Characterization of LSM-YSZ Composites Prepared by Impregnation Methods

Abstract

Composites of La 0.8 Sr 0.2 MnO 3 ͑LSM͒ and yttria-stabilized zirconia ͑YSZ͒ were prepared by impregnating porous YSZ with salts of Sr, La, and Mn to 40 wt % LSM. The effect of calcination temperature on cathode performance at 973 K was then studied using both symmetric cells and solid oxide fuel cells ͑SOFCs͒. Following calcination at 1123 K, the LSM in the composite remained porous. In symmetric-cell tests, LSM͑1123͒-YSZ electrodes exhibited a low loss, 0.5 ⍀ cm 2 , which was unchanged by polarization; however, in fuel cell tests, the performance was poor at current densities above 0.2 A/cm 2 . Following calcination at 1323 or 1523 K, LSM formed a dense layer coating on the YSZ. In symmetric-cell tests, the composite exhibited an ASR greater than 4 ⍀ cm 2 , but this decreased, reversibly, upon cathodic polarization or upon heating in humidified H 2 at 973 K. In fuel cell tests, the performance of composites calcined at 1323 K was superior to ones at 1523 K, primarily because the ohmic resistance of the cell was 0.25 ⍀ cm 2 higher after 1523 K, probably due to solid-state reactions with the electrolyte. The optimal conditions for forming impregnated LSM-YSZ cathodes and the reasons for the observed hysteresis in cathode polarization are discussed based on these results.

Synthesis and Stability of a Nanoparticle-Infiltrated Solid Oxide Fuel Cell Electrode

“…Note that the applied current density was initially set at 150mA/cm 2 , but declined somewhat after 366 hours to a low of ~ 141 mA/cm 2 , due to a LBNL-62011 slight experimental instability; upon readjustment to 150 mA/cm 2 at 457 hours, the cell performance once again returned to the original voltage. These results may be contrasted to those reported by Huang et al, 9 which appear to show a significant performance decline after 100 hours at 700°C.…”

“…Nanoparticulate catalysts may be infiltrated into already formed SOFC electrodes to enhance electrode performance [1][2][3][4] , and new electrode designs have been devised utilizing continuous nanoparticulate networks or connected nanoparticle rafts [4][5][6][7][8][9] . In these electrode designs, the nanoparticulates not only serve as reaction sites, but also provide an electron pathway from the current collector to the individual reaction sites.…”

Nanostructured Solid Oxide Fuel Cell Electrodes

“…[27][28][29][30][31] Figure 11. SEM image of FIB corss-sectioned nanoparticulate LSM-infiltrated cathode.…”

“…Hence, persistent connectivity of the nanoparticulate networks and limited coarsening are essential to stable electrode function. Although a number of papers have been published on nanoparticle-infiltrated electrodes, [26][27][29][30][31] little mention has been made of the extended stability of such structures. The difficulty is that SOFC electrodes operate under demanding operating conditions: elevated temperatures (600°C -1000°C), thermal cycling, high local current densities, and high local potential gradients.…”

A study of carbon formation and prevention in hydrocarbon-fueled SOFC

“…These slurries included graphite and polystyrene pore formers, so that the slabs had a porosity of 65% after having been fired to 1823 K. The slabs had a bimodal pore-size distribution, with 1.5-µm pores arising from the graphite pore formers and 20-µm pores from the polystyrene [28]. The BET surface area of the slabs was 0.7 m 2 /g [29].…”