Preparation And Properties Of Graft Modified PVDF/SPEEK Composite Proton Exchange Membranes

Sulfonate polyetheretherketone(SPEEK)is regarded as one of ideal alternatives to commercial proton exchange membrane Nafion(?)for high proton conductivity,excellent methanol barrier properties,good chemical and thermal stability,outstanding mechanical properties,easy preparation and low cost.However,the performance of the pure SPEEK membrane is highly dependent on the degree of sulfonation(DS).As the the degree of sulfonation increase,the conductivity increases,while the alcohol resistance and dimensional stability deteriorate.Herein,an approach of using organic blending and doping proton conductors is adopted,using PVDF graft copolymer and Ui O-66-NH₂ as dopants,to study its impact on the various performance of proton exchange membrane(PEM).First,a one-step method of atom transfer radical polymerization(ATRP)is used to synthesize PVDF-g-PSPMA and PVDF-g-PSSA,and their structures and stability are characterized.Secondly,the effects of two PVDF graft polymers(PVDF-g-PSPMA and PVDF-g-PSSA)on the performance of SPEEK membrane are studied experimentally.The Study fully utilizes their high stability and high proton conductivity.The results display the contribution of PVDF-g-PSSA to proton conductivity is greater than that of PVDF-g-PSPMA,and the optimal doping ratio of PVDF-g-PSSA is 5.0 wt.%.Furthermore,the conductivity increase rate of the SPEEK/PVDF-g-PSSA-5.0 composite membrane is55.98%at 20 ^oC,which is much greater than that of the SPEEK/PVDF-g-PSPMA-2.5(the increase rate is 10.03%).Finally,the system is doped with MOF material Ui O-66-NH₂ as a proton conductor.Owing to the hydrophilic and water-retaining capabilities of Ui O-66-NH2,and the characteristics of-NH₂ and-SO₃ forming a Lewis acid-base pair,the three-phase SPEEK/PVDF-g-PSSA/Ui O-66-NH₂ blending membrane can be successfully fabricated.According to the experimental results,the doping of Ui O-66-NH₂ can not only improve the proton conductivity of SPEEK/PVDF-g-PSSA composite membrane,but also effectively limits the swelling of the membrane and improving the dimensional stability of the composite membrane.And the addition of PVDF-g-PSSA still has better conductivity than PVDF-g-PSPMA.Moreover,the conductivity of SPEEK/PVDF-g-PSSA-5/Ui O-66-NH₂-2 composite membrane at 20 ^oC is 22.88%higher than that of the pure SPEEK membrane,and is 2.29%higher than that of SPEEK/PVDF-g-PSSA composite membrane.The swelling ratio of SPEEK/PVDF-g-PSSA-5 and SPEEK-PVDF-g-PSSA-5/Ui O-66-NH₂-2.0 composite membrane are 6.6%and 5.27%at 50 ^oC respectively,which improves the dimensional stability of the composite membrane.