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 Photons  nm =0.1-10  m Phonons  =10-100 nm =1 nm Electrons  =10-100 nm =10-50 nm  ---Mean free path ---wavelength Molecules  nm =1 nm Increased surface area Interface and size effects

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 generation and water splitting Catalytic nanostructured hydrogen storage materials Radiation transport to maximize absorption Two phase flow Electrochemical transport Multiscale, multiphysics transport Mass transport Heat transfer (intake and release) Small scale thermodynamics Two phase flow Multiscale and multiphysics

7. Thermoelectrics Devices COLD SIDE HOT SIDE Power Generation I NP I I Cold Side Hot Side Diffusion Figure of Merit: Thermal Conductivity Electrical Conductivity Seebeck Coefficient Critical Challenges: Reduce phonon heat conduction while maintaining or enhancing electron transport ElectronPhonon Power Generation: T(hot)=500 C, T (cold)=50 C ZT=1, Efficiency = 8 % ZT=3, Efficiency =17 % ZT=5, Efficiency =22 % Refrigeration

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

9. State-of-the-Art in Thermoelectrics PbTe/PbSeTe S 2  (  W/cmK 2 ) 32 28 k (W/mK) 0.6 2.5 ZT (T=300K) 1.6 0.3 BulkNano Harman et al., Science (2003) Bi 2 Te 3 /Sb 2 Te 3 S 2  (  W/cmK 2 ) 40 50.9 k (W/mK) 0.6 1.45 ZT (T=300K) 2.4 1.0 BulkNano Venkatasubramanian et al., Nature, 2002. Bi 2 Te 3 alloy PbTe alloy Si 0.8 Ge 0.2 alloy Skutterudites (Fleurial) PbSeTe/PbTe Quantum-dot Superlattices (Lincoln Lab) Bi 2 Te 3 /Sb 2 Te 3 Superlattices (RTI) AgPb m SbTe 2+m (Kanatzadis) Dresselhaus

10. Gasoline 100 kJ 10kJ 30kJ35kJ Parasitic heat losses CoolantExhaust 9kJ 10kJ 6kJ Auxiliary Driving Mechanical losses Coolant Exhaust Gasoline 100kJ 10kJ 30kJ 35kJ 9kJ 10kJ 6kJ Auxiliary Driving Mechanical losses Parasitic heat losses Exhaust 10% energy conversion efficiency = 26% increase in useful energy In US, transportation uses ~26% of total energy. Heating Refrigeration & Appliances TPV & TE Recovery PV Electricity Oil or Nat’l Gas Entropy Thermal Power Electrical Power Heating Refrigeration & Appliances Losses Electricity Oil or Nat’l Gas Entropy Thermal Power Electrical Power Potential Applications Transportation In US, residential and commercial buildings consume ~35% energy supply Residential

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