Side-chain-type Anion Exchange Membranes With Different Cationic Groups

As an environmently benign energy technology,fuel cell has been receiving extensive attention from academic societies.Compared to proton exchange membrane fuel cell(PEMFC),alkaline fuel cell(AFC)has some unique advantages.Because of the acidic environment,PEMFC depends on these noble metal catalysts(such as Pt)while the alkaline environment of AFC allows the use of non-precious metals(such as Ag,Ni,Fe,et al)as the catalysts,making AFC relatively cost effective.However,as a key component of AFC,the commercialization of anion exchange membrane(AENM)is still hinderded by its low ion conductivity and poor chemical stability.To solve these issues and develop high-performance membranes for AFC,in this thesis,various cationic groups were connected to the polymer backbone via flexible spacer to investigate the effect of cationic structures on the performance of the membranes.On the basis of the obtained results,a novel AEM with N-spirocyclic quaternary ammonium cations was prepared.The main research contents and conclusions are as follows:(1)Via Williamson reaction,trimethylammonium,imidazoliums and cyclic quaternary ammoniums were grafted to polymer backbone to fabrncate five kinds of side-chain-type AEMs.Using the prepared membranes,the effects of cationic structures on the conductivity,dimensional stability,thermal stability and alkaline stability of the membrane were investigated.The results indicate that both the mechanical property and the thermal stability of all the AEMs meet the requirements for the application of fuel cells.Furthermore,the AEMs with cyclic cations(PES-MPRD and PES-MPY)exhibit higher conductivity and more robust stability in alkaline condition.The IEC of PES-MPY remained 90.7%after immersing in 2 M NaOH solution at 60? for 672 h.This research will be favorable to obtain excellent AEMs by choosing high-performance cationic groups.(2)According to the above results,the N-spirocyclic quaternary ammonium cations with five-and six-membered ring were connected to poly(ether sulfone)backbones with good mechanical and solubility as the hydrophilic side-chain.The prodigious steric hindrance of spirocyclic structure obviously enhances the stability of cationic groups in alkaline solution.The IEC of the AEM still remained 86.2%after immersing in harsh environment(80?,2 M NaOH solution)for 864 h.Besides,the high density of N-spirocyclic quaternary ammonium cations in side-chain benefits the formation of clear micro-phase separation,which can increase the conductivity as well as limit the swelling.The highest conductivity was 95.5 nS cm-1 at 80? while the swelling was only 7.69%.