Simulations of Nanomaterials: Carbon Nanotubes, Graphene and Gold Nanoclusters Iván Cabria, María J. López, Luis M. Molina, Nicolás A. Cordero, P. A. Marcos, A. Mañanes and Julio A. Alonso Dpto. de Física Teórica, Universidad de Valladolid, Valladolid, Spain Group of Physics of Nanostructures

Universidad de Valladolid Group of Physics of Nanostructrures University of Valladolid J. A. Alonso I.Cabria M. J. López L. M. Molina University of Cantabria A. Mañanes University of Burgos N. A. Cordero P. A. Marcos UAM Mexico: UAM Mexico: J. Arellano Univ. Guanajuato Mexico: J. Robles DIPC San Sebastian: DIPC San Sebastian: A. Rubio University of Pennsylvania: University of Pennsylvania: L.A. Girifalco, K. Mahadevan, J. Fischer Instituto del Carbón, CSIC, Oviedo: Nacho Paredes, Juan M. Tascón Argonne National Laboratory: Stefan Vajda Other collaborators Group of Simulations of Materials

Main Lines of Research Related with Nanomaterials and Nanotechnology Can be focused on Materials and/or on Technological Applications Simulations of Properties and Dynamics of Nanomaterials

Main Lines of Research - Carbon Nanotubes - Hydrogen Storage for Hydrogen Cars - New Catalysts made of Gold Nanoclusters

The discovery of Carbon nanotubes After the C 60 fullerene discovered in 1985 CNTs are the new breakthrough of carbon, discovered in 1991 Multiwall Carbon Nanotubes (MWCNTs) were produced by the arc discharge technique Nested cylinders of Carbon 4-30 nm in diameter 1 µm in length Iijima, Nature 354, 56 (1991) Ebbesen, Ajayan, Nature 358, 220 (1992) 3 nm

Single Wall Carbon nanotubes Bethune et al, Nature 363, 605 (1993) iron catalyst cobalt catalyst produced by the arc discharge technique with a metal catalyst Iijima, Ichihashi, Nature 363, 603 (1993)

Geometrical Construction of SWCNTs Chiral vector: C h Hamada et al, Phys Rev Lett 68, 1579 (1992) Saito et al, Appl Phys Lett 60, 2204 (1992) (n,m) uniquely specifies all posssible tube structures Translation vector: T Translation vector: T Chiral angle: θ Chiral angle: θ θ = angle ( a 1, C h ) by wrapping around a graphene strip in a seamless cylinder

Types of CNTs structures (5,5) Armchair, θ = 30º Hamada et al, Phys Rev Lett 68, 1579 (1992) Saito et al, Appl Phys Lett 60, 2204 (1992) (9,0) Zigzag, θ = 0º (10,5) Chiral, 0º <θ< 30º

Conducting character of SWCNTs Hamada et al, Phys Rev Lett 68, 1579 (1992) Saito et al, Appl Phys Lett 60, 2204 (1992) n = m  metallic n - m = 3q  small gap semiconductor n – m ≠ 3q  moderate gap semiconductor

Carbon Nanotubes Microelectronics needs nanotubes of the same electronic character Surfactants and nitronium molecular ions are used to attack selectively and separate the nanotubes in the bundles Separation of nanotubes by its metallic or semiconducting character Application of finite nanotubes to Spintronic: electrical current with spin polarization

Chemical sensors based on nanotubes very sensitive to different gases Funcionalization of nanotubes with molecules and/or clusters Changes of the electrical conductivity of nanotubes due to extremely small amounts of gases adsorbed on the surface of the nanotubes Applications: environmental, medical, clean room control, etc. Carbon Nanotubes

Hydrogen Economy  Production  Hydrogen Storage  Use: Fuel Cell Three Aspects of an Economy based on Hydrogen - Hydrogen could be an alternative to conventional fossil-fuel sources of energy - Hydrogen is abundant and non contaminant - Hydrogen is NOT a primary source of energy but an energy vector

Hydrogen Economy  Natural Gas: 50 % Production, most common  Water electrolysis: for cheap electricity  Biomass, pirolysis, photobiological processes (bacteria) Production Electrolysis of water

Hydrogen Economy Production: Prices 1 Kg Hydrogen Natural gas reforming USDUntaxed 1 Kg Hydrogen Electrolitic H, May USDUntaxed 4.02 L Gasoline Spain, July USDTaxed taxes=49 % 4.02 L Gasoline USA, September USDTaxed taxes=18 % 1 Kg hydrogen contains the same energy than 4.02 L of gasoline 1 Kg hydrogen occupies 1/ = L at normal conditions

