•Sulfonated polyimides containing benzimidazole group (SPIBI) are synthesized.•The cross-linked membranes are prepared by SPIBI and glycidyl ether POSS.•The cross-linked membranes exhibit improved hydrolytic and oxidative stability.•The cross-linked membranes show improved mechanical property.A new series of organic–inorganic hybrid proton exchange membranes (PEMs) were prepared using sulfonated polyimides containing benzimidazole (SPIBIs) and glycidyl ether of polyhedral oligomeric silsesquioxanes (G-POSS). SPIBIs were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 5-amino-2-(4-aminophenyl) benzimidazole (APBIA) and 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS). The organic–inorganic cross-linked membranes can be prepared by SPIBIs with G-POSS by a thermal treatment process. The cross-linking density of the membranes was evaluated by gel fractions. The water uptake, swelling ratio, mechanical property, thermal behavior, proton conductivity, oxidative and hydrolytic stability of the cross-linked organic–inorganic membranes were intensively investigated. All the cross-linked membranes exhibit high cross-linking density for the gel fraction higher than 70%. Compared to pristine membranes (SPIBIs) and membranes without benzimidazole groups (SPI), the anti-free-radical oxidative and hydrolytic stabilities of cross-linked membranes are significantly higher. The anti-free-oxidative stability of SPIBI-100-P (cross-linked SPIBI membrane with 100% degree of sulfonation) is nearly four-fold higher than that of SPIBI-100. The proton conductivity of the cross-linked membranes ranges from 10−3 S cm−1 to 10−2 S cm−1 depending both on the degree of sulfonation (DS) of the SPIBI and temperature.

The degradation of membranes in proton exchange fuel cells by chemical oxidation is one of the main factors limiting their lifetime. The effect of electric field on the oxidative degradation of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI) was investigated using electro-Fenton tests. The degraded PBI was characterized by measuring the sample's intrinsic viscosity (ηint) and weight loss and using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), and X-ray photoelectron spectroscopy (XPS). When the intensity of the electric field was increased from 0 V/m to 5000 V/m, the membrane's weight decreased, while the ηint of PBI decreased rapidly. Meanwhile, a larger number of larger pores formed on the PBI membranes, according to SEM images. The thermal stabilities of the degraded PBI membranes decreased significantly when the intensity of the electric field increased. FTIR, 1H NMR, and XPS spectra revealed that an electric field accelerated the formation of amide and amino groups after the breakdown of benzimidazole rings in PBI. The amino groups were stabilized by protonation in the acidic Fenton reagent. A possible mechanism for the increased oxidative degradation of PBI in an electric field was proposed.