Atomic Eu Substitution in Cu 2 O Tailors C 1 and C 2+ Product Selectivity by Frustrated Deep Hydrogenation in Electrochemical CO 2 Reduction

The electrochemical CO2 reduction reaction (eCO2RR) is an important method to obtain high-value chemicals; however, selectively tailoring C1 and C2+ products remains a challenge. Herein, we propose a novel and effective rare-earth Eu substitution strategy to tailor the selectivity of C1 and C2+ products on Cu2O sites by frustrated deep hydrogenation in the eCO2RR. The incorporation of atomic Eu into Cu2O can shift the dominant product from C2+ at low Eu content to CH4 at high Eu content. For low Eu-doped Cu2O (LD-Eu/Cu2O), the total Faradaic efficiency (FE) of C2+ products reaches 79.39% with ethylene (C2H4) as the predominant product (FE: 49.27%) in the H-type cell; whereas high Eu-doped Cu2O (HD-Eu/Cu2O) promotes the formation of C1 products, achieving a total FE of 50.25% with methane (CH4) as the main product (FE: 47.21%). Eu substitution for tailoring the selectivity of C1 and C2+ products on the Cu2O site is also verified in the flow cell. Electrochemical in situ characterization and theoretical calculations suggest that low levels of Eu incorporation in Cu2O weakens the π* antibonding interaction over the C═O bond, facilitating C–C coupling to lead the C2+ pathway via the frustrated deep hydrogenation of *CHO; whereas high Eu incorporation in Cu2O strengthens the π* antibonding interaction, facilitating the deep hydrogenation of *CHO to CH4 via the C1 pathway. This work provides a new perspective on tailoring product selectivity by rare-earth-induced frustrated deep hydrogenation during the eCO2RR.