One of the most promising strategies being investigated to mitigate emissions of carbon dioxide (CO2) 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, a challenge has been finding a catalyst that is efficient and fast enough for practical use.
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 his 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 rhenium. A rhenium atom forms the catalytic center supported by organic fragments composed of carbon, nitrogen, oxygen, and hydrogen. The group created three new versions by strategically “decorating” it with positively charged molecules or cations at varying distances from the rhenium metal center.
The group found that this spacing significantly impacts effectiveness. At a key distance, catalytic activity increased by about 800 times without requiring much additional electrical energy. Computational chemistry revealed that cations stabilize later parts of the reaction and unlock a low-energy pathway not typically observed for rhenium-based molecular catalysts. This discovery was achieved using computational resources from Brookhaven’s Center for Functional Nanomaterials and Scientific Data and Computing Center.
“This basic catalytic framework is well known in the research community,” said Rotundo, lead author on the paper. “While there have been many efforts to tailor its catalytic properties, our findings highlight substantial rate increases through subtle geometric changes in its organic scaffold.”
Researchers used several methods including cyclic voltammetry—an electrochemical technique measuring energy characteristics—and infrared spectroelectrochemistry providing structural change information during reactions. To execute these techniques effectively they utilized novel apparatus developed by some team members described in last year’s publication.
Future plans involve integrating light absorbers based on semiconductors like silicon into their catalytic system to see if they can partially drive reactions with captured light energy reducing direct electrical needs aligning with CHASE's mission: developing photoelectrodes capturing sunlight converting CO2/water into liquid fuels.
Other collaborating researchers include Adam Pearce Hannah Nedzbala James Mayer (Yale University); Samuel Bottum James Cahoon (UNC Chapel Hill).