화학공학소재연구정보센터
Electrochimica Acta, Vol.43, No.7, 763-769, 1998
CO2 reduction in molten 62/38 mole% Li/K carbonate mixture
The product of the square root of the diffusion constant and the solubility of CO2, S root D, is an important parameter for the correct interpretation of electrochemical results on the complicated mechanism of the oxygen reduction in molten carbonates, in which CO2 participates. We studied the CO2 reduction with linear sweep voltammetry (LSV) and chronoamperometry (CA) to obtain S root D values for CO2, independent of the oxygen reduction. The measured LSV voltammograms and CA responses are well described by the theoretical response of a simple charge transfer step of the form Ox + e(-) = Red with the Red species initially not present. S root D values for CO2 in the 62/38 mole% Li/K carbonate mixture were determined from the LSV responses in a straightforward way using little assumptions in a (small) temperature interval between 575 degrees C and 650 degrees C. These values obeyed Arrhenius law and a combined activation energy for S root D of 32.20 kJ/mole was determined. In an earlier study Nishina et al. showed that the oxygen reduction is rate-limited by the CO2 diffusion [1]. They measured S root D values in the 62/38 mole% Li/K melt in a temperature range between 615 degrees C and 700 degrees C which they could ascribe to CO2 by making various assumptions. Since these values for S root D, and moreover their combined activation energy fdr S root D, are very close to our values, our study supports Nishina's interpretation of his results and his conclusion that the oxygen reduction is rate-limited by the CO2 diffusion.