Mohammad A. Halim

The 18th Chemistry Colloquium Contest’2011

Artificial Light Harvesting: Solution for Sustainable Energy and Fuel

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.

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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

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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%11%

OilCoalNatural GasNuclearRenewable

Source: Energy Outlook, 2010

Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2 Light

Chlorophyll

4Zhou et. al. Adv. Mater. 2010, 22, 951-956.

Photosynthetic Pigments

Beta-Carotene

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Chlorophyll

Paul May, http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm

430453

662

642

451470

Photosynthesis

6Stochel et. al. Bioinorganic Photochemistry, Wiley, 2009.

6CO2 + 6H2O C6H12O6 + 6O2 Light

Chlorophyll

PDB ID: 2AXT

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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

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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.

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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.

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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

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Photoelectrochemical Cell

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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 powerThe 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

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

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Operation Principle of DSC

Grätzel, M. Inorg. Chem. 2005, 44, 6841-6851.

Sensitizer (S) excitation by lightElectron 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

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The incident photon to current efficiency

Performance of DSSC

Grätzel, M. Inorg. Chem. 2005, 44, 6841-6851.

Overall Conversion Efficiency

Iph = Photocurrent densityVoc = Open-current photovoltageff = Fill factor of cellIs = Intensity of incident current

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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

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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

Epilogue

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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”

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তী�বং�সং�বেবংগা�নং�আসংনং�

“Only Strong Passion Speeds up into the Success”

“Saying” in Sanskrit.......

Thanks ......