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 CO 2 reduction reaction (eCO 2 RR) is an important method to obtain high-value chemicals; however, selectively tailoring C 1 and C 2+ products remains a challenge. Herein, we propose a novel and effective rare-earth Eu substitution strategy to tailor the selectivity of C 1 and C 2+ products on Cu 2 O sites by frustrated deep hydrogenation in the eCO 2 RR. The incorporation of atomic Eu into Cu 2 O can shift the dominant product from C 2+ at low Eu content to CH 4 at high Eu content. For low Eu-doped Cu 2 O (LD-Eu/Cu 2 O), the total Faradaic efficiency (FE) of C 2+ products reaches 79.39% with ethylene (C 2 H 4 ) as the predominant product (FE: 49.27%) in the H-type cell; whereas high Eu-doped Cu 2 O (HD-Eu/Cu 2 O) promotes the formation of C 1 products, achieving a total FE of 50.25% with methane (CH 4 ) as the main product (FE: 47.21%). Eu substitution for tailoring the selectivity of C 1 and C 2+ products on the Cu 2 O site is also verified in the flow cell. Electrochemical in situ characterization and theoretical calculations suggest that low levels of Eu incorporation in Cu 2 O weakens the π* antibonding interaction over the C═O bond, facilitating C–C coupling to lead the C 2+ pathway via the frustrated deep hydrogenation of *CHO; whereas high Eu incorporation in Cu 2 O strengthens the π* antibonding interaction, facilitating the deep hydrogenation of *CHO to CH 4 via the C 1 pathway. This work provides a new perspective on tailoring product selectivity by rare-earth-induced frustrated deep hydrogenation during the eCO 2 RR.