diffusion coefficients as a function of temperature and electrolyte mass fraction for two classical alkaline electrolytes (KOH, NaOH). Thus, the different boundary layers growing on the electrodes can be calculated with precision. Different interpolation models from various authors are compared to raw experimental data. The goal of this article is to give to the modeler the correlations needed for the simulation of alkaline water electrolysis.

Hydrogen is an excellent energy source for long-term storage and free of greenhouse gases. However, its high production cost remains an obstacle to its advancement. The two main parameters contributing to the high cost include the cost of electricity and the cost of initial financial investment. It is possible to reduce the latter by the optimization of system design and operation conditions, allowing the reduction of the cell voltage. Because the CAPEX (initial cost divided by total hydrogen production of the electrolyzer) decreases according to current density but the OPEX (operating cost depending on the cell voltage) increases depending on the current density, there exists an optimal current density. In this paper, a genetic algorithm has been developed to find the optimal evolution parameters and to determine an optimum electrolyzer design. The optimal current density has been increased by 10% and the hydrogen cost has been decreased by 1%.

International audience; The effectiveness factor, E f, (fraction of the electrode surface that participates effectively in the investigated reaction) of fast (Fe3+/Fe2+), moderate (Cl2/Cl−) and slow (O2/H2O) redox couples has been estimated using IrO2-based electrodes with different loading. The method of choice was linear sweep voltammetry (measurement of the anodic peak current) for the Fe3+/Fe2+ redox couple and steady-state polarization (determination of the exchange current) for the O2 and Cl2 evolution reactions. The results have shown that the effectiveness factor depends strongly on the kinetics of the investigated redox reaction. For the Fe3+/Fe2+ redox couple, effectiveness factors close to zero (max 4%) have been obtained contrary to the O2 evolution reaction where effectiveness factors close to 100% can be achieved, all being independent of IrO2 loading. For the Cl2 evolution reaction, intermediate values of the effectiveness factor have been found and they decrease strongly, from 100% down to about 60%, with increasing loading.

The effectiveness factor; E f , defined as the fraction of the surface that participates effectively in a given reaction, is an important parameter when operating three-dimensional (3D) electrodes. The rotating disk electrode (RDE) technique with the Fe3+/Fe2+ redox couple as a probe reaction has been used for the evaluation of the effectiveness factor of 3D Ti/IrO2 electrodes with different IrO2 loading. For this purpose, steady-state polarization measurements using Ti/IrO2 rotating disk electrodes in 0.5 M Fe3+/Fe2+ in 1 M HCl were carried out under well-defined hydrodynamic conditions. The low-field approximation relation has been used for the estimation of the exchange current densities j 0, of the Fe3+/Fe2+ redox couple. It was found for this redox couple that the effectiveness factor is very low (

International audience; During two-phase electrolysis processes, for example for hydrogen production, there are bubbles which are created at electrodes. This implies a great vertical motion source in the normal earth gravity field and then a quite important natural two-phase convection. All other fields are then affected. Heat, mass and electricity transfers are modified due to both bubbles screening (at surface and in volume) and to bubbles transport promotion. Many numerical modeling for two-phase processes such as kerosene pulverization in engines or coal combustion sciences have shown the difficulties of these multi-physics processes. Both particles and reactor scales must be considered according with a strong coupling modeling. In these processes the particles injection is "in the flow". In boiling or electrolysis processes, a new difficulty is added: particles birth or injection is strongly coupled to the local flow properties and leads to a complex boundary condition at surfaces. Electrical and electrochemical properties and processes are disturbed. This disturbance can lead to the modification of the local current density and to anode effects for example. There is few works concerning the local modelling of electrochemical processes during a two-phase electrolysis process. There are also few local experimental measurements in term of chemical composition, temperature or current density which will allow the numerical calculations validation. The present work shows the started numerical modeling strategy and the first results, both experimental and numerical obtained.

Chemical bath electro deposition process is used in many industrial applications to obtain a thin layer material on a target surface. Numerous metal, magnetic or semi-conductor materials, such as oxide, chalcogenure or alloys are obtained in electrochemical cells at laboratory scale. Some of these materials are interesting to be produced at industrial scale, for example for electronics, fuel cells or photovoltaic applications. In industrial electrochemical cells, dimension is larger and many parameters such as hydrodynamics or electro active specie transport are heterogeneous. There are many industrial electrochemical techniques in which the electrode moves with respect to the solution. These systems, like the rotating electrodes, are called hydrodynamic electrochemical processes. It is also interesting to notice that micronic structure, such as roughness, columnar structure or porosity of material deposit is local flow dependent. Then, it appears, that the material deposit composition and structural quality need integrated information from the micronic scale to the industrial scale, using, of course, the laboratory scale measurements. The aim of the present work is to model and to numerically simulate the hydrodynamics, electrochemical and chemical coupled phenomena, which are occurring during the chemical bath electro deposition process for laboratory and industrial configurations. Experimental measurements obtained at laboratory scale with zinc oxide thin layer deposit are used to identify transport or kinetic data input which are conserved during the scale-up. Flow and chemical species concentration field properties are calculated in the working electrode surface vicinity taking into account homogeneous and heterogeneous reactions. The numerical method used is the finite volume method. In addition, using a Monte Carlo method, micronic information is calculated such as the roughness and the porosity of the thin layer material obtained.

