A standalone system that transforms sunshine, carbon dioxide and water into a carbon-neutral fuel has been developed by researchers, without needing any external components or electricity.
The system, created by a University of Cambridge team, is a crucial step towards the achievement of artificial photosynthesis, a method that mimics plants’ ability to turn sunlight into electricity. It is built on advanced ‘photosheet’ processing which transforms oxygen which formic acid into air, carbon dioxide and water — a storable fuel that can be be immediately used or converted into hydrogen.
The results, reported in the journal Nature Energy, represent a new method for the conversion of carbon dioxide into clean fuels. The wireless device could be scaled up and used on energy ‘farms’ similar to solar farms, producing clean fuel using sunlight and water.
Solar energy processing to turn carbon dioxide into fuel is a viable way to minimize carbon emissions and step away from fossil fuels. However, without unnecessary by-products, producing these renewable fuels is difficult.
“It’s been hard to achieve artificial photosynthesis with a high degree of selectivity, because you’re turning as much sunlight as possible into the fuel you like, rather than being left with a lot of waste,” said first author Dr Qian Wang of Cambridge’s Chemistry Department.
“In addition, storage of gaseous fuels and separation of by-products can be complicated — we want to get to the point where we can cleanly produce a liquid fuel that can also be easily stored and transported,” said Professor Erwin Reisner, the paper’s senior author.
In 2019, Reisner’s group researchers built a solar reactor focused on the concept of a ‘artificial leaf,’ which also uses sunlight, carbon dioxide, and water to create a liquid, called syngas. The new technology looks and behaves very similar to the artificial leaf, but functions and develops formic acid in a particular manner.
Although the artificial leaf used solar cell components, these components are not needed by the new system and depend solely on photocatalysts embedded on a substrate to create a so-called photocatalyst substrate. The sheets are composed of semi-conductor powders, which can be quickly and cost-effectively prepared in large quantities.
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 20 square centimetres in size, but the researchers say that it should be relatively straightforward to scale it up to several square metres. 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.”
The cobalt-based catalyst which transforms carbon dioxide is simple to produce and relatively stable. While this system would be simpler to scale than the artificial leaf, there is also a need to boost the efficiencies before any commercial rollout can be contemplated. The researchers are working with numerous catalysts to enhance both stability and efficacy.
In collaboration with the team of Professor Kazunari Domen from the University of Tokyo, a co-author of the analysis , the current findings were obtained.
The researchers are now focusing on more device optimization and performance enhancement. In addition, they are studying other catalysts for using different solar fuels on the unit.
“We hope this invention paves the way for efficient and realistic manufacturing of solar fuel,” Reisner said.
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