In Situ Micro Raman Study of the NO3− Electrochemical Behavior in Molten NaNO3–KNO3 Mixtures

Abstract

We have designed a high-temperature Raman micro-furnace and cell that is suited for the electrochemical process study of the NO3− in molten NaNO3–KNO3 (fraction of NaNO3 50 wt%) salt. During the cycle voltammetry and constant potential electrolysis process, the Raman laser beam was focused near the electrode; subsequently, the Raman spectra are obtained and the reduction process of NO3− is analyzed. In the CV cathodic scan process, the new peak attributed to the ν1 mode of NO2− emerges, and the peaks assigned to superoxide ions (O2−) and peroxide ions (O22−) are not found. In the constant electrolysis process, the peaks at 1130 and 800 cm−1 appear when the potentials are between −2.0 V and −3.2 V (vs. Pt). The results show that when the NO3− is reduced in molten the NaNO3–KNO3 mixtures, the reduction product O2− cannot stably exist, and O2− will react with NO3− to form of superoxide ions (O2−) and peroxide ions (O22−).