Block Polyolefin-based Anion Exchange Membrane:Preparation And Their Performance

Nowadays,energy and environment have become hot topics that have received much attention.Fuel cell has been widely accepted as an environment-benign energy source.Alkaline anion exchange membrane is core components of alkaline fuel cell,its performance determines the performance of alkaline fuel cell.In view of the current problems of low ion conductivity and poor alkali stability of alkaline anion exchange membranes,this paper uses polyolefin polymer as for membrane materials main chain,through the construction of"crystalline-non-crystalline"block and star topology structure to promote the membrane micro-phase separation and aggregation of ion-conducting groups,improving the stability and conductivity of membrane materials.The specific research work is as follows:Through a simple"acid-base"reaction,three monobenzyl scandium catalysts 1,2 and 3were synthesized with yield of 54.2%,48.6%and 45.3%,respectively.The structure of the three catalysts were characterized by NMR spectroscopy,shows their successful preparation.By coordination polymerization method,using monobenzyl scandium as catalyst,polyisoprene-b-syndiotactic polystyrene(PIP-b-sPS)block copolymer was prepared,further processes such as addition,functionalization and ion exchange produce,successfully prepared anion exchange membrane AEM-PIPsPS,syndiotactic polystyrene fragments have excellent crystallization ability.Studies have shown that the prepared membrane material has excellent ion conductivity,and its ion conductivity increases with the increasing of IEC.The AEM-PIPsPS-3 membrane shows the highest ion conductivity,which was 83.2 mS/cm at80°C,indicating that the introduction of block structure can significantly improve the ion conductivity of the membrane material.At 80°C,the water uptake of AEM-PIPsPS-3 is92.8%,and the swelling ratio is 29.5%,which shows that the crystallization segments in the membrane materials can limit the swelling in the membrane and improve membrane dimensional stability.In addition,the membrane also has excellent alkali stability,after immersion in 1 mol/L KOH solution for 168 hours at 80°C,the ion conductivity and IEC retention is 82.8%and 83.7%,respectively.By anionic polymerization method,using butyllithium as the initiator,a star block copolymer of polyisoprene-b-polymethylstyrene(PIP-b-P4MS-star)was synthesized,through further bromination,membrane formation and functionalization,three different block ratios star anion exchange membranes AEM-SCP-1,AEM-SCP-2 and AEM-SCP-3 were prepared.Among them,AEM-SCP-3 has the highest IEC and the anion conductivity of 68.1 mS/cm(80°C),which is 78.7%higher than the corresponding linear structure anion exchange membrane AEM-LCP,indicating a star shape topological structure can effectively promote the aggregation of the hydrophilic and hydrophobic phases and improve the conductivity of the membrane materials.The AEM-SCP membrane has excellent alkali stability,after immersed in 2 mol/L KOH solution for 720 hours at 60°C,the ion conductivity and IEC of AEM-SCP-3 are retention at 75.6%and 78.5%,respectively.At 60°C,the single cell performance test shows,when the open circuit voltage is 1.02V,the current density is 280mA/cm~2,the maximum power density is 120.2 mW/cm~2.