Engineering Catalyst Materials for Carbon Utilization

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Combustion of fossil fuels produces carbon dioxide - a greenhouse gas having little commercial value. Catalyzed electrochemical processes (electrocatalysis) offer an opportunity to upgrade carbon dioxide to commercially important fuels or chemical precursors. Copper stands out as an electrocatalyst for its ability to convert carbon dioxide (and carbon monoxide) into chemical compounds that contain several carbon atoms. This research project will build upon the preliminary discovery that copper nanoparticles having a sheet-like structures can efficiently promote the electrocatalytic reaction of carbon monoxide with water to produce acetate ions. The studies will aim to refine the technique for synthesizing copper nanosheet particles and investigate additional modifications to the catalysts to improve their efficiency and selectivity for converting carbon monoxide and carbon dioxide to a range of valuable chemicals. Efficient conversions of greenhouse gases to useful chemicals will help to address key sustainability and environmental challenges facing our nation. The research project will also include educational and outreach activities in collaboration with Delaware State University that will broaden the participation of underrepresented groups in STEM, especially female and African American students. Upgrading carbon dioxide to high-value multi-carbon (C2+) products is one promising avenue for sustainable fuel and feedstock production. Current state-of-the-art carbon dioxide electrocatalysts are able to convert carbon dioxide to C1 products, such as carbon monoxide and formate ions, with selectivities greater than 80%. There is a need for electrocatalysts that can reduce carbon dioxide to more valuable multi-carbon chemicals with appreciable selectivity. Among all the metals, copper attracts most attention for this application due to its unique capability to produce a wide range of C2+ chemicals; however, such reactions suffer from poor selectivity. In order to improve catalytic properties of copper, numerous attempts have been made to control the morphology and structure of copper catalysts. Still the challenge remains that it is technically challenging to prepare high-quality copper nanomaterials that selectively expose specific facet(s). In preliminary studies, the research team has successfully synthesized freestanding triangular (111)-exposing copper nanosheets, and these materials are able to electrochemically convert carbon monoxide into acetate ions with a Faradaic efficiency of approximately 48%. The high observed acetate selectivity is presumably due to the unique capability of the copper(111) facet to promote acetate formation under the reaction conditions. The objectives of this research project encompass three main thrusts: 1) establish a new synthetic route to obtain high-quality copper(111) and copper(100) nanoscale materials, 2) construct copper / metal oxide interfaces and single-atom sites based on the copper model surfaces to understand carbon dioxide / carbon monoxide reduction reaction mechanisms, and 3) investigate the stability of the synthesized catalysts under electrochemical reaction conditions. The outcomes of these efforts will (1) lead to new synthetic methods that can produce high-quality copper nanostructures with well-defined exposed facets; (2) provide an electrochemical approach to produce high-value multi-carbon chemicals using carbon dioxide as the feedstock; (3) advance fundamental understandings of structure-property relationships in copper-based electrocatalysts; (4) gain important mechanistic insights into copper-catalyzed carbon dioxide / carbon monoxide reduction reactions; and (5) demonstrate a catalyst design strategy that might be extended to other important chemical reactions, such as dinitrogen reduction to ammonia and methane partial oxidation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.