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WS-21: HYDROGEN AS A FUTURE ENERGY CARRIER

PROGRAMME Part 3:ABSTRACTS

WS-21: HYDROGEN AS A FUTURE ENERGY CARRIER

PROGRAMME Part 3:ABSTRACTS

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S1-INV.1 CONVENTIONAL H2 PRODUCTION

Ib ChorkendorffCenter for Individual Nanoparticle Functionality (CINF) NanoDTU, Department of Physics, Technical University of Denmark, DK-2800 Lyngby, DK

As fossil fuel reserves become depleted in the future, alternative energy carriers such as H2 may become more prominent. H2 can easily be produced from fossil fuels and can be a primer for a later sustainable and clean production from solar or wind energy if those are coupled to water electrolysis. Unfortunately, the hydrogen evolution reaction is catalyzed most effectively by Pt-group metals which are scarce and expensive. If this scheme is to become viable, new materials are needed. In this talk I will first discuss the possibilities for enhancing and improving the conventional catalytic methods for hydrogen production through processes related through the steam reforming process [1]. Here we will demonstrate on extended single crystals that the detailed atomic structure on the surface has a great potential for enhancing the reactivity of the nanoparticles, if we can control the presence of the reactive centers [2].In the second part I will focus on developing new structured electro-catalysis materials for hydrogen evolution by electrolysis. It will be shown how Pt can be modified by less expensive metals to introduce surface alloys with new properties. Here 736 different systems were ranked theoretically by DFT taking not only reactivity, but also the stability towards phase separation and corrosion into account. We have subsequently tested the most promising candidate, the Bi-Pt surface alloy toward the Hydrogen evolution reaction and found it being improved compared to the standard Pt electrode material [3]. Finally, new materials inspired by biomimetics will be discussed and it will be demonstrated how the detailed atomic structure, measured by STM, and the hydrogen evolution reaction on for example MoS2 clusters are strongly correlated [4,5].

F. Abilgaard-Pedersen, O. Lytken, J. Engbæk, G. Nielsen, I. Chorkendorff, and J. Nørskov, ”Methane dissociation on plane and stepped Ni surfaces”, Surf. Sci. 590 (2005) 127-137.

M. P. Andersson, F. Abild-Pedersen, I. Remediakis, J. Engbaek, O. Lytken, S. Horch, J. H. Nielsen, J. Sehested, J. R. Rostrup-Nielsen, J. K. Nørskov, and I. Chorkendorff,, “H2 Induced CO dissociation on nickel surfaces”, In Preparation (2007).

J. Greeley, T. Jaramillo, J. Bonde, I. Chorkendorff, and J. K. Nørskov, “Computational High-Throughput Screening: New Electrocatalytic Materials for Hydrogen Evolution”Nature Materials 5 (2006) 909-913.B.

Hinnemann, P. G. Moses, J. Bonde, K. P. Jørgensen, J.H. Nielsen, S. Horch, I. Chorkendorff & J. K. Nørskov “Biomimetic hydrogen evolution”, JACS 127 (2005) 5308-5309.

T.F. Jaramillo, K.P. Jørgensen, J. Bonde, J.H. Nielsen, S. Horch, I. Chorkendorff, “Identifying the active site: Atomic-scale imaging and ambient reactivity of MoS2 nanocatalysts” , SCIENCE 317 (2007) 100.

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S1-IA.1 AN OVERVIEW ON THE RESEARCH PROJECT “HYDROGEN PRODUC-TION BY CATALYTIC STEAM REFORMING OF BIOMASS PYROLYSIS LIQUIDS (BIO-OIL)”.

J.A. Medrano; F. Bimbela; M. Oliva; J. Ruiz; L. García, J. ArauzoThermo-Chemical Processes Group (GPT), Aragón Institute of Engineering Research (I3A), University of Zaragoza, María de Luna 3, 50018 Zaragoza, Spain. Authors Email: qtarauzo@unizar.es, luciag@unizar.es

A century ago no one would have bet that topics such as fossil fuels depletion, fuel cells or hydrogen as an energy carrier should stand as highlights in the world of scientific research. Nowadays, all these items are all the rage among scientists devoted to energy production, environmental issues and upgrading of residues. The generalized opinion is that hydrogen constitutes the most serious alternative to become the main energy source of the 21st century. Fed into a fuel cell, hydrogen yields electricity with high energetic efficiency, upper than that of processes based in combustion of fossil fuels. Besides, the only product generated in the electrochemical reaction is water, which is a clean and environmentally friendly product.However, there still remains the challenge of obtaining hydrogen by means of a sustainable, cost-competitive and environmentally friendly method, instead of the currently, massively followed, catalytic steam reforming of natural gas and naphthas. Biomass is considered as a main alternative and bio-oil may constitute an attractive option, since it has several advantages, both social (development of new jobs to cultivate rapid growth energy crops) and environmental (it allows the upgrading of lignocellulosic and sewage sludge residues, apart from being a renewable and sustainable energy source with no net CO2 emissions), as well as implying less dependance of external energy sources for countries under development or without crude reserves.There are mainly three thermochemicalpaths to obtain hydrogen from biomass [1]: aqueous phase reforming (involving high pressures and moderate temperatures), gasification and pyrolysis. The first option has been deeply investigated by Dumesic and his co-workers in the last decade [2], and still requires further development. Gasification draw great attention throughout the last three decades, whereas pyrolysis is increasingly gaining force. Several pyrolytic routes are under development up to date, being the catalytic steam reforming of pyrolysis liquids from biomass (bio-oil) one of the most important. This process has some advantages compared to the rest: less tar production, delocalisation of the power plant from the raw material, and possibility of heterogeneous feeds into the power plant. On the other hand, biomass has circa 6 % by unit weight of hydrogen content. The catalytic steam reforming of bio-oil allows the production of a hydrogen-rich gas current with yields as high as 12-14 % by unit weight. This fact has encouraged important investments in the research and development of industrial scale processing of residues so as to facilitate the approach to the zero target: zero emissions and zero residues, while upgrading those residues obtaining valuable products.The bio-oil is a complex mixture of oxygenated organic compounds and water in a 85/15 mass ratio. Its main constituents comprise alcohols, carboxylic acids, sugars, aldehydes and ketones, as well as more complex carbohydrates and lignin derived materials [3]. Two main fractions can be obtained and separated by means of the addition of water: the first is an organic fraction, water insoluble, with lignin derived materials, mainly high molecular weight olygomers. This fraction, usually cited as pyrolytic lignin, may be used for the production of fine chemicals and high added value products such as phenolic resins [4]. The other is an aqueous fraction, less valuable, that can be catalytically steam reformed for hydrogen production [5]. In the catalytic steam reforming process several metallic catalysts have been typically employed, some of them based in noble metals. However, nickel based catalysts are preferred, as they combine a high catalytic activity with a relatively low cost [6].The present work follows the aforementioned strategy: to develop a process for catalytic steam reforming of the aqueous fraction of bio-oil. This research has received financial support from the Spanish Research

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Council (research project ref. num. CTQ2004-06279) and from the Government of Aragon (Research Project Ref. Num. PIP185/2005). The work has been structured into several tasks. First of all, exhaustive experimental work is being performed at different scales and types of reactors with nickel based catalysts prepared by coprecipitation following the method described by Al-Ubaidand Wolf [7]. At a microscale level, the catalytic steam reforming of model compounds of the aqueous fraction of bio-oil has become a matter of study. The influence of several parameters has already been analysed: the reforming reaction temperature, the catalyst reduction time, the weight of catalyst/organic flow rate ratio and the nickel content in the catalyst. The presence of modifiers such as magnesium, lanthanum or cobalt will also be taken into account. Acetic acid [8], acetol, 1-butanol and fructose have been the model compounds chosen and tried, and further experimentation with the aqueous fraction of bio-oil will be completed.Along with the microscaletests, another part of the experimental work has been developed at a bench-scale fluidized bed facility. Extracting information from the microscale results, the influence of the weight of catalyst/organic flow rate ratio was studied for the catalyst that had displayed the best performance at a microscale. On the other hand, an attrition study was fulfilled to check the mechanical resistance of the catalysts tested at the fluidized bed setup. Acetic acid was the chemical employed in these tests. The final goal is to perform experiments with the aqueous fraction of bio-oil in the fluidized bed. The information extracted from these results will enable the scaling up of the process, with the purpose of developing a commercial process for hydrogen production by means of catalytic steam reforming of bio-oil at an industrial scale fluidized bed.

References

T.A. Milne, C.C. Elam, and R.J. Evans (NREL, Colorado, USA). Hydrogen from biomass. State of the art and research challenges. Golden (CO): A report for the International Energy Agency. ref. IEA/H2/TR-02/001 (2001).

R.R. Davda, J.W. Shabaker, G.W. Huber, R.D. Cortright, J.A. Dumesic, Appl. Catal. B: Env. 56, 171 (2005).

A.Oasmaa and D. Meier, J. Anal. Appl. Pyrol. 73, 323 (2005).

B.S.S. Kelley, X.M. Wang, M.D. Myers, D.K. Johnson and J.W. Scahill in Bridgwater, A.V. and Boocock; D.G.B. (eds.): “Developments in thermochemical biomass conversion”. London: Blackie Academic & Professional; 1997. p. 557.

S. Czernik, D. Wang, D. Montané, and E. Chornet in Bridgwater, A.V. and Boocock, D.G.B. (eds.): “Developments in thermochemical biomass conversion”. London: Blackie Academic & Professional; 1997. p. 672.

J.R. Galdámez, L. García, and R. Bilbao, Energ. Fuel. 19, 1133 (2005).Al-Ubaid and E.E. Wolf, Appl. Catal., 40, 73 (1988).

F. Bimbela, M. Oliva, J. Ruiz, L. García and J. Arauzo, J. Anal. Appl. Pyrol., article in press, corrected proof, doi: 10.1016/j.jaap.2006.11.006 (2006).

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S1-IA2 H2 PRODUCTION FROM BIOMASS.

N. Homs. Catalytic Materials, Dept. of Inorganic Chemistry and Institute of Nanoscience and Nanotechnology, University of Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain.

