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

Abstract 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 (Li 0.52 Na 0.48 ) 2 CO 3 –(Li 0.62 K 0.32 ) 2 CO 3 , (Li 0.62 K 0.32 ) 2 CO 3 –(Li 0.44 Na 0.30 K 0.26 ) 2 CO 3 , and (Li 0.44 Na 0.30 K 0.26 ) 2 CO 3 –(Li 0.52 Na 0.48 ) 2 CO 3 binary systems decrease with the increase of Li 2 CO 3 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 (Li 0.52 Na 0.48 ) 2 CO 3 is over 70 mol% in (Li 0.52 Na 0.48 ) 2 CO 3 –(Li 0.62 K 0.32 ) 2 CO 3 system while over 50 mol% in (Li 0.44 Na 0.30 K 0.26 ) 2 CO 3 –(Li 0.52 Na 0.48 ) 2 CO 3 system. On the contrary, the equilibrium vapor pressure of oxygen molecule abruptly increases at the same composition range.