Jong Hoon Joo

Investigation of Electrochemical Properties of Model Lanthanum Strontium Cobalt Ferrite-Based Cathodes for Proton Ceramic Fuel Cells

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

Novel oxygen transport membranes with tunable segmented structures

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.

A new strategy for enhancing the thermo-mechanical and chemical stability of dual-phase mixed ionic electronic conductor oxygen membranes

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).

Elucidation of the Oxygen Surface Kinetics in a Coated Dual-Phase Membrane for Enhancing Oxygen Permeation Flux

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.

Simultaneous conversion of carbon dioxide and methane to syngas using an oxygen transport membrane in pure CO2 and CH4 atmospheres

The utilization of CO2, coupled with partial oxidation of methane (POM) by using an oxygen transport membrane, has been investigated. The stability of both the membrane itself and the coating layers was simultaneously considered to develop a highly stable membrane under pure CO2 and CH4 conditions. The chemically stable La0.8Ca0.2FeO3−δ (LCF) and Ce0.9Gd0.1O2−δ (GDC) composite was used as the membrane. The LCF–GDC composite and NiO–GDC–LST (La0.3Sr0.7TiO3−δ) composite were adopted as the coating layer for CO2 reduction (feed side) and methane conversion (permeate side), respectively. A higher production of CO from CO2 was obtained in a pure CO2 atmosphere. Furthermore, CH4 was selectively converted to synthesis gas with 100% CO by adopting coking resistance on the coating layer. Using this chemically stable dual-phase membrane, 13.6 mL cm−2 min−1 of synthesis gas was produced at the permeate side, and the membrane was extremely stable over more than 100 h at 900 °C. These results suggest the potential possibility for the application of CO2 utilization coupled with methane conversion by using an oxygen transport membrane under a pure gas atmosphere to real industrial applications.