There is a growing interest to replace fossil sources in fuels and chemicals production. In thiscontext, biomass can play a significant role in reducing global warming when it is used to displace fossil fuels. Furthermore, biomass can be efficiently converted into energy and chemicals. Whenbiomass is considered as a fossil-fuel substitute, agricultural and forest residues, that can be economically recovered, are potential sources of biomass-derived energy. The technology of biomass conversion is approaching maturity, with many small-scale installations and much research having being accumulated in the past few years. An approach to the use of biomass is its conversioninto alternative fuels, the so-called then, bio-fuels. Among them, liquid bio-fuels are attractive forsome reasons as easy handle and transport. In this way, the incorporation of hydrogen within thesefuels is also a route to alternative H2 storage systems. Hydrogen is a fascinating carrier of energy. Time has come to shift the attention for a “Hydrogen Economy” and to direct manpower and resources to find technical solutions for a sustainable energy production.In this presentation a brief survey of the so called bio-energy will be given. In this context, a short introduction to potential uses of bio-fuels will lead us to focus on the opportunities for hydrogen production from biomass-derived substrates.

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S1-IA.3 HYDROGEN FROM BIOALCOHOL: FROM MICRODEVICES TO INDUSTRIAL APPLICATION

Jordi Llorca. Institute of Energy Technologies. Technical University of Catalonia.Diagonal 647, 08028 Barcelona, Spain. E-mail: jordi.llorca@upc.edu

Low temperature fuel cells are attractive electric power sources for portable devices, transportation, and small and medium stationary power plants. However, among the most daunting challenges impeding their implementation is the development of an appropriate hydrogen supply that has to rely on stand-alone processes for the generation of hydrogen (fuel processors). Bioalcoholsare particularly appealing as primary fuels for fuel processors since they can be obtained from renewable biomass (gasification and fermentation), they are easy and safe to store and transport, and since water is consumed during their conversion into hydrogen, there is no need for absolute alcohol to be produced. Here we present our results related to the production of hydrogen from bioethanol in autothermal microreactors for portable devices as well as in catalytic wall reactors for large-scale application.

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S2-INV.2 HIGH-THROUGHPUT SYNTHESIS AND SCREENING OF ELECTRODE CATALYSTS FOR FUEL CELLS:-ALLOYS, PARTICLE SIZE AND SUBSTRATE OPTIMISATION

Brian E. HaydenSchool of Chemistry, University of Southampton, Southampton SO17 1BJ, U.K.beh@soton.ac.uk

High-Throughput Physical Vapour Deposition (HT-PVD) based on Molecular Beam Epitaxy methods 1 has been used to synthesise libraries of catalysts which have subsequently been screened for their electrochemical activity and stability. A screening method is described 2 which has been applied to measurements on both high area catalysts, and the HT-PVD catalyst libraries. Examples of the screening of ternary alloy catalysts for oxygen reduction activity include both platinum lean 3 and platinum free systems. The effect of particle size is demonstrated for the high area supported platinum catalysts, and the HT methodology is extended to investigate the effect of particle size and support on the HT-PVD electrocatalysts.4 The kinetics of oxygen reduction and CO oxidation at gold particles on both carbon and sub-stoichiometric titania is described for mean particle diameters in the range 1.4 nm to 7 nm. There is a strong particle size effect on the catalytic activity of the gold centres supported on titania or carbon for oxygen reduction.5 Loss of activity is observed for very small centres with diameters below 2.5 nm and the trend implies that centres below 1 nm are totally inactive. In the case of titania supported Au particles, a weak maximum in oxygen reduction activity is also observed at particle sizes of ca. 3nm. In the case of the electrocatalytic oxidation of CO on titania supported gold particles,6 the induced activity by titania leads to activity at an overpotential lower than those on carbon supported Au of even the open pack faces of bulk gold. In addition the optimum particle size for CO electroxidation on titaniasupported Au iis ca. 3nm (Figure). The similarities with the low temperature oxidations exhibited by supported Au in heterogeneous catalytic are highlighted, and the possibilities in designing and optimising electrocatalysts by choice of particle size and support emphasised.1.Samuel Guerin, Brian E.Hayden; J. Comb. Chem. 8 (2006) 66-73.2. Sam Guerin, Brian E. Hayden, Christopher E. Lee, Claire Mormiche, John R. Owen, Andrea E. Russell, Brian Theobald and David Thompsett; J.Combinatorial Chemistry, 6 (2004) 149 - 158.3. Samuel Guerin, Brian E. Hayden, Christopher E. Lee, Claire Mormiche, Andrea E. Russell; J.Phys.Chem.B 110 (2006) 14355-14362.4.Samuel Guerin, Brian E. Hayden, Derek Pletcher, Michael E. Rendall, Jens-Peter Suchsland and Laura J. Williams; J. Comb. Chem. 8 (2006) 791-798.5.Samuel Guerin, Brian E. Hayden, Derek Pletcher, Michael E. Rendall and Jens-Peter 6.Brian E. Hayden, Derek Pletcher and Jens-Peter Suchsland; Angewandte Chemie International Edition 46 (2007) 3530-3532

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S2-IA.4 PREPARATION OF PD FILMS AND EVALUATION OF THEIR ABILITY TO BE USED AS HYDROGEN PERMEABLE ANODES ON FUEL CELLS

M. C. OliveiraDepartamento de Química, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real. Portugal.

The increasing demand for pure H2 has catalysed the research in production of Pd membranes for separation and purification of H2. Among the different techniques to prepare Pd films (chemical vapour deposition, chemical displacement, electrodeposition, electroless plating, sputtering), electroless plating (ELP) has been the most attractive technique, particularly, on the preparation of supported Pd based membranes. Despite much work has been devoted to correlate the microstructure, morphology, composition and thickness of Pd based membranes (prepared by ELP) with their performance, i.e. H2 permeability and selectivity, the electrochemical characterization of these films and evaluation of their electrocatalaytic activity towards hydrogen oxidation reaction has never been reported. In this work, electroless Pd membranes will be prepared from different plating conditions (duration, temperature and bath composition) and the effect of the Pd film morphology and structure on their electrochemical behaviour in 0.1 M NaOH and 0.1 M H2SO4 solutions will be investigated within a potential domain suitable for hydrogen oxidation reaction. The prospective use of these films in fuel cells where the anode material is selectively permeable to hydrogen and serves as catalyst as well will be analysed. Characterization of the surface films will be

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S2-IA.5 INFLUENCE OF THE OPERATION CONDITIONS ON HYDROGEN PRODUCTION BY ELECTROLYSIS

T. González-Ayuso, M.A. Folgado, J.L. Serrano, A.M. Chaparro, CIEMAT, Avda. Complutense, 22. 28040 MadridL. Daza, CIEMAT, Avda. Complutense, 22. 28040 Madrid AND I. Catálisis y Petroleoquímica (CSIC), C/. Marie Curie 2, 28049 Madrid.

This communication shows an analysis of hydrogen production by means of a commercial electrolyser under different operation conditions. The study is carried out in view of the integration of the equipment in a renewable energy conversion system. The electrolyser tested is a PEM type (Hogen20, Proton Energy Systems) with 0.5 m3·h-1 nominal production rate. The operation has been carried out under constant and variable production modes, and parameters like gross current consumption, electrolysis voltage and temperature have been monitored. It is observed that power consumption per generated hydrogen unit varies with the production rate. At the lower rates (0.1 to 0.2 m3·h-1) the consumption gets values above 15 kW·m-3, which supposes efficiencies as below as 7%. At highest rates (over 0.5 m3·h-1) the production efficiency increases above 33%. Temperature, in the operation range from 20 to 45 °C, has minor influence. The electrolyser is able to produce hydrogen at maximum rate at a supply pressure of 14 bar. When the pressure of the connected metal-hydride hydrogen storage system achieves this value, the electrolyser stops the generation. The data recorded will help in the integration of a system for solar and wind energy conversion and storage.

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S2-IA6 EFFECTS OF SURFACE CHEMISTRY ON NANOCLUSTERS FOR ELECTROCATALYSIS

B.L. Abrams, T. F. Jaramillo, J. Bonde, P.C.K. Vesborg, I. Chorkendorff. Department of Physics, Technical University of Denmark, DK-2800 KongensLyngby, Denmark

Nanocluster catalysts in the small size regime (<10nm) offer the opportunity for enhancedcatalytic reactivity due to increased active site availability. This reactivity is also materialsdependent and related to how tightly or weakly the nanocatalyst binds the reactants of interestsuch as hydrogen for the hydrogen evolution reaction (HER) [1,2]. Corresponding to the decreasein size is an increase in nanocatalyst surface area. The high surface area of nanoclusters in thissmall size regime thus allows for the ability to impact their catalytic properties by altering theirsurface chemistry. In this work we tune the cluster surface chemistry by varying the type ofsurfactants present on metal and metal alloy nanoclusters such as Pt, Au, AuPt, AgPt. Thesenanoclusters are synthesized using a modified inverse micelle [2] technique where the presence ofsurfactant molecules (non-ionic or cationic) is crucial to maintaining the nanoclustermonodispersity. Following synthesis in the solution phase, the nanoclusters are deposited onto a carbon support and evaluated electrochemically as a function of surfactant type and amount. In the case of Pt nanoclusters stabilized by a non-ionic surfactant, the HER activity is comparable tobulk polycrystalline Pt. The negligible suppression of HER by the surfactant indicates that they do not significantly block the critical sites necessary for HER. This opens up the possibilities forenhancing reactions such as HER relative to the currently utilized Pt electrocatalysts by choosingdifferent surfactants with different nanocluster binding properties. An evaluation of the chargetransfer processes and reactions as revealed by electrochemical measurements will be presentedfor each material as a function of surface chemistry alterations. Preliminary result for otherreactions of interest to fuel cells such as the hydrogen oxidation reaction and the oxygenreduction reaction will also be discussed.

[1] J.K. Nørskov, T. Bligaard, A. Logadottir, J.R. Kitchin, J.G. Chen, S. Pandelov, U. Stimming, “Trends in the Exchange Current for Hydrogen Evolution” J. Electrochem. Soc. (152), J23 (2005).

[2] Greeley, J.; Jaramillo, T.F.; Bonde, J.; Chorkendorff, I.; Nørskov, J.K., “Computational High-Throughput Screening of Electrocatalytic materials for Hydrogen Evolution”, Nature Materials, 5, 909-913 (2006).

[3] Wilcoxon, J.P; Abrams, B.L., “Synthesis, Structure and Properties of Metal Nanoclusters”, Chemical Society Reviews, 35, 1162-1194 (2006).

