Nanoporous Fluorine-Containing Polynaphthoylenebenzimidazole Films: Implications for High-Temperature Hydrogen Recovery

Developing effective approaches for the synthesis of nanomaterials with enhanced properties for applications in high-temperature hydrogen recovery and gas separation technology is a challenging task. Nanoporous polymer films hold significant potential for a diverse range of applications owing to their distinctive characteristics, such as high surface area, adjustable pore size, and selectivity for chemical interactions. The study presents a two-stage method (enabling less toxic solvents) for the production of nanoporous films of heat-resistant and highly permeable fluorine-containing polynaphthoylenebenzimidazole (or polybenzimidazobenzophenanthroline) (PNBI-6F), produced from polymer solutions in DMSO and N-MP. Nanoporosity of the samples is revealed by the CO₂ adsorption method. It has been determined that the selection of the solvent can influence the characteristics and structure of the nanoporous polymer matrix. The gas transport properties of the films in the temperature range 20–250 °C have also been examined. All of the obtained nanoporous PNBI-6F films retain their mechanical properties at the maximum temperature for an extended period of time. The XRD and DMA methods and gas transport properties unexpectedly reveal a unique two-state behavior with distinct activation energies for gas permeability for each state. The initial state is characterized by lower gas permeability and free volume upon initial heating below 150 °C. A second state, which is metastable and characterized by an increase in gas permeability and free volume, occurs above 150 °C and persists in the sample over a prolonged period of time after cooling. Overcoming high-temperature gas separation challenges for H₂–CO₂ mixtures is essential for improving current hydrogen recovery processes and for better purification of reformed hydrogen. Therefore, it is important that the obtained gas transport characteristics significantly exceed the upper bound of the 2008 H₂–CO₂ Robeson diagram. The obtained results suggest the application of the nanoporous material in high-temperature hydrogen recovery technology.