Laurea degree (summa cum laude) in physics from the University of Pisa, in 1992 and the PhD in physics from Scuola Normale Superiore of Pisa, in 1997

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1 Vittorio PELLEGRINI Graphene for energy applications Laurea degree (summa cum laude) in physics from the University of Pisa, in 1992 and the PhD in physics from Scuola Normale Superiore of Pisa, in 1997 Director of research at the Istituto Nanoscienze of the Italian National Research Council CNR. His research interests currently focus on the physics and application of lowdimensional semiconductor systems and graphene, in particular spectroscopic measurements of collective electronic properties of two-dimensional systems and quantum dots. The most recent activity focuses on the magneto-optical properties of graphene and graphite and on graphene-hydrogen systems.

2 Graphene for energy Vittorio Pellegrini NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy

Graphene as a platform to interact with the nano-world With

world by: Selectively graft (bio-)molecules Tuning the

/ magnetic properties Converting molecular vibrations into

3 Graphene as a platform to interact with the nano-world With graphene we can fully exploit proximity to the molecular world by: Selectively graft (bio-)molecules Tuning the interaction between molecules and graphene Sensing chemical / magnetic properties Converting molecular vibrations into electric signals A. Candini, et al. ACS Nano 4 (12), pp 7531 (2010).

4 Graphene production Courtesy of A. Ferrari

5 Chemical production of soluble, functionalized graphene GO can be obtained by controlled chemical oxidation of graphite. The sheets are characterized by epoxy and hydroxyl groups covalently linked to the C atoms of the graphene basal plane. Selective intercalation or adsorption of molecules V. Palermo, et al. Journal of the American Chemical Society, 131, (2009) V. Palermo, et al. Journal of Materials Chemistry, 20, 9052 (2010) V. Palermo, P. Samorì et al. Journal of Materials Chemistry, 21, 2924 (2011)

Graphene-organic composites for optoelectronics Graphene-organic electronic devices GOT4 GO GO GO+T4 + T4-Si A1 A2 A3 A4 A5 A6 POLAR APOLAR POLAR APOLAR POLAR APOLAR New chemical properties

6 Graphene-organic composites for optoelectronics Graphene-organic electronic devices GOT4 GO GO GO+T4 + T4-Si A1 A2 A3 A4 A5 A6 POLAR APOLAR POLAR APOLAR POLAR APOLAR New chemical properties Charge-energy transfer 100µ P3HT + RGO I D (A) 10µ 1µ RGO V G (V) V. Palermo, P. Samorì et al. Journal of the American Chemical Society, 131, (2009) V. Palermo, P. Samorì et al. Journal of Materials Chemistry, 20, 9052 (2010) V. Palermo, P. Samorì et al. Journal of Materials Chemistry, 21, 2924 (2011)

7 Production of reduced graphene oxide by electrochemical patterning AFM (5 um x 5 um) PROJECT V. Palermo, P. Samorì et al. Journal of the American Chemical Society, 132, (2010)

8 Graphene - Graphane + H 2 Each C atom is saturated with a H atom Graphane is very stable among hydrocarbons of similar saturation Graphane is an insulator (2.5 ev gap) D. C. Elias et al. Science 323, 5914, (2009)

9 Graphene - Graphane J.O. Sofo et al., Phys. Rev. B 75, (2007)

10 Nanostructuring Graphene in Graphane Structure merges gradually from graphene-like to graphane like at the interface The hybrid system has finely tunable semiconducting properties V. Tozzini, V. Pellegrini Phys. Rev. B 81, (2010)

11 Energy applications

12 Graphene as a platform to interact with the molecular and atomic worlds for energy applications Energy storage: supercapacitors Hydrogen storage Photovoltaics

Supercapacitors Supercapacitors store and release energy by nanoscopic charge separation between an electrode and an electrolyte Compared to conventional dielectric capacitors supercapacitors can

13 Supercapacitors Supercapacitors store and release energy by nanoscopic charge separation between an electrode and an electrolyte Compared to conventional dielectric capacitors supercapacitors can store much more energy Compared to batteries, supercapacitors have fast chargedischarge rates Lithium-ion batteries can have energy density of 150 Wh/Kg and 2-6 hours of recharge time Supercapacitors can have recharge time of 2 minutes but typically lower energy densities. NMP projects AUTOSUPERCAP ELECTROGRAPH

14 Graphene double-layers Supercapacitors The capacitance comes from the charge accumulated at the electrode/electrolyte interface. M.D. Stoller, et al. Nano Letters 8, 3498 (2008) Large surface area 2600 m 2 /g

Graphene double-layers Supercapacitors The capacitance comes from the charge accumulated at the electrode/electrolyte interface. M.D. Stoller, et al.