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S3-INV.3 ELECTROCATALYSIS FOR POLYMER ELECTROLYTE FUEL CELLS: PROGRESS AND CHALLENGES

A.N. Kuznetsovaa, P.S. Ruvinskyaa, S.N. Pronkinbb, E.R.Savinovaa,baBoreskov Institute of Catalysis, SB RAS, 630090 Novosibirsk, Russian Federationb. b l'Ecole Européenne Chimie Polymères Matériaux, Université Louis Pasteur, 67000 Strasbourg, France

Polymer Electrolyte Fuel Cells (PEMFC) transforming chemical energy of hydrogen fuel into electrical energy and considered as environmentally friendly energy converters for the future society. In this presentation we will discuss recent progress in electrocatalysis of the anode and the cathode reactions occurring in PEMFCs. We will mainly focus on the data obtained by the authors but will also present a brief selected review of the literature.The main topics which will be covered are: size [1-4], structural [5,6], composition [7] and support [8] effects, tolerance of the anode catalysts to carbon monoxide [6,7] and stability of the catalysts [6] during electrochemical processes. AcknowledgementsFinancial support from RFBR, Russian Federation (Grant No. 06-03-32737) and ANR, France (Grant No. 7AN12) is gratefully acknowledged.

References

[1] O.V. Cherstiouk, P.A. Simonov, A.L. Chuvilin, and E.R. Savinova, in: “The global climate change: a coordinated response by electrochemistry and solid-state science and technology” (A. Wieckowski, E. W. Brooman, E. J. Rudd, T. F. Fuller, and J. Leddy, Eds.), ECS Inc., Phoenix, 2001.

[2] O.V. Cherstiouk, P.A. Simonov and E.R. Savinova, Electrochim. Acta. 48 (2003) 3851.

[3] O.V. Cherstiouk, P.A. Simonov, V.I. Zaikovskii and E.R. Savinova, J. Electroanal. Chem., 554-555C (2003) 241.

[4] F. Maillard, M. Eikerling, O.V. Cherstiouk, S. Schreier, E.R. Savinova, and U. Stimming, Faraday Discussions 125 (2004) 357-377

[5] A.N. Gavrilov, E.R. Savinova, P.A. Simonov, V.I. Zaikovskii, S.V. Cherepanova, G.A. Tsirlina, and V. N. Parmon, submitted to PCCP.

[6] A.N. Kuznetsov, P.A. Simonov, V.I. Zaikovskii, E.R. Savinova, in preparation.

[7] S.N.Pronkin, P.S.Ruvinsky, E.R.Savinova, in preparation.[8] J. Kaiser, P.A. Simonov, V.I. Zaikovskii, L. Joerissen and E.R. Savinova, accepted to J. Applied Electrochemistry.

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S3-IA.7 SYNTHESIS AND CHARACTERIZATION OF NANOSTRUCTURED MATERIALS FOR PEMFC.

L. Calvillo, M.J. Lázaro. Instituto de Carboquímica (CSIC), Miguel Luesma Castán 4, 50018 Zaragoza, Spain.N. Tsiouvaras. Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, 28049 Madrid Spain. J.J. Quintana, G.García, M.V. Martínez-Huerta and E. Pastor. Dpto. Química Física, Univ. La Laguna, Avda. Astrofísico Francisco Sánchez s/n, 38071 La Laguna, Santa Cruz de Tenerife, Spain.

Catalysts design is one of the key points in the development of polymer electrolyte membrane fuel cells (PEMFC). In this work, we present different approaches to this problem. First, novel non-conventional carbon materials were used as supports for the preparation of Pt and Pt/Ru catalysts. Thus, ordered mesoporous carbons were obtained from mesoporous silica materials. They have controllable pore sizes, high surface areas and large pore volumes, but contain a small amount of oxygenated surface groups. Therefore, functionalization is needed for anchoring metal particles on the support. Activity of Pt supported at these materials will be established from electrochemical studies. On the other hand, the use of trimetallic carbon supported catalysts by introduction of a third metal to Pt-Ru ones is other possibility to improve the efficiency of the PEMFCs. We show the effect of the addition of Mo on the CO tolerance of bimetallic Pt-Ru alloys.Finally, a whole in-situ process for the production of greatly active Pt and Pt-Ru unsupported mesoporous electrodes for micro fuel cell applications is described. These electrodes were obtained from electrochemical reduction of metallic salts dissolved in the aqueous domains of a liquid crystal solution by means of a potential step. Surface modification with Ru adatoms was carried out by spontaneous deposition from an aged solution of Ru+3. The importance of application of in-situ spectroelectrochemicalmethods, as differential electrochemical mass spectrometry (DEMS) and Fourier transform infrared spectroscopy (FTIR), for the study of CO tolerance (adsorption and oxidation of CO) at these materials will be emphasized. Particular designs of the electrochemical cells for technical catalysts will be present. AcknowledgmentsThe authors gratefully acknowledge financial support given by the spanish Ministry of Education and Science (MEC) under the projects MAT2005-06669-C03-01 and NAN2004-09333-C05-04 (FEDER). J.R.C.S. and M.V.M.H. thanks MEC for the research and Juan de la Cierva contracts, and J.J. Quintana and L. Calvillo for the grants.

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S3-IA.8 HYDROGEN MANAGEMENT IN APU HYBRID SYSTEM WITH FUEL CELL (GELSHI)T.

González-Ayuso, M.A. Folgado, J.L. Serrano, A.M. Chaparro, J.L. Ortiz andL. Daza*CIEMAT, Avda. Complutense, 22. 28040 Madrid, * Also at I. Catálisis y Petroleoquímica (CSIC), C/. Marie Curie 2, 28049Madrid.

GELSHI can be used as an auxiliary power unit and autonomous power generator, with energy storage in the form of hydrogen. The system integrates a polymeric fuel cell stack, a solar panel and a battery. Under daylight the solar panel (Isofoton, 94 W) provides the energy for the application, whereas, in darkness, the power consumption is switched to the battery. The fuel cell (MESDEA, 500 W) is started up when the state of charge of the battery drops below a certain limit. Hydrogen for the fuel cell is stored in a metal hydrides system working under pressure control. One of the main objectives of the project has been the design of the strategy for the energy management system, in order to optimise working conditions for the different components and the efficiency. GELSHI has been tested with a programmable load under different conditions, including periods of constant and variable power demand, and demonstrated capability to provide continuous power during grid failures.

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S3-IA.9 H2 CONVERSION IN FUEL CELLS

D. GuineaInstituto de Automática Industrial .CSIC. ES

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S3-IA.10 BIOGAS AND FUEL CELLS: FROM WASTE TO CLEAN ENERGY

M. Benito, L. Rodríguez, R. Padilla, L. Daza,

Instituto de Catálisis y Petroleoquímica (CSIC), C/ Marie Curie 2, CampusCantoblanco, 28049 Madrid, Spain

The sustainable development approach in great cities is related to taking advantage of municipal solid waste coming from landfill or the residual water treatment plants. From an environmental point of view, the revaluation of these remainders and their transformation into hydrogen presents a synergetic effect since it avoids the greenhouse gas emissions to the atmosphere such as methane and carbon dioxide obtaining a clean fuel. Taking into account economic aspects, biogas represents the greatest potential of renewable energy sources and only is taken advantage of 15%. Biogas processing could favour a decentralised economy and could mitigate the energy dependence of external supplies.Nevertheless, some technical barriers have to be overcome in order to take advantage of biogas. The first one is related to biogas composition. From this point of view, biogas composition oscillates between 60-80% CH4 and 20-40% CO2 depending on biogas source. Nowadays, biogas is emitted directly to atmosphere or fed to internal combustion engines to power generation. Streams with low methane concentration produces ignition problems in internal combustion engines and the presence of contaminants such as H2S, siloxanes, ammonia…, can produce corrosion, and abrasion damages that limit the operation of internal combustion engines in spite of its low concentration.An alternative to usage low methane concentration streams is to process them in order to obtain hydrogen, or feed them directly to high temperature fuel cells. Opposite to internal combustion engines where CO2 is a diluter that produces ignition problems, CO2 can be used as an oxidant in “dry methane reforming” to obtain syngas streams. Prior to perform the reforming process, biogas must to be upgraded in order to remove H2S, siloxanes, ammonia in order to preserve reforming catalyst. Syngas streams obtained in reforming process can be used in GTL processes or purified in order to obtain a high purity hydrogen grade. From this stand point, the scientific goal is the development of enough active and stable reforming catalysts to perform this process stage.Other strategies for biogas revaluation as a fuel are to feed it directly to high temperature fuel cells (SOFC and MCFC). These types of fuel cells can tolerate the presence of contaminants in biogas composition. The development of catalysts to perform an internal reforming in anode is the scientific aim in this research area. In this work we will present an overview about this subject matter and some experimental results obtained in the biogas reforming catalyst development and the operation of fuel cells with synthetic biogas streams in PEMFC.

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S3-IA.11 H2 PRODUCTION FROM BIOSYNGAS USING A WGS MEMBRANE REACTOR

J.M. Sánchez, M. Maroño, E. Ruiz and A. CabanillasCIEMAT, Avenida Complutense, 22, E- 28040 Madrid (SPAIN)

The relevance of biomass as a significant component in the global sustainable energy mix is increasing worldwide. Electricity production and application in the transport sector represent promising finalist users of renewable biomass and biomass-derived fuels, especially hydrogen. Furthermore, hydrogen or hydrogen-rich gas produced from biomass could also be used in present natural gas or petroleum derived hydrogen energy conversion devices such as in gas turbines and in fuel cells. Its use is also highly desirable from an environmental point of view since it would help reduce the emission of greenhouse gases.Among the thermo-chemical processes for the conversion of biomass to hydrogen, oxygen/steam gasification can be considered as the most efficient and with the highest H2-production potential nowadays. However, in order to make use of the hydrogen contained in the gasification gas in fuel cells of for production of chemicals, it is necessary firstly to remove gas pollutants, tars, and other inorganic contaminants and then to adjust and optimise the hydrogen content and to separate it from the other gas components. Basically this means to adjust the CO/H2 ratio of the clean for synthesis of chemicals or to produce pure hydrogen. This adjustment in composition is usually accomplished through the Water Gas Shift Reaction (WGS), which utilizes water to transform CO into CO2 and H2. The reaction is reversible, thermodynamically limited and with the forward WGS reaction being mildly exothermic. WGS is usually carried out in two stages, using high (Fe/Cr) and low (Cu/Zn) temperature shift catalysts in series. Excess steam is required to improved CO conversion and to minimize undesirable side reactions that compete with the WGS reaction. Hydrogen separation is normally conducted in a pressure swing adsorption (PSA) system. New approaches to carry out the WGS reaction are under development. One very promising system is to perform the WGS reaction in a membrane reactor, which basically is a combination of a permselective hydrogen separation membrane and a water gas shift catalyst. For hydrogen separation there are two classes of membranes being used: dense phase metal and metal alloy membranes and those based on porous ceramics. As for the catalyst, commercial ones are most often used. The catalytic membrane reactor provides several advantages over conventional WGS reactors. The reaction can be conducted at a single higher temperature stage instead of the two adiabatic stages required in conventional WGS. The trade off between rate and conversion can be avoided. Due to the continuous removal through the membrane of one of the reaction products, H2 or CO2, the chemical equilibrium in the reaction zone is prevented. It is also possible to feed steam at a rate close to the stoichiometric ratio, avoiding expensive excess of steam. Another advantage of the membrane reactor is that independently from the reaction that is taking place in the reactor, the gas at the reactor outlet is split into two different streams. In this case a hydrogen rich stream is produced where the second one has a high concentration of CO2 ready to be captured.CIEMAT is currently involved in several R&D Projects which focus on catalytic membrane reactor for hydrogen separation, such as the CHRISGAS project (EU Project FPVI IP SES6-CT-2004-502587) and the HENRECA project (ENE2004-07758-C02-01).In this work, the current state of the art of hydrogen separation membranes and WGS membrane reactors are reviewed, discussing their advantages and limitations. In addition to that, results obtained in the above mentioned projects will be presented.

