The electrochemical CO 2 (carbon dioxide) reduction reaction takes harmful pollutants, and transforms them into valuable products like fuel. However, selectively tailoring various processes in this reaction to successfully and efficiently arrive at a particular desired outcome remains a challenge.
"We want to be able to tailor this reaction so we can accurately predict what the result will be each time - and to control what that result is," explains Hao Li (Distinguished Professor, Advanced Institute for Materials Research (WPI-AIMR)).
The team of researchers from Tohoku University found that the rare-earth element Europium (Eu) was the key to controlling the selectivity of this reaction for C1 or C 2+ products. When atomic Eu was incorporated into Cu 2 O, it was able to shift the dominant product depending on whether Eu concentration was high or low. For example, low Eu-doped Cu 2 O achieves a high Faradaic efficiency of nearly 80% for C 2+ products, while higher Eu doping tips the pathway toward C1 products such as CH 4 .
Theoretical calculations and other observations imply that the mechanism behind this involves the way Eu facilitates different reactions depending on its concentration. At low Eu concentrations, certain bonds are weakened that lead to C-C coupling and produce C 2+ via the frustrated deep hydrogenation of *CHO. For high Eu concentrations, certain bonds become strengthened instead, which facilitates the deep hydrogenation of *CHO to CH 4 via the C 1 pathway.
This work establishes a clear, intrinsic mechanism for switching between C 1 and C 2+ products in electrochemical CO 2 reduction by using Eu as an electronic modulator in Cu 2 O-based catalysts. By leveraging the reversible Eu 3+ /Eu 2+ redox couple and its impact on the *CHO intermediate, this study shows how subtle changes in electronic structure can selectively favor either C-C coupling (toward C 2+ products) or deep hydrogenation (toward CH 4).
This research provides a design concept for "dialing in" desired carbon products from CO 2 using earth-abundant Cu-based catalysts and rare-earth promoters. Such precise control over CO 2 -to-fuels conversion supports the development of electrified, CO 2 -based production routes for high-value chemicals and fuels. In the long term, this can contribute to carbon-neutral chemical manufacturing, more efficient use of renewable electricity, and the mitigation of greenhouse gas emissions.
The findings were published in the Journal of the American Chemical Society on December 1, 2025.
About the World Premier International Research Center Initiative (WPI)
The WPI program was launched in 2007 by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).
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Advanced Institute for Materials Research (AIMR)
Tohoku University
Establishing a World-Leading Research Center for Materials Science
AIMR aims to contribute to society through its actions as a world-leading research center for materials science and push the boundaries of research frontiers. To this end, the institute gathers excellent researchers in the fields of physics, chemistry, materials science, engineering, and mathematics and provides a world-class research environment.
AIMR site: https://www.wpi-aimr.tohoku.ac.jp/en/
Journal of the American Chemical Society
Atomic Eu Substitution in Cu2O Tailors C1 and C2+ Product Selectivity by Frustrated Deep Hydrogenation in Electrochemical CO2 Reduction
1-Dec-2025