15 Graphene double-layers Supercapacitors The capacitance comes from the charge accumulated at the electrode/electrolyte interface. M.D. Stoller, et al. Nano Letters 8, 3498 (2008) Large surface area 2600 m 2 /g Main achievements: 90 Wh/Kg with curved graphene with ionic liquids electrolytes operating at large voltages Chenguang Liu, et al. Nano Letters 10, 4863 (2010) Timeline for commercial applications??

16 Hydrogen storage

17 Hydrogen fuel cell Hydrogen has highest energy-to-mass ratio of any chemical Non-toxic Combustion product: water Unlimited resource An hydrogen fuel cell

18 Hydrogen-fuelled vehicles

19 Hydrogen storage Storing enough hydrogen on-board a vehicle to achieve a driving range of greater than 500 km is a significant challenge. On a weight basis, hydrogen has nearly three times the energy content of gasoline (120 MJ/kg for hydrogen versus 44 MJ/kg for gasoline). However, on a volume basis the situation is reversed (8 MJ/liter for liquid hydrogen versus 32 MJ/liter for gasoline). On-board hydrogen storage in the range of 5 13 kg H 2 is required to encompass the full platform of light-duty vehicles. Source: U.S. Department of Energy

20 Hydrogen storage Compressed Gas Cryogenic Liquid Catastrophic failure of a compressed hydrogen cylinder installed on a vehicle

21 Hydrogen storage Compressed Gas Cryogenic Liquid Storage in Materials Metal Hydrides Carbon-Based Materials or High Surface Area Sorbents Chemical Hydrogen Storage Source: U.S. Department of Energy

Hydrogen can be stored in different forms In tanks High pressure (300 700 bar) Low temperature

22 Hydrogen can be stored in different forms In tanks High pressure ( bar) Low temperature (T < 20 K) In Materials NaAlH 4 = 1/3 Na 3 AlH 6 + 2/3 Al+H 2 Source: U.S. Department of Energy

23 Key Requirements for Hydrogen Storage On-Board a Vehicle High gravimetric and volumetric densities (light in weight and conservative in space) Fast kinetics (quick uptake and release) Appropriate thermodynamics (e.g., favorable heats of hydrogen absorption and desorption) Long cycle life for hydrogen charging and release, durability, and tolerance to contaminants Low system cost, as well as total life-cycle cost Minimal energy requirements and environmental impact Safety is an inherent assumption and requirement Source: U.S. Department of Energy

24 DOE objectives 9 wt% 6 wt% (kg H 2 / kg system) Source: U.S. Department of Energy

25 Graphene for hydrogen storage Graphene is lightweight, inexpensive, robust, chemically stable Balog et al., JACS (2009)

such as calcium or transisiton metals Lee et al., Nano Lett.

26 Decorated Graphene for hydrogen storage Functionalized graphene has been predicted to adsorb up to 9 wt% of hydrogen Modify graphene with various chemical species, such as calcium or transisiton metals Lee et al., Nano Lett. 10 (2010) 793 Yang et al., PRB 79 (2009) Durgen et al., PRB 77 (2007) Capacity up to 5-9 wt%

27 Layered Graphene for hydrogen storage A. Patchkovskjj et al., PNAS 102, (2005)

28 Layered Graphene for hydrogen storage Layered spaced Graphene Sheets Can uptake large quantities of hydrogen Jin et al, Chem. Mater. 2011, 23, 923 Graphene oxide and boron-carboxylic pillars. NIST & Univ of Pennsylvania

29 Hydrogen adsorption/desorption Current hydrogen storage devices exploit changes in temperature and pressure Methods to uptake/release hydrogen at fixed temperature Exploit changes in curvature?

