Bifunctional porous SnO2/Ag nanofibers for efficient electroreduction of carbon dioxide to formate and its mechanism elucidation by in-situ surface-enhanced Raman scattering

Monitoring the reaction intermediates and revealing the real active sites are of great importance for elucidation mechanism and designing ideal catalysts. Here, bifunctional porous SnO2/Ag nanofibers (P-SnO2/Ag) are prepared and present high Faradaic efficiency (FE) of 92.4% for formate with a current density of 24.6 mA cm−2 at − 0.9 V (vs. RHE). The in-situ SERS spectra reveal that tin-oxide in P-SnO2/Ag nanofibers are easy reduced, indicates metallic tin likely be the real active site rather than Sn (IV) and Sn (II) oxide species in CO2RR. The characteristic SERS peak at around 1420 cm−1 corresponding to the key *OCHO* intermediate for HCOO- production is also captured, favorably formed after the first *CO2- intermediate suitably adsorbed on P-SnO2/Ag nanofibers via oxygen atoms. Combining the intrinsic SERS properties and excellent catalytic performance of P-SnO2/Ag nanofibers, a real correlation is established between the composition and chemical structure of the materials and their catalytic performance.