Preparation And Properties Of Branched Poly(2,6-dimethyl-1,4-phenylene Oxide) Anion Exchange Membrane

Hydroxide exchange membrane fuel cells?HEMFCs?receive growing interest due to the usability of non-precious metal catalysts in the basic operating environment.Anion exchange membrane?AEM?as one of the core components of AEMFC,its performance greatly affects the performance of the battery.At present,AEM is facing the main bottleneck problem is the low hydroxide ion conductivity and poor stability in strong alkali environment.Here,chloromethylated poly?2,6-dimethyl-1,4-phenylene oxide??PPO-CH₂-Cls?with dfferent degree of substitution was prepared by chloromethylation of poly?2,6-dimethyl-1,4-phenylene oxide??PPO?.?PPO-CH₂-Im?with different ion exchange capacity was synthesized by Menshutkin reaction of 1,2-dimethyl imidazolium and?PPO-CH₂-Cls?.But,the membrane hydroxide ion conductivity of?PPO-CH₂-Im?was low.In order to improve the hydroxide conductivity,a novel poly?2,6-dimethyl-1,4-phenylene oxide?with imidazolium-terminated long side chains?PPO-COC5H10-Im?was synthesized by simple and controllable acetylation reaction of PPO and 6-bromohexanoyl chloride in a moderate condition?at room temperature?,followed by the Menshutkin reaction with 1,2-dimethylimidazole.The introduction of long chains between imidazolium groups and polymer main chains facilitates the formation of good hydrophilic/hydrophobic micro-phase separation structure,which is charaterized by TEM.The hydroxide effective mobility in PPO-COC5H10-Im membrane is almost 2-fold that in short side chain imidazolium functionalized PPO?PPO-CH₂-Im?membrane at a certain IEC.Given similar swelling ratios?25% vs.27%?,PPO-COC5H10-Im membrane shows much higher hydroxide conductivity than PPO-CH₂-Im membrane?62 vs.42 mS cm-1?at 60 oC.It indicates that the PPO-COC5H10-Im membranes prepared here exhibits highly enhanced conductivity without scarifying the dimensional stability.In order to further improve the alkaline stability of AEM,stable piperazine was used as the functional group.And the piperazine functionalized PPO membrane?PPOCOPhPi-OH?was prepared by introducing piperazine into anion exchange membrane.?PPOCOPhPi-OH?was synthesized by simple and controllable acetylation reaction of PPO and p-fluorobenzoyl chloride,followed by condensation reaction with N-methylpiperazine,and finally reached the functionalization with methyl iodide.The PPOCOPhPi-OH membrane has good dimensional stability.The swelling ratio of the PPOCOPhPi-OH membrane does not change with the temperature rise from 30 ? to 80 ?.The PPOCOPhPi-OH membrane?1.95 mmol g-1?has a swelling ratio only 27%.The PPOCOPhPi-OH membrane?1.95 mmol g-1?reached 69 mS cm-1 at 30 ?.Futhermore,the alkaline stability of the PPOCOPhPi-OH membrane was also improved.All the membranes remained intact after immersion in 1M NaOH solution at 60 ? for 500 h.The hydroxide conductivity and IEC of the membrane did not decrease with the immersion time.