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.
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
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