Preparation of cathodes for thin film SOFCs

Abstract

Abstract. SOFCs are expected to become competitive devices for electrical power generation, but successful application is dependent on decreasing working temperature from 1000 to 800 ~ without detrimental effects on resistance and on electrode processes. This requires a reduction of the stabilized zirconia electrolyte thickness and an optimization of the electrodes, especially the cathode, where losses are higher. Strontium doped lanthanum manganites are the most common materials tested as cathodes for SOFCs working at high temperature (1000 ~ This cathode material presents high electronic and oxygen-ion conductivities, a thermal expansion coefficient compatible with stabilized zirconia and good catalytic activity.For thin film SOFC devices working at intermediate temperatures (less than 800~ we have studied the optimization of this type of cathode. Strontium doped lanthanum manganite has been deposited on yttria stabilized zirconia electrolyte substrates by spray-pyrolysis and by RF sputtering. The electrode performances depend strongly on cathode microstructure, influenced by processing conditions. With spray-pyrolysis processes, large porosity is expected. This is important for the supply of oxygen, via O2 molecules through the pores to the triple phase boundaries, where the gas, the cathode and the electrolyte are in contact and where oxygen reduction may occur. However, large porosity can have a nefaste effect on electronic conductivity. With RF sputtering, denser films with higher electronic conductivity are obtained. But, in that case, the supply of oxygen occurs via adsorbed O-atoms in a diffusion process through the cathode to the electrolyte. Spraypyrolysis and RF sputtering have been compared relative to electrode properties.

Effect of La 0.8 Sr 0.2 MnO 3 powder addition in the precursor solution on the properties of cathode films deposited by spray pyrolysis

“…Table 3 shows the average crystallite size calculated from Equation 1. The values are in agreement with those in literature related to LaMnO 3 films deposited by spray pyrolysis and doped with divalent cations [19,25], where these crystallite sizes varied from 30 to 60 nm depending on the dopant concentration and on the annealing temperature. Table 3: Average crystallite size of the YSZ-U/LSM and YSZ-U/LSM-CO films.…”

“…The spray pyrolysis technique is a convenient alternative to the traditional methods, because of the simplicity, low cost, versatility, efficiency and low waste production [16]. This technique was used by CHARPENTIER et al [11,19], in the preparation of LSM films by a modified spray pyrolysis method. Instead of producing lanthanum strontium manganite from the precursor solutions directly onto a substrate, the La 0.7 Sr 0.3 MnO 3-δ powder was previously prepared and then added to the solution containing lanthanum nitrate, strontium acetate and manganese nitrate.…”

Spray pyrolysis of La0.6Sr0.4Co0.2Fe0.8O3-δ thin film cathodes

“…also identified the solution-flow rate to have a minor influence on the film morphology, especially as long as a certain limit is not exceeded, which then would result in crack formation. Only one reference is found attributing a major role to the solution flow rate [12]. The authors report a significant change in microstructure from particle aggregates obtained at low solution-flow rates to a more layered structure obtained at high solution-flow rates.…”

“…Electrochromic materials [13,27], catalytically active thin films [14,16,21] and battery components [14,16,21,28] are also fabricated by means of spray pyrolysis. Solid oxide fuel cell (SOFC) electrolytes [6,7,[18][19][20]25], interconnectors [5] and cathodes [4,9,12,23] have also been prepared.…”

SIMS Characterization of La0.7Sr0.3MnO3 Films for Solid Oxide Fuel Cell Applications

“…Therefore, one of the most important research efforts in SOFCs technology consists in reducing the normal operating temperature 5 . A promising approach to this issue can be the synthesis of nanostructured cell component materials, so as to increase the real surface area of the electrodes and thus enhance their performances 6 . Focusing on this target, high surface area La 1-x Sr x MnO 3 (x ≈ 0.3) films were prepared in this work by the nitrate-citrate Pechini process 4,7,8 on silicon wafers substrates.…”