Alkaline Stability Anion Exchange Membrane Based On Polysulfone

The alkaline anion exchange membrane fuel cell?AEMFC?has become a research hotspot in recent years due to its advantages of high efficiency,use of non-precious metal catalysts,and wide fuel selection.As an important component of fuel cells,Anion exchange membranes?AEM?is responsible for transferring anion?OH^-?in the battery to form a complete battery circuit.At present,there are still two key issues seriously restrict the development of AEMFC:the low ion conductivities and poor stabilities of AEMs.This thesis is devoted to use environmental friendly methods to prepare high alkaline stability,high-performance alkaline anion exchange membranes.The main tasks of this thesis are:?1?Quaternary ammonium?QA?-type polysulfone anion exchange membranes?AEMs?with pendant carbonyl groups were designed and synthesized by an environmentally friendly method.Low toxicity 3-chloro-2,2-dimethylpropionyl chloride?CDPC?was chosen as an electrophilic reagent to introduce chloroalkyl groups to PSf,instead of highly toxic chloromethyl methyl ether.After quaternizing with trimethylamine?TMA?,AEMs were prepared by solution casting method.The obtained AEMs showed good ionic conductivity and mechanical stability.The alkaline stability of these AEMs was excellent:the AEMs can maintain 95%of their initial conductivity after immersion in a 1 M NaOH aqueous solution at 80?for 10 days.The reason for this outstanding alkaline stability was evaluated by NMR and density functional theory calculations:The most severe degradation pathway,the S_N2 reaction,can be weakened by the competing reaction between OH^-and carbonyl groups.The formed intermediate oxygen anion can decrease the possibility of S_N2 by reducing the electro-static potential of the QA groups.Because of the reversibility of the reaction between OH^-and carbonyl groups,QA groups can survive longer in strong alkaline conditions at high temperature.Also,the possibility of S_N2 reaction on the aromatic polymer chain can be decreased because of the positive charge carrier,QA groups,which are not directly attached to benzyl groups.Hoffmann elimination can not happen because here was no hydrogen atom on the?-position of QA group.We name this protection of carbonyls as“rat-trap effect”.?2?The imidazole?IM?polysulfone AEMs were prepared by imidazole salt instead of TMA.Although the obtained PSf-DPC-IM-61-OH membranes failed to exhibit excellent thermodynamic properties and hydroxide conductivity,it can provide a moderate conductivity at 20°C and the?can achieve at 20.2 mS·cm^-1.The AEMs can maintain 95%of their initial conductivity after immersion in a 1 M NaOH aqueous solution at 80?for 5 days.Meanwhile,this AEM possess a small water absorption ratio and swelling ratio.Therefore,better performed AEMs can be expected by further exploring the experimental details to synthesize crosslinked PSf-DPC-IM-x-OH-cross AEMs.