Opportunities for Materials Science
in Energy, Sustainability, and Global
Stewardship
George M. Whitesides
Department of Chemistry and Chemical
Biology
Harvard
gwhitesides@gmwgroup.harvard.edu
Outline
• Introduction (from Geosynchronous Orbit)
• Production and/vs. Conservation
• Some energy production technologies
– Combustion of fossil fuel and CO2
management
– Nuclear
– Biomass
– Solar
– Wind
• Personal Perennial Technical Favorites
• Issues in Technology Transfer and Policy
Energy, Climate, Water,
Sustainability
Technology provides options to society
Energy
Wellbeing ≈
People
Options.
•Generate more energy
•Conserve the energy we now generate.
•Have fewer people
Constraints
• Energy and Climate
– Climate change may limit the combustion
of fossil fuel
• Energy and Water
– Water production may become a major use
of energy
• Energy and Nuclear
– Weapons proliferation
Scale and Units
• Energy: the ability to do work–
Joules (J)
• J = Volt·Coulomb
• Power: 1 W = 1 J s-1
• World: 14 TW = 14 x 1012 W =
3 x 1017 BTU/year
• United States usage = 3.3 TW
• Hoover Dam electricity
production = 2 GW
• China: +1 GW/week, coalburning
Some Systems Aspects of the Problem
• 14 TW (now) Æ 30 TW (2050)
• Energy, Power, Climate, Water, Sustainability are linked
• What counts is function and price (along several
dimensions), not energy or power.
• Only a part of the problem is technical
• Radical social change may be part of the
“solution/resolution”
• Other possible technical contributors: IT, biotechnology,
nanotechnology, catalysis, materials
• All plausible solutions are capital intensive; the world
economy is largely capitalist. What about social return?
• Developed and developing economies often in conflict
Risk-Discounted Cash Flow-The Standard
Capitalist Model
Profits
(per year)
Research Costs
(per year)
Total Cash Flow
Is there any economic model that
justifies long-term/non-product
related research in industry?
Warning
• This area is complicated: the answer you get
depends on the question you ask, and what
system/part of a system you are considering.
• There may be an objective truth scientifically,
but not societally.
• Everyone has opinions/prejudices.
• …including me.
Production of Energy: No Free Lunch
•
•
•
•
•
•
•
•
•
Hydrocarbons
Coal
Gas
Nuclear
Hydroelectric
Biomass
Geothermal
Wind
Solar
Climate Change:
CO2, NOx, CH4, SOx
Proliferation, Waste, U/Th Supply
NOx, Food, Water, Soil
Dilution, Efficiency
• H2 (from shift-gas reactions; electrolysis)
Conservation of Energy
• Tribology,
Corrosion, Wear
• New materials to
prevent resistive
heating losses in
power distribution
systems
• Lighting: compact
fluorescents, LEDs
Substantially more than 50
% of produced energy is
lost, somewhere.
Combustion of Carbon-Containing Fuels
• >80% of Energy derived from carbon fuels
– Petroleum (40.1%), natural gas (22.7%), coal (22.9%)
Light-duty vehicle: 16.7
Industrial: 9.5
Freight: 7.0
Aircraft: 3.4
Other*
14.2%
Coal
22.9%
Electricity generation: 20.8
Industrial: 2.0
Commerical: 0.1
Residential: 0.01
Petroleum
40.1%
Natural Gas
22.8%
Industrial: 8.0
Electricity generation: 6.0
Residential: 5.0
Commerical: 3.2
Freight: 0.6
*Hydroelectric (2.7), biomass (2.8), geothermal (0.31), wind (0.15), solar (0.006), nuclear (8.13)
Combustion of Carbon-Containing Fuels:
Examples of Materials Issues
• CO2 Management
• Catalysis
• Fuels (low sulfur diesel, Fischer-Tropsch-derived fuels)
• Emissions (NOx, SOx)
• High Temperature Materials
• Efficiency, NOx/SOx control
• Separations
• CH4/CO2; O2/N2; H2/CO/CO2/H2S; …
• Machinery
• Tribology, wear, corrosion
Internal Combustion of Hydrocarbons:
An Example of Tradeoffs
• CnH2n + O2 Æ CO2 + H2O
• Higher T
–
–
–
–
Greater Carnot efficiency
More demanding on materials
The basis for Diesel engines
More NOx
N2 + O2 Æ NOx
NOx is a pollutant (oxidant)
NOx is also a green house gas
• Higher T thus requires after-treatment
– …which lowers efficiency
Carbon Management
•
•
•
•
•
CO2 Sequestration (“minerals as materials”)
Carbon Trading Credits
CO2 Utilization
CO2 Separation
Biomass Production and Conversion
CO2 Utilization: The Chemistry of CO2 has
not been a hot topic
• Assume: Oxygen-fired coal plants Æ
relatively clean, hot CO2; then ?
• Sequestration: Geochemistry and long-term
fate?
• Photosynthesis
• Other chemistry (carbon source with
negative price)
Reinventing the Chain
CH3CH3
CH2=CH2
HOCH2CH2OH
?
CO2
“Geoengineering”
• Sulfuric Acid Sols
– Tambora (1815) and the “year without a summer”
• CO2 for control
– Inject CO2 into atmosphere for “feedback” climate
control
Nuclear
•
•
•
•
Regulatory Approval/Public Perception
Proliferation
Waste/Decommissioning
U/Th Supply
Photosynthesis
Conceptually some similarity to
semiconductor pn photovoltaic
cells: separate charge (“H-”, H+)
Biomass
• Biomass to ???
