Encapsulating nano-sized cubes of copper can help convert carbon dioxide into other chemicals

September 22 2022

(Nanwerk NewsAs the need to mitigate climate change accelerates, scientists are trying to find new ways to reduce carbon dioxide emissions. One process, called electrochemical reduction or electrolysis, uses electricity and a catalyst to convert carbon dioxide into organic products that can be used in other ways. In contrast to the conversion between water and hydrogen, chemical recycling of carbon dioxide can produce many usable products because carbon can develop large types of organic structures.

One way to achieve the electrochemical reduction of carbon dioxide is by using very small pieces of copper. While bulk copper metal is known to convert carbon dioxide into various organic molecules, these small pieces of copper can further improve the catalytic activity not only by increasing its surface area but also through the unique electronic structure of copper that emerged from the nano-process. The organic layer grown on the nano-copper oxide improved the CO2 The reduction selectivity of the copper species wrapped in it, as well as maintained its cubic structure during stimulation. (Photo: Shoko Komei, Hiroshima University)

In a paper published in chemical communication (Uniform wrapping of copper oxide(1) nanotubes by a self-catalyzed copper azide-alkyne towards carbon dioxide selective electrocatalysis.), the researchers explain a process to improve the way copper nanotubes convert carbon dioxide, by improving their selectivity. Selectivity refers to the ability of a catalyst to produce a desired product over undesirable byproducts.

“Recent developments in CO2 reduction using copper electrocatalysts can convert gas into hydrocarbons and alcohols, but the selectivity of the various copper-related electrocatalysts developed so far remains elusive, as they tend to lose activity through structural reorganization during catalysis. ” , He said. Shoko Kumi, associate professor at the Graduate School of Advanced Science and Engineering at Hiroshima University in Japan.

The researchers discovered that this problem could be solved by growing an organic layer on top of the nanotubes. First, a pair of monomers was added to the CuO nanocube. These monomers were bonded by chemistry on copper oxide and an even organic layer was grown on the surface of the cubes. This new organic layer helps improve the selectivity of CO2 reduction, in part because CO2 has poor solubility and the organic layer the researchers produced has hydrophobic properties, meaning it repels excess water from which unwanted hydrogen is produced.

“Encapsulation improved the CO reduction of copper under this organic layer by suppressing hydrogen evolution, as well as preserving the cubic structure during the catalyst process,” Comey said.

Another important factor for improving the quality of the organic layer is the temperature at the time of growth, with best results found at room temperature. In the best conditions, the layer is flat, several particles thick. Even the thinner layer easily permeates the carbon dioxide and allows the coiled copper to undergo electrical absorption, which protects the metal and helps the cubes retain their shape.

Currently, copper nanotubes are not widely adopted as a CO2 reduction method because they are unstable and do not have the level of selectivity needed to effectively recycle CO2 into other chemical products. The results of this paper highlight a new method for creating an electrocatalyst using copper nanotubes that can solve some of these problems. The researchers also suggest that, looking to the future, the method could be modified to control both selectivity and improve how stimuli work.

“Our current method can introduce a variety of organic structures within the layer, which can be involved in the CO2 reduction process to control its selectivity and efficiency,” Comey said. “It can also be used to control the dynamic behavior of metal species during catalysis, which can develop catalysts with long lifetimes and impurity tolerance.”