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Abstract: Without Sr addition, the sintered La2O3 and CuO powder mixture in a mole ratio of 1:2 formed K2NiF4-structured La2CuO4 with excess CuO. When 15% of strontium was added, La2CuO4 transformed into the single perovskite La1−x Sr x CuO2.5−δ phase with orthorhombic structure. As the strontium addition increased to 20%, the perovskite lattice changed from orthorhombic to tetragonal. These phase transitions may be attributed to the enhanced oxidation of the divalent cupper ions (Cu2+) to trivalent ones (Cu3+) by the strontium addition. Based on the electroneutrality in an ABO3 perovskite lattice, a divalent cation is unstable in the B-site cation sub-lattice when the A-site is occupied by a trivalent cation such as La3+. As strontium was added into the A-site cation sub-lattice, the oxidation of Cu2+ ion into trivalent Cu3+ ion was enhanced. The increase of Cu3+ concentration strengthened the electrostatic bonding (ESB) of copper ions with their neighboring anions. Consequently, the symmetrical tetragonal Sr-doped lanthanum copper oxide was obtained. [Copyright &y& Elsevier]

Abstract: This study presents the woks on the electrochemical characterization and performance evaluation of using La0.75Sr0.25CuO2.5−δ (LSCu) as cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC). The cell performance measurement was conducted on the Ni–YSZ anode supported single cell using the yittria-stabilized zirconia (YSZ) thin film (ca. 8μm) as electrolyte, and porous LSCu layer as cathode (ca. 80μm). The AC-impedance analyses were carried out by electrolyte supported LSCu/YSZ/Pt half-cell because of the thin YSZ film and the unsymmetrical between cathode and anode in the anode supported single cell may lose the accuracy. According to the analyses of the AC-impedance spectra, the spectra can be characterized by two arcs. The larger arc at low frequencies maybe attributed to the electrode polarization caused by the adsorption/desorption of the molecular oxygen, and the diffusion of oxygen ions. On the other hand, the much smaller one at high frequencies was attributed to the polarization during charge-transfer. The interface resistance was decreased by current passing. After 30min of 200mAcm−2 current was passed, the overall resistance was decreased from 5.01 to 0.25Ω. For the performance testing, the maximum power density at 800°C is 0.65Wcm−2 with 150 and 500sccm of hydrogen and air flows, respectively. According to these results, LSCu is a potential cathode material for the IT-SOFC. [Copyright &y& Elsevier]

Abstract: Conventionally, noble metals such as Pt and Pt–Ru bimetallic system were utilized as electrocatalyst for methanol oxidation in acid and alkaline media. However, during the oxidation reaction, these noble metals are poisoned by the methanol oxidation intermediates, such as CO or COH species. Therefore, the utilization of electrochemically active conducting metal oxide (substituted perovskite oxide) may be a solution for avoiding such poisoning effect. In this study, the electrocatalytic activity of Sr substituted lanthanum metal oxide of La1−x Sr x MO3−δ (where M = Co and Cu), were demonstrated towards direct methanol oxidation by cyclic voltammetry measurements. To further enhance the electrochemical activity, the perovskite electrocatalysts in this study was prepared in the nanoscale by the polymer modified sol–gel method using polyacrylic acid as a chelating agent. The strontium substituted lanthanum cobaltite and cuprate were synthesized in homogeneous nanosize particles of about 25–30nm. The characterizations and electrocatalysts of the nanocrystalline perovskite were demonstrated by XRD, TGA, TEM, iodometric titration, and cyclic voltammetry. [Copyright &y& Elsevier]

Oxygen-deficient perovskite type oxides La1-xSrxCuO2.5-δ (LSCu) have been synthesized in the composition range: 0.15≤x≤0.3. Due to their high oxygen vacancy concentration and good electrical conductivity, these materials are characterized as new positive electrode (cathode) materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The valence state of copper ions, thermal expansion, cathodic overpotential, reactivity with yttria-stabilized zirconia (YSZ) and polarization resistance (Rp) of the LSCu|YSZ interface are examined. At 800 °C, the sample with the composition of La0.7Sr0.3CuO2.5-δ exhibits the lowest overpotential of about 10 and 12.6 mV at a current density of 150 and 200 mA cm-2, respectively. LSCu show no reaction against yttria-stabilized zirconia (8YSZ) at 800 °C for 1000 h. Reaction between LSCu and YSZ occurs, however, at 900 °C for 10 h. The formation of SrZrO3 is observed.Based on the results of ac impedance analyses, the polarization resistance of LSCu decreases from 0.85 to 0.25 Ω at 800 °C when the fraction of Sr is increased from 20 to 30%. The reduction of polarization resistance is improved by the presence of oxygen vacancies in LSCu. These oxygen vacancies provide numerous pathways for the diffusion of oxygen ions electrode surface to the triple phase boundary (TPB) and the electrode|electrolyte interface. Therefore, LSCu may be a very attractive cathode material for IT-SOFCs. [Copyright &y& Elsevier]

La1−xSrxCuO2.5−δ (LSCu), which exhibit excellent electrical conductivity and oxygen vacancies were investigated as potential cathode materials for solid oxide fuel cell (SOFC) applications. The structure stability, electrical conductivity, cathodic overpotential, and the reactivity with yttria-stabilized zirconia (YSZ) were examined in this study. It was found that the LSCu perovskite was obtained only when the addition of strontium fell in the range between 15 and 30%. With more than 20% of strontium addition, this material showed excellent electrical property and immunity to the reaction with YSZ at 800 °C. The conductivities of LSCu were as high as 900 S/cm at 600 °C, and 800 S/cm at 800 °C. The cathodic overpotential of this material was approximately 3.8 and 10.6 mV at a current density of 100 mA/cm2 at 850 and 750 °C, respectively. These properties are superior to Sr-doped lanthanum manganite (LSM), which is the state-of-the-art cathode material of SOFCs. [Copyright &y& Elsevier]