Electrochemical stability and solubility of Ni–Fe–Co ternary alloy oxides in Li/Na carbonate eutectic as an alternative material for MCFC cathodes

Abstract

Electric conductivity, cathodic performance, and stability of Ni–Fe–Co alloy oxides in Li/Na carbonate are investigated by means of electrochemical measurements and X-ray diffractometry. Higher electrochemical stability on oxygen reduction was observed with the single-phase oxides of space group Fmm, which were obtained with Co content less than 20 at.% and Ni/Fe/Co=0.19/0.34/0.47. Electrode impedance measurements at 1 kHz revealed that the conductivity of the oxides decreased with increasing the amount of Fe. A newly developed technique for solubility measurements showed that the solubility of Ni²⁺ from Ni–Fe–Co oxides in Li/Na carbonate decreased with increasing the amount of Fe content. In summary, Ni–Fe–Co complex oxides consisting of Fe less than 20 at.% and Co less than 20 at.% demonstrate favorable features for MCFC cathode materials.