A study of perovskite electrolytes and electrodes for intermediate-temperature solid oxide fuel cell applications

Several perovskite electrolytes and electrodes were investigated for intermediate-temperature {dollar}(600{lcub}-{rcub}800spcirc{dollar}C) solid oxide fuel cell (SOFC) applications. All the perovskites studied in this work, including doped {dollar}rm LaAlOsb3{dollar} and {dollar}rm LaGaOsb3,{dollar} exhibit some p-type electronic conduction at high oxygen partial pressure {dollar}(10sp{lcub}-5{rcub}{dollar} to 1 atm). Among them, {dollar}rm (Lasb{lcub}0.9{rcub}Srsb{lcub}0.1{rcub}) (Gasb{lcub}0.8{rcub}Mgsb{lcub}0.2{rcub})Osb{lcub}3-delta{rcub}{dollar} (LSGM) has the smallest electronic conduction at high oxygen partial pressure. The thermal expansion coefficient of LSGM matches that of the other components in a SOFC. LSGM shows the highest oxygen-ion conductivity over a wide range of oxygen partial pressure and temperature, and it is a promising electrolyte material for SOFCs. The chemical compatibility study revealed that perovskite electrode materials, such as {dollar}rm Lasb{lcub}0.6{rcub}Srsb{lcub}0.4{rcub}MnOsb3{dollar} (LSM), {dollar}rm Lasb{lcub}0.6{rcub}Srsb{lcub}0.4{rcub}Cosb{lcub}0.2{rcub}Fesb{lcub}0.8{rcub}Osb3{dollar} (LSCF), {dollar}rm Lasb{lcub}0.6{rcub}Srsb{lcub}0.4{rcub}CoOsb3{dollar} (LSC) and {dollar}rm Lasb{lcub}0.6{rcub}Srsb{lcub}0.4{rcub}Cosb{lcub}0.9{rcub}Nisb{lcub}0.1{rcub}Osb3{dollar} (LSCN) did not react with the perovskite electrolyte (LSGM) to form new phases, but did form solid solutions. The chemical stability study of LSGM in a {dollar}rm COsb2{dollar} environment showed that no carbonates formed and the weight did not increase after prolonged annealing. Study of the microstructure-property relations of several perovskite electrodes on a LSGM electrolyte indicated that electrode powders prepared by aerosol spray pyrolysis (ASP) that were sintered onto the electrolyte at {dollar}1100spcirc{dollar}C possessed the lowest interfacial resistance and overpotential. The lowest interfacial resistance and overpotential were for LSC/LSGM and LSCN/LSGM cells. Oxygen reduction was studied at interfaces between LSGM electrolyte and LSC or LSCN cathode. Charge transfer is the rate-determining process for oxygen reduction at the LSC/LSGM interface. Oxygen dissociation and charge transfer appear to be approximately equivalent to the overall oxygen reduction process at the LSCN/LSGM interface. SOFCs with LSGM based electrolytes had a higher oxygen reduction rate and higher maximum power density at {dollar}800spcirc{dollar}C than YSZ based SOFCs made in this study. The LSC/LSGM cell has the highest maximum power density of all the systems tested in this study, and it is suggested to be suitable for an intermediate-temperature SOFC.