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NANOTECHNOLOGY
APPLICATIONS: ENERGY
“Every day we are bathed in energy” (R. Smalley)
Turaeva Nigora
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Outline
• Solar energy
• Hydrogen society
• Rechargeable batteries
• Energy saving
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Humanity’s Top Ten Problems
for next 50 years
1. ENERGY
2. CLEAN WATER
3. FOOD
4. ENVIRONMENT
5. POVERTY
6. TERRORISM & WAR
7. DISEASE
8. EDUCATION
9. DEMOCRACY
10. POPULATION
2007 6.6 Billion People
2050 10 Billion People
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Energy challenges
Fossil fuels limitations:
• Environmental impact
• Availability is limited
• As the demand for energy increases, so does the cost of
fossil fuels
Nuclear sources: waste disposal issues, safety
Renewable energy sources (solar, wind, geothermal,
hydro, etc.): CO2 neutral
The problem: solar energy is not constant in time, evenly
distributed geographically
Conversion, storage and transport of energy should be
efficient and cost effective
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What can nanotech do to support this
master plan?
• Lowering the cost of photovoltaic 10-fold
• Nanomaterials:
• Photocatalytic reduction of CO2 to methanol
• Direct photoconversion of H2O to H2 fuel sources
• 10-100 fold improvement of batteries, supercapacitors
• CNT and quantum wires for transmission of electricity with
one-sixth the weight of copper
• Hydrogen storage on CNTs, graphene
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Solar Energy
165,000 TW constantly strikes the surface of the earth. Sunlight hitting the dark discs
could power the whole world: If installed in areas marked by the six discs of 10,000
sq.mi. each in the map, solar cells with a conversion efficiency of only 8 % would
produce, on average, 18 TW electrical power. That is more than the total power
currently available from all our primary energy sources, including coal, oil, gas, nuclear,
and hydro. The colors show a three-year average of solar irradiance, including nights
and cloud coverage (Image credit: http://www.ez2c.de/ml/solar_land_area/)
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Solar energy: Photovoltaics
• 1st generation:
• silicon (single crystal (<30%), polycrystalline ~20%)
• Characteristics: highly stable, long life time (25years), high efficient,
but opaque, expensive, rigid
• 2nd generation:
• Thin film technologies (e.g. GaAs, CuInSe2) (16-18%)
• Amorphous Si:H (~12%)
• Characteristics: light in weight, flexible but made of rare materials,
high temperature treatments
• 3rd generation:
• Organic (plastic) cells (~5%)
• Nanostructured solar cells (QDs, nanowires) (~9%, PbS QDs)
• Dye (hybrid) cells (~14%)
• Perovskite cells (~22%)
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Figure 1: Relationship between power conversion efficiency,
module areal costs and cost per peak watt (in $/Wp).
http://www.nature.com/nnano/journal/v9/n12/full/nnano.2014.292.html
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Photovoltaics: Nanotechnology
• QDs and semiconducting nanowires as photoactive and
anti-reflective components
• Benefits:
• a significant reduction in material usage, less processable fabrication
and/or associated final costs (lower module cost);
• photovoltaic devices with a higher limiting efficiency
• Graphene and CNTs as transparent, flexible electrodes
• Buckballs and graphene for exciton dissociation in plastic
solar cells
• Superhydrophobic coatings
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Three examples of nanostructured solar cells
http://www.nature.com/nnano/journal/
v9/n12/full/nnano.2014.292.html
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Dye-sensitized (Gratzel) solar cells
• Mimic photosynthesis
• Components: dyes, TiO2 NPs, redox
electrolyte, electrodes
• Benefits:
• absorb light in wider range than TiO2
• low-cost materials
• cost effective manufacture
• possibility of large areas of solar cells
• Commercial cells have conversion
efficiency of 12% (DyeSol)
• To increase further efficiency: dyes
are replaced by QDs or perovskite
nanocrystals
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Perovskite solar cells
• Perovskite structure has the generic form ABX3 like in
true perovskite mineral. In high efficient perovskite:
• A = An organic cation - methylammonium (CH3NH3)+
• B = A big inorganic cation - usually lead(II) (Pb2+)
• X3= A slightly smaller halogen anion – usually chloride (Cl-) or iodide
(I-)
• Characteristics: thin films (300nm), easy fabrication, low
cost, high power conversion efficiency (3% in 2009 – to 22%
in 2016)
• Drawbacks: weak to water and oxygen, thermal and photoinstable
• No long-term stability
• Nanotechnology: graphene as transparent electrodes,
hydrophobic hole transport conducting polymer layers
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Lotus-mimicking PV coatings
• The problem: the layer
of dirt masks the
absorption of light
• Nanosolution:
Superhydrophobic
surfaces to improve the
performance of PV
• Benefits: cleaner and
more durable panels
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Hydrogen society
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Hydrogen production
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Hydrogen storage
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Hydrogen fuel cells
H 2 1/ 2O2  H 2O
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Hydrogen generation
• Sources: hydrocarbons (methane, conversion efficiency of
50%)
• High operation temperature, CO2 emission
• Photocatalysis : photocatalytic splitting water into hydrogen
and oxygen by a TiO2 photoanode (A.Fujishima, K. Honda,
1972) (conversion efficiency of 24%)
https://cas.umkc.edu/chemistry/images/chenf2.jpg
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Nanotechnology: photocatalytic water
splitting
Two problems to make viable (economic and efficient):
• The limited light absorption in the visible range of the solar
spectrum
• Nanosolution:
• TiO2 nanotube arrays (Dr. Misra, University of Nevada),
• Improving the efficiency of dye molecules
• Improving nanocatalysts
• Fast electron-hole recombination
• Nanosolution: deposition of noble metal NPs (<5nm) onTiO2 NPs
to increase charge separation between metal-semiconductor interface
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Hydrogen storage
• Compression
• Liquefaction
• Issues: hydrogen is explosive, compression or cooling hydrogen is an
energy-intensive process, strong materials for storage canister walls
• gas-on-solid adsorption (e.g. activated carbon or zeolites)
• metal hydrides materials (pure or alloyed metals) (2-10wt%)
The demands of the automotive industry requires a hydrogenstorage capacity of ~10 wt%.
