- ‘Artificial leaf’ mimics photosynthesis, the process plants use to make energy
- In the presence of sunlight, it hides CO2 to eco-fuels ethanol and propanol
- Cars may one day be equipped with the tech as an alternative to electric cars
Electric cars are billed as the future of zero-emission transport, but the ultimate eco-friendly car could be powered by sunshine.
Researchers have created an ‘artificial leaf’ that uses sunlight to hide water and carbon dioxide from low-emission fuels – ethanol and propanol.
If this sounds familiar, the artificial leaf mimics photosynthesis, the famous process used by plants to make their energy.
In the laboratory, the experts immersed the leaf in CO2-infused water before shining light to trigger the reaction and create the green fuels.
But in the future, cars can be built with the technology to take in ambient sunlight, CO2 and water vapor in the air and produce the fuels along the way.
The technology is described in a new study led by researchers from the University of Cambridge and published in the journal Nature Energy.
How does it work?
– Researchers made their ‘artificial leaf’ from multiple layers including copper, glass, silver and graphite.
– The sheet also includes a catalyst that sparks the reaction, made of two elements (copper and palladium).
– In the presence of sunlight, the catalyst turns CO2 into ethanol and propanol, and the water into oxygen.
“Shining sunlight on the artificial leaves and getting liquid fuel from carbon dioxide and water is an amazing bit of chemistry,” said study author Dr Motiar Rahaman.
‘In this work, we have developed an artificial leaf device to generate multicarbon alcohols from CO2 and water with sunlight as the sole energy source.’
Researchers made their ‘artificial leaf’ from multiple layers including copper, glass, silver and graphite.
The artificial leaf contains light absorbers – similar to the molecules in plants that harvest sunlight – which are combined with a catalyst.
This catalyst (which is related to chlorophyll, the catalyst for photosynthesis in a real leaf) is made of two elements, copper and palladium.
In the presence of sunlight, the catalyst turns CO2 into ethanol and propanol, and the water into oxygen.
‘The alcohol products can be extracted from the reaction medium and can then be used in a vehicle,’ Dr Rahaman told MailOnline.
While the technology is still at laboratory scale, the scientists say their ‘artificial leaves’ are an important step in the transition away from fossil fuels currently used in cars – namely petroleum.
Although ethanol is used as a clean fuel in cars and is usually made from biomass such as corn or sugar cane.
READ MORE: Leafy device pulls water from air to produce hydrogen fuel
It is touted as a greener alternative to gasoline because it is made from plants instead of fossil fuels.
Many cars and trucks on the road today run on gasoline containing up to 10 percent ethanol (sold at gas stations as E10 fuel).
One problem, however, is that the production of ethanol takes up agricultural land that could be used to grow food instead.
According to the US Department of Agriculture, nearly 45 percent of all corn grown in the US is used for ethanol production.
And the more demand for this environmentally friendly ethanol grows, the more land is needed.
Fortunately, the Cambridge team’s technology offers an alternative method for ethanol production.
In the future, the lead could be part of a vehicle’s device to produce clean fuel on the go if it can extract water and CO2 from surrounding air while exposed to sunlight.
However, the team cautions that the device is currently only a proof of concept with ‘modest efficiency’.
“Even though there is still work to be done, we have shown what these artificial leaves can do,” said study author Professor Erwin Reisner in Cambridge, who led the research.
‘It is important to show that we can go beyond the simplest molecules and make things that are directly useful when we move away from fossil fuels.’
Back in 2019, the Cambridge team described using their artificial leaf technology to produce synthetic gas or ‘syngas’ – a mixture of hydrogen and carbon monoxide used to produce fuels, pharmaceuticals, plastics and fertilisers.
But now the artificial leaf can directly produce clean ethanol and propanol without the need for the intermediate step of producing syngas.
What’s more, ethanol and propanol are environmentally friendly fuels that have a high energy density and can be easily stored or transported.
“Normally, when you try to convert CO2 into another chemical product with an artificial leaf device, you almost always get carbon monoxide or syngas,” Dr Rahaman said.
‘But here we have produced a practical liquid fuel using just the power of the sun.
‘It is an exciting development that opens up completely new avenues in our work.’
The researchers are now working on improving the light absorbers so that they can better absorb sunlight and also the catalyst so that it can convert more sunlight into fuel.
Further work will also be needed to make the device scalable so it can produce large volumes of fuel – although it is unclear how much this would cost.
HOW DOES PHOTOSYNTHESIS WORK?
Photosynthesis is a chemical process used by plants to convert light energy and carbon dioxide into glucose for the plant to grow, releasing oxygen in the process.
The leaves of green plants contain hundreds of pigment molecules (chlorophyll and others) that absorb light at specific wavelengths.
When light of the right wavelength hits one of these molecules, the molecule enters an excited state – and energy from this excited state is carried along a chain of pigment molecules until it reaches a specific type of chlorophyll in the photosynthetic reaction center.
Here, energy is used to drive the charge-separation process necessary for photosynthesis to continue.
The electron ‘hole’ left in the chlorophyll molecule is used to ‘split’ water to oxygen.
Hydrogen ions formed during the water splitting process are ultimately used to convert carbon dioxide into glucose energy, which the plant uses to grow.