Preparation Of Quaternary Ammonium Functionalized Side Chain Anion Exchange Membranes

Anion exchange membrane fuel cells(AEMFCs)have received widespread attention for its superiority.For instance,the use of non-noble metal(Ag and Ni)as catalyst allows AEMFC with low cost.Besides,high efficiency and the various choice of fuel are also the advantages of AEMFC.As a crucial component of AEMFC,the performance of anion exchange membranes(AEMs)directly affects the life and performance of the cell.However,the development of AEM is blocked by the poor ionic conductivity and the unsatisfied alkaline stability.To improve the ionic conductivity and alkaline stability of the AEM,the structure of membrane needs to be designed.Side-chain type AEMs exhibit better performance than main-chain type AEMs.Extending the distance between the cationic groups and backbone can promote self-assembling behavior to form micro phase separation,thus constructing well-interconnecting channel for ion transportation.The weakened attack from the OH-on the backbone is the other meaningful result.In consequence,on the basis of the side-chain type structure membrane,we designed the structure of membranes combined with other structure.The main work and results are as follows.(1)Side-chain type AEM with multi-cation.A long flexible ionic liquid with three quaternary ammoniums was designed,every two-quaternary-ammoniums was separated by six methyl and the end group of the ionic liquid is-Br.The ionic liquid was grafted onto poly(ether ketone)via Williamson reaction to prepare membrane(TQAPEK-x).The combination structure of side chain and multi-cation made the membrane with obvious micro phase separation,thus an efficient ionic conducting channel was constructed in the membrane.The TQAPEK-0.5 membrane with an IEC of 1.94 mmol g-1 shows a high ionic conductivity of 132.8 mS cm-1 at 80 ℃.Furthermore,the TQAPEK-x membranes show more stable dimensional stability than QAPEK-0.6 membrane.The single cell test shows the membrane has the prospect in application.(2)Crosslinked AEMs.To balance the relationship between IEC and water uptake.and improve the alkaline stability,the crosslinked AEMs(QAPVP-x)with side chain were prepared using the commercialized poly(4-vinyl)phenol as the backbone.The synthesis of copolymer and membranes is straightforward.The crosslinking reaction avoided the use of the OH-in the backbone,which was convenient for the grafting reaction.Unlike the conventional side-chain type membranes,the QAPVP-x membranes had two different side chains.A flexible hydrophilic side chain with cationic groups and a long hydrophobic alkyl chain were grafting onto the backbone,separately.This kind structure membranes not only improves the micro phase separation,but also inhibits the water uptake and swelling ratio.Besides,the all-carbon based backbone allows the membrane with robust alkaline stability.After immersed in a 2 M KOH solution at 80 ℃ for 480 h,the ionic conductivity of QAPVP-5%membrane still remains 91.3%of the initial value.