• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.997-998
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• 2013

• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.29-36
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• 2012

In many applications of functional oxides originally homogeneous materials are exposed to gradients in the chemical potential of oxygen. Prominent examples are solid oxide fuel cells (SOFCs) or oxygen permeation membranes (OPMs). Other thermodynamic potential gradients are gradients of electrical potential, temperature or uni-axial pressure. The applied gradients act as generalized thermodynamic forces and induce directed fluxes of the mobile components. These fluxes may lead to three basic degradation phenomena of the materials, which are kinetic demixing, kinetic decomposition, and morphological instabilities.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.157-163
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• 2010

Solid oxide fuel cells (SOFCs) are commonly composed of ceramic compartments, and it is known that the physical properties of the ceramic materials can be changed according to the operating temperature. Thus, the physical properties of the ceramic materials have to be properly predicted to develop a highly reliable simulation model. In this study, several physical properties that can affect the performance of SOFCs were selected, and simulation models for those physical properties were developed using our own code. The Gibbs free energy for the open circuit voltage, exchange current densities for the activation polarization, and electrical conductivity for the electrolyte were calculated. In addition, the diffusion coefficient-including the binary and Knudsen diffusion mechanisms-was calculated for mass transport analysis at the porous electrode. The physical property and electrochemical reaction models were then simulated simultaneously. The numerical results were compared with the experimental results and previous works studied by Chan et al. for code validation.

• 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 Korean Vacuum Society Conference
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• 2016.02a
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• pp.402.1-402.1
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• 2016

The performance of solid oxide fuel cells (SOFCs) is directly related to the electrocatalytic activity of composite electrodes in which triple phase boundaries (TPBs) of metallic catalyst, oxygen ion conducting support, and gas should be three-dimensionally maximized. The distribution morphology of catalytic nanoparticle dispersed on external surfaces is of key importance for maximized TPBs. Herein in situ grown nickel nanoparticle onto the surface of fluorite oxide is demonstrated employing gadolium-nickel co-doped ceria ($Gd0.2-xNixCe0.8O2-{\delta}$, GNDC) by reductive annealing. GNDC powders were synthesized via a Pechini-type sol-gel process while maximum doping ratio of Ni into the cerium oxide was defined by X-ray diffraction. Subsequently, NiO-GNDC composite were screen printed on the both sides of yttrium-stabilized zirconia (YSZ) pellet to fabricate the symmetrical half cells. Electrochemical impedance spectroscopy (EIS) showed that the polarization resistance was decreased when it was compared to conventional Ni-GDC anode and this effect became greater at lower temperature. Ex situ microstructural analysis using scanning electron microscopy after the reductive annealing exhibited the exsolution of Ni nanoparticles on the fluorite phases. The influence of Ni contents in GNDC on polarization characteristics of anodes were examined by EIS under H2/H2O atmosphere. Finally, the addition of optimized GNDC into the anode functional layer (AFL) dramatically enhanced cell performance of anode-supported coin cells.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.710-714
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• 2007

LSGM$(La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.2}O_{3-{\delta}})$ is the very promising electrolyte material for lower-temperature operation of SOFCs, especially when realized in anode-supported cells. But it is notorious for reacting with other cell components and resulting in the highly resistive reaction phases detrimental to cell performance. LDC$(La_{0.4}Ce_{0.6}O_{1.8})$, which is known to keep the interfacial stability between LSGM electrolyte and anode, was adopted in the anode-supported cell, and its effect on the interfacial reactivity and electrochemical performance of the cell was investigated. No severe interfacial reaction and corresponding resistive secondary phase was found in the cell with LDC buffer layer, and this is due to its ability to sustain the La chemical potential in LSGM. The cell exhibited the open circuit voltage of 0.64V, the maximum power density of 223 $mW/cm^2$, and the ohmic resistance of $0.17{\Omega}cm^2$ at $700^{\circ}C$. These values were much improved compared with those from the cell without any buffer layer, which implies that formation of the resistive reaction phases in LSGM and then deterioration of the cell performance is resulted mainly from the La diffusion from LSGM electrolyte to anode.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.1
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• pp.43-48
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• 2012

