Electro-valorization of carbon dioxide to value-added products

Chemists from the National University of Singapore (NUS) have discovered that the adsorption configuration of carbon monoxide (CO) intermediates, formed during carbon dioxide (CO₂) or CO electroreduction on copper surfaces, influences the production of different chemicals.

Electrochemical CO₂ or CO reduction reactions on copper catalysts have attracted significant attention in recent years as promising methods for closing the carbon cycle. Extensive research efforts have been devoted to understanding the fundamentals of these processes to improve their reactivity and selectivity. Much focus has been placed on examining the effects of factors such as electrode potentials and electrolyte pH. However, the adsorption configuration of the CO intermediate, a crucial factor often overlooked has emerged as a key aspect affecting reaction outcomes. While previous studies have highlighted the importance of this chemical species, its complex behaviour, which is easily influenced by the catalyst and local environment, complicates its analysis. Linearly-bonded CO (*CO_L) and bridge-bonded CO (*CO_B) are frequently observed configurations. However, the precise factors influencing CO adsorption configurations and their impact on reactivity remain unclear.

A research team led by Associate Professor YEO Boon Siang, Jason from the Department of Chemistry at NUS has unravelled the reactivity of these differently-adsorbed *CO intermediates in CO₂ or CO reduction processes. By combining in-situ Raman spectroscopy, isotope-labelling studies, product analyses, and density functional theory (DFT) simulations, they showed that *CO_B selectively reacts to form acetate and 1-propanol, while *CO_L favours ethylene and ethanol formation. Furthermore, they also found that adsorbed *OH domains, which are regions on the copper catalyst surface where hydroxyl groups are adsorbed can displace *CO_L to *CO_B, influencing the reaction pathways. This indicates that the selectivity of CO₂ or CO reduction could potentially be controlled by tuning the catalyst properties and local environment. The research was conducted in collaboration with Professor Núria López from the Institute of Chemical Research of Catalonia, Spain.

The findings were published in the Journal of the American Chemical Society.

Prof Yeo said, “This work is the fruit of an intense collaboration between experimentalists and theoreticians to discover pathways to selectively produce valuable chemicals, such as ethanol, acetate, and 1-propanol from carbon dioxide reduction.”

These insights not only advance the fundamental understanding of the mechanistic pathways of electrochemical CO₂ or CO reduction reactions, but also highlight the potential for optimising reaction conditions or catalysts to favour the production of specific multi-carbon products.

Figure shows the correlation between an increase in OH coverage (θOH), the shift in *CO adsorption configuration from *COL to *COB, and the resulting changes in selectivity from ethylene and ethanol production to acetate and 1-propanol. Unfavoured pathways are indicated by the dotted lines. [Credit: Journal of the American Chemical Society]

Reference

Ma H; Ibáñez-Alé E; You F; López N*; Yeo BS*, “Electrochemical Formation of C₂₊ Products Steered by Bridge-Bonded *CO Confined by *OH Domains” Journal of the American Chemical Society Volume:146 Issue: 44 Page: 30183-30193 DOI:10.1021/jacs.4c08755 Published: 2024.