The electrochemical CO2 (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 C2+ products. When atomic Eu was incorporated into Cu2O, it was able to shift the dominant product depending on whether Eu concentration was high or low. For example, low Eu-doped Cu2O achieves a high Faradaic efficiency of nearly 80% for C2+ products, while higher Eu doping tips the pathway toward C1 products such as CH4.
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 C2+ via the frustrated deep hydrogenation of *CHO. For high Eu concentrations, certain bonds become strengthened instead, which facilitates the deep hydrogenation of *CHO to CH4 via the C1 pathway.
This work establishes a clear, intrinsic mechanism for switching between C1 and C2+ products in electrochemical CO2 reduction by using Eu as an electronic modulator in Cu2O-based catalysts. By leveraging the reversible Eu3+/Eu2+ 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 C2+ products) or deep hydrogenation (toward CH4
This research provides a design concept for "dialing in" desired carbon products from CO2 using earth-abundant Cu-based catalysts and rare-earth promoters. Such precise control over CO2-to-fuels conversion supports the development of electrified, CO2-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.
- Publication Details:
Title: Atomic Eu Substitution in Cu2O Tailors C1 and C2+ Product Selectivity by Frustrated Deep Hydrogenation in Electrochemical CO2 Reduction
Authors: Yang Liu, Xuan Wang, Zichun Mao, Jiaxiong Zhang, Meng Li, Dongmei Sun, Yawen Tang, Hao Li, Gengtao Fu
Journal: Journal of the American Chemical Society
DOI: 10.1021/jacs.5c19360
