Energy and Nanotechnology - MIT

Motivati on Energy and Nanotechnology Gang Chen Rohsenow Heat and Mass Transfer Laboratory Mechanical Engineering Department Massachusetts Institute of Technology Cambridge, MA 02139 Sources http://www.sc.doe.gov Nano for Energy Increased surface area Interface and size effects Molecules nm =1 nm Photons nm =0.1-10 m ---Mean free path ---wavelength Electrons

=10-100 nm =10-50 nm Phonons =10-100 nm =1 nm 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 Examples Grtzel cell for photovoltaic generation and water splitting Radiation transport to maximize absorption Two phase flow Electrochemical transport Multiscale, multiphysics transport

Catalytic nanostructured hydrogen storage materials Mass transport Heat transfer (intake and release) Small scale thermodynamics Two phase flow Multiscale and multiphysics Thermoelectrics Devices I I I N P Diffusion Hot Side Cold Side

Power Generation Figure of Merit: Electrical Conductivity ZT Seebeck Coefficient 2 S T ke kp Electron Phonon Thermal Conductivity COLD SIDE Media Clip HOT SIDE Refrigeration Power Generation: T(hot)=500 C, T (cold)=50 C ZT=1, Efficiency = 8 % ZT=3, Efficiency =17 %

ZT=5, Efficiency =22 % Critical Challenges: Reduce phonon heat conduction while maintaining or enhancing electron transport Nanoscale Effects for Thermoelectrics Interfaces that Scatter Phonons but not Electrons Electrons =10-100 nm =10-50 nm Phonons =10-100 nm =1 nm Electron Molecular Dynamics (Freund) Phonon State-of-the-Art in Thermoelectrics FIGURE OF MERIT (ZT) max 3.0

PbTe/PbSeTe Nano PbSeTe/PbTe Quantum-dot Superlattices (Lincoln Lab) S2 (W/cmK2) k (W/mK) AgPbmSbTe2+m (Kanatzadis) 1.5 1.0 Bi2Te3/Sb2Te3 Superlattices (RTI) Bi2Te3 alloy PbTe alloy 0.5 0.0 1940 Si0.8Ge0.2 alloy 1960

1980 YEAR Skutterudites (Fleurial) Dresselhaus 2000 28 2.5 ZT (T=300K) 1.6 0.3 Harman et al., Science (2003) 2.5 2.0 32 0.6 Bulk 2020 Bi2Te3/Sb2Te3

Nano Bulk S2 (W/cmK2) k (W/mK) 40 0.6 50.9 1.45 ZT (T=300K) 2.4 1.0 Venkatasubramanian et al., Nature, 2002. Potential Applications Transportation Mechanical losses 9kJ Exhaust Gasoline 100 kJ

Gasoline 100kJ10kJ Mechanical losses 10kJ 9kJ 30kJ 30kJ 6kJ 10kJ 35kJ 35kJ 6kJ Driving Driving Auxiliary Auxiliary 10kJ Parasitic heat losses Coolant Parasitic heat losses Coolant

Oil or Oil or Natl Gas Natl Gas Exhaust Exhaust Entropy Entropy Losses Thermal Heating Thermal PowerPower Heating TPV & TE Recovery Refrigeration Refrigeration & & Electrical Electrical Power Power Appliances Appliances Electricity Electricity PV

In US, transportation uses ~26% of total energy. 10% energy conversion efficiency = 26% increase in useful energy Residential In US, residential and commercial buildings consume ~35% energy supply 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