The pure Cu and bimetallic f oams exhibited several peaks bet ween 411 cm -1 and 5240 cm -1 under CO2 electrolysis at all investigated potentials. These peaks could be assigned to either a single or a mixture of Cu oxide/(oxy)hydroxide surface species. For example, Cu85In15 (CO selective) and Cu25In75 (HCOO -selective) exhibited a strong peak (at 530-536 cm -1 ) combined with pre-shoulder peak (at 455-467 cm -1 ) under CO2 electrolysis at all the studied potentials (between -0.4 V and -0.9 V). These two peaks could be attributed to a mixture of Cu(OH)2 and basic Cu carbonate (Cux(CO3)y(OH)z, malachite/azurite) phases, since their positions match some of the obtained peaks for our internal measured Cu(OH)2 and malachite standards. Additionally, the pure Cu f oam exhibited a strong peak at 498 cm -1 with a pre-shoulder peak at 461 cm -1 , which can be attributed to Cu(OH)2 based on alignment with that standard. Moreover, Cu85Sn15 (CO-selective) and Cu40Sn60 (HCOO --selective) also showed a strong peak at 597-598 cm -1 assigned to Cu(OH)2. Cu40Sn60 showed additional peaks that can be assigned f or malachite/azurite, as shown in Figure . We will ref er to the all observed peaks between 400 cm -1 and 630 cm -1 as mixture of copper (oxy)hydroxide and carbonate, species, since the obtained peaks in this region f or our synthesized Cu-based bimetallic f oams exhibited broad peaks compared to the measured Cu standards (see Figure ). Indeed, the obtained operando SERS results provide evidence f or the persistence of copper oxide surf ace species and their in-situ f ormation and transf ormation under CO2 electrolysis conditions. Important to note is that in the absence of CO2, neither of these peaks assigned to surface copper (oxy)hydroxide/carbonate species were observed. This highlights the essential role of the local environment changes developed during CO2 electrolysis, such as local pH increase, on the dynamic transformation of Cu2O/CuO of the as-prepared catalysts into Cux(CO3)y(OH)z under CO2 electrolysis conditions. That is, the surf ace Cu2O/CuO of the as-prepared samples in-situ converted into a mixture of Cu hydroxide (Cu(OH)2) and basic Cu carbonate (malachite/azurite) during CO2 electrolysis. The equilibrium between these two copper surf ace species are strongly dependent on the developed local environmental changes under CO2 electrolysis. It is worth mentioning here that there are no peaks were identified to either In or Sn oxides under the applied measurement conditions.