Artificial photosynthesis could be one of the most revolutionary scientific breakthroughs in the near future. The implications for global energy economics are astounding
Mimicking nature is a difficult but worthwhile exercise, as it could result in breakthroughs worth hundreds of billions of dollars. But this set of scientists is attempting to improve nature by a substantial margin, and that too a technique nature has been practising for 3.5 billion years.
Photosynthesis is the best way to tap non-polluting energy for this planet, but it is not commercially viable at nature’s efficiencies. “We need a commercial system that is ten times more efficient than photosynthesis,” says Peidong Yang, head of the Joint Center for Artificial Photosynthesis ( JCAP) at Berkeley in the US. Yang believes that his lab could do it in five to 10 years.
Your Own Leaf
While JCAP takes an end-to-end approach to developing artificial photosynthesis systems, others focusing on different parts of the process are making significant advances. At the Massachusetts Institute of Technology (MIT), Daniel Nocera, professor of chemistry and one of the stars in the university, had recently made an artificial leaf that he is now improving for commercial launch.
Put this artificial leaf in water in the presence of sunlight, and hydrogen begins to bubble through. “I was amazed by the Nocera device,” says Wendy Flavell, professor of surface physics at the University of Manchester.
Flavell is herself part of a consortium of researchers that are developing nano devices that can use the sun’s energy to split water. Elsewhere, researchers are tweaking biology itself to increase the efficiency of photosynthesis. At Penn State University, professor of biochemistry and biophysics John Golbeck has made a biology-based device that produces hydrogen at twice the efficiency of plants.
At the University of Glasgow, professor of botany Richard Cogdell is engineering bacterial systems to use sunlight and thin air to produce automobile fuel. At the Arizona State University, assistant professor Anne Jones is developing systems that can use energy that is otherwise wasted during photosynthesis to produce auto fuel. “Plants absorb quite a lot of sunlight,” says Jones, “but the majority is not converted to food.”
The Sun and Us
In theory, solar radiation is superabundant on earth. Researchers often say that the sunlight that falls on the earth in one hour is enough to power the earth for one year. But this information is meaningless because no one can put collectors all over the earth.
A more precise calculation is not simple as it involves factors that vary with the location, weather, time of the day, the efficiency of conversion and so on. But here is a simplified result for the next 50 years. We need to mine coal in twice the area that we would need if we use photovoltaic cells that work at 30% efficiency.
This is the theory, but other factors intrude in practice. High price of solar cells is one factor. Solar cells produce only electricity, and modern technology needs energy in other forms as well (like liquid fuel for transport). The sun shines only during the day. Clouds often reduce the sunlight that photovoltaic cells can use.
Artificial photosynthesis can solve all these problems at one stroke, as it would also provide a method of storing energy either as hydrogen or as a carbonbased liquid fuel like petrol. Natural photosynthesis operates at efficiencies that are unacceptable in commercial systems, but scientists are now confident that they can improve nature substantially.
The Catalysts
Among all the artificial photosynthesis researchers, MIT’s Nocera is the closest to producing a commercial system. He set up a company, Sun Catalytix, to commercialise this invention. Sun Catalytix has a partnership with the Tata Group, but not much is known about it as the Tatas have chosen not to talk about it.
Nocera hit the headlines in 2008 when he developed a catalyst that produces oxygen from water. When used with other catalysts like platinum, which produces hydrogen from water, you could create a fuel cell that produced energy. Platinum is expensive while Nocera’s catalyst isn’t.
Nocera’s crucial breakthrough consisted of developing the catalyst that works in water instead of alkaline fluids widely used in industry. Three years later he advanced his system into a cheap device that can split water and produce hydrogen.
This system requires no wires and can use water at room temperature even straight from the tap. He has coated two sides of a silicon wafer with catalysts: one side produces hydrogen and the other oxygen. All you need to do is to create a barrier between them and collect the two gases separately. Nocera published his work in the journal Science six months ago.
This device does not use platinum. Instead it has cheap catalysts that use abundant and cheap natural materials. The MIT team is now busy tweaking the device to improve its utility and reduce the cost. “We are trying to use more plastic and reduce the amount of semiconductor material,” says Nocera.
