Could floating leaves generate a clean energy future?

Artificial leaf testing on the River Cam. Image: Virgil Andrei.

Researchers have developed floating ‘artificial leaves’ that generate clean fuels from sunlight and water - and could eventually operate on a large scale at sea.

The researchers from the University of Cambridge, UK, designed ultra-thin, flexible devices which take their inspiration from photosynthesis – the process by which plants convert sunlight into food. Since the low-cost, devices are light enough to float, they could be used to generate a sustainable alternative to petrol without taking up space on land.

Outdoor tests of the lightweight leaves on the River Cam - near iconic Cambridge sites including the Bridge of Sighs, the Wren Library and King’s College Chapel - showed they can convert sunlight into fuels as efficiently as plant leaves.

This is the first time that clean fuel has been generated on water. If scaled up, the artificial leaves could be used on polluted waterways, in ports or at sea, and could help reduce the global shipping industry’s reliance on fossil fuels. The results are reported in the journal Nature.

While renewable energy technologies, such as wind and solar, have become significantly cheaper and more available in recent years, for industries such as shipping, decarbonisation is a much taller order. Around 80% of global trade is transported by cargo vessels powered by fossil fuels, yet the sector has received remarkably little attention in discussions around the climate crisis.

Dr Virgil Andrei with one of the artificial leaf devices. Image: Virgil Andrei

For several years, Professor Erwin Reisner’s research group in Cambridge has been working to address this problem by developing sustainable alternatives to petrol, which are based on the principles of photosynthesis. In 2019, they developed an artificial leaf that creates syngas – an intermediary in the production of many chemicals and pharmaceuticals – that is generated from sunlight, carbon dioxide and water.

The earlier prototype generated fuel by combining two light absorbers with suitable catalysts. However, it incorporated thick materials which made the device 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 co-lead author Virgil Andrei from Cambridge’s Yusuf Hamied Department of Chemistry.

“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."

Erwin Reisner, University of Cambridge

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, revolutionising the field. The devices were covered with micrometre-thin, water-repellent carbon-based layers that prevented moisture degradation. They ended up with a device that not only works, but also looks like a real leaf.

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.”

While additional improvements will need to be made before they are ready for commercial applications, the researchers say this development opens whole new avenues in their work.

Image: Virgil Andrei

“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). Virgil Andrei and Erwin Reisner are Fellows of St John’s College, Cambridge.