Plasma based platinum nanoaggregates deposited on carbon nanofibers improve fuel cell efficiency

Improved platinum catalytic utilization has been achieved by creating an open support structure based on aligned carbon nanofibers (CNFs) attached to carbon loaded carbon cloth electrodes [known as gas diffusion layer (GDL)]. The nickel catalyst used to initiate the CNFs growth; the CNFs themselves and the 5nm Pt nanoaggregates were deposited sequentially in the same low pressure plasma reactor. This oriented catalyst structure was incorporated into a membraneelectrode assembly and tested with and without CNFs and on carbon paper or GDL. The performance of the fuel cells based on CNFs and GDL was better over the entire range of operating current.One of the authors A.C. gratefully acknowledges ARC Australian Research Network for Advanced Materials, CNRS GDR-I “Plasmas” and ANU for financial support

Do not forget the electrochemical characteristics of the membrane electrode assembly when designing a Proton Exchange Membrane Fuel Cell stack

International audienceThe membrane electrode assembly (MEA) is the key component of a PEMFC stack. Conventional MEAs are composed of catalyzed electrodes loaded with 0.1-0.4 mgPt cm−2 pressed against a Nafion® membrane, leading to cell performance close to 0.8 W cm−2 at 0.6 V. Due to their limited stability at high temperatures, the cost of platinum catalysts and that of proton exchange membranes, the recycling problems and material availability, the MEA components do not match the requirements for large scale development of PEMCFs at a low cost, particularly for automotive applications. Novel approaches to medium and high temperature membranes are described in this work, and a composite polybenzimidazole-poly(vinylphosphonic) acid membrane, stable up to 190 ◦C, led to a power density of 0.5 W cm−2 at 160 ◦C under 3 bar abs with hydrogen and air. Concerning the preparation of efficient electrocatalysts supported on a Vulcan XC72 carbon powder, the Bönnemann colloidal method and above all plasma sputtering allowed preparing bimetallic platinum-based electrocatalysts with a low Pt loading. In the case of plasma deposition of Pt nanoclusters, Pt loadings as low as 10 g cm−2 were achieved, leading to a very high mass power density of ca. 20 kW g−1 Pt . Finally characterization of the MEA electrical properties by Electrochemical Impedance Spectroscopy (EIS) based on a theoretical model of mass and charge transport inside the active and gas diffusion layers, together with the optimization of the operating parameters (cell temperature, humidity, flow rate and pressure) allowed obtaining electrical performance greater than 1.2 W cm−2 using an homemade MEA with a rather low Pt loading

Selective Electrooxidation of Glycerol Into Value-Added Chemicals: A Short Overview

A comprehensive overview of the catalysts developed for the electrooxidation of glycerol with the aim of producing selectively value-added compounds is proposed in the present contribution. By presenting the main results reported in the literature on glycerol electrooxidation in acidic and alkaline media, using different kinds of catalytic materials (monometallic catalysts based on platinum group metals and non-noble metals, multimetallic alloys, or modification of surfaces by adatoms, etc.) and under different experimental conditions, some general trends concerning the effects of catalyst composition and structure, of reaction medium and of the electrode potential to enhance the activity for the glycerol oxidation reaction and of the selectivity toward a unique value-added product will be presented and discussed. The objective is to provide a guideline for the development of electrochemical systems which allow performing the electrooxidation of glycerol at the rate and selectivity as high as possible

A high-resolution map of the Nile tilapia genome: a resource for studying cichlids and other percomorphs

Background: The Nile tilapia (Oreochromis niloticus) is the second most farmed fish species worldwide. It is also an important model for studies of fish physiology, particularly because of its broad tolerance to an array of environments. It is a good model to study evolutionary mechanisms in vertebrates, because of its close relationship to haplochromine cichlids, which have undergone rapid speciation in East Africa. The existing genomic resources for Nile tilapia include a genetic map, BAC end sequences and ESTs, but comparative genome analysis and maps of quantitative trait loci (QTL) are still limited. Results: We have constructed a high-resolution radiation hybrid (RH) panel for the Nile tilapia and genotyped 1358 markers consisting of 850 genes, 82 markers corresponding to BAC end sequences, 154 microsatellites and 272 single nucleotide polymorphisms (SNPs). From these, 1296 markers could be associated in 81 RH groups, while 62 were not linked. The total size of the RH map is 34,084 cR3500 and 937,310 kb. It covers 88% of the entire genome with an estimated inter-marker distance of 742 Kb. Mapping of microsatellites enabled integration to the genetic map. We have merged LG8 and LG24 into a single linkage group, and confirmed that LG16-LG21 are also merged. The orientation and association of RH groups to each chromosome and LG was confirmed by chromosomal in situ hybridizations (FISH) of 55 BACs. Fifty RH groups were localized on the 22 chromosomes while 31 remained small orphan groups. Synteny relationships were determined between Nile tilapia, stickleback, medaka and pufferfish. Conclusion:The RH map and associated FISH map provide a valuable gene-ordered resource for gene mapping and QTL studies. All genetic linkage groups with their corresponding RH groups now have a corresponding chromosome which can be identified in the karyotype. Placement of conserved segments indicated that multiple inter-chromosomal rearrangements have occurred between Nile tilapia and the other model fishes. These maps represent a valuable resource for organizing the forthcoming genome sequence of Nile tilapia, and provide a foundation for evolutionary studies of East African cichlid fishes.Additional co-authors: Thomas D Kocher, Catherine Ozouf-Costaz, Jean Francois Baroiller and Francis Galiber

