Suffolk Reporter

UPTON, N.Y. — One of the most promising strategies being investigated to mitigate emissions of carbon dioxide (CO2) — a byproduct of electricity and heat production, transportation, and other industries — is the process of electrochemical reduction. In this approach, electrical energy is used to convert recaptured CO2 into usable products and fuels, such as methanol and ethanol. However, finding a catalyst that is efficient and fast enough for practical use has been challenging.

Motivated by this goal, a group of researchers led by scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory has identified an approach that can improve the speed of catalysis by a factor of 800. The work, a collaboration between Brookhaven, Yale University, and the University of North Carolina at Chapel Hill, is published in the August 27, 2024 online edition of the Journal of the American Chemical Society. It was supported as part of the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE), an Energy Innovation Hub funded by the DOE Office of Science. Brookhaven Lab is one of the CHASE partner institutions.

“There are many materials that are able to catalyze carbon dioxide reduction, but you often need to apply a large amount of energy to the system, which is an economic constraint against large-scale deployment,” said Brookhaven chemist Gerald Manbeck, one of the scientists involved in the work. “The catalyst we studied requires far less energy and displays excellent performance. It may inspire the design of better future catalysts.”

Manbeck and the research group — which included Brookhaven chemists Laura Rotundo, Shahbaz Ahmad (now a postdoctoral researcher at the University of Manchester in the U.K.), Chiara Cappuccino, David Grills, and Mehmed Ertem — started with an existing catalyst based on the metal rhenium. A rhenium atom forms the catalytic center of the molecule and is supported by organic fragments composed of carbon, nitrogen, oxygen, and hydrogen. The group created three new versions of the catalyst by strategically “decorating” it with positively charged molecules or cations; each version had a different distance between these cations and the rhenium metal center.

The group found that this spacing can significantly impact the effectiveness of the catalyst. At a key distance, catalytic activity increased by about 800 times without needing much additional electrical energy. Computational chemistry revealed that cations have a stabilizing effect on later parts of the catalytic reaction; thus unlocking a low-energy pathway not typically observed for rhenium-based molecular catalysts. This discovery was achieved using computational resources from both Brookhaven's Center for Functional Nanomaterials—a DOE Office of Science user facility—and its Scientific Data and Computing Center.

“This basic catalytic framework is well known in the research community,” said Rotundo, lead author on this paper. “While there have been many efforts to tailor its catalytic properties our findings really highlight substantial rate increases achievable through subtle geometric changes in organic scaffolding.”

The researchers used several methods to uncover these findings including cyclic voltammetry—an electrochemical technique measuring energy characteristics and reaction rates—and infrared spectroelectrochemistry which provides information on structural changes during reactions. To execute this technique they utilized an apparatus developed last year uniquely sensitive to observing chemical changes near interfaces between solutions where reactions occur—and electrode surfaces supplying electrical energy.

Future work will involve elaborating on their catalytic system by integrating light absorbers based on semiconductors like silicon—materials capturing incoming light converting it into electrical energy—to see if these absorbers can partially drive reactions reducing direct electrical needs aligning with CHASE's mission developing photoelectrodes capturing sunlight driving CO2 water conversions into liquid fuels.

Other collaborating researchers include Adam Pearce Hannah Nedzbala James Mayer (Yale University); Samuel Bottum James Cahoon (UNC Chapel Hill).