3-D hierarchically porous nanostructured catalyst helps efficiently reduce carbon dioxide

KAIST researchers developed a three-dimensional (3-D) hierarchically porous nanostructured catalyst with carbon dioxide (CO₂) to carbon monoxide (CO) conversion rate up to 3.96 times higher than that of conventional nanoporous gold catalysts. This new catalyst helps overcome the existing limitations of the mass transport that has been a major cause of decreases in the CO₂ conversion rate, holding a strong promise for the large-scale and cost-effective electrochemical conversion of CO₂ into useful chemicals.

As CO₂ emissions increase and fossil fuels deplete globally, reducing and converting CO₂ to clean energy electrochemically has attracted a great deal of attention as a promising technology. Especially due to the fact that the CO₂ reduction reaction occurs competitively with hydrogen evolution reactions (HER) at similar redox potentials, the development of an efficient electrocatalyst for selective and robust CO₂ reduction reactions has remained a key technological issue.

Gold (Au) is one of the most commonly used catalysts in CO₂ reduction reactions, but the high cost and scarcity of Au pose obstacles for mass commercial applications. The development of nanostructures has been extensively studied as a potential approach to improving the selectivity for target products and maximizing the number of active stable sites, thus enhancing the energy efficiency.

However, the nanopores of the previously reported complex nanostructures were easily blocked by gaseous CO bubbles during aqueous reactions. The CO bubbles hindered mass transport of the reactants through the electrolyte, resulting in low CO₂ conversion rates.

In the study published in the Proceedings of the National Academy of Sciences of the U.S. (PNAS) on March 4, a research group at KAIST led by Professor Seokwoo Jeon and Professor Jihun Oh from the Department of Materials Science and Engineering designed a 3-D hierarchically porous Au nanostructure with two different sizes of macropores and nanopores. The team used proximity-field nanopatterning (PnP) and electroplating techniques that are effective for fabricating the 3-D well-ordered nanostructures.

The proposed nanostructure, comprised of interconnected macroporous channels 200 to 300 nanometers (nm) wide and 10 nm nanopores, induces efficient mass transport through the interconnected macroporous channels as well as high selectivity by producing highly active stable sites from numerous nanopores.

As a result, its electrodes show a high CO selectivity of 85.8% at a low overpotential of 0.264 V and efficient mass activity that is up to 3.96 times higher than that of de-alloyed nanoporous Au electrodes.

"These results are expected to solve the problem of mass transfer in the field of similar electrochemical reactions and can be applied to a wide range of green energy applications for the efficient utilization of electrocatalysts," said the researchers.