La documentation des expositions cancérogènes dans les métiers portuaires : histoire d’une mobilisation ouvrière et scientifique

Un projet de mobilisation scientifique issu de la mobilisation associative des portuaires En 2009, à Nantes, une mobilisation s’organise parmi les dockers, majoritairement syndiqués à la Confédération Générale du Travail Portuaire, sous une forme associative, pour dénoncer une hécatombe sanitaire dans les métiers portuaires. L’Association Pour la Protection de la Santé au Travail des Métiers Portuaires (APPSTMP 44) a rendu publique ce bilan sanitaire en mars 2011 au cours d’une journée de pré..

The Electrocatalytic Oxidation of Small Organic Molecules : from Fundamental Studies to Applications in Energy Technology

International audienceThe electrocatalytic oxidation of small organic molecules, such as formic acid and methanol, both in acid and alkaline medium, has been the subject of many investigations due to their fundamental interest in the field of Electrocatalysis [1] and Energy Technology (Fuel Cells [2] and Electrolysis [3-4]). Andrzej Wieckowski was one of the first to carry out fundamental studies on the mechanism of the adsorption and oxidation of formic acid and methanol on platinum electrodes using a radiochemical method coupled to electrochemical techniques [5-7]. The use of single crystal electrodes brought a new insight in understanding the role of the catalytic electrode in the adsorption of both formic acid [8-10] and methanol [11-12] on low-index Pt(h,k,l) and Au(h,k,l) electrodes. On the other hand the early development of Infrared Reflectance Spectroscopy by Alan Bewick allowed identifying unambiguously the presence of linearly adsorbed CO as the main adsorbed species resulting from the dissociative chemisorption of HCOOH or CH3OH and blocking the active sites of smooth Pt electrodes [13-14]. As a consequence the adsorption of CO [15] was particularly studied on carbon supported Pt nanoparticles working as catalytic layers in Direct Methanol Fuel Cells (DMFC) [16] or Direct Formic Acid Fuel Cells (DFAFC) [17]. In order to decrease the amount of adsorbed CO resulting from the chemisorption of HCOOH or CH3OH different bimetallic and ternary Pt-based or Pd-based catalysts were developed, particularly for the Direct Oxidation Fuel Cells [18-19]. In this communication we will present several results on the investigation of the reaction mechanism of the electro-oxidation of formic acid and methanol on well-defined smooth electrodes and carbon supported nanocatalysts using combined electrochemical methods and physico-chemical methods (radiochemical technique and Infrared Reflectance spectroscopy). The understanding of reaction mechanisms leads to a better knowledge of the role of the electrode nature and structure allowing conceiving more efficient electrocatalysts. This will be illustrated by some results relevant of energy technology, e.g. the Direct Oxidation Fuel Cell (DMFC, DFAFC) and the Proton Exchange Membrane Electrolysis Cell (PEMEC) to produce clean hydrogen to feed a Proton Exchange Membrane Fuel Cell (PEMFC). References : [1] Catalysis and Electrocatalysis at Nanoparticle Surfaces, A. Wieckowski, E. Savinova and C. Vayenas (Eds.), Marcel Decker Inc., New-York (2002). [2] Electrocatalysis of Direct Methanol Fuel Cells, H. Zhang and H. Liu (Eds.), Wiley-VCH, Weinheim (2009). [3] S. R. Narayanan, W. Chun, B. Jeffries-Nakamura, T. I. Valdez, US Patent 6533919, March 18, 2003. [4] C. Lamy, A. Devadas, M. Simoes, C. Coutanceau, Electrochim. Acta, 60 (2012) 112-120. [5] A. Wieckowski, J. Sobkowski, A. J. Onska, J. Electroanal. Chem., 55 (1974) 383-389. [6] A. Wieckowski, J. Sobkowski, J. Electroanal. Chem., 63 (1975) 365-377. [7] P. Waszczuk, A. Wieckowski, P. Zelenay, S. Gottesfeld, C. Coutanceau, J.-M. Léger, C. Lamy, J. Electroanal. Chem., 511 (2001) 55-64. [8] R.R. Adzic, W.E. O'Grady, S. Srinivasan, Surf. Sci., 94 (1980) L191-L194. [9] J. Clavilier, R. Parsons, R. Durand, J.-M. Léger, C. Lamy, J. Electroanal. Chem., 124 (1981) 321-326. [10] A. Hamelin, C. Lamy, S. Maximovitch, C.R. Acad. Sci., 282 C (1976) 403-406. [11] J. Clavilier, C. Lamy, J-M. Léger, J. Electroanal. Chem., 125 (1981) 249-254. [12] E. Herrero, K. Franaszczuk, A. Wieckowski, J. Phys. Chem., 98 (1994) 5074-5083. [13] B. Beden, A. Bewick, C. Lamy, K. Kunimatsu, J. Electroanal. Chem., 121 (1981) 343-347. [14] B. Beden, A. Bewick, C. Lamy, J. Electroanal. Chem., 150 (1983) 505-511. [15] C. Rice, Y.Y. Tong, E. Oldfield, A. Wieckowski, F. Hahn, F. Gloaguen, J.-M. Léger, C. Lamy, J. Phys. Chem. B, 104 (2000) 5803-5807. [16] S. Park, Y.Y. Tong, A. Wieckowski, M.J. Weaver, Langmuir, 18 (2002) 3233-3240. [17] C. Rice, S. Ha, R.I. Masel, P. Waszczuk, A. Wieckowski, T. Barnard, J. Power Sources, 111 (2002) 83-89. [18] C. Lamy, A. Lima, V. Le Rhun, F. Delime, C. Coutanceau, J.-M. Léger, J. Power Sources, 105 (2002) 283-296. [19] C. Rice, S. Ha, R.I. Masel, A. Wieckowski, J. Power Sources, 115 (2003) 229-235

