Modification Of Sulfonated Polyarylenethioether Sulfones As Proton Exchange Membranes In Fuel Cell

The proton exchange membrane?PEM?is a core part of proton exchange membrane fuel cell?PEMFC?,which has dual role of providing an ion channel for transferring protons and isolating two polarities,the performance of PEM directly determines the battery performance.Sulfonated polyaryl sulfide sulfone?SPTES?is characterized by excellent high proton exchange capacity?IEC?,excellent proton conductivity,and good thermal stability,but under high humidity or in water the SPTES membranes have high swelling rate.However,the six-membered ring polyimide?PI?has low water absorption and excellent dimensional stability in water.In this paper,SPTES was synthesized via step growth polymerization,and modified by PI block and different SPI composites.Firstly,the aromatic backbone block copolymer consists of hydrophilic segment and hydrophobic segment was synthesized.Due to thermodynamic incompatibility,block copolymers can form proton conducting channels through microphase separation.In this paper,amine terminated sulfonated poly?arylene thioether sulfone??SPTES-NH₂?hydrophilic oligomers and anhydride terminated naphthalene based polyimide?PI?hydrophobic oligomers were synthesized via step growth polymerization.Synthesis of sulfonated poly?arylene thioether sulfone?-b-polyimide?SPTES-b-PI?was achieved by an imidization coupling reaction of hydrophilic and hydrophobic oligomers in a m-cresol/NMP mixed solvent system,producing SPTESx-b-PIy?x=5,10 kg/mol;y=5,10,15,20 kg/mol?with different molecular weights of SPTES-NH₂ and PI.As a result,the membrane prepared from the SPTES10-b-PIy showed excellent thermodynamic stability,lower water absorption and better dimensional stability than SPTES-70.The proton conductivity of SPTES10-b-PIy was higher than the minimum requirement?10 mS/cm?of PEM.Secondly,the synthesis of sulfonated polyaryl sulfide sulfone?SPTES-TEA?in the form of a triethylamine salt.Two kinds of sulfonated polyimide?SPI-BDSA,SPI-ODA?were synthesized by naphthalene-1,4,5,8-tetracarboxylic dianhydride?NDA?reacted with different diamine monomers 2,2'-disulfonic acid benzidine?BDSA?and 4,4'-diaminodiphenyl ether?ODA?.Two types of sulfonated poly?arylene thioether sulfone?/Sulfonated polyimide?SPTES/SPI-BDSA,SPTES/SPI-ODA?blend PEM with different SPI specific gravity were prepared by solution casting method.The SEM results showed that no obvious phase separation was found in the blend membranes,which indicated good miscibility between the two polymers.The water absorption and swelling ratio of the blend membranes decreased.The blend membranes displayed higher dimensional stability than the SPTES-70.Besides the water absorption and swelling ratio of the SPTES/SPI-ODA PEM lower than SPTES/SPI-BDSA PEM.,especially the blend membranes of SPTES/SPI-BDSA.The proton conductivity of the blend membrane is much higher than the minimum requirement of PEM?>10 mS/cm?,and has similar proton conductivity to SPTES-70 under the same conditions.