Construction of highly conductive PBI-based alloy membranes by incorporating PIMs with optimized molecular weights for high-temperature proton exchange membrane fuel cells

There is a great challenge to fabricate the phosphoric acid-doped polybenzimidazole (PA-PBI) membranes simultaneously having high proton conductivity and good mechanical strength through a simple and scalable preparation approach. In this study, the polymers of intrinsic microporosity (PIMs) with two different molecular weights (MWs) are incorporated into an aryether-type PBI (OPBI) matrix to form some novel alloy membranes containing a special intrinsic “porous” structure. It is the first time to observe the great effect of the PIMs’ MWs on the miscibility and properties of the PBI/PIM alloy membranes, and indicate that an obvious improvement on the performance can be achieved by incorporating PIMs with optimized MWs into OPBI matrix. The PIMs addition can bring a large “free volume” into the alloy membranes, which is expected to enhance the PA doping levels (ADLs) and therefore proton conductivity. It may provide an efficient way to overcome the major obstacles of the existing PA-PBI membranes; that is the mechanical stability of the PBI membranes always sharply decreases with the increase of ADLs. Most importantly, a very high proton conductivity of 313 mS cm−1 can be obtained at 200 °C and a peak power density of 438 mW cm−2 is reached at 160 °C, without humidification.