Semi-interpenetrating polybenzimidazole membrane containing polymeric ionic liquid with high power density and...

In phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes designed for high-temperature proton exchange membranes (HT-PEMs), increasing the PA doping is essential. Yet, excessive PA doping causes a decline in mechanical strength, which in turn affects the cell performance. We utilize a strategy that integrates elevated PA absorption, increased mechanical strength, and enhanced PA retention. An azide-type ionic liquid (IL) containing double bonds was synthesized and crosslinked with PBI via free radical polymerization reaction. In addition, the IL can also self-polymerize to form long-chain polymeric ionic liquid (PIL). Together, the two structures together form a semi-interpenetrating polymer network (sIPN) system, which has good mechanical properties. The synthesized alkaline ionic liquid can absorb and retain a large amount of PA through acid-base interactions and inter-ionic interactions. Consequently, the proton conductivity of the amino-type polybenzimidazole (AmPBI)-polymeric ionic liquid (PIL)-30 (where 30 stands for the wt% of IL) membrane in an anhydrous environment at 180 °C reached 138.2 mS cm^-1. After PA retention test at 160 °C/0 % relative humidity (RH) for 240 h, the proton conductivity reached 99.4 mS cm^-1 at 180 °C. The AmPBI-PIL-10 membrane exhibited a significant power density of 635.4 mW cm^-2 at 160 °C. The AmPBI-PIL-X composite membranes exhibited exceptional performance.