Enhanced O2 solubility by RE2O3 (RE = La, Gd) additions in molten carbonate electrolytes for MCFC

The solubilization of O2 reactant gas in mixtures of molten alkali carbonate, which are to be used as electrolytes in the Molten Carbonate Fuel Cells, has been investigated as a function of melt composition, temperature and O2-CO2 gas atmosphere. The baseline content of dissolved oxygen in (52 + 48) mol% Li2CO3 + Na2CO3 and (62 + 38) mol% Li2CO3 + K2CO3 is markedly increased by the additions of 0.5 mol% rare-earth (RE = La and Gd) oxides to the melts. By a curve-fitting method the mechanisms through which oxygen dissolves into the melts are predicted. At 923 K the oxygen dissolution mechanism passes from a superoxide path, which is dominant in the additive-free melts, to either a prevalent peroxide path in the Li-Na melt or a mixture of superoxide and peroxide ions in the Li-K electrolyte. At lower temperature (873 K) RE oxide additives are effective in modifying the oxygen dissolution mechanism only for the Li-Na melts.