Membrane patterned by pulsed laser micromachining for proton exchange membrane fuel cell with sputtered ultra-low catalyst loadings

International audienceProton exchange membranes were nano-and micro-patterned on their cathode side by pressing them against stainless steel molds previously irradiated by a Ti:Sapphire femtosecond laser. The membranes were associated to ultra-low loaded thin catalytic layers (25 µgPt cm-2) prepared by plasma magnetron sputtering. The Pt catalyst was sputtered either on the membrane or on the porous electrode. The fuel cell performance in dry conditions were found to be highly dependent on the morphology of the membrane surface. When nanometric ripples covered by a Pt catalyst were introduced on the surface of the membrane, the fuel cell outperformed the conventional one with a flat membrane. By combining nano-and micro-patterns (nanometric ripples and 11-24 µm deep craters), the performance of the cells was clearly enhanced. The maximum power density achieved by the fuel cell was multiplied by a factor of 3.6 (at 50 °C and 3 bars): 438 mW cm-2 vs 122 mW cm-2. This improvement is due to high catalyst utilization with a high membrane conductivity. When Pt is sputtered on the porous electrode (and not on the membrane), the contribution of the patterned membrane to the fuel cell efficiency was less significant, except in the presence of nanometric ripples. This result suggests that the patterning of the membrane must be consistent with the way the catalyst is synthesized, on the membrane or on the porous electrode

Plasma inhomogeneities near the electrodes of a capacitively-coupled radio-frequency discharge containing dust particles

Small plasma spheroids are evidenced and analyzed in front of the electrodes of a capacitively-coupled radio-frequency discharge in which dust particles are growing. These regions are characterized by a spherical shape, a slightly enhanced luminosity and are related to instabilities induced by the presence of dust particles. Several types of behaviors are identified and particularly their chaotic appearance or disappearance and their rotational motion along the electrode periphery. Correlations with the unstable behavior of the global plasma glow are performed. These analyses are obtained thanks to high-speed imaging which is the only diagnostics able to evidence these plasma spheroids

Formation and behavior of negative ions in low pressure aniline containing RF plasmas

International audienc

INCREASE OF THE NICKEL TARGET TEMPERATURE IN MAGNETRON SPUTTERING

International audienceA Ni target has been disconnected from a water-cooled magnetron in order to induce a rise of its temperature. The time evolutions of the cathode voltage, of the target temperature, of the magnetic field and of the infrared radiation emitted by the target were investigated. An increase in the deposition rate and a change in the thin film microstructure has been observed

INCREASE OF THE NICKEL TARGET TEMPERATURE IN MAGNETRON SPUTTERING

International audienceA Ni target has been disconnected from a water-cooled magnetron in order to induce a rise of its temperature. The time evolutions of the cathode voltage, of the target temperature, of the magnetic field and of the infrared radiation emitted by the target were investigated. An increase in the deposition rate and a change in the thin film microstructure has been observed

PdPt nanocatalyst synthesis via liquid medium sputtering

International audiencePdPt nano-catalysts were synthesized via magnetron sputtering method in vacuum on vegetal glycerin as liquid substrate. The nanoparticles formation and their dispersion in the liquid phase have been studied by varying deposition parameters as the argon pressure, the magnetron power and glycerin temperature. Pt-based nano-catalysts are incorporated into electrochemical cells and their catalytic activities towards oxygen reduction reaction (ORR) are evaluated

Nitrogen incorporation in graphene nanowalls via plasma processes Experiments and simulations

The interest in doped and functionalized graphene nanomaterials for various applications is growing due to the development of new and simple production and treatment methods. Amongst the techniques used to treat graphene nanomaterials dry methods like plasmas or ion beams are of particular interest. In this work a low temperature plasma technique is used to incorporate nitrogen atoms into the carbon network of graphene sheets. In order to gain a better understanding of such processes material analysis techniques NEXAFS and XPS were combined with the results coming from molecular dynamics simulations and plasma know how. The results show that the plasma post treatment of graphene nanowalls can be regarded as a balance between vacancy formation, functionalization, doping and crosslinking. Moreover, MD simulations provided insight into fundamental mechanisms like the formation of different bonds due to the interaction of the surface with different kind of species with variable kinetic energy. This can help to improve different types of doping functionalization techniques using energetic species the study reveals for example the role of N2 species, the kinetics of vacancy formations depending on type and energy of the species, the formation of amines or graphitic nitrogen, and the role of impurities such as NHx specie

Sputtered Ag thin films with modified morphologies: Influence on wetting property

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LIBS in a low temperature plasma for the detection of airborne asbestos

International audienceForbidden in french constructions since 1997, asbestos remains present in most of the buildings constructed before this date. Thus, during work or in case of degradation, asbestos fibres can be emitted in air. The smaller the asbestos particles, the longer they stay in suspension in air, increasing the hazard of inhaling them. The current determination of airborne asbestos presence in France follows a long and cumbersome normative protocol (NF X 43-050), with an analysis carried out on a Transmission Electron Microscope at laboratory after air filtration on-site. Such a protocol induces wasting time between the sampling and the results delayed not less than 48 hours and therefore prevents for the intervention on-site-on-time. Thus, the demand of a real-time measurement increases, even if it is only an alert technique. The PLASMIANTE project aims to develop an apparatus able, on-site and in near-real-time, to analyse the particles present in an air sample and to identify the presence of asbestos. The device will sample air and send the particles in a reactor in which they will be trapped in a low-temperature argon plasma. Among several diagnostics that will be applied directly on the particles in suspension in the plasma, Laser Induced Breakdown Spectroscopy will be used to identify the presence of asbestos in the samples. In this study, we present the first results of LIBS applied to particles of asbestos, building materials and mixtures in suspension in a low temperature plasma