Preparation And Performances Of Side Chain Anion Exchange Membrane For Akaline Membrane Fuel Cell

Alkaline anion exchange membrane fuel cells(AEMFC)have been attracting much attention because of its many advantages such as fast cathode oxygen reduction kinetic rate and the availability of non-precious metal catalysts.Alkaline anion exchange membranes(AEMs),as one of the key components of AEMFC,play an extremely important role in the development and application of AEMFC.However,AEMs face the challenge of relatively low ionic conductivity.To solve this challenge,we can obtain high conductivity by increasing the concentration of ions in AEMs.However,this method usually causes excessive swelling of the membrane,resulting in poor mechanical properties of the membrane.In addition,alkaline anion exchange membrane materials face the problem of relatively poor chemical stability.The quaternary ammonium group and the main chain in the polymer chain structure are vulnerable to the attack of the strong alkaline nucleophilic reagent OH-,which leads to the degradation of the quaternary ammonium group and the main chain,the destruction of the membrane and the loss of the electrical conductivity.Therefore,how to improve the chemical stability of AEMs without loss of conductivity has become another challenge in the development of AEMFC.In this paper,thermoplastic polysulfone(PSF)and poly(biphenyl-isatin)(PIB)without ether bonds were selected as the backbone materials from the perspective of balancing the conductivity and dimensional stability of AEMs as well as the stability of alkali resistance.High-performance AEMs were prepared by grafting long side chains containing multi-quaternary ammonium functional groups to construct hydrophilic/hydrophobic microphase-separated structures,which consisted of the following two aspects.Firstly,a series of chloromethylated polysulfones(CMPSF)with different chloromethyl grafting degrees were prepared,followed by the grafting of long side chains containing multi-quaternary ammonium functional groups to prepare side chain polysulfone polymers(LQAPSF-x)containing multi-quaternary ammonium cations,which were then laid down as AEMs membrane materials.It was found that the LQAPSF-94 membrane exhibited the highest ionic conductivity(110.13 m S/cm)at 80 ℃.The retention of hydroxide ion conductivity at 60 ℃ was 65% after immersing it in 1 mol/L KOH solution for 30 days.In addition,the swelling rate of LQAPSF-x membranes were all at a low level(<20%),exhibiting good dimensional stability.To enhance the stability of the membranes under alkaline conditions,we selected poly(biphenyl-isatin)(PIB)backbone without ether bonds,introduced flexible long chains containing multiple quaternary ammonium cations,and spaced them with long alkyl chains to reduce the attack of hydroxide ions on the backbone and further improve their chemical stability,and successfully prepared quaternary ammonium-functionalized poly(biphenylisatin)anion-exchange membranes with microscopic phase separation structure(LQAPIBx)with microscopic phase separation structure was successfully prepared.The ionic conductivity of LQAPIB-0.8 membrane reached 83.73 m S/cm at 80 ℃,and its swelling rate was only 6.28%.Moreover,the LQAPIB-0.8 membrane exhibited excellent alkali resistance stability,and its retention of hydroxide ion conductivity at 60 °C was up to 89% after 30 days of immersion in 1 mol/L KOH solution.Overall,LQAPIB-x membranes showed great potential for development.