Artificial leaf turns sunlight, water and CO2 into clean fuel
Scientists have developed ultra-thin floating devices, which use solar technology to create a carbon-neutral liquid fuel that can be stored.
Inventors at Cambridge University have developed artificial leaves that produce clean fuel as they float on water.
The ultra-thin, lightweight and flexible devices use solar technology that mimics photosynthesis, the process by which plants convert sunlight into food, to create a carbon-neutral fuel.
As they float they transform sunlight, carbon dioxide and water into a liquid fuel that can be stored. This differs from conventional solar cells, which generate an electrical current.
Scientists at the university created a prototype in 2019, but it was too “bulky” to be scaled up for commercial use. The initial design used thick glass substrates and moisture protective coatings, which made it heavy and fragile.
They have spent the past few years remodelling the device using miniaturisation techniques to make it light enough to float on water.
The researchers said this week that they carried out successful tests of the leaves by placing them on the River Cam, which showed that they could convert sunlight into fuels as “efficiently as plant leaves”.
It was the first time that clean fuel had been generated on water, they said, adding that if it was scaled up the technology could be used on polluted waterways, in ports or even at sea where they could help to reduce the global shipping industry’s reliance on fossil fuels. “Solar farms have become popular for electricity production; we envision similar farms for fuel synthesis,” Virgil Andrei, from the Yusuf Hamied department of chemistry at Cambridge, said. “These could supply coastal settlements, remote islands, cover industrial ponds or avoid water evaporation from irrigation canals.”
The leaves work when water and CO2 are present and sunlight hits a panel that has been coated in a semiconductor powder. It absorbs the light, and electrons in the panel become “excited” before joining with the CO2.
Protons are released from the water, which then reduces the CO2 and a chemical reaction creates formic acid, which can be stored.
The team is led by Professor Erwin Reisner, who hopes the technology could revolutionise the shipping industry, where cargo vessels powered by fossil fuels transport 80 per cent of global trade.
“We wanted to see how far we can trim down the materials these devices use, while not affecting their performance,” he said. “If we can trim the materials down far enough that they’re light enough to float, then it opens up whole new ways that these artificial leaves could be used.
“Many renewable energy technologies, including solar fuel technologies, can take up large amounts of space on land, so moving production to open water would mean that clean energy and land use aren’t competing with one another. In theory, you could roll up these devices and put them almost anywhere, in almost any country, which would also help with energy security.”
The team was tasked with finding a way of downsizing their initial design by attaching light absorbers to lightweight “substrates” that are protected against water infiltration.
They used thin-film metal oxides and materials known as perovskites, which can be coated on to flexible plastic and metal foils, and covered them with micrometre-thin, water-repellent carbon-based layers that prevented moisture degradation.
“This study demonstrates that artificial leaves are compatible with modern fabrication techniques, representing an early step towards the automation and up-scaling of solar fuel production,” Mr Andrei said. “These leaves combine the advantages of most solar fuel technologies, as they achieve the low weight of powder suspensions and the high performance of wired systems.”
The leaves are not ready for commercial applications as additional improvements will need to be made, including creating a method to collect the fuel from the leaf.
– The Times
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