Net zero liquid solar fuels for cars created by University of Cambridge researchers

University of Cambridge researchers have harnessed the power of photosynthesis into fully renewable solar fuels for cars.

The technology converts carbon dioxide, water and sunlight into high density multicarbon fuels – ethanol and propanol – in a single step. They can be easily stored or transported and, unlike fossil fuels, produce net-zero carbon emissions.

And unlike most bioethanol, they do not divert agricultural land away from food production.

The technology is still at the laboratory scale, but the ‘artificial leaves’ are seen as an important step in the transition away from a fossil fuel-based economy.

To achieve it, the researchers developed a copper and palladium-based catalyst optimised to produce ethanol and n-propanol.

It is the first time that such complex chemicals have been produced with an artificial leaf using only the energy from the Sun.

Until now, such artificial leaves have only been able to make simple chemicals, such as syngas - a mixture of hydrogen and carbon monoxide that is used to produce fuels, pharmaceuticals, plastics and fertilisers.

To make the technology more practical requires the ability to create more complex chemicals directly in a single solar-powered step.

“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, a research associate at St John’s College and first author of a paper published in Nature Energy.

“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.”

Bioethanol is touted as cleaner alternatives to petrols, since it is made from plants rather than fossil fuels, and most cars and trucks today run on petrol with up to 10 per cent ethanol - E10 fuel.

But Prof Erwin Reisner, who led the research, noted: “Biofuels like ethanol are a controversial technology, not least because they take up agricultural land that could be used to grow food instead.”

The US is the world’s largest bioethanol producer, with almost 45% of all corn grown in the country is used for ethanol production.

For years, Prof Reisner’s research group in the Yusuf Hamied Department of Chemistry, has been developing artificial leaves to produce sustainable, zero-carbon fuels inspired by photosynthesis – the process by which plants convert sunlight into food.

Now they have been able to produce a proof of concept device that, with modest efficiency, creates clean ethanol and propanol without the need for the intermediary step of producing syngas.

The next step is to optimise the light absorbers so that they can better absorb sunlight and optimise the catalyst so it can convert more sunlight into fuel.

Then more work will be needed to make the device scalable so that it can produce large volumes of fuel.

“Even though there’s still work to be done, we’ve shown what these artificial leaves are capable of doing,” said Prof Reisner, a fellow of St John’s College. “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.”

The research was supported in part by the European Commission Marie Skłodowska-Curie Fellowship, the Cambridge Trust, and the Winton Programme for the Physics of Sustainability.