Developed by researchers at the University of Cambridge, the ultra-thin, flexible devices were inspired by photosynthesis. As the low-cost, autonomous devices are light enough to float, they could be used to generate a sustainable alternative to petrol without taking up space on land, the researchers said.
Outdoor tests of the lightweight leaves on the River Cam in Cambridge reportedly showed they can convert sunlight into fuels as efficiently as plant leaves. If scaled up, the devices could be used on polluted waterways, in ports or even at sea.
Professor Erwin Reisner’s research group has been working to address the problem of decarbonising difficult industries such as shipping by developing sustainable fossil fuel alternatives for several years.
In 2019, they developed an artificial leaf that makes syngas – a key intermediate in the production of many chemicals and pharmaceuticals – from sunlight, carbon dioxide and water.
The earlier prototype generated fuel by combining two light absorbers with suitable catalysts. It incorporated thick glass substrates and moisture protective coatings however, making it bulky.
“Artificial leaves could substantially lower the cost of sustainable fuel production, but since they’re both heavy and fragile, they’re difficult to produce at scale and transport,” said Dr Virgil Andrei, a co-lead author of research on the new devices.
“We wanted to see how far we can trim down the materials these devices use while not affecting their performance,” said Reisner, who led the research. “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.”
For the new version of the artificial leaf, the researchers took their inspiration from the electronics industry, where miniaturisation techniques have led to the creation of smartphones and flexible displays.
The challenge for the researchers was how to deposit light absorbers onto lightweight substrates and protect them against water infiltration. To overcome these challenges, the team used thin-film metal oxides and materials known as perovskites, which can be coated onto flexible plastic and metal foils. The devices were covered with micrometre-thin water-repellent carbon-based layers that prevent moisture degradation.
“This study demonstrates that artificial leaves are compatible with modern fabrication techniques, representing an early step towards the automation and upscaling of solar fuel production,” said Dr Andrei. “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.”
Tests of the new artificial leaves showed they can split water into hydrogen and oxygen, or reduce CO2 to syngas. While additional improvements will need to be made before they are ready for commercial applications, the researchers said this development “opens whole new avenues” in their work.
“Solar farms have become popular for electricity production – we envision similar farms for fuel synthesis,” said Andrei. “These could supply coastal settlements, remote islands, cover industrial ponds, or avoid water evaporation from irrigation canals.”
“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,” said Reisner. “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 research was supported in part by the European Research Council, the Cambridge Trust, the Winton Programme for the Physics of Sustainability, the Royal Academy of Engineering, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).
The results were reported in Nature.
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