Observation of cation diffusion and phase formation between solid oxide layers of lanthanum gallate-based fuel cells

Abstract

The structural irregularities of solid-oxide layers for fuel cells prepared by electrophoretic deposition and co-sintering were examined using electron-probe microanalysis (EPMA) and X-ray analysis. The solid-oxide electrolyte layer with Sr- and Mg-doped lanthanum gallate (LSGM) prepared on a NiO-yttria-stabilized zirconia (YSZ) anode with an inserted Gd-doped ceria (GDC) buffering interlayer was not rigid. EPMA of the cross-section showed diffusion of La and Sr out of LSGM, and Ni, Y, and Zr out of NiO-YSZ. Using synchrotron radiation, X-ray absorption near-edge structures of the layer cross-sections were examined using an X-ray fiuorescence yield method. The spectral features supported the formation of SrLaG3O7 and La-doped GDC by a reaction between the layers. The formation of these and other oxides was also confirmed by X-ray powder diffraction patterns. Because the electrophoretic deposition layers were co-sintered, elemental diffusion must have occurred before the synthetic powders were well fused and fixed in each layer. As an alternative to GDC, La-doped ceria (LDC) was synthesized, and La diffusion between LSGM and LDC was examined using X-ray powder diffraction. LDC, which contains 40% La, seems to be the best material to suppress La migration.