A new diamine monomer having alkyne side-groups (DADAF) has been successfully synthesized, and it was used to prepare a series of sulfonated co-polyimides (DFN-XX) when reacted with 1,4,5,8-naphthalenetetracarboxylic dianhydride along with different mole% of 4,4 '-diaminostilbene-2,2 '-disulfonic acid. The membrane was made from the copolymers by solution casting route, and one of the copolymers DFN-70 was used to prepare crosslinked membranes by adding a different amount of 1,6-hexanediazide during solution casting step. The morphological transformation from non-crosslinked S-coPI to crosslinked S-coPI was observed by employing transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering analyses. Compared to the non-crosslinked DFN-XX membranes, crosslinked DFN-70 copolymer membranes showed low water uptake and improved mechanical and peroxide radical stability. Also, crosslinked DFN-70 copolymer membranes showed significantly higher proton conductivities (0.004-0.06 S cm(-1)) compared to those of DFN-70 (0.003-0.05 S cm(-1)) particularly, at 80 degrees C when the relative humidity increased from 40% to 98%. Furthermore, crosslinked DFN-70 copolymer membranes exhibited significantly enhanced performance in a microbial fuel cell (MFC) as compared to those of non-crosslinked DFN-70 membrane.