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Artificial Photosynthesis of Biomimetics/Biomimicry

Mimicking nature to produce energy

Presentation on Artificial Photosynthesis Spring 2015

What is photosynthesis

It is a process used by plants and other

• rganisms to convert light energy, normally from

the Sun, into chemical energy that can be later released to fuel the organisms’ activities. This chemical energy is stored in carbohydrate molecules, such as sugars which are synthesised from carbon dioxide (CO2) and water. Hence the name photosynthesis.

What is photosynthesis contd

In most cases oxygen is also released as a waste product. Most plants, most algae and most cyanobacteria perform photosynthesis. Such

• rganisms are called photoautotrophs

Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on earth.

How it works

Different species perform photosynthesis differently, but it all begins when energy from light is absorbed by proteins, called reaction centres that contain the green chlorophyll

• pigments. In plants these proteins are held

inside organelles called chloroplasts which are most abundant in leaf cells. In bacteria they are embedded in the plasma membrane.

How it works contd 2

In these light-dependent reactions some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. Two further compounds are also generated: reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP), the ‘energy currency’ of cells

How it works contd 3

In plants, algae and cyanobacteria, sugars are produced by a subsequent sequence of light- dependent reactions called the Calvin cycle, but some bacteria use different mechanisms, such as the reverse Krebs cycle. In the Calvin cycle, atmospheric carbon dioxide is incorporated into the already existing organic carbon compounds, such as ribulose diphosphate (RuBP) Using the ATP and the NADPH produced by the light- dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose.

The Calvin-Benson cycle

History of photosynthetic organisms

The first probably evolved early in the evolutionary history of life and probably used reducing agents hydrogen sulphide, as sources of electrodes rather than water. Cyanobacteria appeared late, the excess

• xygen they produced contributed to the oxygen

catastrophy which rendered the evolution of complex life possible.Today the average energy captured by photosynthesis is 130 terawatts. (3 Xs the current power consumption of humans.)

Photosynthesis converts about 100 – 115 thousand million metric tonnes of carbon into biomass per year.

How it works contd 4

Photosynthetic organisms are called photoautotrophs, meaning they can synthesize food directly from carbon dioxide and water using energy from light. (Not all organisms use light as a source of energy for photosynthesis, photoheterotrophs use organic compounds rather than carbon dioxide as a source of carbon.) In plants, algae and cyanobacteria the process

• f photosynthesis is similar, but some bacteria

do not release oxygen.

The Oriental Hornet ‘vespa orientalis’ converts sunlight into electric power using a pigment called xanthopterin. This is the first evidence of a member of the animal kingdom engaging in photosynthesis

Most energy in higher plants is captured in the leaves, although all cells in the green parts of plants have chloroplasts. Cells in the interior tissues of a leaf are called mesophyll and can contain 450,000 – 800,000 chloroplasts for every square millimeter of leaf.

The surface of the leaf is uniformly coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet light to reduce

• heating. The transparent epidermis allows light to pass through

to the palisade mesophyll cells where most photosynthesis takes place.

Photosynthesis converts water and carbon dioxide into carbohydrates and sugar and refers to any scheme for capturing and storing the energy from sunlight in the chemical bonds

• f a fuel (solar fuel.)

‘Artificial Leaf’ photosynthesis, photocatalytic ‘water-splitting’ under solar light Bioinspired i.e. rely on biomimetics

Work of Dr Daniel Nocera at MIT

Has perfected a low cost artificial leaf-like device that like a real leaf, mimics the process of

• photosynthesis. His achievements were

announced at the 241st National Meeting of the American Chemical Society in 2011. He hopes to use his ‘leaf’ to help make individual homes capable of becoming their own self-sufficient power stations in the future.

This research has developed over 10 years

Initially the process required expensive and rare metals, but Nocera uses inexpensive nickel and cobalt as catalysts to effectively and efficiently split hydrogen and oxygen at a production rate that is 10 times higher than that of Mother Nature

How it is done

Using a simple mixture of sunlight and 1 gallon of water the ‘leaf’ which is the size of a playing card, is made of silicon, electronics and the aforementioned catalysts which speed up the process. Energy is not produced directly as in a photovoltaic cell, rather the ‘leaf’ splits the hydrogen and oxygen atoms, which then produce electricity for personal and household use. The prototype can then produce energy continuously for 45 hours without any fluctuations.

Implications

Could provide an affordable electricity source for developing countries in small remote villages without constructing power lines etc. It is a form

• f renewable, low cost energy.

In fact the ‘leaf’ research was funded by the Department of Energy’s ARPA transformational energy program – via US tax dollars.

Disadvantages

In May 2012, Sun Catalytix, the start-up company based on Nocera’s research, stated it would not be scaling up the prototype of the device, as it offered few savings over other ways to make hydrogen from sunlight. In fact it would not in the short-term make a profit for their investors.

How to harness solar energy and store CO2 in a neutral way?

A fuel is a molecule with a chemical bond that has captured energy which can be used when needed Funding agencies from around the world are now putting unprecedented resources into making fuels using power from the sun.e.g. the US Department of Energy has invested $116 million over 5 ears in Caltech

Two approaches are generally recognized in the construction of solar fuel cells for hydrogen production

• 1. A homogenous mixture where catalysts are

not compartmentalized, meaning hydrogen and

• xygen are produced in the same location. The

drawback is that this can be an explosive mixture,demanding further gas purification. Also all the components must be active in approximately the same conditions

Second general approach

A heterogenous system that has two separate electrodes, an anode and a cathode, making possible the separation of hydrogen and oxygen

• production. The different components do not

necessarily have to work in the same conditions. However the increased complexity of these systems makes them harder to develop and they are more expensive

An alternative artificial photosynthesis method

Alternative Artificial Photosynthesis Methods

The selection and manipulation of photosynthetic microorganisms, namely green microalgae and cyanobacteria, for the production of solar fuels. Many strains are able to produce hydrogen naturally and scientists are working to improve them. Algae biofuels such as butanol and methanol are produced at both laboratory and commercial scales.

Aims of research at Caltech,California

To make hydrogen and other fuels more efficiently than real leaves can make them. Nathan Lewis an inorganic chemist is the scientific director of the JCAP or Joint Center for Artificial Photosynthesis. He says: ‘The biggest energy source we have is the Sun. The best way to store energy other than on the nucleus of an atom is in chemical fuels. It is inevitable that someone is going to take the biggest source and store it in the most dense way.’

Research is ongoing around the world

Royal Society of Chemistry UK, The Netherlands where Biosolar Cells is a 5 year research programme that contributes to photosynthesis research and innovation for sustainable production of food, renewable energy and feedstock for the chemical industry. In Japan they have a large consortium of universities & companies with funding similar to JCAP at Caltech, but

• ver 10 years and not 5. It is called the Japan

Technological Research Association for Artificial Photosynthetic Chemical Process (ARP Chem)

Solar energy Around the Clock pilot project in Netherlands

The approach to developing water- splitting has benefited from the development of synthetic biology

The J Craig Ventnor Institute is exploring ways to produce a synthetic organism capable of biofuel production.