Preparation And Performance Of SPEEK/P4VP Acid-base Composite Proton Exchange Membranes

Proton exchange membrane(PEM)is the key part of proton exchange membrane fuel cell(PEMFC).Sulfonated aromatic polymer have been shown to have considerable promise as the new type membrane material instead of Nation,due to its appropriate mechanical strength and high chemical and thermal stabilities.However,the high swelling phenomena will occur with high degree of sulfonation(DS)and high temperature.The dimension stability becomes poor.While,for membrane material with low DS,the dimension stability at high temperature can be obtained,but obvious reduction of proton conductivity is accompanied.In order to solve the contradiction between dimension stability and the conductivity,this paper is focused on the preparation of acid-base composite membranes.The sulfonated polyether ether ketone(SPEEK)and 4-vinylpyridine(4-VP)were used as the acidic polymer and the basic monomer,respectively.The dimension stability was solved by the ionic crosslinking via acid-base interaction.SPEEK polymers with various degree of sulfonation were synthesized in 95-98% sulfuric acid by controlling the reaction time and temperature.SPEEK(DS＞50%)were selected as the acid material according to the studies of the performances of water-soluble and solvent resistance.SPEEK/P4VP acid-base composite proton exchange membranes were prepared by heat polymerization of 4-vinylpyridine mixed with SPEEK solution.The effects of different kinds and contents of initiator on the properties of the membranes were studied. The results showed that 0.2 wt%AIBN initiator was appropriate for preparing condition of composite membranes.The ionic crosslinking structure was confirmed by the IEC.The dimension stability was increased due to the ionic crosslinking between acid polymer and base polymer.The water uptake and swelling rate of SPEEK56/P4VP-10% composite membranes at 80℃were decreased than SPEEK56 membrane by 46.9%and 41.2%,respectively.Composite membranes had good proton conductivity at high temperature. The proton conductivity of SPEEK56/P4VP-10%membrane(5.5×10^-2S·cm^-1)was a little higher than that of Nafion112 and SPEEK50 membranes at 95℃.Compared with SPEEK50 membrane,the water uptake and swelling rate of composite membranes were decreased by 40.9%and 33.6%,respectively.Thus,by adjusting the DS and the content of 4-VP, SPEEK/P4VP acid-base composite membrane can be prepared,which is a feasible method to solve the problem between dimension stability and conductivity.Besides,the ionic crosslinking interaction caused a further decrease in methanol permeability of membranes.The thermal stability,mechanical strength and oxidation stability were also increased.The above findings indicate that SPEEK/P4VP acid-base composite membranes have higher performance than pure SPEEK membranes.The membranes used as PEMFC and DMFC at medium-high temperature display better prospect.