Sodium Carbonate ion complexes modify water structure at electrode interfaces

Water structure near electrode interfaces may play an important role in controlling CO2 electroreduction. Using plasmon-enhanced vibrational sum frequency generation spectroscopy, we demonstrate the emergence of an interfacial water subpopulation with large electric fields along their OH bonds, when Na2CO3 ions are present near the electrode under applied potential. With molecular dynamics simulations, we show that the approach of aqueous Na2CO3 to electrodes is coupled to the formation of structured and oriented ion complexes, and that the emergent water population is associated with the first solvation shell of these complexes. This water subpopulation is seen even when the sole source of CO3 is its in-situ generation from CO2, indicating that the interfacial species investigated here are likely ubiquitous in CO2 electroreduction contexts.