Chung-Yul Yoo

Substantial Oxygen Flux in Dual-Phase Membrane of Ceria and Pure Electronic Conductor by Tailoring the Surface

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.

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).

Mussel-inspired surface functionalization of porous carbon nanosheets using polydopamine and Fe3+/tannic acid layers for high-performance electrochemical capacitors

A facile mussel-inspired surface modification of interconnected porous carbon nanosheet (IPCN) electrodes is demonstrated through the formation of a polydopamine coating and the subsequent layer-by-layer deposition of ferric ions (Fe3+) and tannic acid, with the aim of developing high-performance electrochemical capacitors. After the deposition of the polydopamine coating, the specific capacitance increases by ∼40% as compared to that of an unmodified IPCN electrode. This increase in the capacitance can be explained based on the pseudocapacitance induced by the catechol groups of polydopamine. Furthermore, the electrodes coated with both polydopamine and layers of Fe3+ and tannic acid exhibit an additional increase in the capacitance to ∼244 F g−1 at 5 mV s−1, which is ∼83% higher than that of the unmodified IPCN electrode. This is attributable to the presence of many redox moieties, which are introduced by polydopamine and tannic acid. Furthermore, the strong interactions between the Fe3+ ions and the catechol groups result in improved capacitance retention even after 1000 cycles. The mussel-inspired surface modification of IPCN electrodes demonstrated in this work can potentially be exploited for developing novel pseudocapacitive electrode materials with excellent performances.