Lowering the Cost of Sustainable Solar Fuel Production

Researchers from the University of Cambridge have created flexible, ultra-thin electronics that are inspired by photosynthesis, the mechanism through which plants turn sunlight into food. The inexpensive, autonomous devices could be used to provide a sustainable substitute for petrol without taking up space on land because they are light enough to float.

Lowering the Cost of Sustainable Solar Fuel Production.
Floating artificial leaf on the River Cam near St John's College, Cambridge. Image Credit: University of Cambridge.

The lightweight leaves were put through outdoor experiments on the River Cam, close to well-known Cambridge landmarks including the Bridge of Sighs, the Wren Library, and King’s College Chapel, and they proved to be just as effective at converting sunlight into fuels as plant leaves.

This is the first instance of clean fuel being produced on the water, and if the artificial leaves were to be scaled up, they might be utilized on polluted waterways, at ports, or even at sea. This would help lessen the dependency of the world’s shipping sector on fossil fuels. The study was published in the journal Nature.

While the cost and availability of renewable energy sources like wind and solar have drastically decreased recently, decarbonization is still a far more difficult task for sectors like shipping. Even though almost 80% of the world’s trade is moved by cargo ships that are powered by fossil fuels, the industry has received surprisingly little attention in talks about the climate crisis.

The Cambridge research team of Professor Erwin Reisner has been working on finding sustainable alternatives to petrol that are based on the principles of photosynthesis for many years in an effort to solve this issue. They created an artificial leaf in 2019 that converts sunlight, carbon dioxide, and water into syngas, a crucial step in the manufacturing of numerous chemicals and medications.

An earlier prototype used two light absorbers along with the appropriate catalysts to produce fuel. The device was hefty due to the use of thick glass substrates and moisture-resistant coatings.

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.

Dr. Virgil Andrei, Study Co-Lead Author, Yusuf Hamied Department of Chemistry, University of Cambridge

We wanted to see how far we can trim down the materials these devices use, while not affecting their performance. 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,” adds Reisner, who led the research.

The researchers drew inspiration from the electronics sector, where the development of smartphones and flexible screens using miniaturization techniques has revolutionized the industry, for the innovative design of the artificial leaf.

The difficult part for the Cambridge researchers was figuring out how to install light absorbers on thin surfaces while keeping water intrusion at bay. The scientists used thin-film metal oxides and perovskites, which can be deposited onto flexible plastic and metal foils, to solve these difficulties.

Water-repellent carbon-based coatings that were only micrometers thick were applied to the devices' surfaces to protect them from moisture damage. They were able to create a device that not only functions in a similar way to a leaf but also resembles a leaf.

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. 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.

Dr. Virgil Andrei, Study Co-Lead Author, Yusuf Hamied Department of Chemistry, University of Cambridge

The new artificial leaves have demonstrated their ability to split water into hydrogen and oxygen as well as convert CO2 to syngas in tests. Even though there is still work to be done before such artificial leaves can be used in commercial settings, the researchers claim this breakthrough opens up entirely new study directions.

Solar farms have become popular for electricity production; we envision similar farms for fuel synthesis. These could supply coastal settlements, remote islands, cover industrial ponds, or avoid water evaporation from irrigation canals.

Dr. Virgil Andrei, Study Co-Lead Author, Yusuf Hamied Department of Chemistry, University of Cambridge

Reisner concludes, “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 study 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).

Journal Reference:

Andrei, V., et al. (2022) Floating perovskite-BiVO4 devices for scalable solar fuel production. Nature. doi.org/10.1038/s41586-022-04978-6.

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