In situ raman spectroelectrochemistry of oxygen species on gold electrodes in high temperature molten carbonate melts

In order to clarify the reaction mechanisms for oxygen reduction related to Superoxide and peroxide ions in molten carbonates, we have attempted to obtain in situ Raman spectra on a gold electrode by a surface-enhanced Raman scattering technique at the three-phase boundary under potentiostatic conditions. In situ experiments were carried out with a gold electrode in molten (62 + 38)mol% (Li + K)CO₃ eutectic at 923 K and in molten Li₂CO₃, at 1123 K. Raman lines at 1047, 1080, and 800 cm^-1 appeared for the (62 + 38)mol% (Li + K)CO₃, and at 735 cm^-1 for the Li₂CO₃ single melt. These Raman lines are assigned to the stretching vibration of Superoxide ions (1047 and 1080 cm^-1), and peroxide ions (800 and 735 cm^-1). These oxide species may be associated with the oxygen reduction at the three-phase boundary interface. The results suggest the oxygen reduction in a Li₂CO₃ melt involves peroxide ions, while the reduction in a (62 + 38)mol% (Li + K)CO₃ melt involves both peroxide and Superoxide ions.