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Chinese Science Bulletin, Volume 64, Issue 2: 172-179(2019) https://doi.org/10.1360/N972018-00716

Preparation and properties of anion exchange membranes based on multiple quaternary ammonium groups

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  • ReceivedJul 18, 2018
  • AcceptedAug 28, 2018
  • PublishedSep 11, 2018

Abstract

Anion exchange membrane fuel cell (AEMFC) has attracting great attention as one of the most clean energy conversion technologies, because it has a facile electrochemical kinetics under alkaline condition and enables the use of non-precious metal catalysts. The reported anion exchange membranes were usually prepared by tethering quaternary ammonium groups (QA) to the backbone of chloromethylated or bromomethylated aromatic polymers by immersing in trimethylamine solution. However, they exhibit much low ionic conductivity and poor alkaline stability, which hinders the further development of AEMFC technology. In order to improve the ionic conductivity of anion exchange membranes, we located multi QA groups on one side chains for enhancing the local density of ionic groups. Therefore, we synthesized a type of small molecule with a quaternary ammonium group and an alkyl bromide. After gethering it onto 1,4-diazabicyclo[2.2.2] octane-functionalized poly(arylene ether ketone) by a quaternization reaction, tri-quaternized poly(arylene ether ketone) (TQPAEK) was successfully prepared with flexible side chains containing multi quaternary ammonium groups. Then a series of anion exchange membranes in OH- form were obtained by solution casting and then alkaline treatment. The ionic exchange capacity of these membranes in the range of 1.75–2.57 meq/g could be adjusted by controlling the degree of bromination of the precursor polymer. The water uptake, swelling ratio and hydroxide conductivity of TQPAEK membranes increased with the increasing IEC values. They also showed good thermal and mechanical stabilities. Especially, the introduction of flexible side chains significantly improved the elongation at the break of membranes, which reached up to 103.2%. Meanwhile, the tensile stress was still higher than 28 MPa. AFM images showed that the hydrophilic/hydrophobic phase-separation morphology was formed in these TQPAEK containing multi-quaternized flexible side chains. Therefore, TQPAEK exhibited high ionic conductivity of 74.35 mS/cm at 80°C. The results indicated that TQPAEK membranes had the potential to be used in alkaline AEMFCs.


Funded by

国家自然科学基金(21474036)


References

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  • Figure 1

    The synthesis of TQPAEK

  • Figure 2

    1H NMR spectrum of BTAH (A) and TQPAEK (B)

  • Figure 3

    TG curves of TQPAEK membranes

  • Figure 4

    The hydroxide conductivity of TQPAEK as a function of temperature

  • Figure 5

    The phase images of atomic force microscope of TQPAEK- 1.25 (a) and TQPAEK-1.50 (b)

  • Figure 6

    The change of ionic conductivity of TQPAEK after treatment in 1 mol/L NaOH with immersing time

  • Table 1   Tensile strength, Young's modules and elongation at break of TQPAEK

    拉伸强度

    (MPa)

    拉伸模量

    (MPa)

    断裂伸长率

    (%)

    TQPAEK-0.81

    35±3

    539±14

    78.3±8.6

    TQPAEK-1.02

    33±1

    464±38

    79.3±7.0

    TQPAEK-1.25

    30±2

    356±40

    93.1±10.8

    TQPAEK-1.50

    28±2

    341±41

    103.2±15.2

  • Table 2   Ion exchange capacity, water uptake and swelling ratio of TQPAEK membrane

    IEC(meq/g)

    WU(%)

    SR(%)

    理论值a)

    实验值b)

    30℃

    80℃

    30℃

    80℃

    TQPAEK-0.81

    1.83

    1.75±0.09

    31.13±1.60

    44.10±2.21

    11.30±0.80

    20.83±1.04

    TQPAEK-1.02

    2.15

    2.05±0.10

    33.84±1.69

    55.38±2.78

    14.33±0.92

    31.86±1.74

    TQPAEK-1.25

    2.42

    2.33±0.12

    45.55±2.73

    76.63±4.61

    19.33±1.16

    42.23±2.52

    TQPAEK-1.50

    2.66

    2.57±0.13

    50.91±3.03

    110.63±7.78

    24.50±1.37

    58.23±3.45

    a) IEC理论值由核磁氢谱计算得到; b) IEC实验值由酸碱滴定方法确定

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