Preparation And Performance Of Poly(2,5-benzimidazole) /Octaammonium POSS Electrolyte Composite Membranes

Currently, the commercial proton exchange membranes have two types of materials, one is perfluorosulphoric acid resin which is suitable for low temperature and high humidity conditions and another is polybenzimidazole resin which for high temperature and anhydrous conditions. Obviously, it's necessary to develop membranes which are qualified for both temperature and humidity conditions. Here we presented an approach to achieve high proton conductivity with slack working conditions. In other words, the protons transfer mainly through phosphoric acid(PA) molecules at high temperatures whilst through water molecules at low temperatures.The membranes of Poly(2,5-benzimidazole)(ABPBI) and ABPBI/AM-POSS(OctaAmmonium polyhedral oligomeric silsesquioxane) composites were prepared by synthesis process and followed casting method, respectively.The mechanical properties, thermostabilities, absorbilities of H2 O and PA for ABPBI and ABPBI/AM-POSS composites, the surface morphology changes and proton conductivities at various PA doping levels are characterized by tensile testing machine, FTIR, TGA, SEM-EDX, electrochemical workstation and so on. The main results are as followed:By changing the ratios of monomer DABA and reaction medium( including methanesulfonic acid(MSA) and P2O5), the reaction time and temperature, the stirring rate and so on, the optimized reaction conditions are suggested as: 1.0 g / 10 mL / 4.0-6.0 g of DABA / MSA / P2O5, 1-4 h of reaction time, 150 oC of reaction temperature and 400 r/min of stirring rate. The chemical structure of achieved product are confirmed by FTIR. Based on this chemical structure and relative results, the mechanism of H2 O and PA uptaking and proton tranfering have been presented.ABPBI/AM-POSS composites with 1%, 3% and 5% of POSS contents were in-situ synthesised, respectively. The uniform dispersion of POSS in ABPBI matrix are shown by SEM-EDX. Compared with those of ABPBI membranes, the tensile strength and Young's modulus of composite membranesareabviously improved, whilst ABPBI/3%AM-POSS compositemembranes achieved up to 258 MPa of tensile strenght and 4.6 GPa of Young's modulus which were about twice ABPBI membranes. By designing a reaction at low temperature, the amidation reaction between DABA and AM-POSS are confirmed by FTIR and NMR results, which are supporting the conception of a novel octopus shaped structure of ABPBI/AM-POSS composites. Based on that, the obviously improved mechanical properties and thermostabilities from composites are well explained. Due to the addition of AM-POSS particles, the composites' absorbilities of H2 O and PA are significantly enhanced, further resulting the greatly increased proton conductivities. Of which, above 0.1 S/cm of proton conductivity from ABPBI/3%AM-POSS with 252% of PA uptake between 80-140 oC. The ABPBI/AM-POSS composite membranes with excellent mechanical properties, thermostabilities and proton conductivities indicate that they are promising condidators for wide temperature PEMFC applications.