Solubility of NiO as cathode material for MCFC in alkali carbonate melts

An optimized alkali carbonate composition of 47.4 mol% Li2CO3/32.6 mol% Na2CO3/20 mol% K2CO3 is proposed for molten carbonate fuel cells. This composition was obtained by considering both the oxygen solubility and the electrolytic conductivity in various electrolyte compositions. Solubility measurements of NiO in this composition is also reported and compared with these in Li/K and Li/Na carbonate melts under atmospheric O-2/CO2=90/10 or O-2/CO2=20/80 gas mixtures. It has been found that under O-2/CO2=90/10 NiO has almost the same solubility in all melts. On the other hand under O-2/CO2=20/80, the 70 mol% Li2CO3/30 mol% Na2CO3 melt exhibits the lowest NiO solubility. If the electric conductivity were the only factor determining cell performance, also the 70 mol% Li2CO3/30 mol% Na2CO3 melt would be selected as the electrolyte of choice for MCFC. On the condition that oxygen solubility, electrolytic conductivity, and NiO solubility were to be considered, the 47.4 mol% Li2CO3/32.6 mol% Na2CO3/20 mol% K2CO3 ternary melt would be the best candidate for MCFC.