Energy

Scientists awaken dormant enzymes to give artificial photosynthesis a boost

Scientists awaken dormant enzymes to give artificial photosynthesis a boost
Scientists have created an artificial photosynthesis device said to absorb more sunlight than natural photosynthesis itself
Scientists have created an artificial photosynthesis device said to absorb more sunlight than natural photosynthesis itself
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Scientists at the University of Cambridge developed a photoelectrochemical cell that connects a red- and blue-light-absorbing photosystem with an enzyme called hydrogenase
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Scientists at the University of Cambridge developed a photoelectrochemical cell that connects a red- and blue-light-absorbing photosystem with an enzyme called hydrogenase
Scientists have created an artificial photosynthesis device said to absorb more sunlight than natural photosynthesis itself
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Scientists have created an artificial photosynthesis device said to absorb more sunlight than natural photosynthesis itself

An ability to recreate and scale up the process of photosynthesis, where plants convert sunlight into usable fuels, would mean huge things for our pursuit of renewable energy. Researchers around the world have made some promising advances of late, but one team of researchers from the University of Cambridge say they can produce better results by reactivating a natural mechanism that vanished through billions of years of plant evolution.

In nature, plants convert sunlight, carbon dioxide and water into carbohydrates, proteins and fats to power their existence, with oxygen produced as a byproduct. Experimental artificial photosynthesis systems, which include artificial leaves and moth-inspired photoelectrochemical cells, use advanced solar cells to split water into oxygen and hydrogen, which can theoretically be funneled into a fuel cell and used to create electricity.

The trouble is that the catalysts needed to trigger this process are often made from materials that are cost-prohibitive and toxic. This means that they can work as proof-of-concept technologies in the lab, but become problematic when scientists try to scale their creations up with a view to industrial use.

One avenue scientists, including those at the University of Cambridge, are investigating is what is known as semi-artificial photosynthesis. As the name suggests, this technique takes manmade components and marries them with natural ones to produce better outcomes. In this case, those natural components involve biological mechanisms discarded by plants through evolution due to the surplus energy they create.

"Natural photosynthesis is not efficient because it has evolved merely to survive so it makes the bare minimum amount of energy needed – around 1 to 2 percent of what it could potentially convert and store," says the University of Cambridge's Katarzyna Sokół, first author of the study.

Scientists at the University of Cambridge developed a photoelectrochemical cell that connects a red- and blue-light-absorbing photosystem with an enzyme called hydrogenase
Scientists at the University of Cambridge developed a photoelectrochemical cell that connects a red- and blue-light-absorbing photosystem with an enzyme called hydrogenase

Sokół and her team developed a photoelectrochemical cell that connects a red- and blue-light-absorbing photosystem with hydrogenase, an enzyme found in algae with photosynthesizing properties. This combination avoids the toxic side effects of using an artificial catalyst, and led to some promising results.

"Hydrogenase is an enzyme present in algae that is capable of reducing protons into hydrogen," says Sokół. "During evolution, this process has been deactivated because it wasn't necessary for survival but we successfully managed to bypass the inactivity to achieve the reaction we wanted – splitting water into hydrogen and oxygen."

Like other work in this area, the team's creation remains a proof of concept for now, but the researchers say that it improves on current devices in terms of the amount of energy produced and stored, and also absorbs more solar light than natural photosynthesis itself. Describing it as a "milestone," they now hope to build on the technology and explore other possibilities in the realm of semi-artificial photosynthesis.

"It's exciting that we can selectively choose the processes we want, and achieve the reaction we want which is inaccessible in nature," says Sokół. "This could be a great platform for developing solar technologies. The approach could be used to couple other reactions together to see what can be done, learn from these reactions and then build synthetic, more robust pieces of solar energy technology."

The research was published in the journal Nature Energy.

Source: University of Cambridge

7 comments
7 comments
Bob Stuart
Converting protons to hydrogen only requires cooling and contact with a grounded electrical conductor. Photosynthesis does not break atoms, just molecules.
piperTom
So, "natural photosynthesis is not efficient because it has evolved merely to survive..."?! This statement reflects a woeful lack of understanding of evolution. It's a highly competitive world out there, yes, for plants, too. High efficiency allows for faster growth, which has obvious advantages. This is especially important in low light areas, such as the forest floor and medium depth oceans.
Expanded Viewpoint
Bob, who was it that came up with that process? When? Can you give us any proof of the claim?
Randy
Ralf Biernacki
@Randy: Who and when came up with this process is a complex issue, but the leading researchers were William Nicholson and Anthony Carlisle, in 1800. For a more detailed timeline read: https://en.wikipedia.org/wiki/Electrolysis#History You can also find a description of this process in just about any elementary school chemistry text. As for proof of the claim, you can provide it yourself by setting up a simple water electrolysis cell. You will see hydrogen gas bubbles appearing at the anode---this hydrogen is the direct product of recombination of protons with electrons supplied by the ground line of the power source, just as Bob described.
Ralf Biernacki
Excess hydrogenase production was turned off in plants because it catalyses conversion of protons into gaseous hydrogen, which is useless biologically. What evolved instead is a process using these protons to capture carbon from carbon dioxide, producing organic compounds that can be used by the plant to build its tissue and provide energy. But we insist on hijacking photosynthesis to produce hydrogen gas (pointlessly IMO---producing renewable hydrocarbons would be much more convenient), so hydrogenase is just the ticket.
Ralf Biernacki
The real reason photosynthesis is inefficient is because RUBISCO---the key enzyme in the carbon dioxide splitting process---has poor selectivity between CO2 and O2, and works backward at least some of the time. At the time, billions of years ago, when photosynthesis originated, oxygen was a scarce contaminant in the atmosphere, and this poor selectivity was a nonissue. But then photosynthesis poisoned its own process, because it used up most CO2 and produced massive amounts of O2 instead; in this new environment RUBISCO is grossly inefficient, but is retained because everything is using it, and it is very difficult for evolution to discard what is already working (poorly) and start from scratch. Evolution is a blind process of gradual improvement (and in fact many clever tweaks have evolved to salvage the RUBISCO process a little) but it has no foresight. It will take the teleological approach (working with the end result in mind) of human engineering to reinvent photosynthesis.
Riaanh
Thanks Ralf, it is a refreshing change to read an informative post, and not only knee-jerking reactions to the articles.