Thermo-electrochemical cell performance and physicochemical properties of the molten carbonate electrolyte dispersed with different solid oxides

Abstract

In molten carbonate thermo-electrochemical cells (thermocells), the dispersion of solid oxide in the molten electrolyte was found to improve conditions of thermoelectric energy conversion. However, stability of the solid oxide in eutectic (Li,Na)2CO3 electrolyte is crucial. The change in cell performance, due to compositional changes in the electrolyte mixture using various selected solid oxides, was studied. The solid oxides of Al2O3 or LiAlO2 were chemically reactive and no stable cell potential was observed when these compounds were added compared to when solid MgO or CeO2 were added. Also, a solid MgO-dispersion in the electrolyte delivered a larger Seebeck coefficient of −1.8 mV/K, favoring this oxide all together. The impact of the surface area of solid grains of MgO on the cell performance was investigated. From the electrical (σ) and thermal (λ) conductivity of the electrolyte mixture, along with the measured Seebeck coefficient (αs), the figure of merit (ZT) was determined. In addition to having a high stability, the dispersion of solid MgO with large surface area provided a better (σ/λ) ratio, and a larger αs (-1.8 mV/K) as well as ZT (1.1).