Nitrogen Dense Distributions of Imidazole Grafted Dipyridyl Polybenzimidazole for a High Temperature Proton Exchange Membrane

The introduction of basic groups in the polybenzimidazole (PBI) main chain or side chain with low phosphoric acid doping is an effective way to avoid the trade-off between proton conductivity and mechanical strength for high temperature proton exchange membrane (HT-PEM). In this study, the ethyl imidazole is grafted on the side chain of the PBI containing bipyridine in the main chain and blended with poly(2,2'-[p-oxydiphenylene]-5,5'-benzimidazole) (OPBI) to obtain a series of PBI composite membranes for HT-PEMs. The effects of the introduction of bipyridine in the main chain and the ethyl imidazole in the side chain on proton transport are investigated. The result suggests that the introduction of the imidazole and bipyridine group can effectively improve the comprehensive properties as HT-PEM. The highest of proton conductivity of the obtained membranes under saturated phosphoric acid (PA) doping can be up to 0.105 S cm(-1) at 160 degrees C and the maximum output power density is 836 mW cm(-2) at 160 degrees C, which is 2.3 times that of the OPBI membrane. Importantly, even at low acid doping content (similar to 178%), the tensile strength of the membrane is 22.2 MPa, which is nearly 2 times that of the OPBI membrane, the proton conductivity of the membrane achieves 0.054 S cm(-1) at 160 degrees C, which is 2.3 times that of the OPBI membrane, and the maximum output power density of a single cell is 540 mW cm(-2) at 160 degrees C, which is 1.5 times that of the OPBI membrane. The results suggest that the introduction of a large number of nitrogen-containing sites in the main chain and side chain is an efficient way to improve the proton conductivity, even at a low PA doping level.

Automated summary

The introduction of basic groups in the polybenzimidazole (PBI) main chain or side chain is an effective approach to improve the properties of high temperature proton exchange membranes (HT-PEMs). In this study, ethyl imidazole is grafted on the side chain of PBI containing bipyridine in the main chain, resulting in a series of PBI composite membranes blended with poly(2,2'-[p-oxydiphenylene]-5,5'-benzimidazole). The results show that the introduction of imidazole and bipyridine groups enhances the proton conductivity and mechanical strength of the membranes, achieving higher output power density and tensile strength compared to the pure OPBI membrane.