Floating artificial leaves can generate clean energy from sunlight and water. The researchers developing the leaves hope they will eventually be widely deployed at sea, where they can produce a sustainable alternative to petrol.
The leaves have been developed by researchers at the University of Cambridge. They are very thin, flexible devices based on photosynthesis. This is a form of biosynthesis in which plants convert sunlight into energy. The leaves are lightweight and can therefore float on water. The researchers hope that their invention will lead to a new sustainable alternative to petrol, without its production taking up space on land.
The researchers' development is in line with the current focus on climate change and its mitigation. The focus here is often on solar and wind energy. However, both are less suitable for shipping. An estimated 80% of global trade is transported by ships powered by fossil fuels, reports the university. The researchers hope their development could help reduce the shipping industry's dependence on fossil fuel. The technology is deployable in rivers, ports and on the high seas.
Already in development for some time
The artificial leaves presented by Cambridge University researchers are a long-standing development. Back in 2019, the researchers presented a prototype that produces syngas, also known as synthesis gas, from sunlight, carbon dioxide and water. Syngas plays an important role in the production of many chemicals and pharmaceuticals. This earlier model generated fuel by combining two light-absorbing materials, which were fitted with catalysts. The prototype used relatively thick glass substrates and moisture-protective coatings. As a result, the model was relatively large.
"Artificial leaves can substantially reduce the cost of producing renewable fuel. But being both heavy and fragile, they are difficult to produce and transport at scale," says Dr Vigil Andrei of the Yusuf Hamied Department of Chemistry at the University of Cambridge, about the earlier prototype.
"We wanted to see how far we could reduce the material use in these devices, without affecting their performance," says Professor of Energy and Sustainability Erwin Reisner from the University of Cambridge, who led the research. "If we can reduce the material consumption far enough so that they are light enough to float, this opens up new ways in which these artificial leaves can be used." With the new model, they have succeeded in this.
Keeping water out
A key challenge the researchers faced was applying light-absorbing material to lightweight substrates and protecting these substrates from water. To do this, the team used a thin film of metal oxides and perovskites, which can be applied as coatings to flexible plastics and metal foils. The devices feature water-repellent carbon-based layers just a micrometre thick, which keep water out. The end result resembles a sheet to some extent.
"This research shows that artificial leaves are compatible with modern manufacturing techniques, which is an early step towards automating and scaling up solar fuel production," Andrei says. "These leaves combine the advantages of most solar fuel technologies by achieving the low weight of powdered suspensions and the high performance of wired systems."
Hydrogen and syngas
The artificial leaves are capable of converting water into hydrogen and oxygen, but can also reduce carbon dioxide to syngas. The researchers point out that the technology needs further development before it can be commercialised. However, they do have high hopes for their development. "Solar parks have become popular for electricity generation; we foresee similar parks for fuel synthesis," Andrei says. Such solar parks could fuel coastal cities and remote islands, according to the researcher, as well as help prevent evaporation of water from irrigation canals.
The researchers also point to the space savings on land possible with artificial leaves. "Many renewable energy technologies including solar fuel technologies take up a large amount of space on land. Moving production to open water means that clean energy and land use are no longer competing," Reisner says. "In theory, you can roll up these devices and put them almost anywhere, in almost any country. This could also help with energy security."
More information is available in Nature, in which the researchers present all their research findings.
Author: Wouter Hoeffnagel
Photo: CAW Photography via Pixabay