During two-phase electrolysis, bubble production occurs at one or two electrodes. This yields a large change for the electrolyser electrical and hydrodynamic properties. Under normal Earth gravity, the bubble production at the electrodes induces a macro-convection in the electrolyser. This leads to a modified local current density distribution at the electrodes. When gravity is avoided, bubbles are no longer subject to buoyancy forces and to the induced natural flow friction forces. Electrolysis was performed using a potentiostat, and gas bubble evolution was observed with cameras. Quantitative evolution laws for the electrochemical cell voltage, bubble diameter and population during two-phase electrolysis are established in function of the current density and gravity variation.

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Spark assisted chemical engraving (SACE) is an unconventional micromachining technology based on electrochemical discharge phenomena for glass and various ceramics. The limits of SACE with respect to small dimensions in the particular case of glass are explored. It is found, using a specially developed set-up based on an AFM, that even using extremely sharp tool-electrodes does not allow us to produce a smaller pattern than typically 25 micrometers. It is concluded that the gas film thickness, in which the electrochemical discharges take place, is the main limiting factor. Further experimental investigations on its formation are investigated. By adding surfactants to the electrolyte, in order to increase the wettability of the tool-electrode and therefore to reduce the gas film thickness, it is observed experimentally that the critical voltage reduces significantly. This observation may lead to a novel method of characterizing the gas film thickness in SACE.

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Hydrogen is seen as a means of storing renewable electrical energy and a promising clean fuel.However, 95% of hydrogen is produced using fossil hydrocarbons. To obtain a decarbonated hydrogen, it will be necessary to produce it by electrolysis of water, the only current process that can produce it in industrial quantities. Water electrolysis is an energy-intensive two-phase process in which about 10% of the energy cost is due to an ohmic loss amplified by the presence of gas (hydrogen and oxygen). It is possible to reduce these ohmic losses by reducing the inter-electrode distance. However, due to the presence of bubbles, there is an optimal inter-electrode distance which depends on the operating conditions (pressure, temperature, mass fraction of electrolyte etc.). In order to reduce the operating cost of hydrogen and thus enable its societal development, the process was numerically modeled using the finite volume method. The computational fluid mechanics calculations carried out lead to a correlation linking the gas fraction with the input parameters of the process rendered dimensionless. This correlation was then integrated into a genetic algorithm, developed and optimized. The final concrete goal of this work is to find a compromise between the profitability of the financial investment (CAPEX) and the financial operational performance (OPEX). The recommended design is a height of 5 cm with an inter-electrode distance between 400 and 800 µm forcurrent density between 1000 and 4000 A m-2., L’hydrogène est vu comme un moyen de stockage de l’énergie électrique renouvelable et un carburant propre prometteur. Cependant, 95% de l’hydrogène est produit en utilisant des hydrocarbures fossiles. Pour obtenir un hydrogène décarboné, il sera nécessaire de le produire par électrolyse de l’eau, seul procédé actuel à pouvoir le produire en quantité industrielle. L’électrolyse de l’eau est un procédé diphasique énergivore dont environ 10% du coût énergétique réside dans une perte ohmique amplifiée par la présence de gaz (hydrogène et oxygène). Il est possible de réduire ces pertes ohmiques en réduisant la distance inter- électrode. Cependant, du fait de la présence des bulles, il existe une distance optimale inter- électrodes qui dépend des conditions d’opérations (pression, température, fraction massique d’électrolyte, etc.). Afin de réduire le coût opérationnel de l’hydrogène et ainsi permettre son développement sociétal, le procédé a été modélisé numériquement en utilisant la méthode des volumes finis. Les calculs de mécanique des fluides numériques menés aboutissent à une corrélation liant le taux de gaz avec les paramètres d’entrée du procédé rendus adimensionnels. Cette corrélation a ensuite été intégrée dans un algorithme génétique, développé et optimisé. Le but concret de ce travail est de trouver un compromis entre la rentabilité de l’investissement financier (CAPEX) et la performance opérationnelle financière (OPEX). Le design préconisé est une hauteur de 5cm avec une distance inter-électrode entre 400 et 800 µm pour des densités de courant entre 1000 et 4000 A m-2.