Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

In this study, the effects of various amounts of Ga³⁺ dopants on the densification, phase structure, microstructure and electrical conductivity of La_9.5Ge_6.0O_26.25 ceramics are examined. The incorporation of Ga³⁺ ions into the La_9.5Ge_6.0O_26.25 lattices leads to the retardation of the densification and an increase in the triclinic structure, caused by the evaporation of GeO2 and the largeness of the size difference between the Ga₃₊ ions and Ge₄₊ ions. Of the compositions studied, the La_9.5Ge_5.7Ga_0.3O_26.1 ceramic sintered at 1450°C shows an electrical conductivity of 4.02×10^-2 Scm^-1 at 800°C, which is higher than that of an 8YSZ ceramic. The calculated thermal expansion coefficient (CTE) of this ceramic of 10.4 × 10^-6K^-1 appears to be compatible with those of the common adjacent materials used in solid oxide fuel cells (SOFCs). A single cell with a La_9.5Ge_5.7Ga_0.3O_26.1 electrolyte 0.51mm in thickness is built and evaluated. The cell has R0 and RP values of 0.80 and 0.28ω-cm², respectively, at 850°C. The open circuit voltage (OCV) and maximum power density (MPD) of the single cell are recorded as 1.002Vand 0.24Wcm^-2 at the measurement temperature of 850°C. Through the incorporating of a thick La_9.5Ge_5.7Ga_0.3O_26.1 layer, the cell performance of the single cell with the La_9.5Ge_5.7Ga_0.3O_26.1 electrolyte is superior to that of SOFC cells with a similar electrolyte thickness reported in the literature, thus qualifying the La_9.5Ge_5.7Ga_0.3O_26.1 ceramic as a potential electrolyte material for SOFCs.