Identifying Intermediates in CO ₂ -to-C ₂ H ₄ Electrochemical Reduction by In Situ Surface-Enhanced Raman Spectroscopy

Production of value-added C 2+ products is an important topic in the research of electrochemical CO 2 reduction reaction (CO 2 RR), and in situ spectroscopy identifies key intermediates and provides important details for a deeper understanding of the reaction mechanism. Applying a “borrowing” surface-enhanced Raman spectroscopy (SERS) strategy, core-shell Au@Cu 2 O nanocatalysts with different shell thickness were used to probe the CO 2 RR pathways on the surface of Cu 2 O in both neutral (KHCO 3 + KCl) and alkaline (KOH) electrolytes. In situ Raman spectroscopic measurements showed that the SERS effect occurs at the apparent shell thicknesses of up to 100 nm. Comparative analysis uncovers the correlation between low-frequency-binding (LFB) and high-frequency-binding (HFB) *CO intermediates and electrochemical selectivity. A higher *CO LFB /*CO HFB ratio favors the generation of C 2 H 4, while abundant *CO HFB leads to predominant CO formation.