Preparation Of High Performance Polybenzimidazole Proton Exchange Membrane By Solid Phase Reaction Of Azides

The proton exchange membrane fuel cell has the advantages of high power,high energy cycle efficiency,low working temperature,fast start-up,and environment friendly.It is the most promising power source for portable power supply,small fixed power station and electric bicycle.Proton exchange membrane(PEM)is the core component of proton exchange membrane fuel cell(PEMFC),which directly affects battery performance,energy conversion efficiency and battery life.The Nafion film,produced by Dupont,is a typical representative of the industrialized proton exchange membranes.Although Nafion film has high proton conductivity and good chemical stability,its poor heat-resistance and high price restrict the use of Nafion in the PEMFC filed.To meet the needs of development,in recent years,scientists have done a lot of work on developing a new type of PEM.Among them,sulfonated polybenzimidazole(s-PBI)is a kind of new PEM.The s-PBI proton exchange membrane has high thermal stability,good mechanical properties,excellent chemical stability and good proton conductivity.Generally,the s-PBI is synthesized by the polycondensation of sulfonated monomer,which has a lower activity in the condensation reaction compared to the common tetramine monomer.Therefore,it is difficult to obtain high molecular weight PBI when using more amount of the sulfonated monomer.A lower molecular weight will seriously affect the membrane formation and the mechanical properties of the s-PBI proton exchange membrane.In this paper,we presented a novel strategy to prepare the s-PBI proton exchange membrane.In this strategy,a two-step method is used for synthesizing the high-performance s-PBI membrane.Firstly,the PBI polymer is prepared by using normal monomers;and then the PBI membrane is modified by using an azide compound containing sulfonic acid group.The structure and properties of the as-prepared s-PBI proton exchange membranes were characterized,analyzed and discussed in this paper.The paper is divided into the following parts:(1)The soluble polybenzimidazole were prepared by polycondensation of 4,4-dicarboxy diphenyl ether(OBBA)and 3,3,4,4-biphenyltetramine(DAB)as monomer,and polyphosphoric acid(PPA)as solvent.Polybenzimidazole proton exchange membrane was prepared by solvent casting method.At the same time,azide benzene sulfonic acid and azide naphthalene sulfonic acid were synthesized from aminobenzenesulfonic acid and aminonaphthalenesulfonic acid.They have the desired structure which was characterized by NMR and FT-IR.(2)Sulfonated polybenzimidazole(s-PBI)was prepared by a solid phase reaction,which is an insertion reaction of azene on unsaturated carbon in high temperature solid phase,that is,the insertion of diazenylbenzenesulfonic acid(formed by azidobenzensulfonic acid)or diazenylnaphthalenesulfonic acid(formed by azidonaphthalenesulfonic acid)on the unsaturated carbons of PBI.A series of s-PBI proton exchange membranes were prepared by changing the content of azide sulfonic acid.The effects of sulfonation degree on the conductivity of the s-PBI proton exchange membranes were systematically investigated.The results show that the proton conductivity of the membranes was increased with the increase of the content of sulfonic acid groups.When the content of azide benzenesulfonic acid was 40 wt%,the conductivity of s-PBI is 4.382 × 10-3 S/cm,and the film still has good mechanical strength and heat resistance(39.72 MPa,elongation at break was 96%,T10% =360?C).And the conductivity of the s-PBI proton film with the azide naphthalenesulfonic acid group was 6.593 × 10-3 S/cm.When the content was 40 wt%,the composite film still has good mechanical strength(41.21 MPa)and thermal stability(T10% = 320?C).(3)The polyaniline(PANI)has good conductivity,so the addition of PANI can also improve the proton conductivity of PBI composite membrane.The s-PBI/PANI composite proton exchange membrane was prepared by physical blending.The effects of different content PANI on the conductivity of PBI/PANI and s-PBI/PANI composite proton exchange membranes were investigated respectively.The results show that the PBI/PANI composite proton exchange membrane containing 40 wt% PANI has the highest proton conductivity(6.036 × 10-3 S/cm),and the mechanical properties is good(32.02 MPa,elongation at break was 49%,T10% = 460?C),the conductivity of s-PBI/PANI composite proton exchange membrane containing 20 wt% PANI and 10 wt% azidobenzensulfonic acid was 5.677 × 10-3 S/cm.