Switching between C 2+ Products and CH 4 in CO 2 Electrolysis by Tuning the Composition and Structure of Rare-Earth/Copper Catalysts.

Rational regulation of the reaction pathway to produce the desired products is one of the most significant challenges in the electrochemical CO 2 reduction reaction (CO 2 RR). Herein, we designed a series of rare-earth Cu catalysts with mixed phases. It was found that the products could be switched from C 2+ to CH 4 by tuning the composition and structure of the catalysts. Particularly at the Cu/Sm atomic ratio of 9/1 (Cu 9 Sm 1 -O x ), the Faradaic efficiency (FE) for C 2+ products (FE C 2+ ) could reach 81% at 700 mA cm -2 with negligible CH 4 . However, the FE of CH 4 (FE CH 4 ) was 65% at 500 mA cm -2 over Cu 1 Sm 9 -O x (Cu/Sm = 1/9), and the FE C 2+ was extremely low. Experiments and theoretical studies indicated that the stable CuSm 2 O 4 phase existed in all the catalysts within the Cu/Sm range of 9/1 to 1/9. At a high Cu content, the catalyst was composed of CuSm 2 O 4 and Cu phases. The small amount of Sm could enhance the binding strength of *CO and facilitate C-C coupling. Conversely, at a high Sm content, the catalyst was composed of CuSm 2 O 4 and Sm 2 O 3 phases. Sm could effectively stabilize bivalent Cu and enrich proton donors, lowering the reaction energy of *CO for deep hydrogenation to generate CH 4 . In both pathways, the stable CuSm 2 O 4 phase could cooperate with the Cu or Sm 2 O 3 phases, which induced the formation of different microenvironments to generate different products. This strategy also had commonality with other Cu-rare-earth (La, Pr, and Eu) catalysts to boost the CO 2 RR for C 2+ or CH 4 production.