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S4-INV.4 HYDROGEN IN MATERIALS: POTENTIALS AND LIMITATIONS

Andreas ZüttelEMPA Materials Sciences and Technology, Dept. Environment,Energy and Mobility, Abt. 138 "Hydrogen & Energy", Überlandstrasse 129, CH-8600 Dübendorf (Switzerland)

The critical point of hydrogen is at a temperature of 33K, therefore, the dense storage of hydrogen is a materials challenge and the interaction of hydrogen with the surface and the bulk of materials is crucial. Hydrogen is stored by six different methods and phenomena:- high pressure gas cylinders (up to 800 bar)- liquid hydrogen in cryogenic tanks (at 21 K)- adsorbed hydrogen on materials with a large specific surface area (at T< 100 K)- absorbed on interstitial sites in a host metal (at ambient pressure and temperature)- chemically bond in covalent and ionic compounds (at ambient pressure)- oxidation of reactive metals and hydrides e.g. Li, Na, with waterOne of the most interesting features of the metallic hydrides is the very high volumetric density of the hydrogen atoms present in the host lattice[i]. Metallic hydrides reach a volumetric hydrogen density of 115 kg·m-3 e.g. LaNi5. Most metallic hydrides absorb hydrogen up to a hydrogen to metal ratio of H/M = 2. Greater ratios up to H/M = 4.5 e.g. BaReH9, have been found , however all hydrides with a hydrogen to metal ratio of more than 2 are ionic or covalent compounds. The highest volumetric hydrogen density known today is 150 kg·m-3 found in Mg2FeH6 and Al(BH4)3, both hydrides belong to the complex hydrides. Recently amides and imides combined with alkali hydrides have been investigated for there hydrogen sorption properties. Furthermore, ideas to destabilize MgH2 have been developed by means of a theoretical[ii] as well as by an experimental approach[iii].

REFERENCES

[i] Züttel A, “Hydrogen Storage Methods”, Naturwissenschaften 91 (2003), pp. 157-172

[ii] Z. Xiao Guo, Department of Materials, Queen Mary, University of London, UK, private communication

[iii] J. J. Vajo, F. Mertens, C. C. Ahn, R. C. Bowman Jr, B. Fultz, J. Phys. Chem. B 108 (2004), 13977-13983

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S4-IA.12 THE CHEMISTRY OF HYDROGEN ADSORPTION ON GRAPHITIC MATERIALS

J. A. Alonso, I. Cabria and M. J. López. Departamento de Física Teórica, Atómica y Optica, Universidad de Valladolid, 47011 Valladolid, Spain.

In the near future hydrogen could replace gasoline as a fuel in cars, and prototypes using electric motors that obtain the energy from the reaction of hydrogen with atmospheric oxygen in fuel cells have already been developed by many car manufacturers. The main remaining challenge is to develop an effective way of storing the required amount of hydrogen in the tank of a car. A hydrogen gravimetric capacity of 6 % in weight and a volumetric capacity of 0.045 kg per litre are the targets established by the USA Department of Energy for the year 2010. Another practical requirement is that hydrogen has to be easily adsorbed and desorbed near room temperature at moderate pressures. One of the most promising storage methods that have been proposed is the adsorption of hydrogen on the surface of light materials with high specific surface area. This is the case of porous graphitic materials, like carbon nanotubes, activated carbons, graphene fibers, etc. Thermodynamic estimations indicate that adsorption energies in the range of 150-200 meVper atom would be required to achieve efficient cyclic adsorption/desorption of hydrogen near room temperature and normal pressures. This condition establishes a narrow window for the adsorption energies. Molecular adsorption is the relevant adsorption process, since atomic chemisorption requires a large amount of energy to dissociate the H2 molecule and, in addition, the chemisorbed atoms would require a high temperature for desorption. Density Functional calculations of the adsorption of molecular hydrogen on graphene layers and on the external surface of single-walled carbon nanotubes deliver binding energies near 100 meV/molecule, or below [1]. Those adsorption energies can be increased in two ways. One is by doping the carbon materials with appropriate elements. Doping with lithium increases the H2 adsorption energies on carbon nanotubes and graphene by a factor of two [2]. The other is by adsorbing the hydrogen inside pores of nanometric size in carbon materials. Models of nanopores are the internal part of a carbon nanotube and the space between two parallel graphene layers with a separation somehow increased with respect to the usual distance in graphite (slitpores). In those pores, there is also an increase of the adsorption energy by a factor of two. The combination of the two strategies may offer a promising route for reaching the required values of the adsorption energies, which is crucial in any attempt to design efficient hydrogen storage materials.

Acknowledgement: Work supported by MEC (Grant MAT2005-06544-C03-01).

[1] J. S. Arellano, L. M. Molina, A. Rubio, M. J. López and J. A. Alonso, J. Chem. Phys. 117, 2281 (2002).

[2] I. Cabria, M. J. López and J. A. Alonso, J. Chem. Phys. 123, 204721 (2005).

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S4-IA.13 HYDROGEN STORAGE ON CARBON AND BN NANOPOROUS MATERIALS: OPTIMAL AVERAGE NANOPORE SIZE

I. Cabria, M. J. López and J. A. Alonso. Departamento de Física Teórica, Atómica y Optica, Universidad de Valladolid, 47011 Valladolid, Spain.

A quantum-mechanical and thermodynamical model of the hydrogen physisorption and hydrogenstorage properties is presented and applied to the hydrogen storage on carbon and BN nanoporous materials, which are simulated as slitpores. This model accounts for the quantum effects, basic to understand those properties on narrow pores not only at low temperatures, but also at 300 K and uses an equation of state of hydrogen based on experimental data in the range 77-300 K and 0-1000 MPa, including the region of solid hydrogen. The model reproduces quantitatively the experimental hydrogen storage properties of different samples of activated carbons [1, 2], ACs, and carbide-derived carbons [3], CDCs, at 77 and 298 K for an average nanopore width of about 5 Å, especially the experimental saturation of the gravimetric capacity with increasing external pressure. Former theoretical models [4, 5] failed completely in predicting the saturation in the gravimetric capacity at 77 K found in the experiments and reproduced with the present model. The model predicts that in order to reach the Department of Energy, DOE, 2010 hydrogen storage targets, the nanopore widths of carbon and BN materials should be larger or equal to 5.5 Å for applications at low temperatures, 77 K, and any pressure, and about 6 Å for applications at 300 K and at least 10 MPa.

Acknowledgement: Work supported by MEC (Grants MAT2004-23180-E and MAT2005-06544-C03-01).

[1] M. A. de la Casa-Lillo, F. Lamart-Darkrim, D. Cazorla-Amorós and A. Linares-Solano, J. Phys. Chem. B 106, 10930 (2002)[2] M. Jordá-Beneyto, F. Suárez-García, D. Lozano-Castelló, D. Cazorla-Amorós and A. Linares-Solano, Carbon 45, 293 (2007)[3] Y. Gogotsi, R. K. Dash, G. Yushin, T. Yildirim, G. Laudisio and J. E. Fischer, J. Am. Chem. Soc. 127, 16006 (2005)[4] M. Rzepka, P. Lamp, M. A. de la Casa-Lillo, J. Phys. Chem. B 102, 10894 (1998) [5] Q. Wang and J. K. Johnson, J. Chem. Phys. 110, 577 (1999)

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S4-IA.14 HYDROGEN STORAGE MECHANISMS IN NANOCRYSTALLINE MG WITH NB2O5 ADDITIVE

A.Fernández1, O.Friedrichs1†, J.C.Sánchez-López1, D. Martínez-Martínez1, T.Klassen 2‡, R.Bormann21 Instituto de Ciencia de Materiales de Sevilla, CSIC-Univ.Seville, Avda. Américo Vespucio 49, 41092 Seville, Spain.2 Institut für Werkstoffforschung, GKSS Forschungszentrum, 21502 Geesthacht, Germany† Present address: Empa-Materials Science & Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland ‡Present address: Institut of MaterialsTechnology, Helmut-Schmidt-University, Holstenhofweg85, D-22043 Hamburg,Germany.*Presenting,author,e-mail: asuncion@icmse.csic.es

Magnesium as a light, abundant and cheap metal with a high reversible hydrogen capacity of 7.6 wt% is a very attractive material for hydrogen storage. In the present communication we review our recent contributions to understand and to improve the hydrogen sorption kinetics in Mg-based nano-crystalline materials.By using nano-crystalline MgH2 powders produced by high energy ball milling [1] significant progress in the sorption kinetics could be achieved compared to bulk polycrystalline Mg. In fact a crystallite size reduction and the formation of grain boundaries and microstructural defects are producing pathways for a favourable H2 charge/discharge process. The addition of additives, mainly transition metals and oxides, during ball milling of MgH2 introduced also a big improvement in the hydrogen sorption kinetics [2]. Nb2O5 was one of the best additives found. However the mechanism by which these oxides are improving the kinetics was not clear. Here we present our results indicating the formation of ternary Mg-Nb-O phases [3] that during migration to the surface produce “pathways” allowing the easy diffusion of hydrogen into the Mg nanocrystals. Hereby we also show the application of Nb2O5-nanoparticles as milling additives [4,5], by which the milling time could be reduced by more than a factor 200 compared to a system of MgH2 milled with microscrystalline Nb2O5.

[1] A.Zaluska, L.Zaluski, J.O.Strom-Olsen, Journal of Alloys and Compounds 288 (1999) 217-225.

