Hae-Ryoung Kim

SOFCs with Sc-Doped Zirconia Electrolyte and Co-Containing Perovskite Cathodes

Recently, much attention has been directed toward the study of Sc-doped zirconia electrolyte for intermediate-temperature SOFCs (IT-SOFCs) due to its fairly good ionic conductivity compared with conventional Y-doped zirconia, which can reduce the internal ohmic loss of the cell. For improving unit cell performance, another important point to be considered is the selection of appropriate electrode materials to reduce the polarization loss at the electrode. In this study, we fabricated anode-supported SOFCs with a 1 mol % CeO 2 codoped 10 mol % Sc 2 O 3 -ZrO 2 (CeSSZ) electrolyte. Various kinds of cathode materials such as La-Sr-Mn-O, La-Sr-Co-O (LSCo), La-Sr-Co-Fe-O, and Sm-Sr-Co-O (SSCo) have been applied in order to identify the most suitable cathode material for Sc-doped zirconia. We evaluated the power-generating characteristics of 5 X 5 cm scaled unit cells as well as the cathode polarization effect via a dc current-voltage measurement, a dc current interruption method, and ac impedance spectroscopy. We also thoroughly investigated the interfacial reaction between the electrolyte and the cathode in order to identify appropriate heat-treatment conditions for each candidate cathode material on the CeSSZ electrolyte. According to the investigation, unit cells with a SSCo and LSCo cathode showed superior power density of 1.13 and 1.33 W/cm 2 , respectively, at 700°C and fairly stable cell performance without any serious interfacial reaction.

Fabrication and Characterization of Composite Sealants for Low Temperature (600∼650 ° C)SOFCs

A proper sealant for low temperature SOFCs should show zero or low leak rates to avoid direct mixing of the fuel and oxidant gases or leakage of fuel gas during the operation of SOFCs. Furthermore, it should be chemically and/or mechanically stable in both oxidizing and reducing environments and chemically compatible with other fuel cell components. In the present work, we developed a novel compressed seal gasket of glass-based composite reinforced with ceramic particulate particles, which can efficiently control the viscous flow of glass matrix as well as the crystallization of glass phase. This novel sealing gasket showed excellent gas tightness under very low compressive load which would be suitable for the operation of SOFCs in the temperature range 600~650℃.

Fabrication of Micro Solid Oxide Fuel Cell by Thin Film Processing Hybridization: I. Multilayer Structure of Sputtered YSZ Thin Film Electrolyte and Ni-Based Anodes deposited by Spray Pyrolysis

Physical properties of sputtered YSZ thin film electrolytes on anode thin film by spray pyrolisis has been investigated to realize the porous electrode and dense electrolyte multilayer structure for micro solid oxide fuel cells. It is shown that for better crystallinity and density, YSZ need to be deposited at an elevated temperature. However, if pure NiO anode was used for high temperature deposition, massive defects such as spalling and delamination were induced due to high thermal expansion mismatch. By changing anode to NiO-CGO composite, defects were significantly reduced even at high deposition temperature. Further research on realization of full cells by processing hybridization and cell performance characterization will be performed in near future.

Performance and Reliability Improvement of Planar SOFC Stack with Advanced Design of Unit Cell and Sealing

Commercialization of SOFC technology requires the development of high performance SOFC stack, combined with an engineering focus on stack reliability and cost. Recently KIST was successful to greatly improve the performance and reliability of SOFC stack based on newly developed 10x10 cm2 anode- supported cells and glass-based compression-seal gaskets. In this study, a novel design of SOFC unit cells with higher thermo-mechanical stability and better electrochemical performance has been introduced and its evaluation results are discussed in terms of its electrical property, structural property and unit cell performance. We also address the key factors and the latest progress in sealing technique in a view point of sealing capability and thermal-cycle stability.

Comparison of the Power Generating Characteristics of KIST- and FZ-Julich SOFCs

We evaluate and compare the power generating characteristics of the anode supported SOFCs which have been fabricated from KIST and FZ-Julich in Germany. The performance and electrochemical property of each unit cell was characterized at the temperature range of 650-850℃ under same operating conditions and its microstructural property was thoroughly investigated via SEM after the performance test. According to the investigation, KIST- and FZJ SOFC showed different power generating characteristics in their temperature dependances due to their different design of electrode microstructure, especially the cathode microstructure. FZJ SOFC showed better performance at high temperature while showed lower performance at lower temperature. From the investigation about the correlation between microstructure and electrochemical property, we found that the superior performance of FZJ SOFC at high temperature was mainly due to its lower cathodic polarization resistance whereas better performance of KIST SOFC at lower temperature was mostly attributed to the lower ohmic resistance.

Electrochemical Behavior of Ni-CZO Cermet Anodes Prepared by Glycine-nitrate-process

The impact of H2O for H2 oxidation on Ni-Ce0.75Zr0.25O2 (Ni-CZO) anode material synthesized by glycine-nitrate-process has been investigated under dry and wet H2 fuel atmospheres over a range of operating conditions using yttria-stabilized zirconia (YSZ) electrolyte. Using electrochemical impedance spectroscopy (EIS), the polarization resistance (comprised of high frequency (HF) and low frequency (LF) features) of Ni-CZO symmetrical cells (NiCZO/YSZ/Ni-CZO) has been studied. The LF arc was almost negligible at all the operating temperatures in wet condition, and the HF arc linearly increased with time at 800 o C only in dry condition. The EIS response in dry and wet H2 conditions clearly exhibited that water vapor enhanced the dissociative adsorption and surface diffusion of hydrogen and achieved stable electrochemical performance at 3PB on the Ni-CZO cermet.

Effect of the LDC Buffer Layer in LSGM-based Anode-supported SOFCs

LSGM(La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ ) 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 0.64 V, the maximum power density of 223 mW/㎠, and the ohmic resistance of 0.17 Ω㎠ at 700℃. 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.

Discharge characteristics of an Li/LiCoO2 cell with poly(acrylonitirile)-based polymer electrolyte

Abstract The electrochemical properties of poly(acrylonitrile) (PAN)-based polymer electrolyte and the discharge characteristics of an Li/LiCoO 2 cell were investigated. The PAN-based polymer electrolyte maintained an ionic conductivity of 1 mS/cm at room temperature, irrespective of storage time. Also, this electrolyte showed high electrochemical stability up to 4.3 V (versus Li + /Li). An Li/LiCoO 2 cell battery with this electrolyte has been fabricated and tested. This battery showed good cycling performance.