– Shift gas (for H2 and synthetic fuels synthesis)
– Ethanol
– Biodiesel
• Fertilizer (Haber Process is energy intensive)
N2 + H2 → NH3 → HNO3 → NH4+NO3-
• Topsoil (soil is a material, and a limited
resource)
• Biomaterials
CH3
O
BioPDO
HO
O
OH
Array of Photovoltaic Modules
Berkeley, CA: www.nrel.gov
Solar
•
•
•
•
•
Photovoltaics (inorganic or organic)
Solar Water Splitting
Furnaces (Solar Thermal)
Artificial Photosynthesis
(Biomass Production)
The Heterojunction Solar Cell
Band diagram of
charge-separated state
excitons
p-type
n-type cathode
material material
EF
EF
+
cathode
Charge transport, collection at electrodes
- - -+ ++
- +
-+ +
++
- ++
+ +
- anode
3
n-type
material
anode
cathode
Charge separation
+ -- + - - -+ +- + +- -+ ++- +
-+-++
anode
2
cathode
p-type
material
Light absorption, exciton migration
anode
1
-
Order Correlates with Performance in Photovoltaics:
Cost vs. Efficiency Tradeoff
NREL
Options for Energy Storage
•Pumped water
•Compressed Air
•Thermal Energy
•Batteries
•Flywheels
•Capacitors
•Superconducting
Magnets
•Redox Fuel Cells
Grand Coulee Dam
Columbia River, WA
Wind
Fuel Cells (and H2)
• Bypass Carnot thermo limitations (but have
others)
• Very materials intensive
• Fuel ? (H2, CH3OH)
– (H2: Generation? Transportation?
Storage?)
• High temperature (SOFC) materials?
– Can use hydrocarbons without reforming
• Catalysis – Design of new catalysts
Proton Exchange Membrane Fuel Cells
Nafion® Membranes
Anode: 2H2
4H+ + 4eCathode: O2 + 4H+ + 4e2H2O
Overall: 2H2 + O2
2H2O + energy
www.fuelcelltoday.com
Dupont
Supported Nanoparticles to Catalyze Reduction of O2 in
Proton Exchange Membrane Fuel Cells
O2 reduction is the rate-limiting step…
e-
H+
H+
O2
H+
H+
H2
…Catalyst: Pt nanoparticle on
mesoporous carbon support
e-
H+
H+
H2O
H+
H+
anode
2H2 Æ 4H+ + 4e-
H+
H+
cathode
O2 + 4H+ + 4eÆ 2H2O
Polymer membrane “electrolyte”
(doped perfluorocarbon)
Ferreira, et al. J. Electrochemical Soc.
2005, 152(11), A2256.
The Oxygen Electrode
Kinetics of cathode reaction are much slower than the anode reaction
and limit economic viability of low temperature fuel cells
Cathode reaction: 4e- + O2 + 4H+
Periodic trends in oxygen reduction activity
Pt is the best!
slow
2H2O
Alloying leads to oxygen reduction
activity enhancements
Pt3M single crystal surfaces
Pt3Co
oxygen binding energy
Volcano relationship between activity
and oxygen binding energy suggest
alloying improve activity
Nørskov et al. J. Phys. Chem. B 108 (2004) 17886
The Special Problem of H2
• Production:
– Electrolysis (nuclear or fossil)
– Shift gas (CHx + H2O Æ H2 + CO2)
– Future direct solar?
• Storage
– Hydrides? Pressure?
• Transportation or on-site generation?
• Platinum? Alloys?
Conservation
A few examples of materials in a very rich field:
• New materials to prevent resistive heating
losses in power distribution systems
(electrical, gas, ..)
• Materials for reduction of friction, wear
• Corrosion resistance
Efficient Use of Energy
spiral type compact fluorescent light bulb
Plasma Display
Diesel Fuel
http://www.de.nec.de/
Strategies for Materials Scientists in
Energy
• Try to solve problems relevant to
energy/sustainability involving materials.
• Work on what you were doing anyway, and
relate it to (or call it) “energy.”
• Join an ideological crusade around a
particular energy.
• Focus on technology transfer and startups
The Logic of University Research
• We have an energy/environmental problem
now.
• Urgency demands an immediate solution:
hence, engineering is the answer.
• Engineering is the application of existing
knowledge to the solution of practical
problems; science is the creation of
knowledge.
• …but what if the knowledge does not exist?
Research Universities: Some Generalities
• Energy/climate/water will be problems forever. Like
mortality.
• Universities must do long-term research: understanding
and radical invention.
-----------------------Energy Production:
Thermal (high T is good)
Electrochemistry (P = I2R = IV;
tradeoff between voltage
and current)
Sunlight is abundant but dilute
Rock, soil, and biomass are
materials (inter alia)
Energy Conservation
Light weight, strong,
corrosion resistant
Water, Climate, Sustainability
Profits
(per year)
Research Costs
(per year)
Total Cash Flow
University Policy
• Education in the systems approach
• Multidisciplinarity
• Emphasize long-term and radical research
(universities bring freedom to explore
different options very inexpensively)
• Design of career paths for energy scientists
and engineers (including unconventional—
industry, foreign, foundation—support).
• Define objectives of tech transfer (solve the
problem; jobs; money for the university?)
Perennial Personal Favorites
• Catalysis as materials science
• Materials with extreme properties: low
corrosion/friction, high temperature stability,
durability, low weight,
• Mobile electrons in matter: Superconductivity,
Band-gap Engineering, photon-electron
interconversions…
• Separations
• Biomimetic and biological materials
• Nanotechnology (catalysis, membranes,
solar…small dimensions)
• “Impossible materials”