[2] W.Oelerich, T.Klassen, R.Bormann, Journal of Alloys and Compounds 315 (2001) 237-242-

[3] O.Friedrichs, F.Aguey-Zinsou, J.R.Ares-Fernández, J.C.Sánchez-López, A.Justo, T.Klassen, R.Bormann, A.Fernández, Acta Materialia 54 (2006) 105-110.

[4] O.Friedrichs, T.Klassen, J.C.Sánchez-López, R.Bormann, A.Fernández, Scripta Materialia 54 (2006) 1293-1297.

[5] O.Friedrichs, J.C.Sánchez-López, C.López-Cartés, T.Klassen, R.Bormann, A. Fernández, Journal of Physical Chemistry B 110 (2006) 7845-7850.

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S5-INV.5 HYDROGEN STORAGE IN CARBON MATERIALS: FROM ACTIVATED CARBONS TO NANOSTRUCTURED MATERIALS

Diego Cazorla-Amorós, Dolores Lozano-Castelló, María Jordá-Beneyto, MirkoKunowsky, Fabián Suárez-García and Angel Linares-Solano. Departamento de Química Inorgánica. Universidad de Alicante. Apartado 99. 03080 Alicante. Spain.

The increasing energy and environmental problems, makes necessary the development and use of renewable and environmental friendly energy sources. Among them, hydrogen is being considered as an ideal energy vector for replacing fossil fuels, such as oil and coal. However, several technological issues like its production and storage are still matter of studies and improvements. In particular, hydrogen storage is one of the limiting steps in the development of hydrogen fuelled vehicles. This reason makes hydrogen storage a challenge for many researchers, especially for material science researchers. Nowadays, there are different methods to store hydrogen, being the most relevant the following: i) liquid hydrogen, ii) compressed gas, iii) metal hydrides and iv) sorption on carbon materials. The different existing storage techniques have to meet the provisional Department of Energy of the United States (DOE) criterion. The DOE has established different targets for on-board hydrogen storage systems. For the 2010 year, the storage system should have a volumetric capacity of 45 kg H2/m3 and a gravimetric capacity of 6 wt.% of H2 (criterion established for a 75 l deposit and an average autonomy of 500 km). A critical parameter in this application is volume. Thus, efforts are focused in reducing the tank volume containing hydrogen.A review of both experimental and theoretical studies published on the field of hydrogen storage on different type of carbon materials shows a large scattering in hydrogen storage values. Results corresponding to activated carbons (AC), activated carbon fibres (ACFs), carbon nanotubes (CNTs) and carbon nanofibres (CNFs), obtained under different experimental conditions of temperature and pressure can be found. In this lecture, an overview of those results about hydrogen storage in carbon materials published by other authors will be presented. In addition, a detailed discussion of our own results obtained in a large variety of carbon materials will be shown. The effect of the porosity (pore volume, pore size distribution,…) on the hydrogen storage capacities will be analyzed, pointing out the importance of reporting the hydrogen storage on a volumetric basis. In this sense, the relevance of increasing the packing density of the materials, in order to obtain high hydrogen storage capacities will be discussed.

Acknowledgements: Authors thank financial support from Ministerio de Fomento (70012/T-05), MEC (CTQ2006-08958), Generalitat Valenciana (ARVIV/2007/063) and UE (HyTRAIN MCRTN-512443). F. Suárez-García thanks MCYT for his contract “Juan de la Cierva” and M. Jorda-Beneytothanks MEC for her PhD fellowship.

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S5-IA.15 A HYDROGEN GENERATION SYSTEM USING SODIUM BOROHYDRIDE FOR THE OPERATION OF A 400W-SCALE PEMFC STACK

Jaeyoung Lee,*, Sun Ja Kimb, Suk Woo NambDepartment of Environmental Science and Engineering, GIST, Gwangju 500-712, KoreabCenter for Fuel Cell Research, Korea Institute of Science and Technology, Seoul 136-791, Korea

Sodium borohydride (NaBH4) in the presence of sodium hydroxide as stabilizer is a hydrogen generation source with high hydrogen storage efficiency and stability. It generates hydrogen by self-hydrolysis in aqueous solution. In this research, we prepared a Co-B catalyst on a porous Ni foam support and a system which could uniformly supply hydrogen at >6.5 L/min for 120 min for driving 400 W-scale polymer electrolyte membrane fuel cells (PEMFCs). For optimization of the system, we changed several experimental conditions and investigated the effect. We observed that, if the concentration of NaBH4 in aqueous solution was increased, the hydrogen generation rate increased, but a high concentration of NaBH4 caused the hydrogen generation rate to decrease because of increased solution viscosity. The hydrogen generation rate also increased when the flow rate of the solution increased. An integrated system supplied hydrogen to a PEMFCs stack, and about 465 W power was produced at a constant loading of 30

A.Keywords: sodium borohydride, hydrogen generation system, Co-B catalyst, PEMFCs

*Corresponding author. Fax: +82-62-970-2434. jaeyoung@gist.ac.kr (J. Lee)

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S5-IA.16 NEW INSTRUMENT TO DETERMINE HYDROGEN CONTENT IN MATERIALS

R. Nevshupa*, E. Roman, J.L. de Segovia, Institute of Material Science of Madrid, C/ Sor Juana Ines de la Cruz 3, Madrid 28049, Spain

Despite of the significant progress in analytical techniques for material characterization, determination of the hydrogen content in solid materials and surface coatings is not a trivial problem. Most of the existent methods suitable for the determination of hydrogen content require large and complex apparatuses, e.g. Nuclear Magnetic Resonance, Elastic Recoil Detection Analysis, Nuclear Reaction Analysis and so on, while the capabilities of the methods for analysis of the spatial distribution of hydrogen are limited. Thus, simple method for determination of hydrogen content in solid materials with features of depth profiling and spatial distribution analysis is highly demanded in various fields of the modern technology including hydrogen storage, metallurgy, transport, chemical and nuclear engineering, etc. New method for analysis of hydrogen and other gases content in solids and surface coatings has being developed on the basis of the phenomenon of tribostimulated desorption. In this method the material being analyzed is placed in a high vacuum system, where it is subject to local rubbing, indentation or rolling by a hard counter body. The amount of desorbed gases is carefully measured using total pressure vacuum gauges and mass-spectrometer. The amount of desorbed gases is proportional to the gas content in material and the volume of the damaged material due to mechanical action. To analyze the contribution of the topmost adsorbed gases to the tribodesorption and the effect of readsorption a model of the phenomenon was developed. The results showed that the contribution of the topmost adsorbed layers is negligible for the residual pressures below certain critical value, which depends on the friction conditions and the set-up configuration. So, below the critical residual gas pressure the most of the desorbed gases proceed from the bulk of the material. The number of readsorbed molecules on the surfaces of the vacuum system increases with time until reaching the steady value after 5 s to 15 s from the beginning of tribodesorption. This steady value increases with decrease of the pressure and with increase of the surface area. However, for typical vacuum system with volume of 14 l at the pressure of 10-6 Pa, the number of readsorbed molecules does not exceed 1% of the number of desorbed molecules. Thus, readsorption has a minor effect on the accuracy of the tribodesorption measurements. Preliminary experiments with stainless steel showed that the method has sensitivity for hydrogen below 4 ppm (wt.) with spatial resolution below 0.2 mm. The method requires very small amount of material, typically below 1 cubic millimeter. * On leave of absence from Bauman Moscow State Technical University, MT-11, 2-Baumanskaia 5, Moscow, 105005, Russia.

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S5-IA.17 HYDROGEN-DEUTERIUM EXCHANGE REACTIONS TO PROBE THE SORPTION MECHANISM OF HYDRIDES.

A. A. BorgschulteBorgschulteEMPA,Materials Science and Technology,Dep.138,Hydrogen & Energy,Überlandstrasse29,CH-8600.Dübendorf, andreas.borgschulte@empa.ch

Dynamic hydrogen-deuterium exchange experiments to probe the surface reactions during the decomposition of metal hydrides are presented. The rate of HD desorbing from a sample is a qualitative measure of the dissociation activity of a material. Dynamic hydrogen-deuterium exchange measurements of the representative metal hydride MgH2 are used to illustrate the functioning of the method. A kinetic model is proposed for the isotopic exchange H2 and D2 on surfaces, from which conclusions on the hydrogen coverage on surfaces during desorption of metal hydrides are drawn. The surface properties of ball-milled MgH2 is studied during hydrogen desorption by means of X-ray photoelectron spectroscopy. At the same time, the desorption rate of hydrogen is monitored, which is compared to the dissociative properties of the surface investigated by hydrogen-deuterium exchange experiments. It is found that MgH2 is oxide covered. The corresponding catalytic sites are associated with special vacancies on the oxide. The maximum surface concentration of these vacancies is very small, which is countered by a very high turnover frequency due to a small activation energy for dissociation of hydrogen on the single vacancy.The surface method is extended by bulk HD-exchange experiments. Here, the exchange of hydrogen by deuterium in the inner of the material is followed by gravimetric and Raman spectroscopy. The bulk processes of hydrogen sorption are in particular important in complex hydrides NaAlH4 and LiBH4. It is found that in these materials the dissociation and diffusion of hydrogen is much faster than the decomposition of the hydrogen complexes.

