Cambridge researchers develop floating ‘leaves’ that produce clean fuel from sunlight

According to a University press statement, this is the first time that clean fuel has been generated on water and this technology could potentially be used on polluted waterways, ports or even at sea to help reduce the global shipping industry’s reliance on fossil fuels. The research has been published in the journal Nature.

The lightweight leaves have already been tested outdoors on the River Cam and they have reportedly demonstrated that they can convert sunlight into fuels as efficiently as plant leaves can. The tests showed that the artificial leaves can split water into hydrogen and oxygen or reduce carbon dioxide to syngas. Syngas or synthetic gas is a mixture of carbon monoxide and hydrogen that can be used as fuel.

Over the years, renewable energy technologies, like wind and solar, have become significantly cheaper and much more accessible. But for many industries, they continue to remain an impractical solution. Shipping is one such industry. According to a 2018 UNCTAD report, more than 80 per cent of global trade is facilitated by cargo ships that are powered by fossil fuels.

Erwin Reisner, a professor at the university and co-lead author of the study, and his research group have been working to address this problem for many years. Reisner and his team focused on developing sustainable solutions to petrol based on the principles of photosynthesis. They developed the first version of the artificial leaf that makes syngas in 2019.

The first prototype generated fuel by combining two light-absorbing materials with suitable catalysts. But the device was bulky because it included thick glass substrates and moisture-protective coatings.

“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,” said Reisner, in a university press statement.

Miniaturisation technologies have revolutionised the electronics industry, leading to the creation of smartphones and flexible displays. Taking inspiration from this, the researchers worked on building a new version of the leaf. But to trim down the device, the researchers needed to find a method to deposit light absorbers onto lightweight substrates while ensuring they are protected against water infiltration.

The team overcame this challenge by using thin-film metal oxides and “perovskite” materials which can be coated onto flexible plastic and metal foils. The device was covered with micrometre thin water-repellent carbon-based layers that prevented moisture degradation. After fabrication, the researchers ended up with a device that both worked and looked like a real leaf.

An artificial leaf with the River Cam and some ducks in the background. (Image credit: University of Cambridge)

“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,” said Virgil Andrei, co-lead author of the paper, in a university press statement.

Andrei envisions using the technology to build solar farms for fuel synthesis that could be used to supply coastal settlements and remote islands. They can also be used to cover industrial ponds or protect irrigation canals from evaporation.