Construction Of Proton Transport Channels And Study Of Membrane Performance For Composite Proton Exchange Membrane

Proton exchange membrane fuel cells(PEMFCs)are a promising power source that is extensively used in various fields.However,the main challenge for PEMFCs is promoting the performance and lifetime of the related components.Proton exchange membrane(PEM),as an essential and primary component for fuel cells,has a significant impact on the cost,durability and performance of fuel cells.However,the widely used commercial Nafion suffers a reduction in the proton conductivity under low humidity,which restricts the efficiency and large-scale use of fuel cells.Designing and developing high-performance PEM is the key to realize the large-scale application of PEMFC.This study mainly aims at enhancing the transport properties of PEM and focuses on the relationship between proton transport mechanism and PEM microstructure.The clue is design of membrane material-regulation of membrane microstructure-enhancement of membrane performance.Different types of organicinorganic composite membranes are designed with the strategy of constructing efficient proton transport channels.The research starts from multi-level structure such as membrane matrix,hybrid filler,filler-polymer interface,transfer channel,etc.The efficient enhancement of PEM performance is realized by synergistically regulating and optimizing the physical and chemical microenvironment of the membrane.Main conclusions are summarized as follows:(1)PSS are encapsulated into the nanochannels of ZIF-8 to prepare compact and continuous PSS@ZIF-8 composite membrane,whereby long-range ordered and continuous nanochannels are created.The proton conductivity of the membrane is significantly enhanced due to optimized channel structure.(2)GO sheets and polymers(SPVA and PDA)are assembled into nacre-inspired layered membrane(GPS)via vacuum filtration,which realizes the ultrathinning of the membrane and significantly enhances the mechanical properties of the membrane.GPS membranes possess penetrated and well-developed 2D channels and ample functional sites,which optimizes the physical and chemical microenvironments of the channel and achieves efficient proton conduction.(3)ZIF-L nanocrystals are deposited on GO sheets through an in-situ growth method and then blended with SPEEK to prepare composite films.The ZIF-L@GO hybrid nanosheets are uniformly dispersed in the membrane matrix,and have good interfacial compatibility with the polymer matrix.Benefiting from the the morphological and compositional advantages of ZIF-L@GO,the proton conduction ability of the composite membrane is significantly improved.The power density of a single-cell based on the composite membrane is 45.1%higher than that of pure SPEEK.(4)The superacidic SO4-MOF-808@GO composite is synthesized and filled into the SPEEK matrix to prepare composite membrane.The uniform dispersion of SO4-MOF808 on the GO surfaces inhibits the agglomeration of SO4-MOF-808 and GO in the SPEEK matrix,ensuring the good dispersibility of the fillers inside the membranes.Furthermore,The Br(?)nsted acidic sites in SO4-MOF-808@GO strongly bond ample water molecules and form sufficient hydrogen bonded water networks,which optimizes the water environment of membrane channel and facilitates proton conduction under low humidity and high temperature.The proton conductivity of composite membrane is up to 43.36 mS cm-1 at 90℃ and 40%RH,7.44-fold that of pure SPEEK.