The Preparation And Performance Research Of High Temperature Proton Exchange Membranes Based On Grafted/Block Polybenzimidazole

Proton exchange membrane fuel cells（PEMFCs）are the most promising technology for efficient power generation.PEMFCs can be applied to vehicles,mobile phones,household appliances,etc.They have the advantages of high power density,zero emissions,and low noise.Proton exchange membranes（PEMs）is the most important part for fuel cells.PEMs have the function of transporting protons and blocking gases.PEMs should have good proton conductivity,mechanical properties and durability.Polybenzimidazole（PBI）is a thermoplastic polymer with excellent mechanical properties and thermal stability with imidazole units.The basic functional groups of PBI can interact with strong acids such as phosphoric acid（PA）to achieve the role of proton transmission.Phosphoric acid doped polybenzimidazole（PA/PBI）can be used as high temperature PEMs.The research on PEMs is mainly to improve the proton conductivity,mechanical properties and long-term stability.On the one hand,we can improve the proton conductivity of the PA/PBI membranes by increasing the PA doping level.But because PA has plasticizing effect,it will cause a decrease of mechanical properties.On the other hand,most of the doped PA is in free state and easy to be leak,which will result in a decrease in proton conductivity and affect the service life of the PEMs.In this paper,the Amino polybenzimidazole was first prepared,and then grafted with ethylphosphonic acid（EPA）side chain.The introduction of EPA groups improves the PA doping level and proton conductivity of the membranes.The obtained membranes have good dimensional and thermal stability,and the PA retention capacity is obviously improved.Among them,the proton conductivity of the PBI-NH₂-EPA-15 membrane is0.062 S cm^-1（170°C）,which is 342%higher than that of the PBI membranes.In order to balance the PA doping level and the mechanical properties,we also prepared block polybenzimidazole（b PBI）.A part of the block has flexible ether bonds,which improves the solubility of b PBI;the other part of the block has a para-position structure,which has strong rigidity and good mechanical properties,which helps control the adsorption of PA.In order to further improve the proton conductivity of the block PBI,we also introduced phosphotungstic acid-ionic liquid（PWA-IL）organic-inorganic fillers.The resulting composite membranes（b PBI-X）exhibits high proton conductivity at low PA doping level,and the proton conductivity of b PBI-1 at 170°C is 0.05 S cm^-1.After 240hours of PA retention capacity test,the proton conductivity of b PBI-1 was 74.2%of the original.This indicates that the block composite membranes have higher PA retention capacity.