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Artificial Photosynthesis

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Ashton Drollinger

on 21 August 2012

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Transcript of Artificial Photosynthesis

Artificial Photosynthesis By: Chase Corley, Zachary Ralston,
Ashton Drollinger, Migel Segoviano, Luke Ellis, Brittany Smedley, Tim Erickson, Farrar Stewart Current Employed ResearchTechniques Joint Center for Artificial Photosynthesis (JCAP) was given $122 million over five years by the DOE.

JCAP is led by Caltech and many other California based laboratories and universities.

Designing highly efficient, non-biological, molecular-level energy conversion “machines” that generate fuels directly from sunlight, water, and carbon dioxide

Goal is to demonstrate a scalable and cost-effective solar fuels generator that, without use of rare materials or wires, robustly produces fuel from the sun 10 times more efficiently than typical current crops

Focus on the construction of light absorbers, catalysts, membranes, and linkers Light absorbers using Earth-abundant elements

Catalysts to drive the oxidation of water and reduction of carbon dioxide to energyrich fuels

Photoelectrochemical membrane layers that provide ionic pathways and good optical and light-scattering properties, while remaining impermeable to the product fuels and to oxygen

Linkers that couple light absorbers and catalysts for the optimal control of the rate, yield, and energetics of charge carrier flow at the nanoscale How it works An upper membrane absorbs light, CO2, and water and would allow oxygen to escape.

An inner membrane catalyzes reactions with customized molecules to produce fuel.

The base layer will wick away fuel to collectors. Topics Covered Overview of Artificial Photosynthesis
Current Research Underway
Research Techniques
Advantages, Disadvantages and Efficiency
Potential Global Impact What is Artificial Photosynthesis? Artificial Photosynthesis is a chemical process that replicates the natural process of photosynthesis using sunlight and water to split water molecules into hydrogen and oxygen.

Artificial Photosynthesis also refers to any scheme for capturing and storing energy from the sunlight in the chemical bonds of a solar fuel. Why Artificial Photosynthesis? Sunlight is the world’s largest source of carbon-neutral power. In one hour, more energy from the sun strikes the Earth than all the energy consumed by humans in a year. Yet, solar energy, in the form of sustainable biomass, provides less than 1.5% of humanity’s energy needs, and solar panels contribute a mere 0.1% of electricity consumption.

Artificial Photosynthesis deserves urgent support as we are nearing the end of our current use of stored photosynthetic products. There are several main components required for the artificial photosynthesis reaction to work. 1. Light Absorbers
Use photochemically stable and Earth-abundant elements to provide the needed voltage and current density for fuel formation.
2. Catalysts
To drive fuel producing reactions such as H20 oxidation and CO2 reduction.
3. Membranes
To separate the reactants and products and provide a physical matrix that supports the whole process.
4. Linkers
The design of the system must be able to efficiently couple light absorbers and catalysts for optimal control at the nanoscale level to for maximum conversion of solar energy to fuel. What does Artificial Photosynthesis produce? Artificial Photosynthesis main technology uses photocatalytic water splitting to split water molecules into hydrogen and oxygen which can be feed into a fuel cell to provide electricity.

Light Driven Carbon Reduction uses sunlight to convert the greenhouse gas CO2 into higher energy products. Current Research Triad Assembly D -Water Oxidizing Catalyst
Splits water molecules and donates electrons to the photosensitizer

P – Photosensitizer
Transfers electrons to the HEC when hit by light

A – Hydrogen Evolving Catalyst
Produces hydrogen gas from protons and electrons Water Oxidizing Catalyst Naturally done by photosystem II
Manganese-calcium cluster
Non-catalyst reaction is endothermic
At least 2500 K
Ruthenium complexes
High valence states
Both catalyst and photosensitizer
Metal Oxides
Low turnover frequency
Slow electron transfer rate 2 H2O → O2 + 4 H+ Photosensitizer Naturally chlorophylls
Artificial pigments
Ruthenium polypyridine complexes
Efficient and long-lived
Metal-free organic complexes
Pyrrole rings Hydrogen Catalyst
enzymes that can either reduce protons to molecular hydrogen or oxidize hydrogen to protons and electrons.
Nickel-iron and iron-iron hydrogenases have been synthesized mimicking the structure of the active site.
Synthesized catalysts
include structural H-cluster models, a dirhodium photocatalyst, and cobalt catalysts. Simplest solar fuel to synthesis hydride anion

2 e− + 2 H+ H+ + H− H2 Light-driven Methodologies Under Development PECs are a kind of solar cell that produce electrical energy from light. They can produce energy in the form of electricity or by producing hydrogen in a similar process like water electrolysis.

“The goal of this research is to develop a stable, cost effective, photoelectrochemical-based system that will split water using sunlight as the only energy input.” -Turner Photo-Electrochemical Cells Photogeneration Cell Dye-sensitized solar cell Ways It Can Work PECs convert light energy into electricity in a cell usually through two electrodes. A H-cluster FeFe hydrogenase model compound covalently linked to a ruthenium photosensitizer. The ruthenium complex absorbs light and transduces its energy to the iron compound, which can then reduce protons to H2. Hydrogen-producing artificial systems NADP+/NADPH coenzyme-inspired catalyst In natural photosynthesis the NADP+ coenzyme is reducible to NADPH through binding of a proton and two electrons. The coenzyme is recyclable in a natural photosynthetic cycle, but this process is yet to be artificially replicated.

