氟代苯基聚降冰片烯单阴离子交换膜的制备及损伤可视化检测

Design,Preparation and Visual Detection of Fluorophenyl Polynorbornene Anion Exchange Membrane with Single Quaternary Ammonium Salt

具有高的离子电导率和碱性稳定性的碱性阴离子交换膜(AEMs)是制备碱性燃料电池的关键.通过合理的分子设计,选用全烷烃基聚降冰片烯嵌段共聚物作为AEMs的主链,可有效避免AEMs在强碱条件下的降解.同时在侧链中引入亲水性含氟苯基季铵盐作为离子导电基元,疏水性三乙基硅基团作为非导电基元,利用二者之间的亲疏水作用,在薄膜中形成可供OH-迁移的离子通道,有助于提高AEMs的电导率.通过调节含氟苯基季铵盐中氟原子的数目,可以调节离子通道的大小,从而实现对薄膜电导率的调控.另外,为了实现AEMs的损伤可视化监测,将具有聚集诱导发光作用的四苯乙烯基二降冰片烯酰亚胺作为交联单体引入聚合物中,通过烯烃的复分解反应,开环聚合制备得到单离子AEMs.聚合物表现出优异的热稳定性(5%热失重温度T_(d)>250℃),力学性能(σ_(b)=36.56 MPa,δ=16.92%)和耐碱性能(在6 mol/L NaOH溶液中浸泡7天后,电导率仅下降3.3%).通过扫描电子显微镜可观测到微相分离形成的离子通道,与已报道的单离子AEMs相比,表现出较高的离子电导率(80℃,24 mS/cm).在365 nm光照下,薄膜发出均匀的绿色荧光,损伤处则无荧光,实现了AEMs的可视化检测.

Alkaline anion exchange membrane(AEMs)is an important component in the preparation of alkaline fuel cells,which should have high ionic conductivity and alkaline stability.In this work,we present a rationally designed block copolymer of polynorbornene as the backbone of AEMs,which maintains excellent stability in strong alkaline media.Furthermore,ionic conducting fluorophenyl quaternary ammonium salt and non-conducting triethyl silicon group are introduced in side chains to attain tunable polymer structures.Due to the hydrophilic and hydrophobic interactions,channels are formed in the polymer membrane for the transfer of hydroxide.In addition,in order to achieve nondestructive detection of AEMs,tetraphenyl ethylene with aggregation-induced luminescence,for the first time,is introduced as crosslinking monomer to prepare block copolymers via ring-opening metathesis polymerization with Grubbs II as catalyst.The copolymers exhibit excellent thermostability,mechanical properties and alkali resistance.The maximum stress and elongation at break of PNB-NOHPhF1-3Si-TPE are σ_(b)=36.56 MPa and δ=16.92%,respectively,and the 5%weight lost temperature is over 250℃.Compared with the reported AEMs with single quaternary ammonium salt,the block copolymers PNB-NOHPhF1-3Si-TPE show better alkali resistance and higher conductivity of 24 mS/cm at 80℃.The ion channels formed by microphase separation can be observed with scanning electron microscopy(SEM)by scanning the polymer cross section.Under 365 nm UV-light,the film emits uniform green fluorescence.Because of the lack of fluorescence at the damage sites,the integrity of film is non-destructively visualized.