NiO Solubility in Molten Li/K Carbonate under Molten Carbonate Fuel Cell Cathode Environments

Abstract

The corrosion of molten carbonate fuel cell (MCFC) NiO cathodes during cell operation has been brought to attention recently and is considered one of the major technical difficulties facing MCFC development at the present time. NiO, solubilized in the molten Li/K carbonate (62/38 mole ratio) at the cathode/carbonate interface, is diffusionally transported through the carbonate reservoir towards the anode. At some location intermediate between the two electrodes, the local cell environment's oxygen partial pressure decreases below the level where NiO is stable and metallic nickel precipitates. Recent evidence obtained from cell tests has shown the extent of cathode degradation to be accelerated by increasing either the PCO/sub 2/ or the total P(CO/sub 2/ + O/sub 2/) supplied to the cathode. This is important since commercial fuel cells are expected to operate with oxidant gases such as humidified 30% CO/sub 2//bal air at elevated pressures of between 6 and 10 atm. Estimations of the extent of cathode degradation occurring under these elevated pressures requires an understanding of how the NiO/carbonate equilibrium changes as a function of changing cathode gas environment. This note documents the measured equilibrium NiO solubility in Li/K carbonate melts under various humidified CO/sub 2//O/sub 2//N/sub 2/ gases containingmore » a constant P /SUB CO2/ /P /SUB O2/ ratio of 2/1.« less