| The use of fossil fuels has caused environmental pollution problems,more and more researchers make efforts to develop clean and efficient energy conversion.Fuel cells are widely considered to be environmentally friendly in the 21 st century.Alkaline anion exchange membrane fuel cells have a unique alkaline environment,and an increased activity of the electrode catalytic.It allowes to use non-precious metals catalyst(such as nickel and silver,etc.)instead of platinum,which has been widespread concerned.Alkaline anion exchange membrane as one of the key components of alkaline anion exchange membrane fuel cell,its main function is to isolate the direct contact of fuel and oxidant and promote transport of hydroxide ion.However,the current issues such as low ionic conductivity,large size swell and poor alkali stability seriously restrict the commercial application of alkaline anion exchange membrane fuel cells.In this paper,a novel strategy is proposed to construct a bis-continuous hydrophilic/hydrophobic micro-phase separation structure,which is essential for high hydroxide conductivity and good dimensional stability of anion exchange membrane(AEM).Firstly,(4-hydroxyphenoxy)alkane containing a flexible segment was synthesized and polycondensated with bis(4-fluorophenyl)sulfone.Then we synthesized an imidazolium cationic group functioned membrane containing a flexible aliphatic chain,the semi-flexible polyethersulfone polymer(Semi-f-PAES).The membrane was prepared by solution casting method.The hydroxide conductivity of the semi-flexible polymer membrane is about 2 times higher than that of the rigid polysulfone ones;At 60 °C,the maximum conductivity of the semi-flexible polymer membrane is 93 m S cm-1,which is higher than that of other random poly(aryl ether sulfone)imidazole AEM(27-81 m S cm-1).By using TEM with a rigid polysulfone matrix membrane,more continuous hydroxide conductive channels formed in the semi-flexible polymer membrane,and a single cell test using a Semi-f-PAES polymer exhibited a maximum power density of 125 m W cm-2 which is also higher than the maximum power density of other random poly(aryl ether sulfone)imidazoliumium AEM(16-105.2 m W cm-2)currently reported.In order to systematically study the effect of the chain length of the flexible chain on the microstructure and properties of the membrane,a semi-flexible polyethersulfone with-(CH2)n-in the polymer repeating unit was prepared.In the given IEC,with the growth of carbon chain,the water absorption and swelling ratio increased.When the IEC of PAES-8C-Im OH membrane increasing from 1.37 mmol g-1 to 1.76 mmol g-1,the hydroxide ion conductivity increased significantly from 30 m S cm-1 to 66 m S cm-1 at 20 °C,while SR is only 36 %.However,when the length is more than 8-CH2-,the water absorption would be excessive resulting in decreased ion concentration,so ion conductivity began to decline.When the carbon chain length increases to 10 C,the swelling ratio of PAES-10C-Im OH membrane significantly increases at high IEC.This is a new issue.To solve it,long aliphatic ether-1-octyl-2-methylimidazole was used to prepare a semi-flexible polysulfone membrane with a comb structure.Attributed to the self-aggregating structures formed by the introduced long alkyl hydrophobic side chains,the ionic conductivity increases at lower IEC while increasing the dimensional stability and alkali resistance of the membrane.When the degree of substitution is 103% and the IEC is 1.27 mmol g-1,the room temperature conductivity of the membrane can reach 42 m S cm-1,and its swelling degree is only about 10%.The chemical stability of 8-Semi-f-10C-PAES membrane has been further improved.After immersing in 144 h,it still maintained a high conductivity(90%),showing excellent thermal alkali stability.The structure of the semi-flexible polyethersulfone functionalized with the long chain alkyl halothiazolium groups is a good choice for the preparation of fuel cells with high performance anion exchange membranes. |
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