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S6-INV.6 SOLAR THERMOCHEMICAL PRODUCTION OF HYDROGEN

A. Vidal, and M. Romero. CIEMAT-PSA; Avda. Complutense, 22; 28040-Madrid. Spain

Solar thermochemistry is a novel and very promising route for the production of valuable fuels and chemicals, in particular, the production of hydrogen by renewable energy is one of the most promising ways to sustainable energy carrier economy. Some high temperature endothermicalreactions for converting solar energy to chemical fuels have been investigated as solar thermochemical process, such as multi-step water splitting reaction, reforming of methane, and coal gasification. This paper reviews the recent developments on these solar thermochemical processes and discuses the feasibility of the solar thermochemical conversion technologies. The ultimate goal is to develop a technically and economically viable technology for a solar thermochemical process that can produce H2. The strategy for reaching this objective involves research on two paths: A long-term approach via H2O-splitting thermochemical cycles and a short-to-mid term approach via decarbonization of fossil fuels. The H2O-splitting cycles require elevated temperatures and the development of a completely novel process engineering technology. It is a long-term project that will bring us to the complete substitution of fossil fuels with solar H2. The decarbonizationprocesses require also require elevated temperatures and a combination of novel and conventional technologies. Traditional materials and reactor concepts are thus possible for the mixed fuel/solar energy technology. Therefore, this approach creates a link between today’s fossil-fuel-based technology and tomorrow’s solar chemical technology, and reduces the lead time for transferring important solar technology to industry.Based on the aforementioned strategy CIEMAT is actually developing: Conversion of Heavy Crude Oil and Petroleum Coke to Syngas and H2O-splitting cycle based on metal oxides redox reactions. The use of high temperature solar heat to drive the endothermic reaction associated with coal gasification has been suggested and investigated in the last 20 years. The steam-gasification of petroleum derivatives and residues using concentrated solar radiation has been proposed more recently as a viable alternative to solar hydrogen production. This study is being carried out within collaboration between Petróleos de Venezuela (PDVSA), the Eidgenössische Technische Hochschule (ETH) in Zurich / Switzerland, and the Centro de Investigaciones Energéticas, Medio Ambientales y Tecnológicas (Ciemat) in Spain to study the feasibility of thermochemical gasification from petroleum coke. On the other hand, thermochemicalcycles may offer a clean sustainable alternative starting from materials that can act as effectivewater splitters in a two step water splitting process. For example, partial substitution of iron in thespinel phase by Mn, Ni, Zn forms mixed metal oxides of the type that are more reducible andrequire more workable operating temperatures. The feasibility of this process is been studied in “Catalytic monolith reactor for hydrogen generation from solar water splitting - HYDROSOL ” a European project funded in the Fifth Framework Program.

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S6-IA.18 SOFC ANODES PREPARED FROM DIRECTIONALLY SOLIDIFIED EUTECTIC PRECURSORS

A. Larrea, M.A. Laguna-Bercero, R. Campana, R.I. Merino, J.I. Peña andV.M. Orera. Instituto de Ciencia de Materiales de Aragón (C.S.I.C.- U. Zaragoza), c/ María de Luna 3, E-50.018 Zaragoza, Spain.

Ni- and Co-YSZ (cubic yttria stabilized zirconia) cermets have been prepared by reduction of laser-assisted directionally solidified NiO- and CoO-YSZ eutectics. The cermets can be prepared in the form of rods for fundamental studies, as well as in the form of plates or tubes to be used directly as the anode of a Solid Oxide Fuel Cell (SOFC). The material presents a channelled microstructure formed by alternating lamellae of porous metal and YSZ. The lamellar width, usually between 100 and 400 nm, can be controlled by changing the laser processing parameters, whereas the uniform metal particle distribution is obtained adjusting the reduction conditions.The channelled microstructure is expected to improve the gas flow, electronic transport and oxygen ion diffusion of the isotropic cermet. Moreover, the electrical conductivity and the pore size distribution present no degradation after 300 hours at 900 ºC under H2/N2 atmosphere. This long-term stability at fuel cell operation temperatures is also an improvement in comparison with conventional Ni-YSZ SOFC anodes. It is related to the good metal-ceramic bonding developed after reduction of the directionally solidified eutectic. In consequence the orientation relationships and the interfaces of the cermets have been studied as a function of the reduction temperature by electron and X-ray diffraction experiments. In the case of Ni-YSZ cermets it has been observed that Ni undergoes an interface-induced crystallographic reorientation to form a low-energy (002)Ni//(002)YSZ interface. Metal-ceramic low energy interfaces prevent Ni particle coarsening and impart long-term stability to the cermet.

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S6-IA.19 PERFORMANCE OF NI/LA-ZR PYROCHLORE STRUCTURE MIXED OXIDE IN BIOETHANOL STEAM REFORMING

M. Benito, R. Padilla, L. Daza.Instituto de Catálisis y Petroleoquímica (CSIC), C/ Marie Curie 2, CampusCantoblanco, 28049 Madrid, SpainJ. Bussi, N. Bespalko, N. Bargueño. Laboratorio de Fisicoquímica de Superficies, DETEMA, Facultad de Química, UdelaR, Gral. Flores 2124, Montevideo, Uruguay

The use of ethanol as a hydrogen carrier presents a series of advantages: a) it can be obtained in high volumes and low cost by means of fermentation processes using renewable raw materials available in great amount (biomass); b) it is much less toxic than methanol, which reduces the environmental risks derived from its large-scale manipulation; c) its storage does not produce explosive atmospheres in contact with air; d) favours local economy development without external energy dependency. Nevertheless, in order to apply ethanol steam reforming reaction as an industrial hydrogen production process, catalysts must allow the reaction to proceed with enough velocity, maximizing hydrogen yield and minimizing that of undesired secondary products. We have carried out the study of a catalyst based on Ni supported on a La-Zr mixed oxide (Ni/LaZr) with the aim of obtaining an active catalyst in terms of ethanol conversion and highly selective towards hydrogen production. Preliminary results with a catalyst containing 17% Ni confirm the total conversion of the alcohol at reforming temperatures around 500 ºC, the hydrogen as the main product and a minimum content of undesired secondary products, such as oxygenated derivates of ethanol (acetaldehyde, acetic acid, acetone).Differences in the thermal treatment during catalyst preparation lead to differences in catalytic activity and products selectivity, achieving the best result with an oxide support impregnated with a nickel content of 17% and further thermal treatment at 850 ºC. At the reaction temperature of 650 ºC, this catalyst leads to a gaseous mixture with a molar composition of 67% hydrogen, 30% CO2 and 3% CO. Unlike the other catalysts tested, this catalyst did not show deactivation signals during the runtime. Nickel stabilization as a consequence of changes of crystalline structure of the support could explain the results obtained.

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C1 NANO-SCALED NON-PLATINUM ELECTROCATALYTIC MATERIALS FOR HYDROGEN EVOLUTION

P. Paunovic. University “Sts. Cyril and Methodius”. R Macedonia

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C2 INTERNAL STRESSES INFLUENCE ON HYDROGEN ABSORPTION PROCESS

N.M. Vlasov. Scientific Research Institute Scientific Industrial Association “Luch”, Zheleznodorozhnaya 24, Podolsk, Russia, 142100, I.I.Fedik. Scientific Research Institute Scientific Industrial Association “Luch”, Zheleznodorozhnaya 24,Podolsk,Russia,142100,E-mail: iifedik@luch.podolsk.ru

Metals and alloys hydrides are used for hydrogen storage. Reversible hydrogen sorption depends on temperature, external pressure and internal stresses available. The examples of the latter ones are temperature and residual stresses as well as the stresses about structural defects. The internal stresses influence on a hydrogen sorption proecess is considered. The process kinetics is described by an equation of a parabolic type under corresponding initial and boundary conditions [1]. Hydrogen absorption in a hollow cylinder with residual stresses is considered as an illustration. The choice of such a model system is defined by the following reasons. Firstly, in the hollow cylinder it is possible to obtain the residual stresses of different signs by discharging and adding (excluding) a part of the material followed by connection of the cut banks. Secondly, a logarithmic dependence on a radial coordinate of the first invariant of the residual stresses tensor allows us to obtain an exact analytical solution of the diffusion kinetics problem. The analytical dependences for the field of hydrogen atoms concentration in the hollow cylinder are given. The hydrogen absorption process is defined by the level and character of the residual stresses distribution. The latter ones lead to changing the diffusion equation symmetry. Acceleration (deceleration) of the absorption kinetics depends on the diffusion equation symmetry and on the values of equilibrium hydrogen concentrations on the area boundaries. A possibility of controlling the hydrogen absorption process at the expense of changing the character of the residual stresses distribution is discussed.Diffusion of hydrogen atoms has been considered taking into account structural and impurities traps [2]. The structural traps are the crystal defects, and the impurities traps are alloying substitution impurities of a small atom radius. The comparative analysis of kinetics of the impurity segregation formation from the hydrogen atoms has been made for edge dislocation, microcrack tip and wedge disclination. As is shown the wedge disclination captures the hydrogen atoms according to a linear law. The formation of the hydrogen segregations for the microcrack tip and edge dislocation runs slower. The hydrogen atoms diffusion in the cylindrical cladding with the impurities traps has been studied. The hydrogen atoms form complexes with the substitution impurities and retard their movement. After breaking down the complex, a hydrogen atom is free to migrate as long as it meets a new trap. Retarding the diffusion process is observed in the macroscopic scale. The relation for the field of the hydrogen atoms concentration are given taking into account the impurities traps. As is shown the hydrogen concentration in the medium with absorption is expressed in the solution of the corresponding problem for free diffusion. The physical meaning of the obtained relations has been discussed. ReferencesVlasov N.M., Fedik I.I. Hydrogen segregation in the area of threefold junction of rain boundaries. Int. J. Hydrogen Energy 2002, 27:921-926.Vlasov N.M., Fedik I.I. Structural and impurity traps for hydrogen atoms. Int. J. Hydrogen Energy 2006, 31:265-267.

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C3

A. Sellstedt

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C4 HYDROGEN STORAGE IN MOFS

A. Monge, E. Gutiérrez-Puebla, F. Gándara, M. A. Luengo, J. Perles, N. SnejkoInstituto de Ciencia de Materiales de Madrid, ICMM, CSIC. Sor Juana Inés de la Cruz, 3, Cantoblanco, 28049 Madrid. Spain

New materials promote new technologies. Micro- and nanoporous metal-organic materials may be compelling examples of this path from materials to technologies as they promise important impacts into new developments in catalysis, sorption, non-linear optics, hydrogen storage. These materials are advances in supramolecular coordination chemistry and metal-based directed assembly chemistry. Predictable synthesis from libraries of building blocks and the nearly infinite number of variations is allowing materials scientists to create materials of truly new design (synthesis of new materials on demand) and synthesize them in a short time. One part of our research in this field is dedicated to the studies of sorption properties of such materials. Among them there are:A Scandium metal-organic framework (scandium terephthalate, [Sc2(C8H4O4)3]), which shows a high thermal stability along with important sorption properties. The apparent specific surface area was determined and gave a BET area of 721 m2 g-1 with a high CBET ) 7000, as expected for microporous solids. The high quantity of sorbed hydrogen makes this material a potentially interesting material for hydrogen storage applications.A Zinc metal-organic framework with 4,4-(hexafluoroisopropylidene)bis-(benzoic acid), for which the nitrogen adsorption–desorption isotherm was measured. For a monolayer coverage of N2 the estimated specific surface area of 1 was 288.9(2) m2g–1 based on the method of Langmuir.An Indium metal-organic framework with 4,4-(hexafluoroisopropylidene)bis-(benzoic acid), which sorption properties are estimated.