Hydrogen Economy  Onboard (cars) and in situ (buildings) storage  Storage methods  Liquid Hydrogen  Compressed Hydrogen  Stored in a solid Storage

Hydrogen Car: Electric Car powered by a Hydrogen Fuel Cell instead of batteries Fuel Cell Electric Vehicle in California Hydrogen Fuel Cell Cars

Technological goal: Hydrogen cars equivalent to Fossil Fuel Cars Bottlenecks: fuel cell efficiency and onboard storage Onboard hydrogen storage targets for 2010: 6 weight % of hydrogen Kg H 2 /L at room temperature and moderate pressures, atms Hydrogen Fuel Cell Cars

Types of Hydrogen Storage: gas, liquid and solid Mechanisms of Solid Hydrogen Storage: physisorption, chemisorption and chemical reactions Materials that store by physisorption: nanotubes, nanoporous carbons (CDCs, ACs, GNFs, etc.), porous materials such as MOFs, COFs, porous polymers, etc., and metal-doped carbons Hydrogen Fuel Cell Cars

Compressed hydrogen km of autonomy vs 500 km of gasoline cars About 2.5 times more expensive than gasoline cars Hydrogen at 350 bars in Japan, at 700 bars in Europe No room for luggage: Tank with 110 H 2 liters at 350 bars 110 CV vs CV of gasoline Norway, Fall 2006: First European public hydrogen station Electric Cars powered by Hydrogen Fuel Cells instead of batteries

Hydrogen Onboard Storage One of the main Hydrogen economy challenges Hydrogen has a high energy density by mass: 120 MJ/kg (LHV) 140 MJ/kg (HHV) (gasoline: 44 MJ/kg) But it has a low energy density by volume: 1.5 MJ/L at 150 bars, 0.01 MJ/L at 1 atm and 300 K, 8.4 MJ/L liquid H 2 (gasoline: 35 MJ/L) Hydrogen Storage is one of the bottlenecks of present technology of Hydrogen Fuel Cell Cars LHV: Lower Heating Value; HHV: Higher Heating Value

Hydrogen Onboard Storage One of the main Hydrogen economy challenges A Storage Capacity of 5-10 kg of hydrogen is needed to provide a range of 480 km for a electric-fuel cell car 60 L of gasoline for 480 km 1 kg H 2 = 4.02 L gasoline  15 kg H 2 15 kg H 2 Fuel cell eficiency = 2-3  5-10 kg H 2

Hydrogen Onboard Storage DOE targets for 2010  Specific energy: 7.2 MJ/kg  Gravimetric capacity: 7.2/120 kg H 2 /kg = 0.06 kg H 2 /kg = 6 weight %  Energy density: 5.4 MJ/L  Volumetric capacity: 5.4/120 kg H 2 /L = kg H 2 /L Note: energy density of hydrogen is 120 MJ/kg for DOE, the LHV value Reversible Hydrogen Storage

Hydrogen Onboard Storage DOE targets for 2010  Operating temperature: 250 – 320 K  Delivery pressure: 2.5 bars  Refueling rate: 1.5 Kg/min or 7 minutes

Hydrogen Onboard Storage Reference gasoline car  Mass fuel storage system: 74 Kg  Volume fuel storage system: 107 L  75 L of gasoline or 55.4 Kg of gasoline  600 Km of autonomy  75 L gasoline × 35 MJ/L gasoline = 2625 MJ  Specific energy: 2625/74 + Fuel cell eficiency= MJ/kg  Energy density: 2625/107 + Fuel cell eficiency= MJ/L

Hydrogen Onboard Storage No current hydrogen storage technology meets the targets ?

Materials for Hydrogen Onboard Storage GOAL: Find new materials that fulfill the DOE targets for onboard hydrogen storage Light Materials Porous Materials Binding energy of H 2 to surface: eV/molecule - Graphene Slitpores, Nanoporous Carbons, Carbide-Derived Carbons - Li doped Graphene Slitpores - Pd doped Graphene Slitpores - Molecular Organic Frameworks, MOFs

Simulation of Slitpores Slitpore of width D: two parallel flat layers at distance D Van der Waals interaction of a molecule with the surface Single Layer Slitpore

Relationship between pore size and shape and storage capacity Models for different pore shapes Two parallel graphene layers: slitpore CNTs: cylidrical pores Fullerenes: spherical pores

