• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1497-1498
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• 2011

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.5
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• pp.345-350
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• 2018

Nanomaterials have considerable potential to solve several key challenges in various electrochemical devices, such as fuel cells. However, the use of nanoparticles in high-temperature devices like solid-oxide fuel cells (SOFCs) is considered problematic because the nanostructured surface typically prepared by deposition techniques may easily coarsen and thus deactivate, especially when used in high-temperature redox conditions. Herein we report the synthesis of a self-regenerated Pd metal nanoparticle on the perovskite oxide anode surface for SOFCs that exhibit self-recovery from their degradation in redox cycle and $CH_4$ fuel running. Using Pd-doped perovskite, $La(Sr)Fe(Mn,Pd)O_3$, as an anode, fairly high maximum power densities of 0.5 and $0.2cm^{-2}$ were achieved at 1,073 K in $H_2$ and $CH_4$ respectively, despite using thick electrolyte support-type cell. Long-term stability was also examined in $CH_4$ and the redox cycle, when the anode is exposed to air. The cell with Pd-doped perovskite anode had high tolerance against re-oxidation and recovered the behavior of anodic performance from catalytic degradation. This recovery of power density can be explained by the surface segregation of Pd nanoparticles, which are self-recovered via re-oxidation and reduction. In addition, self-recovery of the anode by oxidation treatment was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.70.1-70.1
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• 2012

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies of SOFC cathode materials will be discussed in this presentation. The mixed conducting perovskites (ABO3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC). However, the details of the oxygen reduction reaction are still not clearly understood. The information about the type of adsorbed oxygen species and their concentration is important for a mechanistic understanding of the oxygen incorporation into these cathode materials. XPS has been widely used for the analysis of adsorbed species and surface structure. However, the conventional XPS experiments have the severe drawback to operate at room temperature and with the sample under ultrahigh vacuum (UHV) conditions, which is far from the relevant conditions of SOFC operation. The disadvantages of conventional XPS can be overcome to a large extent with a "high pressure" XPS setup installed at the BESSY II synchrotron. It allows sample depth profiling over 2 nm without sputtering by variation of the excitation energy, and most importantly measurements under a residual gas pressure in the mbar range. It is also well known that the catalytic activity for the oxygen reduction is very sensitive to their electrical conductivity and oxygen nonstoichiometry. Although the electrical conductivity of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (Po2), in-situ measurements of the conductivity of these materials in contact with the electrolyte as a SOFC configuration have little been reported. In order to measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance is required for excluding the leakage current of the substrate. It is also hardly possible to measure the conductivity of cracked thin film by electrical methods. In this study, we report the electrical conductivity of perovskite $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in-situ IR spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current to the substrate and cracks in the film.

• Journal of the Korean Ceramic Society
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• v.56 no.2
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• pp.111-129
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• 2019

Recently, all-solid-state batteries (ASSBs) have attracted increasing interest owing to their higher energy density and safety. As the core material of ASSBs, the characteristics of the solid electrolyte largely determine the performance of the battery. Thus far, a variety of inorganic solid electrolytes have been studied, including the NASICON-type, LISICON-type, perovskite-type, garnet-type, glassy solid electrolyte, and so on. The garnet Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte is one of the most promising candidates because of its excellent comprehensively electrochemical performance. Both, experiments and theoretical calculations, show that cubic LLZO has high room-temperature ionic conductivity and good chemical stability while contacting with the lithium anode and most of the cathode materials. In this paper, the crystal structure, Li-ion transport mechanism, preparation method, and element doping of LLZO are introduced in detail based on the research progress in recent years. Then, the development prospects and challenges of LLZO as applied to ASSBs are discussed.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.6
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• pp.670-677
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• 2012

Perovskite-type oxides such as doped barium zirconate ($BaZrO_3$) show high proton conductivity and chemical stability when they are exposed to hydrogen and water vapour containing atmospheres, thus it can be applicable to the hydrogen separation and the fuel cell electrolyte membranes. However the high temperature ($1700-1800^{\circ}C$) and long sintering times (24h) are generally required to prepare the fully densified $BaZrO_3$ pellets. These sintering conditions lead to the limitation of the grain size growth and the degradation of conductivity due to the acceleration of BaO evaporation at $1200^{\circ}C$. Here we demonstrate NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ with lower calcination and sintering temperature, less experimental procedure and lower process cost than the conventional mixing method. The stoichiometry of $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was optimized by the control of excess amount of Ba (5mol%) to minimized BaO evaporation. We found that the crystal size of NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was increased with increase of calcination temperature from XRD analysis. NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ powder was calcined at $1000^{\circ}C$ for 12h when its showed the highest conductivity of $3.3{\times}10^{-2}s/cm$.

• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.208-217
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• 2014

$La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.2-x}Zn_xO_{2.8}$(LSGMZ, X=0-0.05) was prepared using a solid state reaction method. Two secondary phases ($LaSrGaO_4$ and $LaSrGa_3O_7$) of powders were identified by X-ray diffraction analysis. The relative amount of these secondary phases depended on the calcination conditions (temperature and time) and Zn content. The sintering density of LSGMZ was enhanced by increasing the Zn content and calcination temperature at the low sintering temperatures ($1250-1300^{\circ}C$). The relationship between the sintering density of LSGMZ and the synthesis conditions was discussed considering the phase analysis results.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.177-182
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• 2000

At the porous $La_{0.6}Ca_{0.4}MnO_{3-{\delta}}$(LCM)/YSZ electrodes of solid oxide fuel cells (SOFC), the electrochemical redox reaction of oxygen proceeds via the triple boundary (TPB) of gas/LCM/YSZ. The surface diffusion of adsorbed oxygen on LCM has been proposed as the rate determining process, assuming the gradient of oxygen chemical potential from the outer surface of porous layer to TPB. Along with the formation of this gradient, oxygen nonstoichiometry in the bulk of LCM may varies. In this paper, an electrochemical technique was described precisely to determine the variation of oxygen content in LCM of porous LCM/YSZ under polarization. It was shown that the oxygen potential in LCM layer under large cathodic polarization is much lower than that in the gas phase, being determined from the electrode potential and Nernst equation.

• Journal of Electrochemical Science and Technology
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• v.9 no.3
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• pp.212-219
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• 2018

Perovskite type ceramic membranes which exhibit dual ion conduction (proton and oxygen ion conduction) can permeate water and can aid solving operational problems such as temperature gradient and carbon deposition associated with a working solid oxide fuel cell. From this point of view, it is crucial to reveal water transport mechanism and especially the nature of the surface sites that is necessary for water incorporation and evolution. $BaCe_{0.8}Y_{0.2}O_{3-{\alpha}}$ (BCY20) was used as a model proton and oxygen ion conducting membrane in this work. Four different catalytically modified membrane configurations were used for the investigations and water flux was measured as a function of temperature. In addition, CO was introduced to the permeate side in order to test the stability of membrane against water and $CO/CO_2$ and post operation analysis of used membranes were carried out. The results revealed that water incorporation occurs on any exposed electrolyte surface. However, the magnitude of water permeation changes depending on which membrane surface is catalytically modified. The platinum increases the water flux on the feed side whilst it decreases the flux on the permeate side. Water flux measurements suggest that platinum can block water permeation on the permeate side by reducing the access to the lattice oxygen in the surface layer.

• Transactions of the Korean hydrogen and new energy society
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• v.9 no.1
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• pp.8-15
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• 1998

The catalytic hydrogenation of carbon dioxide has been studied for the fixation of carbon dioxide to mitigate global warming problems, but it needed hydrogen, which the price is still high. Recently, the electrochemical reduction of carbon dioxide has been drawn attractions because carbon dioxide could be converted to the valuable chemicals such as methane, ethane and alcohols electrochemically in the electrolyte solution using a catalytic electrode. This system is simple because the water electrolysis and hydrogenation take place at the same time using the surplus electricity at midnight. In this work, a continuous electrochemical reduction system was fabricated, which was composed of the reduction electrode (copper or perovskite type, $2{\times}2cm^2$), reference electrode(platinum, $2{\times}6cm^2$), standard electrode(Ag/AgCl), and potassium bicarbonate electrolyte solution saturated with carbon dioxide. The quality and quantity of the products and reduction current were analyzed, according to the electrolyte concentration and electrode type.

• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.627-631
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• 2005

The $(La_{0.8}Sr_{0.2})_{0.95}MnO_3$/yttria-stabilized zirconia (LSM/YSZ) composites were investigated as anode materials for high temperature steam electrolysis using X-ray diffractometry, scanning electron microscopy, galvanodynamic and galvanostatic polarization method. For this purpose, the LSMperovskites were fabricated in powders by co-precipitation method and then were mixed with 8 mol% YSZ powders in different molar ratios. The LSM/YSZ composites were deposited on 8 mol% YSZ electrolyte disks by means of a screen printing method, followed by sintering at temperatures above $1,100^{\circ}C$. From the experimental results, it is concluded that the electrochemical properties of LSM and the LSM/YSZ composites are closely related to their microstructure and operating temperatures.