Preparation And Properties Of High Temperature Proton Conductor Doped Cross-linked PBI Based High Temperature Proton Exchange Membranes

High-temperature proton exchange membrane fuel cell(HT-PEMFC)has become a research hotspot due to its high efficiency and low pollution.The battery's hydrothermal management system is simple and has high CO tolerance.As the key to HT-PEMFC,proton exchange membranes(PEM)have also received extensive attention.Polybenzimidazole(PBI)is considered to be the most promising material for HT-PEMFC due to its high thermal stability and good mechanical properties.This article explores the following high temperature PBI proton exchange membranes:(1,3,5-triazine-2,4,6-triyl)tris(azadiyl)tris(propane-1-sulfonic acid)(TTPSA)was synthesized from melamine and 1,3-propane sultone.The 4-4'-(phenyl(phosphonomethyl)-amino)propane-1-sulfonic acid diphenylamine)-2-sulfonic acid(PPSA)was synthesized using 4,4'-diaminodiphenylamine-2-sulfonic acid as raw material,prepared by reacting PPSA with zirconium oxychloride(Zr OCl₂·8H₂O)to prepare proton conductor(Zr PPSA).Ethylenediamine tetramethylene phosphonate zirconium(Zr EDTMPS)was synthesized from ethylenediamine tetramethylenephosphonic acid(EDTMPS)and Zr OCl₂·8H₂O.These organic-inorganic proton conductors are insoluble in water and have good compatibility with PBI,and are not easily phase-separated in PBI membranes.The conductivity of TTPSA at180°C and 100%,50%and 0 RH were 0.116,0.056 and 0.02 S cm^-1,respectively.The conductivity of Zr PPSA at 180°C and 100%,50%and 0 RH was 0.103,0.051 and 0.023 S cm^-1,respectively.The conductivity of Zr EDTMPS at 180°C and 100%,50%and 0 RH was0.134,0.063 and 0.012 S cm^-1,respectively.The proton conductor has good thermal stability and can be doped into the PBI membrane as a high temperature proton conductor.Poly 2,5-benzimidazole(ABPBI)was prepared by melt polymerization of 3,4-diaminobenzoic acid(DABA).Hydroxymethylation was carried out using paraformald-ehyde as methylolation reagent and triethylamine was used as a catalyst for ABPBI.Then further reacted with SOCl₂ as chloromethylation reagent to get chloromethylated ABPBI(CMABPBI).The chlorine content of CMABPBI in this work was 8.1%.The sulfonated polyetheretherketone(SPEEK)was prepared by sulfonating polyetheretherketone(PEEK)with concentrated sulfuric acid as the sulfonating reagent,and the degree of sulfonation of the SPEEK used was 81.6%.The SPEEEK/CMABPBI crosslinked composite membrane was prepared by blending SPEEK and CMABPBI.The conductivity of SPEEK/CMABPBI(20%)and SPEEK/CMABPBI(30%)was 0.193 and 0.087 S cm^-1 at170°C and 100%RH,respectively and at 180°C and 50%RH,0 RH was 0.08,0.048,0.0082and 0.0072 S cm^-1,respectively.Low degree of polymerization of poly[2,2'-(m-phenyl)-5,5'-bibenzimidazole]was prepared by melt polymerization using 3,3'-diaminobenzidine(DABz)and isophthalic acid(IPA)as raw materials.5'-bibenzimidazole](m PBI).Chloromethylated PEI(CMPEI)was prepared by using polyetherimide(PEI)as raw material,trimethylchlorosilane and paraformaldehyde as chloromethylation reagents and Sn Cl4 as catalyst.The chlorine content of CMPEI used in this work was 4.3%.Prepared with CMPEI,1,3,5-triglycidyl isocyanurate(TGIC),tetraglycidyl 4,4'-diaminodiphenyl methane(TGDDM)as crosslinker m PBI-CMPEI/TTPSA,m PBI-TGIC/Zr PPSA and m PBI-TGDDM/Zr EDTMPS crosslinked composite membrane.SEM shows that the surface of these composite membranes was smooth,and the cross section was dense and without through holes.TG-DTA shows that the composite membrane has good thermal stability.At the same time,the composite membrane has high mechanical properties,resistance to swelling and oxidation,and low methanol permeability.The conductivity of m PBI-CMPEI(20%)/TTPSA(30%)at 180°C and 100%,50%and 0 RH was 0.113,0.057 and 0.0196 S cm^-1,respectively.The conductivity of m PBI-TGIC(5%)/Zr PPSA(30%)at 180°C and 100%,50%and 0 RH was 0.134,0.071 and 0.025S cm^-1,respectively.The conductivity of m PBI-TGDDM(5%)/Zr EDTMPS(40%)at 180°C and 100%,50%and 0 RH was 0.144,0.07 and 0.041 S cm^-1,respectively.Experiments have shown that a series of properties such as mechanical properties,dry and wet deformability and alcohol permeability can be improved by crosslinking.Moreover,the conductivity of the crosslinked membrane can be improved by doping the water-insoluble proton conductor,and the problem that the phosphoric acid doping is easily leached is solved.The prepared composite membrane was flat,dense and has good thermal stability and can be applied to HT-PEMFC.