Mixed Matrix Membranes Fabricated from Nanofillers of a Porous Organic Polymer for Applications as Proton Exchange Membranes

In recent years, nanofiller-embedded polymer matrix-supported mixed matrix membranes (MMMs) have been the center of attraction for various potential applications. In this study, we have explored the role of porous organic polymers (POPs) as proton conducting materials in a polymer membrane-supported matrix. A triazine-based benzimidazole-linked POP (TBP) was utilized as a nanofiller in an attempt to fabricate oxy-polybenzimidazole (OPBI)-embedded MMMs by loading different weight percentages of TBP-POPs into the OPBI polymer matrix. The MMMs were kept for doping in phosphoric acid (PA) to obtain proton exchange membranes (PEMs). The incorporation of TBP-POPs as nanofillers in the OPBI matrix resulted in highly altered morphology, enhanced thermal, chemical, and mechanical durability, enhanced PA doping level (PDL) and proton conductivity, and remarkable PA retention properties in the OPBI-TBP nanocomposites. The observed proton conductivity obtained for the PA-doped OPBI-TBP-10% membrane is 0.223 S cm–1 at 180 °C. The donor–acceptor type interfacial H-bonded network between the '–N═' atom of the OPBI polymer and the imidazole "N–H" group of TBP nanofillers, or vice versa, generates fibrillar porous morphology, as seen from FESEM analysis, and nanofillers self-assembled network into the polymer matrix, as evident from transmission electron microscopy analysis, for the composite membranes. All of these cumulative factors are responsible for the above-mentioned superior properties of the PEMs. Therefore, our current findings clearly demonstrate the interaction pattern of TBP-POPs as nanofillers to develop OPBI-supported MMMs, which can substantially perform as super proton conductors in the temperature range between 30 and 180 °C (fuel cell operating temperature) under an anhydrous environment. This will be the first report on POP-loaded PBI-based mixed matrix PEMs in the literature to date.