He dreams of a day, not far into the future, where his device will let people produce their own fuel from water in their homes. At the moment, it is more than twice as efficient as natural photosynthesis in converting solar energy into chemical energy.
Total Systems
The MIT artificial leaf is a significant advance in artificial photosynthesis, but still not advanced enough to act as full-fledged commercial systems. By including wires, the artificial leaf can convert solar energy at an efficiency of 4.7%, while photosynthesis operates at 1%. The loss of energy is mostly through the semiconducting material. New semiconductor materials could push up the efficiency. So could other ingenious techniques like punching holes in the semiconductor or increasing the conductivity of the solution. For the moment, the simplicity of Nocera’s device has given a new direction to artificial photosynthesis research. The two JCAP centres, unlike Nocera and all other groups, are taking a total systems approach to artificial photosynthesis. “We are working like one whole institute and not separate groups,” says Yang.
JCAP was set up in 2010 with $122 million funding for five years from the US department of energy. It operates at two places, one at Caltech in southern California and the second at the Lawrence Berkeley National Laboratory in northern California. Caltech professor Nathan Lewis heads the project, while Yang heads the lab at Berkeley. JCAP’s approach differs from that of all other groups in several ways.
To begin with, it is tweaking earth-abundant, stable, inorganic materials to be used as catalysts. Its scientists believe that organic materials, which most researchers use, are not stable enough to work in a commercial system. Unlike the MIT team, JCAP is also developing a light capture device to replace silicon. So its aim is to develop a total system that is inexpensive and easy to manufacture, unlike others who focus on the parts one after the other.
Yang hopes to make fundamental advances in the first five years of JCAP’s operation, and develop a system by the end of its second five-year term. US president Barack Obama is so upbeat about the institute that he has referred to its work in some of his speeches.
Nano Solutions
At other institutes, scientists are working on various aspects of artificial photosynthesis and making rapid progress. A consortium of five research groups in UK universities — Manchester, East Anglia, York and Nottingham — are trying to use nanotechnology to make systems similar to those found in nature.
For example, its researchers are coating nanoparticles with light-harvesting chemicals that mimic chlorophylls in plants. This apparatus will use sunlight to react with carbon dioxide and methane — two greenhouse gases — and produce methanol and carbon monoxide, which then can be used as feed stocks to produce fuel. “We have had success with the catalyst,” says Wendy Flavell. “We are now grafting the bits together.”
Some others are also trying to produce fuel similar to petrol. One of them is Richard Cogdell, molecular biologist and professor at the University of Glasgow. “Most efforts so far of utilising photosynthesis have focused on producing electricity,” says Cogdell. “But we need fuel, especially for transport.”
Codgell’s aim is to increase the efficiency of photosynthesis by using techniques of synthetic biology. Photosynthesis occurs in two stages: efficient light capturing and inefficient energy-to-food conversion. The second step is inefficient because it does not work well in the presence of oxygen (photosynthesis evolved on the earth before oxygen did). Through synthetic biology, Cogdell is creating a fuel-producing enzyme system that lets the reaction proceed without oxygen.
Bio Wires
At the Arizona State University, Jones is using similar principles with different techniques. She separates the two reactions to occur in two locations that are connected by a biowire. By doing this, and letting the second reaction happen in special environments without oxygen, Jones hopes to speed up the carbon fixation reaction.
This method is so powerful that some agriculture scientists are using it — special carbon dioxide-rich environments — to make plants produce more food. Their techniques may be ready by 2050. “We will have three billion more people to feed by 2050,” says Howard Griffiths, professor of plant ecology at Cambridge. Griffiths hopes to increase the efficiency of photosynthesis by 25% and further enhance it through breeding.
In the future, there would be plenty of areas around the plant photosynthetic machinery for scientists to tweak. Golbeck of Penn State University has produced a system that is twice as efficient as natural photosynthesis in producing hydrogen.
Golbeck has simply tethered some proteins involved in photosynthesis using a nanowire. “We have demonstrated its working in a lab device,” says Golbeck, “and we are now developing the technique in a living system.” This is a fundamental advance that is yet to be developed commercially.
Developing artificial photosynthesis needs several such advances, but they have started coming quickly.
:: Hari Pulakkat ET120401
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