Using single nickel atoms as a catalyst for carbon dioxide (CO2) conversion results in greater efficiency, according to researchers at the US Department of Energy’s (DOE) Brookhaven National Laboratory.

The research team found it catalysed the CO2 conversion reaction with a maximum efficiency of 97%, which it claims is a major step towards recycling CO2 for usable energy and chemicals.

In addition to providing more usable energy, successful and efficient CO2 conversion could also recycle excess levels of atmospheric carbon dioxide, which reached record levels last year.

During the process, CO2 is converted into carbon monoxide (CO), a highly energetic molecule that can then be converted to fuel.

“There are many ways to use CO,” said Eli Stavitski, a scientist at Brookhaven and an author on the paper.

“You can react it with water to produce energy-rich hydrogen gas, or with hydrogen to produce useful chemicals, such as hydrocarbons or alcohols.”

Traditional electrocatalysts have not effectively initiated the reaction because a competing reaction, called hydrogen evolution reaction (HER), takes precedence over the CO2 conversion reaction.

There are some noble metals—such as gold and platinum—that can avoid HER and convert CO2 to CO. However, these rare elements are not cost-effective.

Nickel, by contrast, is more abundant and therefore cheaper to source than precious metals, but has not typically been used as an electrocatalyst.

“Nickel metal, in bulk, has rarely been selected as a promising candidate for converting CO2 to CO,” said Haotian Wang, a Rowland Fellow at Harvard University and the corresponding author on the paper.

“One reason is that it performs HER very well, and brings down the CO2 reduction selectivity dramatically. Another reason is because its surface can be easily poisoned by CO molecules if any are produced.”

Single atoms of nickel, however, produce a different result.

“Single atoms prefer to produce CO, rather than performing the competing HER, because the surface of a bulk metal is very different from individual atoms,” Stavitski said.

The conversion reaction was facilitated by the interaction of the nickel atoms with a surrounding sheet of grapheme. Anchoring the atoms to graphene enabled the scientists to tune the catalyst and suppress HER.

The team used a transmission electron microscope to look at the individual nickel atoms on the graphene, and the ultra-bright x-ray beamline 8-ID to gain a detailed view of the material’s inner structure.

Mapping the energy states of the electrons enables the team to discover that single nickel atoms catalysed the CO2 conversion reaction with a maximum efficiency of 97%.

“To apply this technology to real applications in the future, we are currently aimed at producing this single atom catalyst in a cheap and large-scale way, while improving its performance and maintaining its efficiency,” said Wang.

The findings were published in Energy & Environmental Science.