Ji Haeng Yu
University of Science and Technology, Sana'a
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Featured researches published by Ji Haeng Yu.
ACS Applied Materials & Interfaces | 2015
Jong Hoon Joo; Kyong Sik Yun; Jung-Hwa Kim; Younki Lee; Chung-Yul Yoo; Ji Haeng Yu
The oxygen permeation flux of dual-phase membranes, Ce0.9Gd0.1O2-δ-La0.7Sr0.3MnO3±δ (GDC/LSM), has been systematically studied as a function of their LSM content, thickness, and coating material. The electronic percolation threshold of this GDC/LSM membrane occurs at about 20 vol % LSM. The coated LSM20 (80 vol % GDC, 20 vol % LSM) dual-phase membrane exhibits a maximum oxygen flux of 2.2 mL·cm(-2)·min(-1) at 850 °C, indicating that to enhance the oxygen permeation flux, the LSM content should be adjusted to the minimum value at which electronic percolation is maintained. The oxygen ion conductivity of the dual-phase membrane is reliably calculated from oxygen flux data by considering the effects of surface oxygen exchange. Thermal cycling tests confirm the mechanical stability of the membrane. Furthermore, a dual-phase membrane prepared here with a cobalt-free coating remains chemically stable in a CO2 atmosphere at a lower temperature (800 °C) than has previously been achieved.
Electrocatalysis | 2016
Chung-Yul Yoo; Dae Sik Yun; Sun-Young Park; Jaeku Park; Jong Hoon Joo; Haein Park; Minseok Kwak; Ji Haeng Yu
AbstractThe electrochemical properties of La0.6Sr0.4Co0.2Fe0.8O3-δ-based cathodes are studied as model electrodes for proton ceramic fuel cells. The electrochemical performance of symmetric cells with porous cathodes (La0.6Sr0.4Co0.2Fe0.8O3-δ, La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ, and La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ), investigated as a function of oxygen and water partial pressures, follows the order La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ ≥ La0.6Sr0.4Co0.2Fe0.8O3-δ >> La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ. The results indicate that the cathode performance of La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ is enhanced mainly due to the extension of the effective triple phase boundary, whereas that of La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ is lowered due to the poor proton conductivity along the percolated BaZr0.8Y0.2O3-δ particles. From the observed oxygen partial pressure dependence, the rate-determining step of the above cathode polarization reaction is principally ascribed to the oxygen reduction reaction. Graphical abstractSchematics of the cathode reaction mechanism at the surface of the LSCF, LSCF-BCY, and LSCFBZY cathodes
Journal of Materials Chemistry | 2014
Jong Hoon Joo; Kyong Sik Yun; Chung-Yul Yoo; Ji Haeng Yu
A novel oxygen permeation membrane with a tunable segmented configuration obtained by employing the tape casting technique has been developed. According to this new structure, the membrane consists of a robust fluorite oxide matrix and electron conducting perovskite oxide segments. Mixed electron–ion conduction in the membrane can be optimized by controlling the number of the electron conducting segments. This new concept of the membrane with high oxygen permeability is proposed for the industrial oxygen production.
Journal of Materials Chemistry | 2016
Kyong Sik Yun; Jeong Hwan Park; Young-il Kwon; Dong-young Kim; Chung-Yul Yoo; Ji Haeng Yu; Jong Hoon Joo
A mixed ionic electronic conductor (MIEC) membrane with thermo-mechanical and chemical stability has been developed. A fluorite-rich dual-phase composite (80 vol% Ce0.9Gd0.1O2−δ–20 vol% La0.7Sr0.3MnO3−δ) based on the chemically stable pure electronic conductor oxide (LSM) and doped-ceria (GDC) was used as the membrane material. By introducing a thermo-mechanically and chemically stable coating material (Pr2NiO4+δ) to the membranes, this study proposes a new strategy for enhancing the overall stability of the oxygen permeation ceramic membrane. The stability of the dual-phase membrane was assessed in the presence of CO2 at intermediate temperatures, and thermal cycling tests were performed to evaluate its performance under extreme conditions. The dual-phase membrane with Pr2NiO4+δ coating layer not only showed remarkable stability in a pure CO2 atmosphere but also exhibited thermo-mechanical stability during rapid thermal cycling tests (cooling and heating rate: 30 °C min−1).
ACS Applied Materials & Interfaces | 2017
Beom Tak Na; Jeong Hwan Park; Jong Hyuk Park; Ji Haeng Yu; Jong Hoon Joo
The dual-phase membrane has received much attention as the solution to the instability of the oxygen permeation membrane. It has been reported that the oxygen flux of the dual-phase membrane is greatly enhanced by the active coating layer. However, there has been little discussion about the enhancement mechanism by surface coating in the dual-phase membrane. This study investigates the oxygen flux of the Ce0.9Gd0.1O2-δ-La0.7Sr0.3MnO3±δ (GDC 80 vol %/LSM 20 vol %) composite membrane depending on the oxygen partial pressure (PO2) to elucidate the mechanism of enhanced oxygen flux by the surface modification in the fluorite-rich phase dual-phase membrane. The oxygen permeation resistances were obtained from the oxygen flux as a function of PO2 using the oxygen permeation model. The surface exchange coefficient (k) and the bulk diffusion coefficient (D) were calculated from these resistances. According to the calculated k and D values, we concluded that the active coating layer (La0.6Sr0.4CoO3-δ) significantly increased the k value of the membrane. Furthermore, the surface exchange reaction on the permeate side was more sluggish than that at the feed side under operating conditions (feed: 0.21 atm/permeate side: 4.7 × 10-4 atm). Therefore, the enhancement of the oxygen surface exchange kinetics at the permeate side is more important in improving the oxygen permeation flux of the thin film-based fluorite-rich dual-phase membrane. These results provide new insight about the function of the surface coating to enhance the oxygen permeation flux of the dual-phase membrane.
Transactions of the Korean hydrogen and new energy society | 2013
Jaewon Jeong; Chung-Yul Yoo; Jong Hoon Joo; Ji Haeng Yu
In order to reduce the costs and to improve the durability of solid oxide fuel cell (SOFC), the operating temperature should be decreased while the power density is maintained as much as possible. However, lowering the operating temperature increases the cathode interfacial polarization resistances dramatically, limiting the performance of low-temperature SOFC at especially purely electronic conducting cathode. To improve cathode performance at low temperature, the number of reaction sites for the oxygen reduction should be increased by using a mixed ionic and electronic conducting (MIEC) material. In this study, anode-supported fuel cells with two different thicknesses of the MIEC cathode were fabricated and tested at various operating temperatures. The anode supported cell with -thick BSCFZn-LSCF cathode layer showed much lower polarization resistance than that with thick cahtode and higher power density especially at low temperature. The effects of cathode layer thickness on the electrochemical performance are discussed with analysis of impedance spectra.
Chemistry of Materials | 2014
Jong Hoon Joo; Kyong Sik Yun; Younki Lee; Jaewon Jung; Chung-Yul Yoo; Ji Haeng Yu
Solid State Ionics | 2013
Jong Hoon Joo; Geum Sook Park; Chung-Yul Yoo; Ji Haeng Yu
Journal of Power Sources | 2015
Dae Sik Yun; Jong Hoon Joo; Ji Haeng Yu; Hyung Chul Yoon; Jong-Nam Kim; Chung-Yul Yoo
Journal of Alloys and Compounds | 2015
Chung-Yul Yoo; Dae Sik Yun; Jong Hoon Joo; Ji Haeng Yu