Switching between C₂₊ Products and CH₄ in CO₂ Electrolysis by Tuning the Composition and Structure of Rare-Earth/Copper Catalysts

Abstract

Rational regulation of the reaction pathway to produce the desired products is one of the most significant challenges in the electrochemical CO₂ reduction reaction (CO₂RR). Herein, we designed a series of rare-earth Cu catalysts with mixed phases. It was found that the products could be switched from C₂₊ to CH₄ by tuning the composition and structure of the catalysts. Particularly at the Cu/Sm atomic ratio of 9/1 (Cu₉Sm₁-O_<i>x</i>), the Faradaic efficiency (FE) for C₂₊ products (FE_C₂₊) could reach 81% at 700 mA cm^-2 with negligible CH₄. However, the FE of CH₄ (FE_CH₄) was 65% at 500 mA cm^-2 over Cu₁Sm₉-O_<i>x</i> (Cu/Sm = 1/9), and the FE_C₂₊ was extremely low. Experiments and theoretical studies indicated that the stable CuSm₂O₄ 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 CuSm₂O₄ 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 CuSm₂O₄ and Sm₂O₃ phases. Sm could effectively stabilize bivalent Cu and enrich proton donors, lowering the reaction energy of *CO for deep hydrogenation to generate CH₄. In both pathways, the stable CuSm₂O₄ phase could cooperate with the Cu or Sm₂O₃ 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 CO₂RR for C₂₊ or CH₄ production.