Tuning Catalyst Microenvironments for Selective Production of Single C2+ Products

The mechanism of the coverage-driven selectivity shift from ethylene to acetate in high-rate CO₂/CO electrolysis has been unraveled by a research team headed by Profs. Xinhe Bao, Guoxiong Wang, and Dunfeng Gao from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS).

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On January 12^th, 2023, the study was published in the journal Nature Nanotechnology.

The electrolysis of CO₂ to useful chemicals and fuels using renewable energy as a power source has emerged as a viable carbon capture, utilization, and storage technology.

The high selectivity of multicarbon (C₂₊) products at industrial current densities is extremely desirable for pushing the CO₂ electrolysis process toward practical implementation. Tuning the microenvironments surrounding catalyst surfaces has also been shown to be useful in increasing C–C coupling and C₂₊ production.

The scientists optimized the catalyst microenvironment in this work by employing mixed CO/CO₂ feeds that were characteristic of waste gases from steel plants and partial industrial combustion of fossil fuels. They specifically explored CO/CO₂ co-electrolysis in an alkaline membrane electrode assembly (MEA) electrolyzer at high current densities over a nanoporous CuO nanosheet catalyst.

With increasing CO pressure in the feed, the major product gradually shifted from ethylene to acetate and the current density remarkably increased, up to 3.0 A cm^-2 under 0.6 MPa pure CO feed.

Guoxiong Wang, Professor, Dalian Institute of Chemical Physics, Chinese Academy of Sciences

Prof. Gao states, “The selectivity switch was induced by *CO coverage and local pH. Ethylene was preferentially generated at low *CO coverage, whereas acetate formation was favorable at high *CO coverage and high local pH.”

The scientists improved electrolysis performance even further by improving electrolysis conditions. The Faradaic efficiency and partial current density of C₂₊ products were 90.0% and 3.1 A cm^-2, respectively, equating to 100.0% carbon selectivity and 75.0% yield, exceeding thermocatalytic CO hydrogenation.

The CO electrolysis process was scaled up using a stack of four 100 cm² MEAs, with the greatest ethylene synthesis rate of 457.5 mL min^-1 at 150 A and acetate formation rate of 2.97 g min^-1 at 250 A.

Our work highlights the promise of tuning catalyst microenvironments for selective production of single C₂₊ products such as acetate and ethylene, and presents an effective scale-up demonstration of high-rate CO₂/CO electrolysis towards practical application.

Guoxiong Wang, Professor, Dalian Institute of Chemical Physics, Chinese Academy of Sciences

Journal Reference:

Wei, P., et al. (2023) Coverage-driven selectivity switch from ethylene to acetate in high-rate CO₂/CO electrolysis. Nature Nanotechnology. doi.org/10.1038/s41565-022-01286-y.