Determination of the mechanisms of electrocatalytic reactions by combining electrochemical methods and in situ spectroscopy

International audienceMany electrochemical reactions of technical interest (fuel cells, electrolyzers, etc.) need the development of efficient catalysts to increase the reaction rate and selectivity. In order to find new electrocatalysts it is of prime importance to elucidate the reaction mechanisms by identifying the different intermediates involved and elucidating their role in the rate determining step (r.d.s.). Apart from the hydrogen oxidation and evolution reactions, the mechanisms of which are thoroughly established, the oxygen reduction (ORR) and evolution reactions (OER), or the oxidation of low weight alcohols in a Direct Alcohol Fuel Cell (DAFC), are relatively complex since they involve multi electron transfer with the formation of several adsorbed intermediates and reaction by-products. The reaction rate of ORR is very low and it is the main cause of energy efficiency limitation in a Polymer Electrolyte Fuel Cell (PEFC) [1-3]. Alcohols (particularly methanol and ethanol) are of great interest as liquid fuels in a DAFC [4–10], but a rather poor kinetics of their electroxidation is observed with platinum, the only catalyst activating the C–H bond cleavage at ambient temperatures. The adsorption and oxidation of methanol and ethanol on a Pt electrode lead to the formation of poisoning species (mainly adsorbed CO), as observed by in situinfrared reflectance spectroscopy [11-12]. In both cases, the formation of such poisoning species leads to a poor electrocatalytic activity, and the challenge is to enhance the activity of platinum by avoiding the formation of poisoning species through the development of bimetallic or multi-metallic platinum-based electrocatalysts. The elucidation of the reaction mechanisms needs the use of different spectroscopic and analytical techniques under electrochemical control, i.e. the combination of electrochemical methods with other physicochemical techniques. This allows identifying the nature of adsorbed intermediates, the structure of adsorbed layers, the nature of the reaction products and by-products, etc., and determining the amount of these species, as a function of the electrode potential and experimental conditions. This will lead to a deep understanding of the reaction mechanisms, which are depending on the nature of the catalyst, the composition and structure of the electrode. In this communication we will present spectro-electrochemical methods (Infrared Reflectance Spectroscopy [13], Electron Spin Resonance Spectroscopy [14] and UV-visible Reflectance Spectroscopy [15]) able to identify in situthe adsorbed species and reaction products involved in electrochemical reactions of great interest for energy conversion. For the ORR, the comparison of electrochemical data from rotating disc electrodes with results from spectroscopic methods gives information on the reaction mechanism. For alcohol electroxidation reactions, the coupling of electrochemical measurements with Infrared Reflectance Spectroscopy allows the identification of the intermediate species and reaction products as a function of the electrode potential and of its structure. This allowed proposing mechanisms for the reactions involved in electrochemical reactions encountered in the development of Fuel Cells or Electrolyzers: the Oxygen Reduction Reaction and the electroxidation of some alcohols (methanol, ethanol, ethylene glycol, and glycerol). References : [1] G. J. K. Acres, J. C. Frost, G. A. Hards, R. J. Potter, T. R. Ralph, D. Thompsett, G. T. Burstein, G. J. Hutchings, Catal. Today, 38 (1997) 393-400. [2] T.R. Ralph, M.P. Hogarth, Platinum Metals Rev., 46 (2002) 3-14. [3] C.-C. Yang, Int. J. Hydrogen Energy, 29 (2004) 135-143. [4] C. Lamy, A. Lima, V. Le Rhun, F. Delime, C. Coutanceau, J.-M. Léger, J. Power Source,s 105 (2002) 283-296. [5] E. Peled, T. Duvdevani, A. Aharon, A. Melman, Electrochem. Solid State Lett., 4 (2001) A38-A41. [6] C. Lamy, J.-M. Léger, S. Srinivasan, Direct Methanol Fuel Cells: From a twentieth century electrochemist’s dream to twenty-first century emerging technology, in "Modern Aspects of Electrochemistry", J.O’M. Bockris and B.E. Conway (Eds.), Vol. 34, Plenum Press, New York, 2000, Chapter 3, pp.53-118. [7] C. Lamy, E.M. Belgsir, J.-M. Léger, J. Appl. Electrochem., 31 (2001) 799-809. [8] T. Iwasita-Vielstich, in Advances in "Electrochemical Science and Engineering", H. Gerischer and C.W. Tobias (Eds.), Vol.1, VCH Verlag, Weinheim, 1990, p. 127. [9] A. Hamnett, Catal. Today 38 (1997) 445-457. [10] K. Y. Chan, J. Ding, J. W. Ren, S. A. Cheng, K.Y. Tsang, J. Mater. Chem., 14 (2004) 505-516. [11] B. Beden, F. Hahn, S. Juanto, J.M. Léger, C. Lamy J. Electroanal. Chem., 225 (1987) 215. [12] J.M. Perez, B. Beden, F. Hahn, A. Aldaz, C. Lamy, J. Electroanal. Chem., 262 (1989) 251. [13] B. Beden, C. Lamy, Infrared reflectance spectroscopy, in "Spectroelectrochemistry - Theory and Practice", R.J. Gale (Ed.), Plenum Press, New York, 1988, Chapter 5, pp. 189-261 [14] P. He, C. Cha, P. Crouigneau, J.M. Léger, C. Lamy, J. Electroanal. Chem., 290 (1990) 203. [15] O. El Mouahid, A. Rakotondrainibe, P. Crouigneau, J.M. Léger, C. Lamy, J. Electroanal. Chem., 455 (1998) 209