Hydrogen binding energy depends on graphene curvature V. Tozzini and V. Pellegrini, arxiv:1101.

30 Hydrogen binding energy depends on graphene curvature V. Tozzini and V. Pellegrini, arxiv: The hydrogen binding energy on graphene is strogly dependent on local curvature and it is larger on convex parts

31 Hydrogen binding energy depends on graphene curvature Atomic hydrogen spontaneously sticks on convex parts Inverting curvature H is expelled Curvature inversion or control could be obtained by means of charged, polar or magnetic intercalants, or by acoustic waves,

(when functionalized) Flexible Transparent For these

32 Transparent Electrodes based on Graphene for Dye Sensitized Solar Cells Graphene is: Conductive Catalytic (when functionalized) Flexible Transparent For these reasons it is considered an excellent substitute for TCO and/or Pt

window electrodes in inorganic solar cells and aid

33 Silicon solar cells Silicon solar cells dominate the current PV technology Graphene TC Films can be η up to 25% used as window electrodes in inorganic solar cells and aid electron-hole separation and hole transport Tsinghua and Peking Universities

34 Organic solar cells Transparent conductor window Photoactive material Theoretically η > 12% should be possible using graphene as photoactive material Yong, V.,Tour, J. M. Small 6, 313 (2009)

35 Dye-sensitized solar cells Graphene can cover an even larger number of functions in DSSCs Graphene TC Films are used as window electrodes (η 0.2% achieved so far) Graphene can be incorporated into the nanostructured TiO 2 photoanode to enhance the charge transport rate (η 7%) Graphene, due to its high specific surface area, can be used as catalyst to substitute the Platinum counter electrode (η~4.5%)

36 Toward all graphene/carbon-based solar cells? Exploitation of well-known carbon chemistry to build bottom-up graphene nanostructures size-dependent bandgap & large optical absorption Graphene flakes as sensitizer in DSSC X. Yan et al., Nano Lett. 2010, 10, or even blended with C 60 in organic SC Functionalized graphene nano-diodes C. Cocchi et al., J. Phys. Chem. C 2011, 115, 2969 C. Cocchi et al., in preparation 2011 ELECTRON HOLE

nanostructures size-dependent bandgap & large optical absorption Graphene flakes as

2010, 10, 1869 1873 or even blended with C 60 in organic SC Functionalized graphene

37 Toward all graphene/carbon-based solar cells? Exploitation of well-known carbon chemistry to build bottom-up graphene nanostructures size-dependent bandgap & large optical absorption Graphene flakes as sensitizer in DSSC X. Yan et al., Nano Lett. 2010, 10, or even blended with C 60 in organic SC Functionalized graphene nano-diodes C. Cocchi et al., J. Phys. Chem. C 2011, 115, 2969 C. Cocchi et al., in preparation 2011 ELECTRON HOLE fast e-h separation high absorption intensity wide size tunability

38 Carrier multiplication in graphene Inverse Auger recombination T. Winzer et al. NanoLetters 10, 4839 (2010)

39 Graphene for energy Supercapacitors Photovoltaics Hydrogen storage???

40 Thanks to CNR Italy and in particular to: Marco Affronte Francesco Bonaccorso Andrea Ferrari Giuseppe Gigli Stefan Heun Elisa Molinari Vincenzo Palermo Marco Polini Deborah Prezzi Valentina Tozzini

41 Graphene curvature d vs. hydrogen binding energy ΔE = 4. 5d V. Tozzini and V. Pellegrini, arxiv:

42 Control curvature in-situ Suitable intercalates Electro-optical stimuli Magnetic nanoparticles Flexible substrates Piezo motors Pressure difference STM tip

43 Graphene for Photovoltaic (PV) devices Graphene can fulfil multiple functions in PV devices: 1) Transparent conductor window 2) Photoactive material 3) Channel for charge transport F. Bonaccorso et al. Nature Photonics 4, 611 (2010)

Designing Graphene for Hydrogen Storage

Designing Graphene for Hydrogen Storage Stefan Heun NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore Pisa, Italy Outline Introduction to Hydrogen Storage Epitaxial Graphene Hydrogen Storage