Solubility and Transport of NiO Cathodes in Molten Carbonate Fuel Cells

Abstract

Equilibrium NiO solubility measurements were made in Li 2 CO 3 /K 2 CO 3 mixtures as a function of temperature, ambient gas environment, and salt composition for gases containing 3.1% H 2 O. The equilibrium solubility was found to increase with increasing temperature, CO 2 partial pressure, and cation fraction Li + and to decrease slightly with increasing O 2 partial pressure. These results were coupled with theoretical predictions of (1) O 2 , H 2 , and CO 2 activities and (2) compositional gradients which develop across the electrolyte structure of an operating carbonate fuel to explain the two distinct regions of nickel precipitation across the fuel cell. Precipitation occurs near the cathode because NiO solubility decreases commensurate with electrolyte compositional gradients, whereas the second region deeper within the electrolyte matrix results from a decreased O 2 activity.