• Journal of Hydrogen and New Energy
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• v.27 no.3
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• pp.276-282
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• 2016

The effects of conductive additives in a $La_{0.8}Sr_{0.2}MnO_3$ perovskite bifunctional electrode for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated in an alkaline solution. Highly porous carbon black (CB) and Ni powder were added to the bifunctional electrodes as conductive additives. The surface morphologies of electrodes containing CB and Ni were observed by scanning electron microscopy (SEM). The current densities for both ORR and OER were changed by the addition of CB. The conductive additive changed physical properties of bifunctional electrodes such as the sheet conductance, gas permeability and contact angle. It was observed that the air permeability of electrode was most effective to enhance the currents for ORR and OER.

• Journal of Sensor Science and Technology
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• v.17 no.3
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• pp.203-209
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• 2008

Thick film formaldehyde (HCHO) gas sensors were fabricated by using $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramics. The powders of $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) were synthesized by conventional solid-state reaction method. By using the $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) paste, the thick-film formaldehyde sensors were prepared on the alumina substrate by silkscreen printing method. The experimental results revealed that $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramic powder has a perovskite structure and the thick-film sensor shows excellent gas-sensing characteristics to formaldehyde gas (sensitivity of $La_{0.8}Sr_{0.2}FeO_3$, S= 14.7 at operating temperature of $150^{\circ}C$ in 50 ppm HCHO ambient).

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.407-414
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• 1999

We have studied the reduction of NO by CO over perovskite-type oxides prepared by malic and method. The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxides. In the $LaCoO_3$ type catalyst, the partial substitution of Sr into A site enhanced the catalytic activity on the conversion of NO at less than $350^{\circ}C$. In the $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$ catalyst, the partial substitution of Fe or Mn into B site enhanced the conversion of NO, but excess amount of Fe decreased the conversion of NO. In addition, $La_{0.6}Sr_{0.4}Co_{0.8}Fe_{0.2}O_3$ mixed with $SnO_2$ or $MnO_2$ showed the synergy effect on the reduction of NO. The introduction of water into reactants feed decreased the catalytic activity but the deactivation was shown to be reversible. The introduction of $SO_2$ into reactants feed also decreased the catalytic activity.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.162-168
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• 2006

The perovskites with nominal compositions $La_{0.8}Sr_{0.2}Fe_{1-x}M_xO_3$ (M=Co, Mn, Ni, x=0.1-0.3) were fabricated by a solid-state reaction method as cathode materials of low-temperature operating Solid Oxide Fuel Cells (SOFCs). X-ray diffraction analysis and microstructure observation for the sintered samples were performed. The ac complex impedance were measured in the temperature range $600-900^{\circ}C$ in air and fitted with a Solatron ZView program. The electrical conductivity and polarization resistance of $La_{0.8}Sr_{0.2}Fe_{1-x}M_xO_3$ (M=Co, Mn, Ni, x=0.1-0.3) were characterized systematically. The porosities of the sintered samples were in the range of 25% to 38%. The polarization resistance of $La_{0.8}Sr_{0.2}Fe_{0.7}M_{0.3}O_3$ was $0.291{\Omega}cm^2\;at\;700^{\circ}C$.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.33.1-33.1
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• 2011

Strontium doped lanthanum manganite (LSM) with perovskite structure for SOFC cathode material shows high electrical conductivity and good chemical stability, whereas the electrical conductivity at intermediate temperature below $800^{\circ}C$ is not sufficient due to low oxygen ion conductivity. The approach to improve electrical conductivity is to make more oxygen vacancies by substituting alkaline earths (such as Ca, Sr and Ba) for La and/or a transition metal (such as Fe, Co and Cu) for Mn. Among various cathode materials, $LaSrMnCuO_3$ has recently been suggested as the potential cathode materials for solid oxide fuel cells (SOFCs). As for the Cu doping at the B-site, it has been reported that the valence change of Mn ions is occurred by substituting Cu ions and it leads to formation of oxygen vacancies. The electrical conductivity is also affected by doping element at the A-site and the co-doping effect between A-site and B-site should be described. In this study, the $La_{1-x}Sr_xMn_{0.8}Cu_{0.2}O_{3{\pm}{\delta}}$ ($0{\leq}x{\leq}0.4$) systems were synthesized by a combined EDTA-citrate complexing process. The crystal structure, morphology, thermal expansion and electrical conductivity with different Sr contents were studied and their co-doping effects were also investigated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.249-254
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• 2023

