Rare-earth hydroxide promoted water activation drives hydrogen spillover in facilitating asymmetric C–C coupling for CO2 electro-reduction to multi-carbon chemicals

Efficient production of multi-carbon (C₂ ⁺ ) products via CO 2 electroreduction reaction (eCO 2 RR) requires precise modulation of water activation, but still less investigated. In this work, we synthesized series of rare earth hydroxide-modified copper-based catalysts (RE(OH) 3 /CuO) to enhance water activation at the heterogeneous interfaces. Electrochemical evaluation showed significantly increased Faradaic efficiency for C₂ ⁺ products (up to 77.2 % at 500 mA cm −2 ) for the Sm(OH) 3 /CuO catalyst, alongside suppressed hydrogen evolution reaction (HER). This is caused by the facilitated hydrogenation of critical *CO intermediates via hydrogen spillover from the abundant Sm(OH) 3 /CuO interfaces in efficiently dissociating water molecules, promoting asymmetric C–C coupling on the Cu surfaces derived from CuO during eCO 2 RR. Experimental findings combined with DFT calculations indicated the critical role of the asymmetric *CO–*CHO coupling pathway on copper surfaces. This strategy demonstrates that rational design of interface water engineering and activation for a copper-based heterogeneous catalyst effectively promotes multi-carbon product formation in eCO 2 RR.