Nanoscience and our Energy Future

1. Nanoscience and our Energy Future • Present Primary Power Mix • Future Constraints Imposed by Sustainability • Theoretical and Practical Energy Potential of Various Renewables • Challenges to Exploit Carbon-Free Energy Economically on the Needed Scale Nathan S. Lewis, California Institute of Technology Division of Chemistry and Chemical Engineering Pasadena, CA 91125 http://nsl.caltech.edu

2. Mean Global Energy Consumption, 1998 Gas Hydro Renew Total: 12.8 TW U.S.: 3.3 TW (99 Quads)

3. 3E-1 Energy From Renewables, 1998 1E-1 1E-2 2E-3 TW 1.6E-3 1E-4 7E-5 5E-5 Elec Heat EtOH Wind Sol PV SolTh LowT Sol Hydro Geoth Marine Biomass

4. Today: Production Cost of Electricity (in the U.S. in 2002) 25-50 ¢ Cost, ¢/kW-hr 6-7 ¢ 5-7 ¢ 6-8 ¢ 2.3-5.0 ¢ 1-4 ¢

5. Energy Costs $0.05/kW-hr Europe Brazil www.undp.org/seed/eap/activities/wea

6. Energy Reserves Rsv=Reserves Res=Resources Reserves/(1998 Consumption/yr) Resource Base/(1998 Consumption/yr) Oil 40-78 51-151 Gas 68-176 207-590 Coal 224 2160

7. Conclusions • Abundant, Inexpensive Resource Base of Fossil Fuels • Renewables will not play a large role in primary power generation • unless/until: • technological/cost breakthroughs are achieved, or • unpriced externalities are introduced (e.g., environmentally • -driven carbon taxes)

8. Energy and Sustainability • “It’s hard to make predictions, especially about the future” • M. I. Hoffert et. al., Nature, 1998, 395, 881, “Energy Implications of Future Atmospheric Stabilization of CO2 Content • adapted from IPCC 92 Report: Leggett, J. et. al. in • Climate Change, The Supplementary Report to the • Scientific IPCC Assessment, 69-95, Cambridge Univ. • Press, 1992

9. Population Growth to 10 - 11 Billion People in 2050 Per Capita GDP Growth at 1.6% yr-1 Energy consumption per Unit of GDP declines at 1.0% yr -1

10. Total Primary Power vs Year 1990: 12 TW 2050: 28 TW

11. Carbon Intensity of Energy Mix M. I. Hoffert et. al., Nature, 1998, 395, 881

12. CO2 Emissions Data from Vostok Ice Core

13. Projected Carbon-Free Primary Power

14. Hoffert et al.’s Conclusions • “These results underscore the pitfalls of “wait and see”.” • Without policy incentives to overcome socioeconomic inertia, development of needed technologies will likely not occur soon enough to allow capitalization on a 10-30 TW scale by 2050 • “Researching, developing, and commercializing carbon-free primary power technologies capable of 10-30 TW by the mid-21st century could require efforts, perhaps international, pursued with the urgency of the Manhattan Project or the Apollo Space Program.”

15. Lewis’ Conclusions • If we need such large amounts of carbon-free power, then: • current pricing is not the driver for year 2050 primary energy supply • Hence, • Examine energy potential of various forms of renewable energy • Examine technologies and costs of various renewables • Examine impact on secondary power infrastructure and energy utilization

16. Sources of Carbon-Free Power • Nuclear (fission and fusion) • 10 TW = 10,000 new 1 GW reactors • i.e., a new reactor every other day for the next 50 years • 2.3 million tonnes proven reserves; 1 TW-hr requires 22 tonnes of U • Hence at 10 TW provides 1 year of energy • Terrestrial resource base provides 10 years of energy • Would need to mine U from seawater (700 x terrestrial resource base) • Carbon sequestration • Renewables

17. CO2 Burial: Saline Reservoirs 130 Gt total U.S. sequestration potential Global emissions 6 Gt/yr in 2002 Test sequestration projects 2002-2004 DOE, 1999

18. Geological Sequestration in the U.S. • Near sources (power plants, refineries, coal fields) • Near other infrastructure (pipelines) • Need sufficient storage capacity locally • Must be verifiable (populated areas problematic) DOE Vision & Goal: 1 Gt storage by 2025, 4 Gt by 2050

19. Biomass Solar Hydroelectric Wind Geothermal

20. Hydroelectric Gross: 4.6 TW Technically Feasible: 1.6 TW Economic: 0.9 TW Installed Capacity: 0.6 TW

21. Geothermal Mean flux at surface: 0.057 W/m2 Continental Total Potential: 11.6 TW

22. Wind 4% Utilization Class 3 and Above 2-3 TW

23. Biomass 50% of all cultivatible land: 7-10 TW

24. Solar: potential1.2x105 TW; practical 600 TW

25. Solar Land Area Requirements 3 TW

26. Solar Land Area Requirements 6 Boxes at 3.3 TW Each

27. U.S. Single Family Housing Roof Area • 7x107 detached single family homes in U.S. • ≈2000 sq ft/roof = 44ft x 44 ft = 13 m x 13 m = 180 m2/home • = 1.2x1010 m2 total roof area • Hence can (only) supply 0.25 TW, or ≈1/10th of 2000 U.S. Primary Energy Consumption

28. CO H O 2 2 2 e Sugar sc M H O 2 H O 2 O 2 Energy Conversion Strategies Fuel Light Electricity Fuels Electricity e sc M Semiconductor/Liquid Junctions Photosynthesis Photovoltaics

