Preparation And Properties Of Novel Polybenzimidazole Anion Exchange Membranes Containing Steric Hindrance Structure

Polybenzimidazole anion exchange membranes(AEMs)with high ionic conductivity and alkali stability have been the research hotspots of AEMs fuel cells.In this study,a series of modification of polybenzimidazole(PBI)was carried out to prepare an anion exchange membrane with high comprehensive performance such as high ionic conductivity and alkali resistance.The research contents are mainly divided into the following three points:1.A large volume of monomeric tetraphenylterephthalic acid(TP)was designed and polymerized into a new type of non-planar structural polymer mPBI-TP-x with large steric hindrance by microwave condensation polymerization.The dialkylation of a series of alkane iodides gives the mPBI-TP-x-R series of anion exchange membranes.The membranes were characterized and tested.The obtained membranes were found to have excellent OH-conductivity and the ionic conductivity at 80? exceeded 46 mS· cm-1.At the same time,the alkali resistance test showed that the alkali resistance was greatly improved compared with the PBI membranes without introducing a large hindered monomer.The conductivity of the anion exchange membrane was slightly decreased after soaking for 1350 h in 1 M NaOH aqueous solution at room temperature,showing excellent alkali stability.2.In order to solve the problem of increased brittleness of PBI membranes caused by aromatic rigid monomer doping,a flexible chain structure monomer diethyldiphenyl terephthalate monomer(DEDP)was designed,synthesized and introduced into the PBI backbone.The introduction of DEDP not only increases the content of the structure in PBI but further increases the film formation,and also introduces a large volume steric hindrance at the C2 position of PBI,which improves the alkali stability of the PBI membrane.The ionic conductivity and IEC were only decreased for 10%when the series of films were immersed in 1 M NaOH aqueous solution at 60? for 1350 h.3.A thermoplastic mesh polymer membrane(PBI/IMDE-TIPN)of PIMDE interpenetrating PBI was prepared in which the IMDE monomer was polymerized in situ to form an interpenetrating structure with the PBI polymer chain.In TIPN,polymer chains flow at high temperatures to form physical crosslinks rather than chemical crosslinks,which have relatively high flexibility and can promote the aggregation of hydrophilic groups to help form ion channels and form micro-parents in AEMs.The water ion clusters therefore have excellent ionic conductivity and reach 71 mS·cm-1 at 80?.In addition,immersed in 1 M NaOH,only 8%degradation was found after 1350 h at 60?.Therefore,the TIPN structure provides a better solution for balancing the electrochemical and mechanical properties of AEMs.