Combustion Synthesis of Doped Lanthanum Gallate as an Electrolyte for Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cells, SOFCs, have attracted worldwide attention from wide applicability in a large-sized power plant, a distributed power supply, and an efficient cogeneration apparatus with extremely high efficiency of power generation. Doped-lanthanum gallate (La(Sr)Ga(Mg)O3), which has been recently proposed as a new solid electrolyte, replaces Yttria Stabilized Zirconia (YSZ), lowers the operating temperature of SOFC and then improves the mechanical reliability of the cells. In this study, the doped-lanthanum gallate was produced by combustion synthesis and its sintering behavior, the electrical conductivity, and life cycle assessment of this process from energy requirement and a carbon dioxide emission were analyzed by comparing with the conventional solid-state method. In the experiments of the combustion synthesis, lanthanum oxide, strontium carbonate, gallium oxide, metallic magnesium, and sodium perchlorate were well mixed with different substitution ratios of gallium by magnesium; 80, 60, 40, and 30 mole%, by using a ball mill and were ignited at one end of the mixture at nitrogen atmosphere to complete the combustion wave propagation of the exothermic reaction to the other end without any additional energy. As a result, all of the products, except the 80 mole% magnesium-containing lot, showed definite peaks of intermediates containing lanthanum gallate in X-Ray Diffraction (XRD) patterns. Most significantly, the product containing 30 mole% magnesium, which was completely sintered at 100 K lower temperature (1673 K) compared to the solid state method (1773 K), showed the highest electrical conductivity, 0.08 Scm � 1 at 1073 K without the dependency of oxygen partial pressure, being almost the same as the world record. The results demonstrated that the combustion synthesis of SOFC electrolyte had the possibility of an innovative production process with several benefits, such as shortening of processing time, minimizing energy requirement and carbon dioxide emission, and deriving the excellent property of SOFCs.