29. crystalline Si amorphous Si nano TiO2 CIS/CIGS CdTe Efficiency of Photovoltaic Devices 25 20 15 Efficiency (%) 10 5 2000 1980 1990 1970 1950 1960 Year Margolis and Kammen, Science 285, 690 (1999)

30. Cost/Efficiency of Photovoltaic Technology Costs are modules per peak W; installed is $5-10/W; $0.35-$1.5/kW-hr

31. Cost vs. Efficiency Tradeoff Efficiency µ (t/m)1/2 Small Grain And/or Polycrystalline Solids Large Grain Single Crystals d d Long d High t High Cost Long d Low t Lower Cost t decreases as grain size (and cost) decreases

32. Cost vs. Efficiency Tradeoff Efficiency µ (t/m)1/2 Ordered Crystalline Solids Disordered Organic Films d d Long d Low t Lower Cost Long d High t High Cost t decreases as material (and cost) decreases

33. Scientific Challenges • SOLAR ELECTRICITY GENERATION • Develop Disruptive Solar Technology: “Solar Paint” • Grain Boundary Passivation • Interpenetrating Networks while Mimimizing Recombination Losses Increase t Lower d

34. Nanocrystalline Titanium Dioxide • Particle Size ~ 15nm • Surface Area • is larger than single crystal • ~1000 times • No Quantum Size Effects • (large electron effective mass) • Different Electrochemistry • from single crystal semiconductors 35 nm TEM of nanostructured TiO2

35. Semiconductor Photoelectrochemistry nanocrystalline solar cell e- e- work i conducting glass metal film Red h S S* S+ Ox dye-sensitized nanocrystalline TiO2 B. O’Regan, M. Grätzel Nature1991, 353, 737

36. Nanotechnology Solar Cell Design

37. The Need to Produce Fuel “Power Park Concept” Fuel Production Distribution Storage

38. Photovoltaic + Electrolyzer System

39. Solar-Driven Photoelectrochemical Water Splitting

40. POWERING THE PLANET Caltech’s Center for Sustainable Energy Research (CSER) Harry Atwater, Harry Gray, Sossina Haile, Nathan Lewis, Jonas Peters Powering the Planet

41. Conversion Storage Utilization The Vision Electricity Photovoltaic and photolysis power plants H2O, CO2 Fuel: H2 or CH3OH Fuel cell power plant H2O, CO2 Electric power, heating

42. GaInP GaInP 2 2 n n h h = 1.9eV = 1.9eV GaAs GaAs n n h h = 1.42eV = 1.42eV InGaAsP InGaAsP n n h h = 1.05eV = 1.05eV e InGaAs InGaAs n n h h = 0.72eV = 0.72eV Si Substrate Si Substrate The Approaches Solar  Electric Chemical  Electric Solar  Chemical H3O+ ½H2 + H2O CB __S* __S+ S__ H S h = 2.5 eV ½O2 + H2O OH TiO2 O Pt Inorganic electrolytes: bare proton transport VB Photoelectrolysis: integrated energy conversion and fuel generation Extreme efficiency at moderate cost Catalysis: ultra highsurface area,nanoporousmaterials 100 nm Bio-inspired fuel generation Solar paint: grain boundary passivation Synergies: Catalysis, materials discovery, materials processing

43. Summary • Need for Additional Primary Energy is Apparent • Case for Significant (Daunting?) Carbon-Free Energy Seems Plausible • Scientific Challenges • Provide Disruptive Solar Technology: • Inexpensive conversion systems, effective storage systems • Provide the New Chemistry to Support an Evolving Mix in Fuels for Primary and Secondary Energy: • Multi-electron transfer reactions such as methane-to-methanol, direct methanol fuel cells, improved O2 fuel cell cathodes

44. Hydrogen vs Hydrocarbons • By essentially all measures, H2 is an inferior transportation fuel relative to liquid hydrocarbons • So, why? • Local air quality: 90% of the benefits can be obtained from clean diesel without a gross change in distribution and end-use infrastructure; no compelling need for H2 • Large scale CO2 sequestration: Must distribute either electrons or protons; compels H2 be the distributed fuel-based energy carrier • Renewable (sustainable) power: no compelling need for H2 to end user, e.g.: CO2+ H2 CH3OH DME other liquids

45. Hybrid Gasoline/Electric Hybrid Direct Methanol Fuel Cell/Electric Hydrogen Fuel Cell/Electric? Wind, Solar, Nuclear; Bio. CH4 to CH3OH “Disruptive” Solar CO2 CH3OH + (1/2) O2 H2O H2 + (1/2) O2 Primary vs. Secondary Power Transportation Power Primary Power

46. Challenges for the Chemical Sciences • CHEMICAL TRANSFORMATIONS • Methane Activation to Methanol: CH4 + (1/2)O2 = CH3OH • Direct Methanol Fuel Cell: CH3OH + H2O = CO2 + 6H+ + 6e- • CO2 (Photo)reduction to Methanol: CO2 + 6H+ +6e- = CH3OH • H2/O2 Fuel Cell: H2 = 2H+ + 2e-; O2 + 4 H+ + 4e- = 2H2O • (Photo)chemical Water Splitting: 2H+ + 2e- = H2; 2H2O = O2 + 4H+ + 4e- • Improved Oxygen Cathode; O2 + 4H+ + 4e- =2H2O