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 low-

dimensional 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.

Vittorio Pellegrini

NEST, Istituto Nanoscienze-CNRand

Scuola Normale Superiore, Pisa, Italy

Graphene for energy

Graphene as a platform tointeract 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 signalsACS Nano 4 (12), pp 7531 (2010). A. Candini, et al.

Courtesy of A. Ferrari

Graphene production

Chemical production of soluble, functionalized graphene

V. Palermo, et al. Journal of the American Chemical Society, 131, 15576 (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)

GO can be obtained by controlledchemical oxidation of graphite.

The sheets are characterized by epoxyand hydroxyl groups covalently linked tothe C atoms of the graphene basal plane.

Selective intercalation or adsorption ofmolecules

Graphene-organic composites for optoelectronics

A1 A2 A3 A4 A5 A6A1 A2 A3 A4 A5 A6GOT4 GO GO+T4

POLAR APOLAR POLAR APOLAR POLAR APOLAR

GO + T4-Si

A1 A2 A3 A4 A5 A6A1 A2 A3 A4 A5 A6GOT4 GO GO+T4

POLAR APOLAR POLAR APOLAR POLAR APOLAR

GO + T4-Si

-60 -40 -20 0 20 40 601µ

10µ

100µ

I D (A

)

VG (V)

P3HT + RGO

RGO

-60 -40 -20 0 20 40 601µ

10µ

100µ

I D (A

)

VG (V)-60 -40 -20 0 20 40 60

1µ

10µ

100µ

I D (A

)

VG (V)

P3HT + RGO

RGO

Charge-energy transfer

Graphene-organic electronic devices

V. Palermo, P. Samorì et al. Journal of the American Chemical Society, 131, 15576 (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)

New chemical properties

Production of reduced graphene oxide by electrochemical patterning

AFM (5 um x 5 um)

V. Palermo, P. Samorì et al. Journal of the American Chemical Society, 132, 14130 (2010)PROJECT

Graphene - Graphane

+ H2

Each C atom is saturated with a H atom Graphane is very stable among hydrocarbons of similar saturationGraphane is an insulator (2.5 eV gap)

D. C. Elias et al. Science 323, 5914, (2009)

Graphene - GraphaneJ.O. Sofo et al., Phys. Rev. B 75, 153401 (2007)

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, 113404 (2010)

Energy applications

Graphene as a platform tointeract with the molecularand atomic worldsfor energy applications

• Energy storage: supercapacitors

• Hydrogen storage

• Photovoltaics

Supercapacitors

• Compared to conventional dielectric capacitors supercapacitorscan store much more energy

• Compared to batteries, supercapacitors have fast charge-discharge 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 lowerenergy densities.

Supercapacitors store and release energy by nanoscopic chargeseparation between an electrode and an electrolyte

NMP projects

AUTOSUPERCAP

ELECTROGRAPH

Graphene double-layersSupercapacitors

The capacitance comes from the chargeaccumulated at the electrode/electrolyte interface.

Large surface area 2600 m2/g

M.D. Stoller, et al. Nano Letters 8, 3498 (2008)

Graphene double-layersSupercapacitors

The capacitance comes from the chargeaccumulated at the electrode/electrolyte interface.

Main achievements: 90 Wh/Kg with curved graphene withionic liquids electrolytes operating at large voltages

Chenguang Liu, et al. Nano Letters 10, 4863 (2010)

Large surface area 2600 m2/g

M.D. Stoller, et al. Nano Letters 8, 3498 (2008)

Timeline for commercial applications ??

Hydrogen storage

Hydrogen fuel cell

• Hydrogen has highest energy-to-mass ratio of any chemical

• Non-toxic

• Combustion product: water

• Unlimited resource…An hydrogen fuel cell

Hydrogen-fuelled vehicles

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 H2 is required to encompass the full platform of light-duty vehicles.

