A promise for renewable energy..

1. Artificial Photosynthesis
A promise for
Renewable Energy
Komal Lagu
Department of Mechanical Engineering
Cummins College of Engineering for Women
Pune

2. Artificial Photosynthesis
Biomimicry
 Natural processes replicated using synthetic
materials to achieve outputs similar to those
achieved by natural methods
 Inherently a step closer to sustainability
 Applications in industrial optimization, structural
engineering, architecture, chemical engineering,
nanotechnology, display technology, electronics
and energy

3. Artificial Photosynthesis
Applications of Biomimicry

4. Artificial Photosynthesis
Major breakthrough in
Biomimicry
Imitation of photosynthesis, to harness solar
energy and to store the products of the
process

5. Artificial Photosynthesis
Photosynthesis
 It is one of the basic natural processes of energy
conversion
 Conversion of atmospheric carbon dioxide and
water into oxygen and glucose in the presence of
sunlight and a catalyst.

6. Artificial Photosynthesis
Natural Photosynthesis
 Takes place in 2 steps Photosystem II and
Photosystem I
 PS II : solar energy splits water (H2O) into 4
protons (H+), 4 electrons and 1 oxygen molecule
(O2) which is released into the atmosphere.
Chlorophyll acts as catalyst.
 PS I : Energy of protons and electrons used to
convert NADP (nicotinamide adenine
dinucleotide phosphate) to NADPH (reduced
form). This is a primary step to convert carbon
from carbon dioxide into glucose.

7. Artificial Photosynthesis

8. Artificial Photosynthesis
Turning over a new
leaf….

9. Artificial Photosynthesis
Artificial Photosynthesis
 Imitation of the process of photosynthesis in
plants
 Aims at creating hydrogen and oxygen which can be
used to power fuel cells or create a hydrocarbon as a
fuel for transport and industries.
 Uses synthetic strata containing an inorganic catalyst
acting as a “leaf” to produce hydrogen and oxygen or
hydrocarbon in presence of water and sunlight.

10. Artificial Photosynthesis
 Water can be split to produce hydrogen and
oxygen by using electricity, by hydrolysis
 Complex process , requires specific conditions
and a lot of electricity.
 It is more efficient but far more costly than
artificial photosynthesis.
 Key in making artificial photosynthesis work is
to develop a catalyst working as chlorophyll

11. Artificial Photosynthesis
Classification of Photocatalyst
 Photocatalysts : used to aid the light driven
reactions like evolution of oxygen, hydrogen
and reduction of carbon dioxide.
• Hydrogen catalysts
• Oxygen catalysts
• Photosensitizers:
• Carbon dioxide reducing catalysts

12. Artificial Photosynthesis
The Artificial leaf
 Researchers at the Massachusetts Institute of
Technology have developed a device “artificial leaf”
to mimic photosynthesis.
 This device is a solar cell made of silicon.
 Catalysts made from earth abundant elements
homogeneously deposited on the two sides of the
silicon substrate.
 When immersed in water, under incident sunlight,
the artificial leaf produces gaseous hydrogen and
oxygen.

13. Artificial Photosynthesis
Constituents
 Stainless steel plate
 Silicon substrate
• The main body of the leaf
• Silicon is commonly used in electronics and photo voltaic
applications
 Oxygen evolving catalyst
• A cobalt catalyst is used as an Oxygen evolving complex (OEC)
• deposited on the substrate by an electrochemical reaction.

14. Artificial Photosynthesis
 Hydrogen evolving catalyst
• Ternary alloy of Nickel, Molybdenum and Zinc.
• bonded to the cell on as a nickel mesh wired to
substrate
• deposited directly on the substrate (wireless)
 Electrolyte
• The artificial leaf is placed in an open container of
water containing a borate electrolyte

15. Artificial Photosynthesis
Construction
 Stainless steel plate of the size of a playing card is
base
 Amorphous Silicon-Germanium alloy junction and
amorphous silicon on the stainless steel plate.
 The lit side of the plate : layer of Indium-Tin Oxide.
 The Cobalt-OEC is deposited the Indium-Tin Oxide
layer.
 Nickel-Molybdenum-Zinc alloy is deposited on other
side
 This plate is then submerged in a container of water
and illuminated by sunlight

16. Artificial Photosynthesis

17. Artificial Photosynthesis

18. Artificial Photosynthesis
Working
 Sunlight illuminates the artificial leaf, its energy
absorbed by the semiconductor.
 Electrons in the valence band are excited and move
to the conduction band, hole is generated in the
valence band.
 Holes generated are used by the Cobalt-OEC to
produce oxygen molecules.
 OEC brings together two oxygen atoms and removes
an electron from each to satisfy the holes.
 Oxygen atoms become unstable and form an oxygen
molecule.

19. Artificial Photosynthesis
 Electrons and protons are released as a
byproduct of the OEC reaction.
 They are transferred to the other side of the
leaf to the hydrogen evolving NiMoZn catalysts
 Hydrogen is evolved.
 The Hydrogen so formed is used to power Fuel
cell.
 Fuel cells are energy conversion devices that
can efficiently capture and use the power of
hydrogen to produce electricity.

20. Artificial Photosynthesis

21. Artificial Photosynthesis
Efficiency
 Solar cells constituted of earth abundant and cheap
materials :2-5% efficient.
 A wired version of the artificial leaf 4.7% efficient.
 A wireless version of the artificial leaf 2.5% efficient.
 Wireless artificial leaf more attractive and
economically viable option attributes :mobility, and
less cost.
 No restriction on the size

22. Artificial Photosynthesis
Challenges
 Current cost of producing Hydrogen approx
$6/kg.
 One gallon of gasoline contains almost 1
kilogram of hydrogen.
 Cost of gasoline in USA is about $4/galleon.
 The task: to bring down the cost of artificial
leaves to produce a kilo of hydrogen at about
US$ 3 which is half the current estimated price

23. Artificial Photosynthesis
 Use of silicon for long term stability of the
system
 The efficiency of wired and wireless artificial
leaves also needs to be improved for better
economic and commercial viability
 To take the artificial leaf beyond prototype
testing level

24. Artificial Photosynthesis
Commercialization
 Sun Catalytix USA based company founded by
Dr Daniel G. Nocera, working on artificial
photosynthesis
 Working to develop energy storage and
renewable fuel technology
 Currently the artificial leaf developed by
scientists is at prototype testing stage
 Tata group is an investor in Sun Catalytix for
the research, development and future
production of this upcoming technology.

25. Artificial Photosynthesis
 Commercial use of artificial leaves will make
countries like India which have a great
potential for renewable energy practically
energy independent.
 The use of artificial photosynthesis: a
renewable and personalized energy source
definite path breaker on the course of
achieving sustainable development.

26. Thank You !