Jong Geun Seong

Tuning microcavities in thermally rearranged polymer membranes for CO2 capture.

Microporous materials have a great importance in catalysis, delivery, storage and separation in terms of their performance and efficiency. Most microporous materials are comprised of inorganic frameworks, while thermally rearranged (TR) polymers are a microporous organic polymer which is tuned to optimize the cavity sizes and distribution for difficult separation applications. The sub-nano sized microcavities are controlled by in situ thermal treatment conditions which have been investigated by positron annihilation lifetime spectroscopy (PALS). The size and relative number of cavities increased from room temperature to 230 °C resulting in improvements in both permeabilities and selectivities for H(2)/CO(2) separation due to the significant increase of gas diffusion and decrease of CO(2) solubility. The highest performance of the well-tuned TR-polymer membrane was 206 Barrer for H(2) permeability and 6.2 of H(2)/CO(2) selectivity, exceeding the polymeric upper bound for gas separation membranes.

Highly conductive and durable poly(arylene ether sulfone) anion exchange membrane with end-group cross-linking

Here, we demonstrate the improved electrochemical performance and stability of end-group cross-linked anion exchange membranes (AEM) for the first time via the introduction of imidazolium groups in poly(arylene ether sulfone) (Imd-PAES). A novel feature of the cross-linking reaction is that basic additives are not required to prevent gelation with the cationic functional groups. In this work, the sodium salt of 3-hydroxyphenylacetylene acted directly as the end-group cross-linker, and it was cross-linked by thermal treatment at 180 °C. The gel fraction and hydroxide conductivity of the cross-linked membranes (XE-Imds) depended on the cross-linking temperature and time. The prepared XE-Imd70 (70 refers to the degree of functionalization) membranes with an ion exchange capacity (IEC) of 2.2 meq g−1 achieved a high hydroxide conductivity (107 mS cm−1). This material also showed good single cell performance (XE-Imd70: 202 mA cm−2 at 0.6 V and a maximum power density of 196.1 mW cm−2) at 80 °C, 100% relative humidity (RH), and improved durability and alkaline stability. The excellent hydroxide conductivity and electrochemical performance of XE-Imd70 was due to the fact that the ion cluster size of XE-Imd membranes was larger (12.1–14 nm) than that of E-Imd (5.5–8.14 nm), indicating that XE-Imd membranes have a closely associated ion-clustered morphology, which was confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) measurements.

Thermally rearranged (TR) bismaleimide-based network polymers for gas separation membranes

Highly permeable, thermally rearranged polymer membranes based on bismaleimide derivatives that exhibit excellent CO2 permeability up to 5440 Barrer with a high BET surface area (1130 m2 g-1) are reported for the first time. In addition, the membranes can be easily used to form semi-interpenetrating networks with other polymers endowing them with superior gas transport properties.

Highly permeable thermally rearranged polymer composite membranes with a graphene oxide scaffold for gas separation

Thermally rearranged (TR) polymers are an important class of microporous polymers with remarkable gas transport performance, particularly suitable for CO2 permeation and separation over large gas molecules. The fabrication of TR polymers into ultrathin membranes is highly desirable for practical application, but it is very challenging. In this work, a 2D scaffold of graphene oxide (GO) nanosheets was formed inside a TR polymer to assist the fabrication of a defect-free and ultrathin (less than 40 nm) selective layer of thermally rearranged polybenzoxazole-co-imide (TR-PBOI) membranes for energy-efficient CO2 separation. The GO scaffold inside the polymer phase not only enabled the formation of the ultrathin selective layer of TR-PBOI, but also provided mechanical robustness. The resulting membrane showed remarkable gas permeance, while maintaining the gas selectivity of the pristine polymer. In particular, it had a CO2 permeance of 1784 GPU and a CO2/CH4 selectivity of 32, whereas the freestanding TR-PBOI membrane only exhibited a CO2 permeance of 3.7 GPU with a CO2/CH4 selectivity of 35. In other words, the rGO–PBOI (TR-PBOI with reduced GO) membrane has 482 times higher CO2 permeance than the TR-PBOI freestanding membrane at a similar CO2/CH4 selectivity.