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Energy Conversion

Nanostructure Architectures for Solar Energy Conversion. TiO 2. Au. Energy Conversion. Quantum Dot Solar Cells. Organized Hybrid Assemblies. Charge Transfer Processes. -. -. -. -. Prashant V. Kamat http://www.nd.edu/~pkamat. MOTIVATION FOR SOLAR ENERGY RESEARCH.

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Energy Conversion

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  1. Nanostructure Architectures for Solar Energy Conversion TiO2 Au Energy Conversion Quantum Dot Solar Cells Organized Hybrid Assemblies Charge Transfer Processes - - - - Prashant V. Kamat http://www.nd.edu/~pkamat

  2. MOTIVATION FOR SOLAR ENERGY RESEARCH Light Crude Oil (CL, NYMEX)Monthly Price Chart Increasing demand is driving oil prices higher http://politicalhumor.about.com

  3. Carbon Neutral Energy (fossil fuel in conjunction with carbon sequestration) -Need to find secure storage for 25 billion metric tons of CO2 produced annually (equal to the volume of 12500 km3 or volume of lake superior!) Nuclear Power -Requires construction of a new one-gigawatt-electric (1-GW) nuclear fission plant everyday for the next 50 years Renewable Energy Sources - hydroelectric resource 0.5 TW - from all tides & ocean currents 2 TW - geothermal integrated over all the land area 12 TW - globally extractable wind power 2-4 TW - solar energy striking the earth 120,000 TW !!! Possible Options for meeting the 10 TW- Clean Energy Challenge by 2050

  4. e hn Molecular linker CdSe C60 TiO2 n n n n TiO h h h h e e e e e C60 2 Pt Acceptor C60 e e e e e e e e e e Ag Ag Ag h h h h h h h h h h h h h h h TiO TiO TiO 2 2 2 ethanol ethanol ethanol ethanol products products products products e Our Research Focus Photoinduced electron transfer in light harvesting systems Donor- Acceptor Semiconductor-Sensitizer Semiconductor-Semiconductor Semiconductor-Metal Donor

  5. Researchers who make it possible in our group Graduate studentsPost-Docs/Visiting Scientists Brian Seger (Chem. Eng.) Yochiro Matsunaga Matt Baker (Physics) K. Vinodgopal David Becker (Chem. Eng.) Julie Peller Kevin Tvrdy (Chemistry) Clifton Harris (Chemistry) Undergraduate students Pat Brown Meghan Jebb Sahib Hashimi Chris Beesley Recent Graduates Dr. Julie Peller –CHEM ‘03 (Faculty at IUN) Dr. Roxana Nicolaescu – CHEM ‘04 (Scientist at Serim) Dr. V Subramanian – CHEM ‘04 (Faculty, U. Nevada) Dr. Istvan Robel – Physics ’07 (Argonne National Lab.) Summer 2007

  6. e e h h h e hn Ag O O TiO2 S S reactant products S S S S S S S S S S O O O O O O O O O O Properties Design & Synthesis Electron storage, transport and interfacial processes Molecular assemblies, composites & hybrid systems Applications Catalysis, Photovoltaics, Fuel Cells, Sensors

  7. Hydrogen Evolution rates for various Photocatalysts (ml/hr) Pt/TiO2 7.7 Pd/TiO2 6.7 Rh/TiO2 2.8 Ru/TiO2 0.2 Sn/TiO2 0.2 Ni/TiO2 0.1 TiO2 <0.1 – CB – e 2H+ t h t + hn + 4OH- VB Issues: 2H2O+ O2 What about gold and other noble metals? - Explore size dependent properties of nanometals and alloys How to extend the response into the visible? - Design new photocatalysts and composites How to improve the photocatalytic efficiency? -Understand the charge transfer processes at the interface Toshima, J. Phys. Chem. 1985, 89, 1902 H2 2H+ Pt 1. Semiconductor Assisted Catalysis

  8. (b) (c) (c) (a) 5 nm a b 10 nm 5 nm 10 nm No Au 8 nm Au 5 nm Au 3 nm Au Effect of Gold Particle Size on the Catalytic Reduction Efficiency of TiO2 particles Vaidyanathan, Wolf, Kamat J. Am. Chem. Soc., 2004, 126, 4943-4950

  9. 2. Quantum Dot Solar Cells Tunable band edge Offers the possibility to harvest light energy over a wide range of visible-ir light with selectivity Hot carrier injection from higher excited state (minimizing energy loss during thermalization of excited state) Multiple carrier generation solar cells. Utilization of high energy photon to multiple electron-hole pairs

  10. 3.0nm 2.3nm 3.7nm 2.6nm

  11. CB R O VB TiO2 CdSe e e e h h h Tuning the Photoresponse of Quantum Dot Solar Cells

  12. 3. Carbon nanostructures as conduits to transport charge carriers c …..towards achieving ordered assemblies on electrode surface Pt • Advantages • High surface area • Good electronic conductivity, excellent chemical and electrochemical stability • Good mechanical strength • Goal • Effective utilization of carbon nanostructures for improving the performance of energy conversion devices • To develop electrode assembly with CNT supports • Improve the performance of light harvesting assemblies • Facilitate charge collection and transport in nanostructured assemblies

  13. m 1 m Photocurrent Generation CFE/TiO2 versus CFE/SWCNT –TiO2 UV light CFE/TiO2 and CFE/SWCNT/TiO2 films were tested for their photoelectrochemical response with UV irradiation (l>300 nm)

  14. hn e O/R EF EF O/R h e Stepwise charging of semiconductor nanoparticle followed by equilibration with SWCNT and redox couple facilitates determination of apparent Fermi level of the composite system E*f (TiO2)= Efb = E0O/R + 0.059 log ([O]/[R]) EF Charge Equilibration in SWCNT-Semiconductor Composite Kongkanand, A.; Kamat, P.V., Electron Storage in Single Wall Carbon Nanotubes. Fermi Level Equilibration in Semiconductor–SWCNT Suspensions. ACS Nano, 2007. 1, 13-21

  15. September 16, 2006 ……The third technique, being developed by Prashant Kamat of the University of Notre Dame, Indiana, and his colleagues, uses that fashionable scientific tool, the carbon nanotube. This is a cylinder composed solely of carbon atoms, and one of its properties is good electrical conductivity. In effect, nanotubes act as wires a few billionths of a metre in diameter. … Carbon Nanotubes could boost efficiency of solar cells -- Researchers at the University of Notre Dame in Indiana say they have found a new and promising way to boost the efficiency of solar cells. In preliminary studies, carbon nanotubes that were engineered into the architecture of semiconductor solar cells. In some cases, the efficiency of solar cells jumped from 5 percent to 10 percent in the presence of carbon nanotubes, according to Prashant Kamat, Ph.D., a professor of chemistry at the University.

  16. Where do we go from here?

  17. CdSe CdSe 2 TiO 200nm 2 TiO2 TiO 2 TiO 500nm OTE/TiO2 nanoparticles Ti/TiO2 nanotubes

  18. Current & Future Research Rainbow Solar Cells

  19. A e e h hn e e h CB B CB 200 nm Eg1 Eg2 Stacked-Cup Carbon Nanotubes for Photoelectrochemical Solar Cells, Angew Chem. Int. Ed. 2005, 45, 755-759 VB VB 50 nm Organized light harvesting assembly using carbon nanostructures Charge collection Charge separation

  20. What will the future hold? Over the last twenty years, the per-kWh price of photovoltaics has dropped from about $500 to nearly $5; think of what the next twenty years will bring.

  21. DOMER RUN 2006

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