1. Motivati
on

2. Energy and Nanotechnology
Gang Chen
Rohsenow Heat and Mass Transfer Laboratory
Mechanical Engineering Department
Massachusetts Institute of Technology
Cambridge, MA 02139

3. Sources
http://www.sc.doe.gov

4. Nano for Energy
• Increased surface area
• Interface and size effects
Molecules Photons
Λ = 1−100 nm Λ > 10 nm
λ=1 nm λ=0.1-10 µm
Λ---Mean
free path
λ---wavelength
Electrons Phonons
Λ=10-100 nm Λ=10-100 nm
λ=10-50 nm λ=1 nm

5. Nanoscience Research for Energy Needs
• Catalysis by nanoscale materials
• Using interfaces to manipulate energy
carriers
• Linking structures and function at the
nanoscale
• Assembly and architecture of
nanoscale structures
• Theory, modeling, and simulation for
energy nanosciences
• Scalable synthesis methods
National Nanotechnology Initiative Grand Challenge Workshop, March, 2004

6. Examples
Grätzel cell for photovoltaic Catalytic nanostructured
generation and water splitting hydrogen storage materials
• Radiation transport to maximize • Mass transport
absorption • Heat transfer (intake and release)
• Two phase flow • Small scale thermodynamics
• Electrochemical transport • Two phase flow
• Multiscale, multiphysics transport • Multiscale and multiphysics

7. Thermoelectrics Devices
Hot Side
Diffusion
COLD SIDE
I I
I N P Media Clip
HOT SIDE
Cold Side
• Refrigeration
Power Generation
• Power Generation:
Figure of Merit: T(hot)=500 C, T (cold)=50 C
Electrical Seebeck ZT=1, Efficiency = 8 %
Conductivity Coefficient
2 ZT=3, Efficiency =17 %
σS T
ZT = ZT=5, Efficiency =22 %
ke + kp
• Critical Challenges:
Electron Phonon Reduce phonon heat conduction while
Thermal Conductivity
maintaining or enhancing electron transport

8. Nanoscale Effects for Thermoelectrics
Interfaces that Scatter Phonons but not Electrons
Electrons Phonons
Λ=10-100 nm Λ=10-100 nm
λ=10-50 nm λ=1 nm
Electron Phonon
Molecular Dynamics (Freund)

9. State-of-the-Art in Thermoelectrics
PbTe/PbSeTe Nano Bulk
PbSeTe/PbTe
Quantum-dot S2σ (µW/cmK2) 32 28
Superlattices AgPbmSbTe2+m k (W/mK) 0.6 2.5
3.0 (Lincoln Lab) (Kanatzadis)
ZT (T=300K) 1.6 0.3
Harman et al., Science (2003)
2.5
max
FIGURE OF MERIT (ZT)
Bi2Te3/Sb2Te3
2.0
Superlattices
(RTI)
1.5 Bi2Te3/Sb2Te3 Nano Bulk
Skutterudites S2σ (µW/cmK2) 40 50.9
Bi2Te3 alloy
1.0 (Fleurial) k (W/mK) 0.6 1.45
PbTe alloy
0.5 ZT (T=300K) 2.4 1.0
Si0.8Ge0.2 alloy Venkatasubramanian et al.,
Dresselhaus Nature, 2002.
0.0
1940 1960 1980 2000 2020
YEAR

10. Potential Applications
Transportation
Mechanical losses
In US,
9kJ
Mechanical losses Driving transportation
Exhaust 10kJ
Gasoline 9kJ uses ~26% of
6kJ Driving
100 kJ 10kJ Auxiliary total energy.
Gasoline 6kJ
30kJ 35kJ Auxiliary
100kJ10kJ 30kJ 10% energy
35kJ
conversion
10kJ
Parasitic efficiency
heat losses Coolant Exhaust = 26% increase
Parasitic
Exhaust in useful energy
heat losses Coolant
Residential
Entropy
Entropy
Oil or Losses
Oil or Thermal Power Heating
Heating In US, residential
Nat’l Gas Thermal Power
Nat’l Gas and commercial
TPV & TE Recovery
buildings consume
Refrigeration & &
Electrical Power Power
Electrical Refrigeration ~35% energy supply
Appliances
Appliances
Electricity
Electricity PV

11. Challenges and Opportunities
• Mass production of nanomaterials
• Energy systems: high heat flux
• Nanomaterials are trans-boundary
• Basic energy research leads to
breakthroughs
• Transports (molecular, continuum) are
crucial
• Inter-departmental collaborations