Intermediate Temperature Solid Oxide Fuel Cells Using LaGaO[sub 3] Electrolyte II. Improvement of Oxide Ion Conductivity and Power Density by Doping Fe for Ga Site of LaGaO[sub 3]

Abstract

Solid oxide fuel cells (SOFC) provide a new and clean electric power generating system At present, Y 2 O 3 -stabilized ZrO 2 (YSZ) is commonly used as the electrolyte of a solid oxide fuel cell. Since the oxide ion conductivity of YSZ is insufficient for the electrolyte of fuel cells, a thin electrolyte film without gas leakage and an excessively high operating temperature such as 1273 K are essential for the high power density of SOFCs when YSZ is used as electrolyte. On the other hand, all the advantages of SOFC such as a high efficiency and a variety of usable fuels can be obtained at decreased temperatures such as 1073 K. Furthermore, the choice of the materials for cell construction becomes wider; in particular, cheap refractory metals such as a stainless steel will be usable by decreasing the operating temperature to 900 K. Consequently, decrease in operating temperature is an important subject for the development of the cheap but the reliable SOFCs. 1 In order to develop the intermediate temperature SOFC, an active electrode, in particular, the cathode electrode catalyst, and an electrolyte with a low resistance are essential. Ceria doped with Gd or Sm is considered for the candidate electrolyte of the intermediate temperature SOFC. 2 However, ceria-based oxide exhibits a significant electronic conduction in the reducing atmosphere, 2 which causes various problems for the application of SOFC. 3-5 On the other hand, preparation of a very thin YSZ film (less than 10 m thick) is another solution method for decreasing the operating temperature, and various methods are now under investigation. 6 Except for making a very thin YSZ film, it is of great importance for the intermediate temperature SOFCs to develop new electrolyte materials which exhibit a high oxide ion conduction over a wide range of oxygen partial pressures. In our previous study, the oxide ion conductivity in the perovskite oxide was investigated, and it was found that the LaGaO 3 -based perovskite-type oxide exhibits high oxide ion conductivity, 7,8 which is comparable to that of CeO 2 -based oxide. In particular, LaGaO 3 doped with Sr for La and Mg for Ga sites (denoted as LSGM) exhibits a high oxide ion conductivity stably over a wide range of oxygen partial pressure. 9-12 It is generally believed that doping with a transition metal cation is undesirable for the ionic conductor due to the appearance of electron or hole conduction. 13 However, it was found that the oxide ion conductivity was also improved by doping Co for Ga site of LSGM, although hole conduction appeared slightly in the high oxygen partial pressure range. Furthermore, it became clear that the application of Co-doped LSGM for the electrolyte of SOFC greatly improves the power density of the cells at low temperature. On the other hand, it was found that doping Fe also has similar positive effects on the electrical conductivity in LaGaO 3 -based oxide. In the present study, therefore, effects of Fe doping on the oxide ion conductivity in LSGM were studied systematically. In addit...

Electrode materials: a challenge for the exploitation of protonic solid oxide fuel cells

“…For a couple of decades, HTPCs have been recognized as particularly suitable electrolytes for IT applications, because, compared with oxygen-ion conductors, they show lower activation energy (between 0.4 and 0.6 eV) [12][13][14][15] and larger conductivity values in the IT range (figure 1) [14,[16][17][18][19]. Moreover, for HTPC-based FCs, water is produced at the cathode rather than at the anode, avoiding fuel dilution, which reduces the cell efficiency.…”

Sol–gel synthesis, X-ray photoelectron spectroscopy and electrical conductivity of Co-doped (La, Sr)(Ga, Mg)O3− perovskites

“…[1][2][3] Following the initial discovery, [1][2][3][4][5] numerous experimental studies have been carried out on LSGM materials, which also include the effect of transition-metal doping. [6][7][8][9][10][11] It is generally believed that doping with a transition-metal cation is undesirable for * Corresponding author. Tel.…”

Sol–gel synthesis and characterization of Co-doped LSGM perovskites

“…4 Following the initial discovery, [1][2][3][4][5] numerous experimental studies have been carried out on LSGM materials, which also include the effect of transition-metal doping. [6][7][8][9][10][11] It is generally believed that doping with a transition metal cation is undesirable for the ionic conductor due to the appearance of n-or p-type conduction. However, it was found that the oxide ion conductivity was also improved by doping Co for Ga in LaGaO 3 -based perovskites, 7 although hole conduction was detected at high oxygen partial pressures.…”