Electroreforming of glucose/xylose mixtures on PdAu based nanocatalysts

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Highly efficient and selective electrooxidation of glucose and xylose in alkaline medium at carbon supported alloyed PdAu nanocatalysts

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Modification of Carbon Substrates by Aryl and Alkynyl Iodonium Salt Reduction

International audienceDifferent carbon materials were modified using iodonium ion reduction creating radicals, which after reaction with carbon surfaces formed grafted layers of molecules Several molecules (4-bromophenyl, 4-fluorophenyl, 6-chlorohexyne, and 4-bromobutyne) were grafted on glassy carbon and Vulcan XC72 carbon substrates Carbon substrates were shown to be free of halogen atoms: therefore, the quantification of the grafted groups containing halogen atoms was facilitated The grafting of the different molecules was first electrochemically studied on glassy carbon electrodes using cyclic voltammetry, in order to determine the reduction potential of the corresponding iodonium ions Voltammetric study using Fe(CN)(6)(4-) and Fe(CN)(6)(3-) probe molecules and X PS characterization were also used to evidence the effectiveness of grafting from iodonium ion reduction reaction Reduction potentials were found in the range from -0 9 V vs SCE to -1 0 V vs SCE. lower than those for corresponding diazonium ion reduction I cachou on glassy carbon (close to -0 3 V vs SCE) Therefore, grafted layers from iodonium ions were carried out on carbon Vulcan XC72 powder using NaBH(4) as reducing agent Functionalized carbon powders were characterized by elemental analysis, thermogravimetric analysis, and X-ray photoelectron spectroscopy to evidence the presence of grafted molecules On the materials However, low grafting yields were obtained Then, several synthesis parameters were studied to optimize the grafting reactions, such as the control of the addition of reactants and their concentrations, leading to Increase the surface concentration by a factor 2 At last, according to XI'S measurements the grafting of alkinyliodonium ions led to very low surface concentrations (0 5 wt % for 6-chlorohexyne), whereas elemental analysis and TGA indicate ca 2 4 wt % and ca 5 wt %, respectivel