Probing the role of surface speciation of tin oxide and tin catalysts on CO2 electroreduction combining in situ Raman spectroscopy and reactivity investigations

Electrochemical CO2 reduction to formate is a promising approach to store renewable electricity and utilize CO2. Tin oxide catalysts are efficient catalysts for this process, while the mechanisms underneath, especially the existence and role of oxidized tin species under CO2 electroreduction conditions remain unclear. In this work, we provide strong evidence on the presence of oxidized tin species on both SnO2 and Sn during CO2 reduction via in situ surface-enhanced Raman spectroscopy, while in different nature. Reactivity measurements show similar activity and selectivity to formate production on SnO2 and Sn catalysts. Combined analysis of Raman spectra and reactivity results suggests that Sn(IV) and Sn(II) oxide species are unlikely the catalytic species in CO2 electroreduction to formate.