Study on the mechanism of ionic mobility in molten carbonate mixtures.

点击翻译按钮获取中文摘要

The molten binary systems (Li, K)_2CO_3 and (Li, Na)_2CO_3 at their eutectic compositions are the candidates for the electrolytes for the molten carbonate fuel cells (MCFC). The internal mobilities in the system (Li, Na)_2CO_3 have been measured by countercurrent electromigration ; those in the system (Li, Na)_2CO_3 at were previously measured In the former system the mobility of Na^+ is somewhat greater than that of Li^+ at all the investigated range of composition and temperature. The internal mobilities of Li^+, u_<Li>, in these two systems are well expressed by the empirical equation : u_<Li>=[A/ (V_m-V_0)] exp (-E/RT), where V_m is the molar volume of the mixture ; V_0, A and E are constants nearly independent of the second cation. The mobilities in the ternary system (Li, Na, K)_2CO_3 at the eutectic composition (43.5-21.5-25.0 mol%) have also been measured. The order of the mobilities of these cations is as follows : u_<Li>-u_K<u_<Na> (at 500ﾟC), u_<Li><u_<Na>-u_K (at 600ﾟC) and u_<Li><u_<Na>-u_K (at 750ﾟC). These results can be interpreted in terms of the dynamic dissociation model previously presented by us. This suggests that the internal mobilities of other cations could be semi-quantitatively predicted by this model. Polarized Raman spectroscopy has been applied for systems (Li, Na)_2CO_3 to investigate the rotational relaxation of the C_<3V> axis of the CO_3^<2-> ion. No appreciable relation has been found between the mobility and the rotationa motion.