La_0.7-xCe_xSr_0.3MnO₃ specimens were fabricated by a solid state reaction method and structural and electrical properties with variation of Ce⁴⁺ contents were measured. All specimens exhibited a polycrystalline rhombohedral crystal structure, and the (110) peaks were shifted to low angle side with increasing the amount of Ce⁴⁺ contents. As Ce⁴⁺ ions with different ion radii and charges are substituted with La³⁺ ions, electrical properties are thought to be affected by changes in the double exchange interaction between Mn³⁺-Mn⁴⁺ ions due to distortion of the unit lattice, a decrease in oxygen vacancy concentration, and an increase in lattice defects. Resistivity gradually decrease as the amount of Ce⁴⁺ added increased, and negative temperature coefficient of resistance (NTCR) properties were shown in all specimens. In the La_0.5Ce_0.2Sr_0.3MnO₃ specimens, electrical resistivity, TCR and B-value were 31.8 Ω-cm, 0.55%/℃ and 605 K, respectively.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.715-719
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• 2007

STS444 with or without $La_{0.9}Sr_{0.1}MnO_3$ (LSM)-coating was contacted to $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3$ (LSCF) cathode on various electrolyte materials and the polarization resistance $(R_p)$ was measured by impedance spectroscopy. By making a symmetric half-cell and contacting only one side of the cathode with the interconnect, the effect of chromium (Cr) poisoning was separated from the aging effects. When the LSCF cathode was contacted with LSM-coated STS (stainless steel), $R_p$ of LSCF was lower than that contacted with the uncoated STS. Impedance patterns measured for the working electrode (W.E.), the counter electrode (C.E.) at $600^{\circ}C$ in air were analyzed. Normalized data of net Cr effect showed that $Ce_{0.9}Gd_{0.1}O_2$ (GDC) electrolyte is more tolerant to the chromium poisoning than $La_{0.9}Sr_{0.1}Ga_{0.8}Mg_{0.2}$ (LSGM) or 8 mol% $Y_2O_3-doped$ $ZrO_2$ (YSZ) electrolytes.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1679-1683
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• 2013

Intergrowth perovskite type complex oxides $La_{0.8}Ln_{0.2}Sr_2MnCrO_{7-{\delta}}$ (Ln=La, Nd, Gd, and Dy) have been synthesized by sol-gel method. Rietveld profile analysis shows that the phases crystallize with tetragonal unit cell in the space group I4/mmm. The unit cell parameters a and c decrease with decreasing effective ionic radius of the lanthanide ion. The magnetic studies suggest that the ferromagnetic interactions are dominant due to $Mn^{3+}$-O-$Mn^{4+}$ and $Mn^{3+}$-O-$Cr^{3+}$ double exchange interactions. Both Weiss constant (${\theta}$) and Curie temperature ($T_C$) increase with decreasing ionic radius of lanthanide ion. It was found that the transport mechanism is dominated by Mott's variable range hopping (VRH) model with an increase of Mott localization energy.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Journal of the Korean Electrochemical Society
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• v.8 no.2
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• pp.88-93
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• 2005

Anode-supported solid oxide fuel cell (SOFC) was investigated to increase the cell power density at intermediate temperature through control of the cathode structure. The anode-supported SOFC cell were fabricated by wet process, in which the electrolyte of $8mol\%\;Y_2O_3-stabilized\;ZrO_2 (YSZ)$ was coated on the surface of anode support of Ni/YSA and then the cathode was coated. The cathode has two- or three- layered structure composed of $(La_{0.85}Sr_{0.15})_{0.9}MnO_{3-x}(LSM),\;LSM/YS$ composite (LY), and $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3{LSCF)$ with different thickness. Their single cells with different cathode structures were characterized by measuring the cell performance and ac impedance in the temperature range of 600 to $800^{\circ}C$ in humidified hydrogen with $3\%$ water and air. The cell with $LY\;9{\mu}m/LSM\;9{\mu}m/LSCF\;17{\mu}m$ showed best performance of $590mW/cm^2$, which was attributed to low polarization resistance due to LY and to low interfacial resistance due to LSCF.