With the rise of energy costs, membrane technology for separating gases plays a significant role in reducing the environmental impact and costs of industrial processes. Polymer-based gas separation membranes offer advantages over conventional technologies (cryogenic distillation, amine absorption, etc.) including, low capital and operating costs, minimum energy requirements, ease of operation, and environmental friendliness. However, gas separation in polymers has reached seemingly reached the trade-off between permeability and selectivity, as plotted on the 2008 Robeson plot. Inorganic membranes, on the other hand, display excellent permselectivity properties but incur high fabrication costs and lack membrane mechanical stability. Mixed-matrix membranes (MMMs) comprising thermally stable polymers and inorganic additives for target gases combines the polymers’ mechanical properties with the additives’ permselectivity properties. Our group focuses on MMMs consisting of zeolitic imidazolate framework (ZIF) materials in various polymer matrices, including polybenzimidazole (PBI), 6FDA-based polyimides, and polymers of intrinsic microporosity-1 (PIM-1) for industrially relevant gas separations. ZIFs belong to a subclass of highly porous metal-organic frameworks (MOFs) having structures similar to zeolites. The presence of organic linkers in ZIFs results in a better affinity between the polymer and ZIF, compared to a nonfunctionalized zeolite.
Supercapacitors, also known as electrochemical double layer capacitors (ECs) or ultracapacitors, are energy devices that store energy by the electric field present between a charged electrode and the counterions of the electrolyte. They possess relatively high energy density in the order of hundreds of times greater compared to conventional capacitors. Compared to conventional batteries or fuel cells, EDLCs also have a much higher power density.
Among various carbon materials, such as particles, papers, or nanotubes, carbon nanofibers are good candidates for electrode materials since they provide high surface area and porosity. These desirable properties can be attributed to their small fiber diameters and an entangled and interconnected structure. Carbon nanofibers are generally prepared by electrospinning of carbon precursor polymers and thermal treatment, which is called carbonization or graphitization.
Our research focuses on the preparation of carbon nanofibers derived from new polymer precursors such as blends or copolymers. Specific interactions between polymer precursors determine the resultant carbon structure, which is crucial for supercapacitor performance. We have also investigated several strategies to increase capacitance, energy and power density, including increasing the porosity and conductivity of the carbon-based electrodes, and the use of high voltage electrolytes such as ionic liquids. Increasing the surface area in carbon fibers can be achieved by the inclusion of pore-forming agents, such as volatile salts, polymer sacrificial templates, or polymers with inherent porosity upon carbonization.
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