Designing High Content Carbonylated β-Cyclodextrin/PBI Mixed Matrix Membrane as HT-PEM to Reduce H₃PO₄ Loss

The high-temperature proton exchange membranes suffer from weak binding strength for phosphoric acid molecules, which seriously reduce the fuel cell efficiency, especially operation stability. Introduction of microporous material in the membrane can effectively reduce the leaching of phosphoric acid. However, due to the poor compatibility between the polymer and fillers, the membrane's performance significantly reduced at high fillers content. Therefore, in this work, the strategy of micropore confinement was developed; the β-cyclodextrin was carbonylated and introduced into PBI casting solution as solution state rather than dry powder for reducing the interface energy between two phases, thus further reducing interface defects and increasing the content of effective confined micropores within the membrane. By this way, carbonylated β-cyclodextrin/PBI (50 wt %) mixed matrix membranes were obtained, the proton conductivity reached 142 ± 4 mS cm^-1, while the conductivity attenuation was only 16.6%.