Design And Synthesis Of Three-Dimensional Poly(ionic Liquid)s And Their Proton Conduction Properties

Proton exchange membrane fuel cells have attracted more and more attention from domestic and foreign researchers due to their high energy conversion efficiency,low noise,low pollution and good chemical stability.The commercialized proton exchange membrane-perfluorosulfonic acid membrane,due to its shortcomings such as high cost and high requirements for temperature and water content,limits its wide application in proton exchange membrane fuel cells.Therefore,the development of new proton conducting materials with low cost and high conductivity has become the focus of this field.Poly（ionic liquids）are a type of polyelectrolyte constructed from ionic liquid（IL）monomers through the polymer backbone,and have unique charge characteristics of ionic liquids.Poly（ionic liquid）s can be regarded as composed of a skeleton structure and guest ions,and the guest ions and the skeleton structure interact through electrostatic interaction.These guest ions act as proton carriers in the process of proton transfer.In recent years,poly（ionic liquid）s have received more and more attention due to their adjustable structure and potential applications.This topic mainly selects monomers based on 3,3’-methylene divinylimidazole dibromide（[C₁DVIM]Br₂）and 3,3’-ethylene divinylimidazole dibromide（[C₂DVIM]Br₂）.Designed and synthesized a series of new three-dimensional poly（ionic liquid）s with high proton conductivity through different synthesis methods.The specific research content can be divided into the following three aspects:（1）Six three-dimensional poly（ionic liquid）s（PIL-1～6）based on the structure of 3,3’-methylene divinylimidazole dibromide salt were synthesized by different synthesis methods,and their structures and properties were characterized.The results of the study show that,except for the microscopic morphology,the chemical structure and thermal stability of the poly（ionic liquid）s prepared by the ionic liquid thermal method are similar to those of the poly（ionic liquid）s prepared by the solvothermal method.PIL-1～6 show good thermal stabilities,and their decomposition temperatures are higher than 280℃.Since these materials have strong swelling properties under high humidity（98%RH）,it is difficult to accurately measure their proton conductivity at high humidity.Therefore,only their proton conductivities under low and medium humidity（80%RH）has been studied.Poly（ionic liquid）s prepared by solvothermal and ionothermal have similar structures,so their proton conductivity properties also are similar.Compared with the solvothermal method,the ionothermal method has the advantages of safe preparation method,can be carried out in an atmospheric atmosphere,high yield,and ionic liquid solvent can be recycled,making it cost-effective and easy to scale up.（2）In order to develop higher performance proton conducting materials,by introducing different anions(SO₄^2-,H₂PO₄^-and BF₄^-)as proton carriers into the poly（ionic liquid）s structure,three three-dimensional poly（ionic liquid）（SPIL,PPIL and BPIL）have been characterized.The results show that SPIL,PPIL and BPIL have good thermal stability and high proton conductivity.Among them,BPIL has the highest thermal stability,and its decomposition temperature is 314.4℃;SPIL has the highest proton conductivity,which can reach 1.89×10^-2 S·m^-1 at 80℃and 98%RH.The ultra-high proton conductivity is comparable to the reported conductivity of high-performance proton conducting materials.In addition,the poly（ionic liquid）s has long-term stability,and its conductivity does not significantly decrease after one week of continuous operation under strict conditions.The simple and green synthesis of these high-performance poly（ionic liquid）s provides a new way for the development of new proton conductive materials with high performance.（3）In order to further explore the relationship between the structure of the three-dimensional poly（ionic liquid）s and proton conductivity,and obtain a method for regulating the proton conductivity,3,3’-ethylene divinylimidazole dibromide is used as the monomer,and the poly（ionic liquid）s were prepared by solvothermal and ionothermal synthesis method,and the proton carriers(SO₄^2-,H₂PO₄^-)with high proton conductivity were introduced into the three-dimensional poly（ionic liquid）s by the post-synthesis method,and five poly（ionic liquid）s（EPIL-1～5）were designed and synthesized.These poly（ionic liquid）s have good thermal stabilities and high proton conductivities.Among them,EPIL-3 has the highest thermal stability,and its decomposition temperature is 286.8℃;EPIL-4 has the highest proton conductivity.At 80℃and 98%RH,the proton conductivity of EPIL-4 reaches 1.63×10^-2 S·m^-1.