Graft Modified Polymer Based On Crown Ether To Build Anion Exchange Membranes

In order to alleviate the energy crisis and reduce environmental pollution,people are eager to find alternative energy sources.Based on the research progress at home and abroad,the exchange membranes suitable for fuel cells were prepared with the help of grafting crown ether onto modified polymers.The specific research contents are as follows:1.4-formyldibenzo-18-crown-6?FDB18C6?was synthesized using dibenzo-18-crown-6?DB18C6?as a raw material,FDB18C6 was grafted onto polyvinyl alcohol?PVA?skeleton by acetal reaction,which an anion exchange membranes were prepared and designated as F_X%-P membranes?X is the mass percentage of FDB18C6?.The F_X%-P membranes were then immersed in a 2 mol?L^-1 KOH solution to prepare a F_X%-P-K membranes?K⁺complex with crown ether holes?.The results show that the F_X%-P-K membranes have been successfully synthesized,the water content of F_20%-P-K membrane is reduced to 25.0%,which effectively inhibits the excessive expansion of PVA.In addition,it is particularly prominent that the conductivity of the F_X%-P-K membranes gradually increases from 7.63mS?cm^-1 at 70 ^oC,and the F_20%-P-K membrane increases to a maximum value of 25.32 mS?cm^-1,indicating excellent ion conductivity.After the prepared membrane was subjected to alkali treatment,F_15%-P-K membrane has the best alkali resistance stability,the conductivity loss rate was less than 8.6%.Next,an equal mass of glutaraldehyde?GA?and FDB18C6 are separately added to the PVA membrane to form a polyvinyl alcohol crosslinked glutaraldehyde membrane?P-G membrane?and a polyvinyl alcohol grafted crown ether membrane?P-F membrane?,and then An equal mass of GA was added to the P-F membrane to form polyvinyl alcohol grafted crown ether film crosslinked glutaraldehyde membrane?P-F-G membrane?.The effects of crosslinkers and crown ethers on PVA matrices were compared for these four membranes and their application in fuel cells was investigated.The results show that the mechanical properties of P-G membrane and P-F-G membrane with cross-linking agent are enhanced,Adding FDB18C6 to PVA increases the ion exchange capacity and conductivity.The ion exchange capacity ranges from0.31 mmol?g^-1 to 0.48 mmol?g^-1,the conductivity increased from 7.04mS?cm^-1 to 13.21 mS?cm^-1.2.Diformyldibenzo-18-crown-6?DDB18C6?was synthesized from dibenzo-18-crown-6?DB18C6?,and chitosan?CS?was added to DDB18C6by Schiff reaction to synthesize several CS-DDB18C6 membranes with different crown ether contents,namely D_X%-C membranes?X is the mass percentage of DDB18C6?.Thereafter,the D_X%-C membrane was separately immersed in a KOH solution and a CuCl₂ solution,and an anion exchange membranes were prepared by adsorbing K⁺and Cu²⁺in the crown ether,that is,D_X%-C-K membranes and D_X%-C-Cu membranes,respectively.Then the physical and chemical properties of the prepared membrane,such as molecular structure,thermal stability,mechanical strength,water content,ion exchange capacity and electrical conductivity,were analyzed by characterization and performance testing to explore the application in alkaline fuel cells.The adsorption mechanism of the optimal adsorption performance of D_X%-C-Cu membranes were studied by the kinetics and thermodynamic fitting of the adsorption process.The results show that the D_X%-C membranes have been synthesized by characterization.At 70 ^oC,the conductivity of D_X%-C-K membranes increase from 29.46 mS?cm^-1 to 52.18 mS?cm^-1,showing excellent conductivity.The conductivity of the prepared membranes before and after immersion in a 6 mol?L^-1 KOH solution at 70 ^oC for 480 h,wherein the maximum decrease in conductivity was only 5%,showed excellent chemical stability.