Preparation Of Functionalized Side Chain Anion Exchange Membranes

Anion exchange membrane fuel cell(AEMFC)is regarded as one of the most perspective energy conversion devices due to its high efficiency(40%?70%).Furthermore,AEMFC enable the use of non-precious metal catalysts(snuch as silver and nickel)and various fuels(such as methanol,ethanol,hydrogen gas)selection,which have attracted great attentions over the past decades.As a critical component of AFCs,anion exchange membranes(AEMs)play a role in separating the fuel and oxidant and simultaneously conducting hydroxide ions,which determine the performance and long-term use of AFCs.Recent years a large number of AEMs have been reported,however,most of membrane materials still meet the dilemma of low conductivity and poor alkaline stability.Increasing the distance between the cationic functional group and backbone,can not only effectively improve the local motility of cationic groups making it self-assembled to form ion clusters,but also help to build obvious micro phase separation structure and well-interconnected ion conducting channel thus significantly enhance the ionic conductivity.However,the relationship between the structure and performance of membrane is not clear yet.Herein,we designed and prepared a series of side chain type AEMs and the results are listed as follows:(1)We provided a facile synthesis of poly(ether sulfone)-based anion exchange membranes(AEMs)bearing flexible pendent quaternary ammonium groups for fuel cells.(2,3-Epoxypropyl)trimethyl ammonium chloride was directly grafted onto the hydroxyl-bearing poly(ether sulfone)s backbone via one-step ring-opening reaction to introduce ion conductive moieties.This approach is more straightforward than the conventional two-step functionalization approach via chloromethylation or radical-initiated bromination and Menshutkin reactions.The results showed that cationic groups can aggregate and self-assemble in the functionalized-PES solutions which were in favor of fabricating phase separated morphology.In addition,the as-synthesized PES-100-IL membrane not only exhibited a reasonable hydroxide conductivity(46.8 mS cm-1),but also had a high power density,and desirable durability in a single fuel cell,which are of guiding significance for developing side chain type membrane materials.(2)In the previous work,we found that the OH-would attack the poly(ether sulfone)s backbone redulting in the degradation of the membranes under alkaline condition.In order to solve this problem,we designed claw side chain structure AEMs free of strong electron-withdrawing sulfone groups.The QA groups are linked to the backbone via long flexible spacers,which will weak the electron-withdrawing effect of cationic groups on the backbone thus improving the alkaline stability.In addition,the hydrophilic functionalized side chains are immiscible with hydrophobic poly(arylene ether)s backbone so that the as-prepared AEMs exhibited well-developed micro-phase separated morphology and constructed high efficient ion conducting channels.The highest conductivity of FPAE-3B-3.0-PD was achieved up to 98.19 mS cm-1 at 80 ?.In addition,the FPAE-3B-3.0-PD membrane showed excellent alkaline resistance performance,after immersing at 80 ? 1 M KOH solution 600 h,it still retained 94%of its initial ionic conductivity and 93%of IEC.The highest power density of H2/O2 type single cell reached at 156 mW cm-2,showing the good fuel cell performance.(3)Increasing the ionic exchange capacity(IEC)of AEMs is the direct way to improve the conductivity,however,this often comes with an increased swelling and loss of mechanical properties.To disentangle the conductivity-swelling dilemma in AEMs,we developed novel crosslinked poly(arylene ether)s AEMs via olefin metathesis using Grubbs 2 catalyst and thermal crosslinking.The crosslinked structure was effective for enhancing the dimensional stability of the membranes while remained a low swelling ratio.The conductivity of the C-FPAE-PH-1.5 membrane reached up to 81.1 mS cm-1 at 80 ?.Furthermore,the crosslinked AEMs showed robust alkaline stability,maintaining 93.1%of its original conductivity after immersed the membrane into a 1 M aqueous KOH solution at 60 ? for 360 h,indicating that the as-prepared AEMs hold promise as a novel AEMs materials.