A new device developed by a team in Cambridge marks a breakthrough in artificial photosynthesis technology, due to its efficiency and scalability. It converts sunlight, carbon dioxide and water into oxygen and formic acid. Utilising the greatest renewable energy source available to us – the sun – this technology does not require electricity to power it so is wireless and self-sufficient.
The process also does not use up any additional components, and makes very little waste products. With a 97% selectivity – that means 97% of the output is the desired product, formic acid, give or take 3% – its efficiency even surprised its creators.
“Sometimes things don’t work as well as you expected, but this was a rare case where it actually worked better”, said chemist Dr Qian Wang, the first author of the paper that reported the new technology.
The device comprises a photocatalyst sheet designed to capture sunlight to power its chemical reactions, which in this case has the benefit of being scalable: increasing the size of the sheet does not significantly decrease its efficiency. The final prototype, with an area of 20cm2, produced formic acid just as successfully as the 1cm2 test samples.
Two different semiconducting powders are embedded in a gold layer, making up the photocatalyst sheet. A cobalt-based catalyst is fixed onto the sheet to enable the reaction without external power sources. The sheet is submerged in a solution saturated with carbon dioxide and exposed to sunlight. Electrons are transferred from one semiconducting component through the gold layer to the other. One converts carbon dioxide to ions of formic acid, and simultaneously, the other oxidises water to produce oxygen.
The same laboratory saw the creation of a similar device resembling an “artificial leaf” in 2019. However, it produced syngas as its main product, a mixture of hydrogen and carbon monoxide, rather than formic acid and oxygen. While syngas is also useful in the energy industry, it is more difficult to store unless it is converted to a liquid fuel first.
Formic acid is a more versatile product, which can easily be stored before being converted to other types of fuel as required. It can also be used as fuel directly: recent innovations include the first formic acid fuel cell, created by a company called GRT Group in 2018.
Scientists have made many attempts at realising artificial photosynthesis previously, but this development is a major step forward in terms of robustness and practicability on a real-world scale. Future versions of the device could be as large as several square metres, the researchers say. Ultimately, solar farm-like arrays could be achieved with this technology.
There is also a possibility of replacing the gold layer with materials other than precious metals for larger sheets. Using carbon or metal oxides in its place could further boost the sustainability factor in the production of the devices.
The photosynthesising sheet is not ready for commercial use yet. The team is still working on optimising the chemical processes and testing different catalysts, but in the meantime we can begin to plan how this incredible material can be put into practical use.
An element of urgency colours research in the field of artificial photosynthesis, as demand for clean and renewable fuel grows. The success of this device in transforming energy from the sun may move a little closer to a sustainable future.
Written by Catriona Roy and edited by Ailie McWhinnie.
Catriona’s thoughts… A “machine that makes energy by photosynthesis” was one of the machines I most wished existed when I was at school – surely it would solve all of the world’s energy problems instantly! Learning that there really is such a thing was awesome, but learning that they’ve been around for years and still aren’t efficient enough, less so. Inventions are ever improving, however, and this is one more achievement to prove we are on the right track.
It seems the sun holds the key to our energy problems: we can absorb energy from it in solar cells or artificial leaves, or create our own mini sun in the process of nuclear fusion. With the solution posed in the article however, in the environmental crises the Earth is going through right now, it seems fitting that the technology that could save us simply mimics the method plants use to power themselves, whilst plants fall victim to human-induced destruction.