Source: U.S. Department of Energy

Hydrogen storage

• Compressed Gas

• Cryogenic Liquid

Catastrophic failure of a compressed hydrogen cylinderinstalled on a vehicle

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

Source: U.S. Department of Energy

High pressure(300 – 700 bar)

Low temperature(T < 20 K)

NaAlH4 = 1/3 Na3AlH6 + 2/3 Al+H2

Hydrogen can be stored in different formsIn tanks

In Materials

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

DOE objectives

6 wt% (kg H2 / kg system)

9 wt%

Source: U.S. Department of Energy

Graphene for hydrogen storage

• Graphene is lightweight, inexpensive, robust, chemically stable

Balog et al., JACS 131 8744 (2009)

Decorated Graphene for hydrogen storage

• Functionalized graphene has been predicted to adsorb up to 9 wt% of hydrogen

Yang et al., PRB 79 (2009) 075431

• Modify graphene with various chemical species, such as calciumor transisiton metals

Durgen et al., PRB 77 (2007) 085405Lee et al., Nano Lett. 10 (2010) 793

Capacity up to 5-9 wt%

A. Patchkovskjj et al., PNAS 102, 10439 (2005)

Layered Graphene for hydrogen storage

Layered Graphene for hydrogen storage

Layered spaced Graphene Sheets Can uptake large quantities of hydrogen

NIST &Univ of Pennsylvania

Graphene oxide and boron-carboxylic “pillars.

Jin et al, Chem. Mater. 2011, 23, 923

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 ?

The hydrogen binding energy on graphene is strogly dependent on local curvature and it is larger on convex parts

V. Tozzini and V. Pellegrini, arXiv:1101.1178

Hydrogen binding energy dependson graphene curvature

Inverting curvature H is expelledAtomic hydrogen spontaneously sticks on convex parts

Curvature inversion or control could be obtained by means of charged, polar or magnetic intercalants, or by acoustic waves, …

Hydrogen binding energy dependson graphene curvature

Transparent Electrodes based on Graphene for Dye Sensitized SolarCells

Graphene is:

• Conductive

• Catalytic (when functionalized)

• Flexible

• Transparent

For these reasons it isconsidered an excellent substitutefor TCO and/or Pt

Silicon solar cellsSilicon solar cells dominate the current PV technology

η up to∼25%

Graphene TC Films can beused as window electrodesin inorganic solar cells and aidelectron-hole separation and hole transport

Tsinghua and Peking Universities

Organic solar cells

Theoretically η > 12% should be possible using graphene as photoactive material

Yong, V. ,Tour, J. M. Small 6, 313 (2009)

• Transparent conductor window

• Photoactive material

Dye-sensitized solar cells

• Graphene TC Films are used as window electrodes (η ∼ 0.2% achieved so far)

• Graphene can be incorporated into the nanostructured TiO2 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%)

Graphene can cover an even larger number of functions in DSSCs

Graphene flakes as sensitizer in DSSCX. Yan et al., Nano Lett. 2010, 10, 1869–1873

or even blended with C60in organic SC

Toward all graphene/carbon-basedsolar cells ?

Exploitation of well-known carbon chemistry to build bottom-up graphene nanostructures size-dependent bandgap & large optical absorption

Functionalized graphene nano-diodesC. Cocchi et al., J. Phys. Chem. C 2011, 115, 2969C. Cocchi et al., in preparation 2011

HOLE

ELECTRON

Graphene flakes as sensitizer in DSSCX. Yan et al., Nano Lett. 2010, 10, 1869–1873

or even blended with C60in organic SC

Toward all graphene/carbon-basedsolar cells ?

Exploitation of well-known carbon chemistry to build bottom-up graphene nanostructures size-dependent bandgap & large optical absorption

Functionalized graphene nano-diodesC. Cocchi et al., J. Phys. Chem. C 2011, 115, 2969C. Cocchi et al., in preparation 2011

HOLE

ELECTRON

• fast e-h separation• high absorption intensity• wide size tunability

Carrier multiplication in graphene

Inverse Auger recombination

T. Winzer et al. NanoLetters 10, 4839 (2010)

Graphene for energySupercapacitors

Photovoltaics

Hydrogen storage

???

Thanks to CNR Italy and in particular to:

Marco AffronteFrancesco BonaccorsoAndrea FerrariGiuseppe GigliStefan HeunElisa MolinariVincenzo Palermo Marco PoliniDeborah PrezziValentina Tozzini

Graphene curvature d vs. hydrogen binding energy

V. Tozzini and V. Pellegrini, arXiv:1101.1178

dE 5.4−=Δ

Control curvature in-situ

• Suitable intercalates– Electro-optical stimuli

– Magnetic nanoparticles

• Flexible substrates

• Piezo motors

• Pressure difference

• STM tip

Graphene forPhotovoltaic (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)