Effect of Potassium Carbonate Additions on the Oxygen Reduction Current and the NiO Solubility in a 52/48 mol% Li/Na Carbonate Melt

Abstract

Adding 5 wt% of K₂CO₃ to a 52/ 48 mol% Li/Na carbonate melt increased the oxygen reduction current in Steady State Voltammograms (SSV) measured in half cell set-up's with a factor of 3 at 650°C. A gas atmosphere with a P (O₂) and P (CO₂) of 5% with balance Nitrogen was used. Adding more K₂CO₃ proved not to be more beneficial. This increase varied with temperature between 600 and 750°C, but was never lower than a factor of two. The NiO solubility increased from 0.35 to 0.6 and even 0.8µmol cm⁻³ at 650°C by adding 5 and 8 wt% of K₂CO₃ respectively.

These results indicate that adding 5 wt% of K₂CO₃ to the Li/Na electrolyte will increase MCFC performance, using the important cathode gasses lean in oxygen and/ or CO₂, but lower MCFC cathode endurance due to NiO solubility substantially. However despite the large increase of NiO solubility this work in half cell set-up's shows that it is worthwhile trying to optimize MCFC cathode polarization versus endurance by adding small amounts of K₂CO₃ to the 52/48 mol% Li/Na electrolyte.