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‘Artificial photosynthesis’ device makes clean fuel by converting sunlight, CO2 and water

A new device is able to take in sunlight, carbon dioxide and water to create a new carbon-neutral fuel without any outside source of electricity, its developers claim.

University of Cambridge experts behind the device say it uses a form of ‘artificial photosynthesis’ – the process used by plants to convert sunlight into energy.

The device is based on an advanced ‘photosheet’ technology and converts sunlight, carbon dioxide and water into oxygen and formic acid – a storable fuel.

This type of fuel can be either used directly in specially developed generators or by converting it into hydrogen, according to the Cambridge team. 

The wireless device could be scaled up and used on energy ‘farms’ similar to solar farms, producing clean fuel using nothing but sunlight and water as its inputs.

Harvesting solar energy to convert carbon dioxide into fuel is a promising way to reduce carbon emissions and transition away from fossil fuels, experts claim.

However, it is challenging to produce these clean fuels without unwanted by-products that are costly and complicated to remove.

‘It’s been difficult to achieve artificial photosynthesis with a high degree of selectivity, so that you’re converting as much of the sunlight as possible into the fuel you want, rather than be left with a lot of waste,’ said first author Dr Qian Wang.  

Senior author, Professor Erwin Reisner, said storage of gaseous fuels and the separation of by-products can be a complicated process. 

‘We want to get to the point where we can cleanly produce a liquid fuel that can also be easily stored and transported,’ Professor Reisner added.

In 2019, researchers from Reisner’s group developed a solar reactor based on an ‘artificial leaf’ design, which also uses sunlight, carbon dioxide and water to produce a fuel, known as syngas. 

The new technology looks and behaves quite similarly to the artificial leaf but works in a different way and produces formic acid.

While the artificial leaf used components from solar cells, the new device doesn’t require these components and relies solely on photocatalysts embedded on a sheet to produce a so-called photocatalyst sheet. 

The sheets are made up of semiconductor powders, which can be prepared in large quantities easily and cost-effectively.

In addition, this new technology is more robust and produces clean fuel that is easier to store and shows potential for producing fuel products at scale. 

The test unit is about three square inches in size, but the researchers say that it should be relatively straightforward to scale it up to several square feet. 

In addition, the formic acid can be accumulated in solution, and be chemically converted into different types of fuel.

‘We were surprised how well it worked in terms of its selectivity – it produced almost no by-products,’ said Wang. ‘Sometimes things don’t work as well as you expected, but this was a rare case where it actually worked better.’

Thee device is easy to make and relatively stable, according to the study authors.  

While this technology will be easier to scale up than the artificial leaf, the efficiencies still need to be improved before any commercial deployment can be considered. 

The researchers are experimenting with a range of different catalysts to improve both stability and efficiency.

The current results were obtained in collaboration with the team of Professor Kazunari Domen from the University of Tokyo, a co-author of the study.

The researchers are now working to further optimise the system and improve efficiency and see if they can produce different solar fuels.

‘We hope this technology will pave the way toward sustainable and practical solar fuel production,’ said Reisner. 

The findings have been published in the journal Nature Energy. 

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