Preparation And Properties Of Quaternized Polysulfone Membranes Doped Polydopamine By In-situ Polymerization

Hydroxide exchange membrane fuel cells?HEMFCs?have the advantages of lower catalyst requirements,simple water management,low fuel permeability,and a wide range of fuel sources.Therefore,as a core component of HEMFCs,the magnitude of the hydroxide conductivity?HC?of the hydroxide exchange membrane?HEM?greatly influences the energy density and efficiency of HEMFCs.Directly increasing the density of ion exchange groups is one of the most common methods for improving the conductivity of hydroxide.However,this method often results in the excessive water uptake of the membrane,dissipating the water-resistant plasticizing capacity of the membrane,further increasing the membrane size dramatically,and deteriorating the mechanical properties of the membrane.Herein,polysulfone?PSf?is used as a substrate,and trimethylamine quaternized polysulfone?PSf-QaCl?with different degree of substitution is prepared by homogeneous quaternization and passed through dopamine in situ during its film formation.Polymerization constructs a semi-interpenetrating network structure that restricts the movement of the polysulfone backbone and improves the swelling resistance of the membrane.First,trimethylamine quaternized polysulfone alkaline membranes?PSf-QaOH?with different degrees of substitution were prepared.Based on the measurements of HNMR,IR,and actual ion exchange capacity?IEC?,it has been demonstrated that trimethylamine and chloromethyl groups have high reactivity and good ion exchange properties,providing a basis for subsequent casting film conditions.In addition,it was found that the theoretical IEC of 1.50mmol g^-1 trimethylamine quaternized polysulfone membrane has a high conductivity of 30 mS cm^-1 at 20?,but the membrane swells at an operating temperature of alkaline fuel cell at 60?.The rate is as high as 76%,losing its application performance.Therefore,in order to improve its swelling resistance,a semi-interpenetrating network junction PSf-QaOH?PSf-QaOH/PDA?constructed by polydopamine was prepared by in-situ polymerization of dopamine?DA?during film formation.Analytical infrared and scanning electron microscopy measurements show that DA in-situ polymerization can form a semi-interpenetrating network structure with PSf-QaOH.In addition,polydopamine-doped quaternized polysulfone membranes have excellent high temperature swelling resistance.Taking PSf-QaOH with 78%substitution as an example,when W_DA is 0.09,DA is added for in-situ polymerization and the swelling rate of the film at 60?is 42.0%.The microstructure of polysulfone membrane was characterized by SEM.It was found that with the increase of DA content,the membrane formed a more connected and dense ion transfer channel,indicating that the introduction of the semi-interpenetrating network structure promotes the formation of connected transfer channels effect.Although the PSf-QaOH/PDA membrane has good high temperature swelling resistance,its hydroxide conductivity has a certain attenuation.To address the above issues,polydopamine-doped quaternized polysulfone membranes?M-PSf-QaOH/PDA?containing different metal ions were prepared.The test results show that the film containing metal ions has high conductivity and good swelling resistance.For example,when W_DA is 0.09 and R_F/D is 0.3,the conductivity of M-PSf-QaOH/PDA 84%is 65.4 m S cm^-1?60??and its swelling ratio is 40.8%?60??.