Storage requirements: Safe, efficient, light in weight, compact
and economical
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Hydrogen storage
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Hydrogen storage: Nanotechnology
• Nanomaterials: light
weight, low volume, high
hydrogen loading capacities,
good hydrogen desorption
kinetics, low cost
• Storage materials:
• Carbon based materials:
CNTs, Graphene (max
14wt%)
• Nanostructured Complex
metal hydrides: LiBH4
(19wt%), NaBH4 (11wt%),
NaAlH4 (8wt%)
http://2.bp.blogspot.com/_VyTCyizqrHs/TUA7sDPYWhI/AAAAAAAAKIw/epBMW3oOqI/s1600/cellafueltanks.jpg
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Hydrogen fuel cell
Use hydrogen and oxygen as fuel to
generate electricity
Result: Max 1.2 V and 1 W/cm^2
Challenges to make fuel cells an
economical viable alternative to
combustion engines :
• The nature of Catalyst (e.g. Pt)
• Electrolyte (e.g. aqueous KOH)
H 2 1/ 2O2  H 2O
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Hydrogen fuel cell: catalysts
• Conventional used materials: Pt
• Problems: expensive, sensitive to
CO, sulphur species, operate at
high temperature (>70C)
• Nanomaterials:
• Pt NPs dispersed in a support
• carbon nanomaterials (e.g.
carbon foams, CNTs) supporters
• Benefits:
• increasing the material catalytic
activity (increased surface-tovolume ratio)
• reducing of rare metal usage
SLAC National Accelerator Laboratory,
2010
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Rechargeable batteries
• Rechargeable batteries: lead acid
batteries, lithium ion batteries with
graphite anode (e.g. LiCoO2)
• Characteristics to be improved: energy
capacity (an ampere-hour), power capacity,
charge rate, lifetime, safety (at >130C
thermal runaway)
• Nanotechnology can improve capacity
(e.g. Si nanowires) and safety (ceramic heatresistant and still flexible separators)
Schematic representation of a
lithium-ion battery
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Li rechargeable batteries: Si nanowires
• Graphite anode: 372 mA*h/g (an
ampere-hour) energy capacity
• Bulk silicon: ~4200 mA*h/g
• Drawbacks: 400% change in volume
during lithium ions insertion and
extraction which lead to cracking and
pulverization
• Si nanowires as anode: facial strain
relaxation, efficient 1 D electron transport,
good contact with current collector
• Benefits:
• 10 times the energy density of graphite
anodes
• Structurally stable after many cycles
• Discharge capacity close to 75% of this
maximum
Chan et. al, Nature Nanotech, 2007
Yi Cui et al. Stanford University, 2007
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Energy saving
• Improving insulation of residential homes and
offices
• Reduction of fuel consumption:
• Using lighter and stronger materials in transport vehicles
• Wear resistant, lighter engine components
• Switchable glasses (“smart” windows)
• More efficient electric grid to transport energy
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Insulators and “smart” coatings
• Nanoporous silica aerogels to improve thermal
insulation (e.g. Aspen Aerogels products)
• “Smart” materials
• Electrochromic coatings for darkening window, low E-glass
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Advanced materials
• Lighter materials
less fuel consumption (e.g.
transport vehicles on the roads and in the air)
• Higher tensile strength
higher possible loads (e.g.
wind turbines)
• Anti-corrosive nano-coatings
a longer service life
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Energy-harvesting materials
“Energy-scavengers”: piezoelectric
zinc oxide nanowires
Vibrations below 10 Hz frequency
to be converted into electrical
energy: footsteps, heartbeats,
noises, airflow, light winds, body
movement
Applications: soft, flexible
technologies used to power personal
electronics, in sensing and defense
technologies, textiles
http://www.nature.com/nature/journal/v451/n7180/fig_tab/nature
06601_F1.html
Georgia Institute of Technology, 2008
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Efficient energy transport