This paper presents the characterization of micro-tubular SOFCs using three different anode current collecting methods of inlet current collection (IC), both current collection (BC) and total current collection (TC). The maximum power densities of SOFCs at $750^{\circ}C$ using IC, BC and TC were 56 mW/$cm^2$ (0.43 V, 0.13 A/$cm^2$), 236 mW/$cm^2$ (0.43 V, 0.55 A/$cm^2$) and 261 mW/$cm^2$ (0.43 V, 0.61 A/$cm^2$) respectively. It was confirmed by impedance spectroscopy that both the polarization resistance and the ohmic resistance were dramatically increased at SOFC with IC.

• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.265-270
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• 2014

Among the Ruddlesden-Popper series, $La_4Ni_3O_{10}$ has received widespread attention as a promising cathode material by reason of its favorable properties for realizing high performance of intermediate temperature solid oxide fuel cells (IT-SOFCs). The $La_4Ni_3O_{10}$ cathode is prepared using the facile sol-gel method by employing tri-blockcopolymer (F127) to obtain a single phase in a short sintering time. There are no reactions between the $La_4Ni_3O_{10}$ cathode and the $Ce_{0.9}Gd_{0.1}O_{2-\delta}$ (GDC) electrolyte upon sintering at $1000^{\circ}C$, indicating that the $La_4Ni_3O_{10}$ cathode has good chemical compatibility with the GDC electrolyte. The maximum electrical conductivity of $La_4Ni_3O_{10}$ reaches approximately 240 S $cm^{-1}$ at $100^{\circ}C$ and gradually decreases with increasing temperaturein air atmosphere. The area specific resistance value of $La_4Ni_3O_{10}$ composite with 40 wt% GDC is $0.435{\Omega}cm^2$ at $700^{\circ}C$. These data allow us to propose that the $La_4Ni_3O_{10}$-GDC composite cathode is a good candidate for IT-SOFC applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.510-515
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• 2016

Single-chamber solid oxide fuel cells (SC-SOFCs) consist of only one gas chamber, in which both the anode and the cathode are exposed to the same fuel-oxidant mixture. Thus, this configuration shows good thermal and mechanical resistance and allows rapid start-up and -down. In this study, the unit cell consisting of $La_{0.8}Sr_{0.2}MnO_3$ (cathode) / $Zr_{0.84}Y_{0.16}O_{2-x}$ (electrolyte) / $Ni-Zr_{0.84}Y_{0.16}O_{2-x}$ (anode) was fabricated and its electrochemical property was investigated as a function of temperature and the volume ratio of fuel and oxidant for SC-SOFCs. Impedance spectra were also investigated in order to figure out the electrical characteristics of the cell. As a result, the cell performance was governed by the polarization resistances of the electrodes. The cell exhibited an acceptable cell-performance of $86mW/cm^2$ at $800^{\circ}C$ and stable performance for 3 hs under 0.7 V.

• Journal of the Korean Ceramic Society
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• v.43 no.5 s.288
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• pp.270-276
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• 2006

LSGM(($La_xSr_{1-x})(Ga_yMg_{1-y})O_3$) electrolyte is known to show very serious interfacial reaction with other unit cell components, especially with an anode. Such an interfacial reaction induced the phase instability of constituent component and deterioration of the unit cell performance, which become the most challenging issues in LSGM-based SOFCs. In this study, we fabricated LSGM($La_{0.8}Sr_{0.2}Ga_{0.83}Mg_{0.17}O_x$) electrolyte supported-type cell in order to avoid such interfacial problem by lowering the heat-treatment temperature of the electrode fabrication. According to the microstructural and phase analysis, there was no serious interfacial reaction at both electrolyte/anode and electrolyte/cathode interfaces. Moreover, from the electrochemical characterization of the unit cell performance, there was no distinct deterioration of the open cell voltage as well as an internal cell resistance. These results demonstrate the most critical point to be concerned in LSGM-based SOFC is either to find a proper electrode material which will not give any interfacial reaction with LSGM electrolyte or to properly adjust the processing variables for unit cell fabrication, to reduce the interfacial reaction.