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C6 NEW MATERIALS SYSTEMS FOR PHOTOELECTROCHEMICAL HYDROGEN PRODUCTION

P. C. K. Vesborg, B. L. Abrams, J. Bonde, T. F. Jaramillo, I. ChorkendorffCenter for Individual Nanoparticle Functionality, Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

The inherent problems of oxide based photocatalysts (i.e., ZnO, TiO2) for water splitting such as inadequate stability or too large a bandgap have created interest in alternative non-oxide based materials systems for water photolysis. Recently, using the adsorption energy for hydrogen as a descriptor for materials that catalyze the hydrogen evolution reaction (HER) (criterion: ΔGH≈0) DFT calculations have predicted MoS2 to be a good HER replacement catalyst for platinum cathodes. This has also been shown experimentally [1,2]. MoS2 is a semiconductor with a bandgapwhich is tunable with particle size [3]. Thus MoS2 supported nanoparticles are interesting as potential photocathodes for HER in the overall water splitting. The properties of supported MoS2 nanoparticles in terms of optical absorption, photoreduction of water and stability towards corrosion will be discussed.

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C7 MICROSTRUCTURAL AND CHEMICAL CHARACTERIZATION OF THE LIBH4+MGH2 HYDRIDE COMPOSITE SYSTEM FOR H2 STORAGE

E.Deprez1*,A.Justo1,D.Martínez-Martínez1,T.C.Rojas1,A.Fernández1,

U.Bösenberg 2, M. Dornheim2, R.Bormann21 Instituto de Ciencia de Materiales de Sevilla,CSIC-Univ.Seville,Avda. Américo Vespucio 49, 41092 Seville, Spain. 2 Institut für Werkstoffforschung, GKSS rschungszentrum, 21502 Geesthacht, Germany

Reactive hydride composites reveal great potential as hydrogen storage materials as they overcome the thermodynamic limitations hindering the use of light-weight complex hydrides. In the present communication the effect of Ti-based additive has been studied in the system LiBH4+MgH2. In order to do that, samples of LiBH4+MgH2 and LiBH4+MgH2+additive were milled, characterized and compared.X-Ray diffraction (XRD) has been used to identify the crystalline phase present in the samples. Moreover, we have used the Williamson-Hall method to get information about the microstrain and the crystal size of the different phases. For both samples, the LiBH4 showed larger crystal size than MgH2. However, the sample containing additive showed increased crystal size for LiBH4 and reduced crystal size for MgH2 in comparison to the sample without it. Besides, the microstrain is found to be one order of magnitude bigger for both phases milled with the additive.After the desorption, this sample evolves to a mixture of LiH and MgB2 phases with reduced levels of microstrain. The crystal sizes of both phases are found to be similar, and intermediate between the ones of the preceding LiBH4 and MgH2 phases. These sizes are bigger than the ones from the milling of LiH and MgB2 without additive.In addition, Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) have been used to get further information such as degree of oxidation, particle size and chemical state of light elements and additives. Finally, the Hydrogen re-absorption effects will be also discussed.

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S7-INV.7 PHOTOCATALYSIS IN NANOMATERIALS

Jiefang Zhu, Christoph Langhammer, and Michael ZächChalmers University of TechnologyDepartment of Applied Physics412 96 Göteborg, Swedenzaech@fy.chalmers.se

Although heterogeneous catalysis implicitly has always dealt with phenomena on the nanoscale, the recent rise of Nanoscience and Nanotechnology (N&N) has added a new (nano-)dimension to the field. Powerful tools for the controlled fabrication and characterization of nm-sized structures, as provided by N&N, have enabled a novel field, which often is referred to as nanocatalysis. In this talk, I will review the many opportunities that N&N opens to catalysis in general and to photocatalysis in particular. My focus will be on a rather generic pathway, namely the use of N&N to fabricate and characterize nanometer-sized noble metal nanoparticles with unique light-harvesting properties. Such nanoparticles are of particular relevance for solar water splitting and photocatalytic emission cleaning, two important application areas that we are studying in our group.The typical scheme of photocatalysis involves harvesting of (solar) photons in a semiconductor (most commonly TiO2), and subsequent conversion of these photons to electronic excitations, which then induce the desired chemical reaction on the semiconductor surface. Due tothe large bandgap of, for instance, titania, the light-harvesting ability of such photocatalysts isoften confined to high-energy UV-photons, where the solar irradiation is much weaker than in thevisible. An alternative approach to harvest solar light is to use nanometer-sized metal nanoparticles, which have a high cross-section for photon capture in the visible via the excitation of localizedsurface plasmons (LSPs). Since one of the decay channels of LSPs is into electron-hole (e-h) pairs, such particles could constitute interesting photocatalysts, despite the typically short recombination time for e-h pairs in metals. Recent work in our group has scrutinized the plasmonicproperties of catalytically active materials such as Pt and Pd, which essentially have not beenconsidered by the LSP-community earlier (silver and gold have traditionally deserved the highestattention). We have found that Pt and Pd nanoparticles exhibit particularly interesting plasmonicproperties, namely an advantageous branching ratio between radiative and non-radiative decaychannels. While LSPs in Ag and Au preferentially decay radiatively, i.e. by emission of photons, LSPsin Pt and Pd thus have a high cross-section for decay into e-h pairs, which is desirable in thecontext of photocatalysis. In a parallel effort, we are studying the plasmonic properties of metallichetero-dimers, i.e. nanofabricated arrangements of two metallic nanoparticles with differentchemistries in close proximity to one another, as a means of fine-tuning the wavelength interval in which LSPs can be excited and light can be absorbed efficiently.

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S7-IA.20 HYDROGEN RETENTION IN THE FIRST WALL OF TJ-II UNDER PLASMAS OPERATION

F.L. Tabarés, J.A. Ferreira and D. TafallaLaboratorio Nacional de Fusión. As. Euratom/Ciemat. 28040 Madrid. Spain

Plasma operation in hydrogen isotopes leads to the their retention in the facing materials. This has a crucial impact on plasma density control, through recycling, and safety issues in a reactor (Tritium inventory) and much work has been devoted to the topic. Contrary to hydrogen storage research, but closely linked to it through the physio-chemical background, high energy particles are mainly responsible for the retention, and effective methods for hydrogen release form plasma facing materials are continuously sought. This is particularly demanding in the case of carbon materials, of especial appeal as first wall components in Fusion due to their excellent thermo-mechanical properties and low atomic number.The TJ-II stellarator has been operative at Ciemat for near a decade, and more than 17.000 plasma shots in hydrogen, of 200-300 ms duration each, have been generated in this period. Several strategies were applied in order to keep good control of hydrogen recycling and plasma contamination in this period. Thus, after a first full-metal scenario, the vessel was boronized by plasma techniques. Although this led to an improved control of impurities in the plasma, only a transient control of recycling was achieved. This control was not good enough to allow for plasma operation under extra heating by neutral beam injection, and stronger hydrogen gettering effect was needed to avoid plasma collapse by the extra gas injected simultaneous to the heating beam. In the last months, full lithiumization of the TJ-II Vacuum Vessel has been performed. A stark improvement in plasma reproducibility and density control has been observed upon Li coating, directly linked to the highly efficient trapping, in the form of HLi, of the plasma particles. In this work, a summary of the hydrogen retention studies in TJ-II through the different conditioning scenarios will be given and the implication for H storage technology will be addressed.

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S7-IA.21 CONVERSION OF BIO-ETHANOL INTO HYDROGEN IN A MOLTEN CARBONATE FUEL CELLS.

W. Nam, H. Devianto*, J. Han, S.P. Yoon, T.-H. Lim, S.-A. Hong, H.-I. Lee*Korea Institute of Science and Technology, Seoul 136-791, Korea* Seoul National University, Seoul 151-744, Korea

In recent years there has been growing interest in reforming of bio-ethanol to produce hydrogen for fuel cell. A variety of catalyst and reaction systems have been investigated to minimize carboncoking and to prevent sintering of the catalysts toward the bio-ethanol reforming. Since thereforming was realized at relatively high temperatures, researchers at Instituto CNR-TAE havesuggested to use bio-ethanol as a fuel for molten carbonate fuel cell (MCFC) which operates near650oC. Up to now, however, external reforming system to produce hydrogen out of the MCFC has been thoroughly examined. In this study, we investigated internal reforming of bio-ethanol in theMCFC. That is, bio-ethanol was directly introduced to the anode compartment of the MCFC andreforming reaction was carried out on the surface of the Ni-based anode. Effects of currentdensities, flow rates of the feed and electrode modification on activity of the anode to produce hydrogen-rich gas were extensively studied. Cogeneration of hydrogen-rich gas and electricity in the MCFC was examined for more than 1,000 hours and factors affecting degradation of the cellperformance were analyzed.

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S7-IA.22 ANODES FOR DIRECT METHANE SOFCS AND SYMMETRICAL ELECTRODES.

Jesús Canales-Vázquez1, Juan Carlos Ruiz-Morales2 and John Irvine3.

1Instituto de Energías Renovables, Universidad de Castilla la Mancha, 02006 Albacete, Spain.2Departamento de Química Inorgánica, Universidad de La Laguna, 38200 La Laguna, Spain.3School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, UK.

Solid Oxide Fuel Cells (SOFCs) are at the forefront of the clean technologies that will replace the combustion fossil fuels to provide energy. There are however several relevant issues that must be addressed prior their mass-scale commercialisation and among them, the production of efficient anodes can be considered as a crucial step. Despite the state of the art Ni-YSZ cermets offer excellent performances, they exhibit problems in the long-term, mostly related to the formation of carbon deposits, metal particle coarsening, stability upon redox and temperature cycles, etc.Overthe last decade, there has been a growing interest in ceramic-based anodes, especially based upon perovskite such as Cr-manganites [1], titanates [2] or more recently double perovskites [3]. Despite these materials exhibit fairly low lateral conductivity, they present certain activity towards hydrocarbon oxidation and with the use of adequate current collectors may compete with cermets. In the case of titanates, the control over the oxygen stoichiometry in addition to the partial replacement of Ti by other cations such as Sc, Mn and Ga leads to phases that exhibits very low polarisation resistances and very high stable OCVs (>1.2 V) under methane fed.On the other hand, Cr-manganites and certain titanates could probably find application simultaneously as both anode and cathode in a novel SOFC concept: the symmetrical fuel cell [4]. The development of such concept would simplify notably the fabrication process, hence lowering the costs, and also would result in fuel cells with higher tolerance to potential carbon deposits.

References.