Storage capacities from the slitpore model Y. Gogotsi, et al. JACS 127, (2005) Jordá-Beneyto,et al. Carbon 45,293 (2007) The measured storage capacities can be mimicked through slitpores of a single size or a combination of sizes

Pure Graphene Slitpores - Optimal Slitpore Width: around 6 Å - Volumetric and gravimetric goals ARE REACHED above 10 MPa at 300 K - Volumetric and gravimetric goals are reached at moderate pressures at 77 K and for slitpore widths larger than 5.5 Å

Concavity and Li doping H2H2H2H2 electronic density redistribution  = dark +2, white -2  e/au 3 E b = meVE b = meV Li  = green:+1, yellow -1,  e/au 3 H2H2H2H2 Li

Near Li inside: 0.30 eV/molecule!! A binding energy of eV/H 2 molecule is required for reversible uptake and release at room T Li et al., JCP 119, (2003) Metal impurities increase binding energy and hydrogen storage Burgos, November 6th 2009, Project Meeting JCP 128, (2008) and JCP 123, (2003)

molecular adsorption Interaction of H 2 with Pd doped Graphene

Metal Organic Frameworks (MOFs)  inorganic metal oxide cluster + organic linker High Specific Surface Area, SSA = 2000 – 4700 m 2 /g High porosity volume = 80% High Specific Pore Volume = 1 cm 3 /g  Promise for hydrogen storage: changing the linker tunable pore size: changing the linker changing the metal tunable functionality: changing the metal Yaghi & coworkers, Nature (1999) MOFs: New family of highly porous, crystalline materials

MOF-5 structure MOF-5 cube red: Znblue: Ogray: Cwhite: H crystalline lattice: fcc forms cubes: corners: OZn 4 clusters edges: BDC organic linkers Lattice parameter = Å Porosity: two types of pores of 15 Å and 12 Å

MOF-5 adsorption sites Direct determination of the adsorption sites using inelastic neutron diffraction: Yaghi & coworkers, Science 300, 1127 (2003) 2 sites: one associated with the Zn and one with the BDC linker 2 sites: one associated with the Zn and one with the BDC linker Yildirim & Hartman, Phys. Rev. Lett. (2005) 2 more sites are identified around the Zn-oxide cluster 2 more sites are identified around the Zn-oxide cluster Theoretical investigation find three main adsorption sites:  CUP between three Ocore-Zn-O-C-O-Zn hexagons  O 3 plane above Zn  Benzene Adsorption around the Zn-oxide cluster should be responsible for the high storage capacity of MOFs

Comparison of MOFs with other nanoporous materials AC from Linares, CDC from Gogotsi, MOF from Yaghi MOFs perform better than Activated Carbons and Carbide Derived Carbons at moderate pressures

New Catalysts made of Gold Nanoclusters Gold is noble metal, chemically inactive But small clusters and nanostructures of gold have catalytic properties They are very efficient for different chemical reactions of industrial interest GOAL: Design new catalysts made of gold nanoparticles for each specific chemical reaction

New Catalysts made of Gold Nanoclusters We have shown the selective oxidation of propene to form propylene oxide, used in the production of polyurethane

Model for Au n /Al 2 O 3 Clusters are supported on different surfaces and environments and these change their catalytic properties

Bimetallic Au-Ag alloy nanoparticles 1ML of Ag 1.83 O on top of Au(111) corresponds to the situation of a bimetallic alloy with high Au concentration. Perspectives

- European Directive February 2003: take-back and treatment (recycling) of 4 kg of electronic waste per inhabitant and year - Organization of the take-back - Optimization of take-back costs - Molecular dynamics algorithm applied to this economic problem Parallel MD Algorithm applied to Economic Organization of Recycling

Interest of Research The results of our research are useful for new technologies and materials related to important activity sectors of our region such as automotive and clean energies

- Ministerio de Educación y Ciencia de España y FSE, Programa “Ramón y Cajal”, - Ministerio de Educación y Ciencia de España: Programa Nacional de Investigación. Planes Nacionales I+D/I+D+I, MAT C and - Ministerio de Educación y Ciencia de España: Programa Nacional de Investigación. Planes Nacionales I+D/I+D+I, MAT C and MAT C Junta de Castilla y León, Programa Gral. de Apoyo a Proyectos de Investigación, VA039A05, and GR23 - Junta de Castilla y León, Programa Gral. de Apoyo a Proyectos de Investigación, VA039A05, VA017A08 and GR23 Acknowledgments Thanks for your attention