Dynamic (Sub)surface-Oxygen Enables Highly Efficient Carbonyl-Coupling for Electrochemical Carbon Dioxide Reduction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• High-valent copper species (Cu^δ+) are known to enhance multi-carbon production in the electrochemical carbon dioxide reduction reaction (CO₂RR).
• However, inconsistent average valence states and dynamic changes in Cu^δ+ during CO₂RR lead to ambiguity in understanding their mechanism and role.
• Accurate determination of active high-valent Cu species is challenging, hindering mechanistic insights into enhanced multi-carbon production.

Purpose of the Study:

• To propose a new descriptor, the (sub)surface-oxygenated degree (κ), to quantify active high-valent Cu species.
• To investigate the correlation between κ and multi-carbon production efficiency in CO₂RR.
• To elucidate the role of high-valent Cu species in regulating carbonyl (*CO) coupling for enhanced C2+ product formation.

Main Methods:

• Development and application of the (sub)surface-oxygenated degree (κ) as a descriptor for active high-valent Cu species.
• Electrochemical CO₂ reduction reaction (CO₂RR) experiments using optimized Cu₂O@Pd_2.31 catalysts.
• Correlation analysis between the κ descriptor and catalytic performance metrics, including *CO coupling efficiency and multi-carbon partial current density.

Main Results:

• The (sub)surface-oxygenated degree (κ) effectively quantifies active high-valent Cu species on the catalyst surface.
• A strong correlation was validated between κ and the efficiency of carbonyl (*CO) coupling, a key step for multi-carbon production.
• An optimized Cu₂O@Pd_2.31 catalyst achieved a high multi-carbon partial current density of ≈330 mA cm^-2 with 83.5% faradaic efficiency, attributed to the optimized κ value.

Conclusions:

• The (sub)surface-oxygenated degree (κ) serves as a critical factor regulating multi-carbon production in CO₂RR.
• This work provides a promising approach to accurately unveil the role of high-valent Cu species in CO₂ electroreduction.
• The findings contribute to the rational design of catalysts for efficient multi-carbon synthesis, advancing efforts towards carbon neutralization.