Scientists make fuel of CO2 with copper and light

Now this is some kind of alchemy, you might think, but scientists claim to have found a way to transform CO2 into sustainable fuel using copper and light.

An international team of researchers say they have successfully transformed CO2 into methanol by shining sunlight on single atoms of copper deposited on a light-activated material. The discovery is said to pave the way – or should that be light the way? – for creating new green fuels.

The team from Nottingham University’s School of Chemistry – along with researchers from the universities of Birmingham, UK; Queensland, Australia, and Ulm in Germany – have designed a material made up of copper anchored on nano-crystalline carbon nitride.

They have published their research in the journal, Sustainable Energy & Fuels.

The paper explains how copper atoms are nested within the nano-crystalline structure, which allows electrons to move from carbon nitride to CO2; an essential step in the production of methanol from the gas under the influence of solar irradiation.

In photocatalysis, light is shone on a semiconductor material that excites electrons, enabling them to travel through the material to react with CO2 and water, leading to a variety of useful products, including methanol. Despite recent progress, however, this process suffers from a lack of efficiency and selectivity.

Carbon dioxide is the greatest contributor to global warming, of course. Although, the scientists say it is possible to convert CO2 to useful products, traditional thermal methods rely on hydrogen sourced from fossil fuels.

As a consequence, they say it is important to develop alternative methods based on photo- and electrocatalysis, “taking advantage of the sustainable solar energy and abundance of omnipresent water”.

Dr Madasamy Thangamuthu, research fellow in Nottingham’s School of Chemistry, said: “There is a large variety of different materials used in photocatalysis. It is important that the photocatalyst absorbs light and separates charge carriers with high efficiency. In our approach, we control the material at the nanoscale. We developed a new form of carbon nitride with crystalline nanoscale domains that allow efficient interaction with light as well as sufficient charge separation.”

The researchers devised a process of heating carbon nitride to the required degree of crystallinity, which they say maximises the functional properties of this material for photocatalysis. Using magnetron sputtering, they deposited atomic copper in a solvent-free process, allowing intimate contact between the semiconductor and metal atoms.

Tara LeMercier, a PhD student who carried out the experimental work at Nottingham’s School of Chemistry, said: “We measured the current generated by light and used it as a criterion to judge the quality of the catalyst. Even without copper, the new form of carbon nitride is 44 times more active than traditional carbon nitride. However, to our surprise, the addition of only 1 mg of copper per 1 g of carbon nitride quadrupled this efficiency. Most importantly the selectivity changed from methane, another greenhouse gas, to methanol, a valuable green fuel.”

Professor Andrei Khlobystov, from the School of Chemistry, added: “Carbon dioxide valorisation holds the key for achieving the net-zero ambition of the UK. It is vitally important to ensure the sustainability of our catalyst materials for this important reaction. A big advantage of the new catalyst is that it consists of sustainable elements – carbon, nitrogen and copper – all highly abundant on our planet.”

This invention is said to represent a significant step towards a deep understanding of photocatalytic materials in CO2 conversion. Additionally, the scientists claim it opens a pathway for creating “highly selective and tuneable catalysts” where the desired product could be dialled up by controlling the catalyst at the nanoscale.

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