Predictions of the optimum ternary alkali-carbonate electrolyte composition for MCFC by computational calculation

Various kinds of phase diagrams for Li–Na–K ternary carbonate systems were plotted and the vapor pressures of chemical species such as alkali cations and oxygen molecule at various compositions and various temperatures were calculated by computational manipulation of thermodynamic databases. The liquidus temperature of (Li0.52Na0.48)2CO3–(Li0.62K0.32)2CO3, (Li0.62K0.32)2CO3–(Li0.44Na0.30K0.26)2CO3, and (Li0.44Na0.30K0.26)2CO3–(Li0.52Na0.48)2CO3 binary systems decrease with the increase of Li2CO3 content without any ternary intermediate compound. Total vapor pressure of alkali metal species governed by the summation of the vapor pressure of free Na and K and the vapor pressure of alkali metal species starts to decrease abruptly when the content of (Li0.52Na0.48)2CO3 is over 70 mol% in (Li0.52Na0.48)2CO3–(Li0.62K0.32)2CO3 system while over 50 mol% in (Li0.44Na0.30K0.26)2CO3–(Li0.52Na0.48)2CO3 system. On the contrary, the equilibrium vapor pressure of oxygen molecule abruptly increases at the same composition range.