Cambridge team’s artificial leaf creates fuels direct from Sun

Scientists around the world are aiming to create synthetic fuels in a variety of ways, hoping to mitigate the climate damage being caused by our reliance on fossil fuels. Much of the research attempts to mimic photosynthesis, the sun-powered process from which plants get their energy using CO2 and water.

Led by Professor Erwin Reisner, the Cambridge team has been exploring the use of ‘artificial leaves’ to recreate the photosynthetic process, using solar power to create multicarbon fuels. Until now, however, this technique has always relied on the intermediary step of creating syngas, a mixture of hydrogen and carbon monoxide that can then be further processed to produce fuels, pharmaceuticals, plastics and fertilisers. In research published in Nature Energy, Resiner’s team describes how it used a copper and palladium-based catalyst that allowed its artificial leaf to produce more complex chemicals, specifically ethanol and n-propanol, without first having to produce syngas.

“Shining sunlight on the artificial leaves and getting liquid fuel from carbon dioxide and water is an amazing bit of chemistry,” said Dr Motiar Rahaman, the paper’s first author.

“Normally, when you try to convert CO2 into another chemical product using an artificial leaf device, you almost always get carbon monoxide or syngas, but here, we’ve been able to produce a practical liquid fuel just using the power of the Sun. It’s an exciting advance that opens up whole new avenues in our work.”

According to the researchers, other scientists have been able to produce similar chemicals using electrical power, but this is the first time such complex chemicals have been produced using energy direct from the Sun. At present, the device is a proof of concept and shows only modest efficiency. The researchers are working to optimise the light absorbers so that they can better absorb sunlight and optimising the catalyst so it can convert more sunlight into fuel. Further work will also be required to make the device scalable so that it can produce large volumes of fuel, potentially competing with bioethanol production, which is problematic due to the land use it requires.

“Biofuels like ethanol are a controversial technology, not least because they take up agricultural land that could be used to grow food instead,” said Prof Reisner.

“Even though there’s still work to be done, we’ve shown what these artificial leaves are capable of doing. It’s important to show that we can go beyond the simplest molecules and make things that are directly useful as we transition away from fossil fuels.”