1) The document discusses artificial light harvesting systems as a solution for sustainable energy and fuel. It outlines the context of climate change due to greenhouse gases and the need for renewable energy sources like solar. 2) Natural photosynthesis is then described as harvesting light via chlorophyll to convert carbon dioxide and water into glucose and oxygen. Various components of the photosynthetic system are highlighted. 3) The document then reviews efforts to create artificial photosynthesis systems, including the use of antenna/reaction center complexes, photoelectrochemical cells, and dye-sensitized solar cells. While progress has been made, fully functional systems have not yet been achieved.

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 ......