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  • 1. Mohammad A. Halim The 18th Chemistry Colloquium Contest’2011 Artificial Light Harvesting: Solution for Sustainable Energy and Fuel
  • 2. Our Common Future Sustainable ....... “ ...that meets the needs of the present without compromising the ability of future generations to meet their own needs.... ” Brundtland, G. (Ed.), Our Common Future, Oxford Uni. Press., 1987. 2
  • 3. Context Leif and Sharon, Acc. Chem. Res. 2009, 42, 1859-1860. IPCC(2007).... “ Warming in climate systems is unequivocal ” Environ. threat due to GHGs and geo-political problem 3 Major challenge is to develop renewable energy sources One hour solar energy can be used in one year Need to harvest less than 0.02% solar energy 34% 27% 23% 6% 10% Oil Coal Natural Gas Nuclear Renewable Source: Energy Outlook, 2010
  • 4. Photosynthesis 6CO2 + 6H2O C6H 12O6 + 6O2 Light Chlorophyll 4 Zhou et. al. Adv. Mater. 2010, 22, 951-956.
  • 5. Photosynthetic Pigments Beta-Carotene 5 Chlorophyll Paul May, http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm 430 453 662 642 451 470
  • 6. Photosynthesis 6 Stochel et. al. Bioinorganic Photochemistry, Wiley, 2009. 6CO2 + 6H2O C6H 12O6 + 6O2 Light Chlorophyll
  • 7. PDB ID: 2AXT 7 Bacterial Photosystem Loll et. al. Nature 2005, 438, 1040-1044. Hu et. al. PNAS, 1998, 95, 5935-5941. Koepke et. al. Structure, 1996, 4, 581-597. Antenna/RC
  • 8. 8 Artificial Photosynthesis Sunlight to electric power H2 fuel from water by using hydrogenage or Pt Carbon-based fuels by reduction of CO2 Antenna/RC complexes to harvest light Charge-separated systems Catalysts for water oxidation But no real systems yet exists, progress on necessary components Scope for Energy and Fuel Generation Basic Components Gust et. al. Acc. Chem. Res. 2009, 42, 1890-1898.
  • 9. 9 Antenna/RC Complex Zn-based porphyrin and Ru-based polypyridyl complexes are frequently used as A/RC complex  similar properties like chlorophyll arrays in plants  high molar absorption coefficients  fast energy/e- transfer to other components Obvious candidate for LHAC are porphyrin arrays Konrad et. al. Chem. Rev. 2005, 105, 2647-2694.  Lifetime 380 ns  Product Yield 58%  Quantum Yield 24% Imahori et. al. JACS, 2001, 123, 6617-6628. Grätzel, M, J. Photochem. Photobio. C 2003, 4, 145-153.
  • 10. 10 Antenna/RC Complexes Gust et. al. Acc. Chem. Res. 2009, 42, 1890-1898. BPEA, 450 nm (2.8 ns) BDPY, 513 nm, 260ps ZTP, 418, 557,598 nm . BPEA BDPY
  • 11. 11 Photoelectrochemical Cell
  • 12. 12 Dye-Sensitized Solar Cell (DSC) DSCs received great attention as a low-cost alternative to silicon-based Two types of cells i) regenerative ii) photosynthetic Type I converts light to electric power The type II convert light to H2 fuel Grätzel, M. Nature, 2001, 414, 338-344. Advantage Disadvantage Low cost materials Slightly lower efficiency No elaborate apparatus Breakdown of the dye Work in low light condition Band gap slightly larger than Si High price/performance ratio Liquid electrode can leak M. Grätzel
  • 13. Sensitizing Dye TiO2 film on FTOElectrolyte 3I-/I3 - Redox Couple Dye-Sensitized Solar Cell (DSC) (20 nm) Grätzel, M. Inorg. Chem. 2005, 44, 6841-6851. 13
  • 14. 14 Operation Principle of DSC Grätzel, M. Inorg. Chem. 2005, 44, 6841-6851. Sensitizer (S) excitation by light Electron injection to the conduction band of TiO2 Recapture of the CB electrons by 3I-/I3 - to regenerate the S+ http://esamultimedia.esa.int/images/science_on_stage/IT_Giambelluca_Gratzel_cell_energia.swf
  • 15. 15 The incident photon to current efficiency Performance of DSSC Grätzel, M. Inorg. Chem. 2005, 44, 6841-6851. Overall Conversion Efficiency Iph = Photocurrent density Voc = Open-current photovoltage ff = Fill factor of cell Is = Intensity of incident current
  • 16. 16 IrO2.nH2O act as a water oxidation catalyst QE is 0.9% due to slow e- transfer from IrO2.nH2O to the dye Also back e- transfer from TiO2 to the dye is not effective Hydrogen Fuel Cell Justin et. al. JACS, 2009, 131, 926-927. Ru-complex act as a dye and molecular bridge Modified ps/ns
  • 17. 17 Hydrogen Fuel Cell Porphyrin sensitized nanoparticle TiO2 supported by fluorine- doped tin(IV) oxide (FTO) act as photoanode Pt and carbon felt/CaHydA (FeFe hydrogenage) act as cathode NADH used as a sacrificial electron donor Michael et. al. JACS, 2008, 130, 2015-2022. Average H2 production rates over an ~60-min illumination period  23.4 nmol H2 min-1 for carbon felt/ CaHydA  19.8 nmol H2 min-1 for platinum
  • 18. Epilogue 18 Natural photosynthesis process is highly complex and tough to mimic entirely Zn-porphyrin and Ru-polypyridyl frequently used as dye Ru-dye showed better performance in DSC and 11.18% efficient More studies need to develop dye, electrolyte and long-lasting cell Prospect of hydrogen fuel is promising but still in laboratory scale The Solar to Fuel and Back Again Symposium-2009 Imperial College, London “If the leaf can do it we can do it even better” “Nature took 2.7 billion years and we only spent 40 years”
  • 19. 19 “Only Strong Passion Speeds up into the Success” “Saying” in Sanskrit....... Thanks ......