Effect of Cs2CO3 in Li/K and Li/Na Carbonate on the Oxygen Reduction Reaction for MCFC

Electrolyte properties are significantly important for the long-term stability and performance of molten carbonate fuel cells (MCFCs). The Li/Na carbonate is considered an attractive electrolyte for MCFCs due to its high ionic conductivity and low volatility. However, low oxygen solubility is a serious drawback in Li/Na carbonate electrolytes, which hinders the oxygen reduction reaction (ORR) at the MCFC cathode. Several additives have been found to enhance the oxygen solubility in alkali carbonate electrolytes. In this study, the effect of Cs2CO3 in Li/Na and Li/K carbonate mixtures was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The oxygen reduction activity improved with the increasing Cs concentration (1, 3, and 5 mol%) in all the studied carbonate melts. The addition of Cs2CO3 (5 mol%) to the Li/Na carbonate (68.0/32.0) resulted in an approximately 30% increase of the mass transfer parameter (C-0 root D-0) of the dissolved oxygen species from 0.99 x 10(-9) to 1.29 x 10(-9) mol/cm(2) s(1/2) at 620 degrees C. The changes in the ionic conductivity of the molten electrolytes with the Cs additive were also studied. (C) 2016 The Electrochemical Society. All rights reserved.