Polymer Electrolyte Membranes Based On Immobilized Phosphotungstic Acid For Performance Improvement

The proton exchange membrane is the core device of the proton exchange membrane fuel cell,which functions to separate the anode and cathode,conduct protons and prevent electrons from passing through.Nafion membrane is the most widely used proton exchange membrane,which has high proton conductivity and chemical stability,but its high price,non-degradability,high fuel permeability and loss of conductivity under high temperature and low humidity conditions limit its development.Finding proton exchange membranes that can replace Nafion membranes has become the focus of researchers.Composite membranes is a novel proton exchange membrane prepared by compounding polymer matrix with other organic or inorganic fillers.It has good physical and chemical properties and can add substances with high proton conductivity to enhance the proton conductivity of the membranes.Therefore,it has received widespread attention.Phosphotungstic acid(HPW)is a kind of heteropolyacid with Keggin structure and good proton ionization ability,which can be used for the modification of SPEEK membrane to improve its proton conductivity.However,HPW is highly soluble in water,which causes serious loss of HPW in the composite membrane.In previous studies in our laboratory,it was found that polydopamine-coated halloysite nanotubes(DHNTs)combined with HPW and SPEEK to form a membrane,and the basic amino group of polydopamine(PDA)can form an acid-base interaction with HPW.It acts to anchor HPW,which effectively improves the proton conductivity of the composite membrane.However,due to the limited number of basic amino groups on DHNTs,HPW is still lost,and its conductivity decreases with time.In order to introduce more basic amino groups,we have successfully prepared halloysite nanotubes with cross-linked polyehylenimine(PEI)/PDA coatings(PEI-DHNTs)by utilizing the property that PEI has a large number of basic amino groups and can be crosslinked with PDA.the introduction of a large number of basic amino groups successfully immobilized HPW,enhanced the proton conductivity of the composite membrane while inhibiting the loss of HPW,The proton conductivity of the SPEEK/PEI-DHNTs/HPW(90/10/50)nanocomposite membrane increased by 100%,and no significant decrease in proton conductivity after one-year immersion in liquid water.In order to anchor HPW more effectively,we mixed one-dimensional nanomaterial DHNTs with two-dimensional materials dopamine-coated graphene oxide(DGO),and mixed with HPW and SPEEK to form membranes.In addition to using the acid-base interaction formed in the membranes to anchor HPW,the multi-dimensional doped composite membrane forms a mutual bridge between the DHNTs and DGO,the intricate membrane structure also inhibits the loss of HPW and provides a richer channel to transfer protons.The conductivity of the SPEEK/DGO/DHNTs/HPW(90/5/5/60)nanocomposite membrane was 2.48 times higher than that of the pure SPEEK membrane,and the conductivity of the composite membrane did not decrease in the 30-day test of conductivity stability.We prepared β-CD-coated polydopamine-coated halloysite nanotubes(β-CD-DHNTs)via the self-polymerization of dopamine,and the related characterization confirmed the existence of β-CD in β-CD-DHNTs.The β-CD-DHNTs were combined with HPW and SPEEK to form membranes.The composite membranes exhibited excellent ability to anchor HPW.In the 30-day conductivity stability test,The proton conductivity of the SPEEK/β-CD-DHNTs/HPW(90/10/60)nanocomposite membrane remained stable and was 2.2 times that of the pure SPEEK membrane.It was confirmed that β-CD and HPW can undergo complexation to form a compound,which is an effective way for immobilizing HPW.