Development of lanthanum strontium manganite based solid oxide fuel cell electrode by advanced mechanochemical process

Abstract

In this research, synthesis of La[subscript 0.8]Sr[subscript 0.2]MnO[subscript 3] (LSM) power by advanced mechanochemical process using a mixture of industrial-grade La[subscript 2]O[subscript 3], SrCO[subscript 3] and Mn[subscript 3]O[subscript 4] powders was investigated. In the present milling process, no media balls were employed, and mechanical activation was applied through frictions among particles in powder mixture. Under humid atmosphere (RH 70% at 25 degree celsius), XRD peak intensities of the starting powder decreased, and the specific surface area of the powder mixture increased during the early stage of the milling (<10min). During further milling, the peaks of LSM started to appear. Differential thermal analysis (DTA) suggests that the present mechanical activation brought about the decomposition of SrCO[subscript 3] and the phase change if Mn[subscript 3]O[subscript 4]. Single phase of LSM was obtained by annealing the milled powder mixture (after 60 min of milling) at relatively lower temperature of 900 degree celsius, and its particle size was about 100 nm. The present process resulted considerably lower release of contamination from the milling media. In addition, the influence of the water content of the starting powder mixture on the mechanochemical synthesis of La[subscript 0.8]Sr[subscript 0.2]MnO[subscript 3] (LSM) powder was investigated. The water content of the starting powder mixture was varied up to 2.0 wt.% With water content of 2.0 wt.%, disordering of the crystalline starting powders rapidly processed. However, single phase LSM powder was not obtained. At a proper water content (<0.2 and at 0.8 wt.%), fine grinding of the mixture occurred during the early stage of the milling and single phase LSM powder was obtained after 120 min of milling. The specific surface area (SSA) of the LSM powder was 5.0 m[superscript 2]/g and the particle size calculated from the SSA was approximately 180 nm. Furthermore, La[subscript 0.8]Sr[subscript 0.2]MnO[subscript 3] (LSM)/ Y[subscript 2]O[subscript 3] stabilized ZrO[subscript 2] (YSZ) composite powders were mechanically prepared. By changing the mechanical conditions, three composite powders with different size distributions were obtained. They were used to fabricate the cathodes of solid oxide fuel cells (SOFCs). Microstructures of the cathodes were carefully characterized by scanning electron microscope (SEM). Losses of internal resistance (IR) and polarization between the electrolyte and the cathode were measured with a current interruption technique. The cathode fabricated from the composite particles with narrow particle size distribution showed fine grains, uniform porous structure, and good contact within the electrolyte layer, and therefore it showed low IR and polarization losses. In contrast, the cathode fabricated from composite particles with large amount of coarse particles exhibited a non-uniform structure in grains and pore structure, resulting in high IR and polarization losses.