Current goal is to obtain a NADPH-inspired catalyst capable of recreating the natural cyclic process. http://www.nrel.gov/hydrogen/pdfs/41568.pdf
"In Vitro Hydrogen Production-using Energy from the Sun." - Physical Chemistry Chemical Physics (RSC Publishing). Web. 12 Apr. 2012. <http://pubs.rsc.org/en/Content/ArticleLanding/2011/CP/c0cp01163k>.
Berger, Michael. "Nanotechnology Artificial Leaves for Hydrogen Production." 18 Mar. 2010. Web. 12 Apr. 2012.
Andreiadis, E. S., Chavarot-Kerlidou, M., Fontecave, M. and Artero, V. (2011), Artificial Photosynthesis: From Molecular Catalysts for Light-driven Water Splitting to Photoelectrochemical Cells. Photochemistry and Photobiology, 87: 946–964. doi: 10.1111/j.1751-1097.2011.00966.x
Wang, H.; Deutsch, T.; Turner, J. A. A. (2008). "Direct Water Splitting Under Visible Light with a Nanostructured Photoanode and GaInP2 Photocathode". ECS Transactions. 6. pp. 37. doi:10.1149/1.2832397
Joint Center for Artificial Photosynthesis. California Institute of Technology, 2012. Web. 12 April 2012. <http://solarfuelshub.org>.
http://harlemchildrensociety.org/pdf/students/Narciso_Correa/Applicability%20of%20Photocatalytic%20Water%20Splitting.pdf Photobiological Production of Fuels Hydrogen Production Terrestrial plants are not capable of any photoproduction of hydrogen.

Cyanobacteria are able to evolve hydrogen using the enzyme nitrogenase.

Many microalgae and cyanobacteria can synthesize hydrogenases that can reduce protons to gaseous hydrogen. Hydrogen Production from Nitrogenase Proton-reducing activity in the absence of N2, and actively evolve H2 if provided with reductant and ATP in the absence of nitrogen.

Each electron requires 2 ATP molecules

Requires 50 atm of pressure

Very sensitive to oxygen Hydrogen Production from Hydrogenases Cyanobacteria and many eukaryotic algae possess at least one hydrogenase able to catalyze the reaction.
-2H+ + 2e- = H2

Many organisms possess both “uptake” hydrogenases and “bidirectional” hydrogenases.

Very sensitive oxygen

Do not require ATP Efficiency Achieve commercial success by the use of solar photons.

Better than bioethanol, biodiesel, or biomass gassification. Integrated System Project This project aims at developing the photo-bioreactor technology for industrial scale production of hydrogen fuel and mitigation of carbon dioxide.

It offers a cheap, efficient, scalable, autonomous, and reliable system for producing hydrogen from microbial consumption of carbon dioxide and light absorption. An integrated system where the photobiological hydrogen production takes place in light transparent panels arranged in a space radiator configuration to maximize the light perception area. Anabeana variabilis
-High hydrogen production capacity in the absence of nitrogen

-Good carbon dioxide consumer

-Approximately 5mm in diameter and 100mm long Filamentous, heterocystous cyanobacteria Their genome is sequenced. Efficiency Comparison One way to evaluate photosynthetic efficiency is in terms of energy released in combustion of biomass/time*solar irradiance

This assumes perfect access to carbon sources and that an equal amount of energy is harvested from an equivalent amount of biomass in a combustion event Average plants get 1% efficiency, bioreactors as high as 3

The main limiting factor is that plants use chlorophyll to absorb light

Light energy comes at different wavelengths

Chlorophyll b and a are present in most plants and absorb respective wavelengths of 650-700 and 400-475 nanometers

Green light, from 475-650 is not used by green chloroplasts and is reflected Remember, E = hc/w Artificially photosynthetic devices can be made to absorb all parts of the visible spectrum and some others (those that can penetrate the atmosphere), giving practical yields of 2.5-5 %

In labs, yields of 8% have been achieved While artificial photosynthesis has the upper hand with regards to light absorption efficiency, it is not good with diffuse amounts of carbon such as that present in the atmosphere

All artificial photosynthesis experiments I discovered had to be given supplemental carbon at some point References Photocatalytic Water Splitting -the term for the production of hydrogen and oxygen gases from water by directly utilizing the energy of light
-different systems use different powers of light and photocatalysts as well as cocatalysts to speed up hydrogen gas production
-the object is to use a photocatalyst that not only splits water quickly but also must fulfill the band requirements to split water NaTaO3:La K3Ta3B2O12 Pt/TiO2 Cobalt based systems GaN-Sb alloy Highest water splitting rate

U-V based

NiO cocatalyst assist in hydrogen gas production lower water splitting rate

U-V based

no cocatalyst (Ga.82Zn.18)(N.82O.18) most effective photocatalyst

U-V light based

does not easily corrode highest light yield: uses visable light

high temperatures- limit photocatalytic activity

can use Rh/Cr to give best performance theoretical systems Current Problems with Renewables
Byproducts Solar and Wind?
Energy Storage Advantages Immediate conversation
Clean Byproducts Disadvantages -Corrosion -Water -Oxygen
-Photodamage -Cost “Unfortunately, artificial photosynthesis is still in its infancy. Researchers reckon that, at least in the laboratory, they can make fuel direct from sunlight far more efficiently than can the fastest-growing plants. But no-one can yet do so at a cost that would make the process economic. Nor can they make it robust enough to work continuously, year in and year out, under the full glare of the sun. And they are years away from integrating the various steps—from capturing the sunlight in the first place to producing the finished fuel—into working prototypes, let alone commercial-sized factories capable of producing something resembling petrol.” –The Economist, Feb 2011 Potential Global Impact -Fuel Source -Production Requirements Advantages
Solar Energy

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