Artificial Photosynthesis A promise for Renewable Energy Komal Lagu Department of Mechanical Engineering Cummins College of Engineering for Women Pune
Artificial PhotosynthesisBiomimicry 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
Artificial PhotosynthesisApplications of Biomimicry
Artificial PhotosynthesisMajor breakthrough inBiomimicryImitation of photosynthesis, to harness solarenergy and to store the products of theprocess
Artificial PhotosynthesisPhotosynthesis 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.
Artificial PhotosynthesisNatural 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.
Artificial PhotosynthesisTurning over a newleaf….
Artificial PhotosynthesisArtificial 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.
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
Artificial PhotosynthesisClassification 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
Artificial PhotosynthesisThe 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.
Artificial PhotosynthesisConstituents 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.
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
Artificial PhotosynthesisConstruction 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
Artificial PhotosynthesisWorking 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.
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.
Artificial PhotosynthesisEfficiency 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
Artificial PhotosynthesisChallenges 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
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
Artificial PhotosynthesisCommercialization 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.
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.