S. Tao and J. T. S. Irvine, Nature Materials 2 320-323 (2003).

J. C. Ruiz-Morales, J. Canales-Vázquez, C. Savaniu, D. Marrero-López, W. Zhou and J. T. S. Irvine, Nature 439 568-571 (2006);

J. Canales-Vázquez, J. C. Ruiz-Morales, J. T. S. Irvine and W. Zhou, J. Electrochem. Soc. 152 1458-1465 (2005).

Y.H. Huang, R.I. Dass, Z.L. Xing and John B. Goodenough, Science 312 254-257 (2006).J. C. Ruiz-Morales, J. Canales-Vázquez, J. Peña-Martínez, D. Marrero-López and P. Núñez, Electrochim. Acta 52 [1] 278-284 (2006);

J. Canales-Vázquez, J.C. Ruiz-Morales, D. Marrero-López, J. Peña-Martínez, P. Núñez and P. Gómez-Romero, J. Power Sources, in press (2007)

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S8-IA.23 IT-SOFCS BASED ON DOPED CERIA ELECTROLYTES

X. García. Dept. Ciencia de los Materiales e Ingeniería Metalúrgica. Universidad de Barcelona. E-08028 Barcelona. Spain.M.Segarra. Dept. Ciencia de los Materiales e Ingeniería Metalúrgica. Universidad de Barcelona. E-08028 Barcelona. Spain.

The use of fuel cells is still not economically nor environmentally feasible, thus it is considered as a medium term option. Due to their working temperatures, so high that fuel reforming takes place in the anode itself, alternative fuels can be used, as hydrogen in-situ precursors. Therefore, problems associated to transport and storage can be minimized although these high operating temperatures lead to complex materials problems: the system works under high thermal stress and requires materials with great chemical and mechanical stability, not easily available. To decrease the working temperature, preferably between 500 - 700ºC, some materials with good ionic conductivity can be used as electrolytes, such as cerium oxide doped with rare-earths, frequently Sm and Gd. In order to obtain a SOFC with a high performance, the electrolyte must be as dense as possible, while anode and cathode must remain porous to facilitate the transport and diffusion of gases. From the different configurations of a planar SOFC, the electrolyte supported one seems to be easier to conform. So, in this work, electrodes have been screen-printed on a high density piece of electrolyte obtained by tape casting, but obtained results are not as good as expected due to the great thickness of the electrolyte that make the electrical properties to decrease. Therefore, a sequential process has been tested related to conformation and syntherization of the different components of the fuel cell, that seem to be promising.

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S8-IA.24 DETERMIANTION OF THE SYNERGETIC EFFECT OF THE OPERATION VARIABLES IN COPROX CATALYSTS BY MULTIFACTORIAL ANALYSIS

R. Padilla, M. Benito, L. Daza. Instituto de Catálisis y Petroleoquímica (CSIC), C/ Marie Curie 2, CampusCantoblanco, 28049 Madrid, Spain

The aim of preferential oxidation of carbon monoxide (COPROX) is to remove CO from hydrogen-rich gas streams that come from hydrocarbon reforming processes. In the last years there has been an increasing interest in the development of catalysts for CO preferential oxidation in the presence of H2. To integrate this reaction stage in a fuel processor destined to the hydrogen production, the COPROX catalyst must overcome the following conditions: high activity for CO oxidation, high selectivity towards the formation of CO2 opposite to H2O formation, intermediate operation temperature between reforming/water gas shift processes and operation temperature of the downstream processes (fuel cell), high resistance to active sites blocking by CO2 and H2O present in the gas stream usually fed. From this standpoint is necessary to optimize the operation conditions such as temperature, O2/CO ratio, space velocity and particle size to avoid H2 oxidation reaction and reverse water gas shift reaction, as well as diffusion phenomena.The goal of this work is to quantify the effect of each variable and the synergetic effect between the operation variables on the catalyst activity of Pt/Al2O3 based catalysts for COPROX reaction in presence of H2. To achieve this goal, experiments design and multi-factorial analysis were the statistical methods used. A mathematical model that represents a response surface based on the variables that influence significantly on Pt/Al2O3 activity and selectivity was obtained. This experimental method minimizes the number of reaction tests, and allows determine the combined effect of a pair variables. The multi-factorial analysis using a pure factorial design "24" has allowed us to establish the minimum number of experiments to determine the temperature and l effect individually and demonstrate that the combined l- temperature effect is really significant in the activity of oxidation of CO in the presence of H2. The response surface obtained presents certain curvature grade. In order to adjust the experimental results a more complex experimental design type was considered (22+E+C). A second order mathematical model that represents the response surface for CO conversion on the basis of the temperature, l and the combined effect of l- temperature has been obtained. The synergetic effect obtained can be explained on account of CO and O2 are adsorbed on the same type of surface sites. Therefore CO preferential oxidation takes place when a part of CO adsorbed on platinum surface sites is desorbed to facilitate the dissociate adsorption of O2. Optimising the l (O2/CO ratio) and the temperature, CO partial desorption and O2 adsorption is favoured and selectivity to CO2 is enhanced.

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S8-IA.25 COMPUTATIONAL FLUID DYNAMICS (CFD) AS AN USEFUL TOOL TO ASSESS POTENTIAL RISKS ASSOCIATED TO HYDROGEN

P. Dieguez-Elizondo. Universidad Pública de Navarra

Safety during production, transport, storage, delivery, and utilization of hydrogen is a critical issue that has to be addressed in order to realize the transition to a hydrogen economy. This is because the general public still considers hydrogen as an extremely dangerous fuel. Great effort has to be devoted to change this opinion by means of thorough studies investigating the potential risks and hazards associated to hydrogen storage and utilization. In this contribution, we will show how accidental hydrogen leaks can be modelled by means of computational fluid dynamics (CFD) in scenarios involving enclosed and unenclosed spaces. Models are built using ANSYS-FLOTRAN and ANSYS CFX software. Due to the limitations of ANSYS-FLOTRAN, work with this code was carried out in 2D with up to 60,000 volume elements. In contrast, ANSYS CFX allowed managing 3D models with up to a million elements. Models of leaks into enclosed vented and non-vented spaces were validated experimentally by means of controlled hydrogen releases in a dedicated gas-proof room with four gas sensors. Leakages considered were the release of gaseous hydrogen in ambient air through holes and breaks in pipes and compressed storage tanks. Hydrogen motion was characterized by pressure difference-driven convection; buoyancy phenomena were relevant due to the low hydrogen density. Natural and forced convection and sonic flow through the leak were considered. The spatial and temporal distributions of the hydrogen concentration within the flammability limits in air were established. This allowed determining optimum venting procedures and hydrogen sensors locations. The best option to remove hydrogen from an enclosed room was found to place a high vent (extractor fan) and introduce air or inert gas through a low vent (blower). Examples will be shown illustrating the evolution of hydrogen leakages from stationary vehicles parked at homes and in parking garages, tankers and storage tanks in fuelling stations.

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S8-INV.8 HYDROGEN EVOLUTION VIA WATER SPLITTING ON CADMIUM-ZINC SYSTEMS UNDER VISIBLE LIGHT IRRADIATION

R. M. Navarro, F. del Valle and J.L.G. Fierro. Instituto de Catálisis y Petroleoquímica, CSIC, Cantoblanco, 28049 Madrid, Spain

INTRODUCTION

The conversion of solar energy to hydrogen by means of water splitting processes assisted by photo-semiconductor catalysts is one of the most interesting, challenging ways to achieve clean and renewable energy systems [1]. Sulfide photocatalysts, which have narrow band gaps and valence bands at relatively negative potentials compared to oxides, can be good candidates for visible-light-driven photocatalysts. Nanosized CdS is an interesting photocatalyst material since it has a narrow band gap (2.4 eV) and also has a suitable conduction band potential able to reduce effectively the H+. However, the photocatalytic properties of CdS are limited due to its photocorrosion under visible light irradiation. Photocorrosion can be minimized by using suitable sacrificial reagents such as Na2S/ Na2SO3 mixture. Thus, this work was undertaken with the aim to combine CdS with ZnOand CdO semiconductors to study the effect of structural changes associated to thermal treatments and also the effect of Pt- and Ru-loading on their performance for water splitting reaction.EXPERIMENTAL

The semiconductor powders (CdS:CdO:ZnO=90:6:4 wt%) were prepared by sequential precipitation of CdS and CdO-ZnO from Cd and Zn-acetate aqueous solutions (1 M) using Na2S and NaOH as precipitating agents at 298 K. The dried precipitates were annealed under He flow at 573 K (CZSO-5), 773 K (CZSO-7) and 923 K (CZSO-9). Ru (0.5 wt%) and Pt(0.5 wt%) were photodeposited on CZSO-7 substrate. Chemical composition (TXRF), specific surface areas, crystal structure (XRD), light absorption properties (UV-vis), and chemical state and surface composition by XPS were determined for all semiconductor samples. Photocatalytic activity was determined in a closed Pyrex glass reactor (200 mL) using 0.1 g semiconductor powder suspended in an aqueous solution (150 mL) containing 0.1 M Na2S/0.04M Na2SO3 as sacrificial reagents and irradiated with a xenon OF 150 W arc lamp. Samples of the evolved gases were extracted periodically and analyzed by GC with TCD.

RESULTS AND DISCUSSION

XRD patterns of CZSO catalysts annealed at different temperatures show a mixture of cubic CdS(JCPDS 10-454), hexagonal CdS (JCPDS 06-314) and cubic CdO (JCPDS 75-594) and absence of crystalline ZnO. Both crystallinity and percentage of hexagonal CdS phase increased with increasing calcination temperature. Photodeposition of Pt or Ru on CZSO-7 led to a decrease in both percentage and crystal size of hexagonal CdS phase. Photoelectron spectra confirmed results derived by XRD. The binding energies of Cd3d5/2 peak revealed the presence of major CdS phase and a minor proportion of CdO (<21%); this latter component disappeared upon annealing at 923 K, while that of Zn2p3/2 was characteristic of ZnO. The absorption edges of CZSO catalysts gradually shifted from 549 nm to 526 nm upon increasing the annealing temperature. Band gap for each catalyst calculated from absorbance spectra was slightly lower than 2.4 eV reported for pure crystalline CdS. Hydrogen evolution under visible light irradiation was observed on all CZSO samples and the amounts of H2 produced followed the sequence: CZSO-7 > CZSO-9 > CZSO-5. The levels of hydrogen evolution over the Pt or Ru-loaded samples was much higher than on the noble metal-free CZSO counterparts, i.e. the rate of H2 production on the Ru-CZSO-7 sample was almost 50 times higher than on the CZSO-7 sample. 1. J. Nowotny, T. Bak, M.K. Nowotny, L.R. Sheppard, J. Phys. Chem. B 2006, 110, 18492.