The Construction Of Transfer Channel And Efficient Proton Conduction Of Hybrid Membrane

Proton exchange membrane(PEM)is considered as the heart of proton exchange membrane fuel cell(PEMFC),and its proton conduction property determines the current density and power density of PEMFC.To explore the universal method and theory on intensification of proton conduction of PEM,this study focuses on two key issues,including the construction of proton transfer pathway and the optimization of chemical composition along the transfer pathways.Inorganic materials with different shape and compounding type were used to construct long-range interfacial transfer channel,and the influence of inorganic filler shape on membrane transfer channel was explored.Based on the above findings,two-dimensional(2-D)graphene oxide(GO)was selected and functionalized with polymer quantum dots(PQD),which was then utilized to construct long-range proton transfer channels with ordered acid-base pairs.Additionally,in-situ molecular-level hybridization technology was utilized to exactly and continuously decorate the ionic channel(nanophase)of sulfonated poly(ether ether ketone)(SPEEK)membrane with high degree of sulfonation(DS)through PQD networks.Through these stuies,it is expected to provide a certain reference for the material selection and design as well as the intensification of mass transfer property of organic-inorganic hybrid membrane.The details were summarized as follows:(1)Exploring the influence of nanofiller shape on proton conduction ability of interfacial channel.Zero-dimensional sulfonated silica(0-D SSiO2),one-dimensional sulfonated halloysite nanotube(1-D SHNT),and two-dimensional sulfonated graphene oxide(2-D SGO)with similar surficial composition were selected,and incorporated by respectively,single kind,two kinds,or three kinds,into SPEEK(nanophase-separated structure)and chitosan(CS,non-nanophase-separated structure)matrix to prepare hybrid membranes.The influence of nanofiller shape and size on proton transfer property of hybrid membrane was investigated.It was found that the shape of nanofiller affected the proton conduction property of hybrid membrane by regulating the shape of interfacial channel:hybrid membrane based on 2-D SGO,which featured with strong flexibility,high surface area,and aspect ratio,possessed wide and long-range proton transfer channels,and thus better proton conduction property than the hybrid membranes based on 0-D and 1-D nanofillers.Notably,there was no synergistic effect among different kinds of fillers,and the simultaneous incorporation of several kinds of nanofillers or overloading would increase the tortuosity of proton transfer pathway,leading to the elevation of transfer energy barrier.Additionally,the performance improvement of hybrid membrane upon the incorporation of SGO was limited,due to the randomly distributed transfer sites on the surface.(2)Exploring the influence of chemical composition on proton conduction ability of interfacial channel.PQD functionalized GO nanosheets(nPGO)were incorporated into SPEEK matrix to prepare hybrid membranes,which constructed long-range proton transfer channels with ordered acid-base pairs at nPGO-SPEEK interfaces.PQD possessed abundant acidic groups(-COOH)and basic groups(-NH/-NH2),which could form ordered acid-base pairs(-NH/-NH2…-COOH).By uniformly anchoring PQD on GO surface,long-range proton transfer channels with ordered acid-base pairs could be constructed.These interfacial transfer channels served as fast proton transfer pathways,dramatically reducing the transfer energy barrier and enhancing the proton conduction property of hybrid membrane.Meanwhile,the proton conduction property of hybrid membrane could be regulated by controlling the quantity of acid-base pairs.Throuth the optimization of PQD content,the proton conductivity of hybrid membrane increased to 76.5 mS cm-1,90%higher than that of control membrane.The maximum power density and current density of fuel cell based on hybrid membrane were 60%and 70%higher than those of SP control membrane,respectively.(3)The continuous and exact decoration of ionic channel of nanophase separated membrane.In-situ molecular-level hybridization was utilized to realize the exact hybridization of polymer matrix.Concretely,the ionic channel of SPEEK membrane was firstly impregnated with PQD precursors through heat-swelling adsorption,which were in-situ converted into continuous PQD networks via microwave-assisted polycondensation process.The exact and continuous decoration of ionic channel highly enhanced the proton conduction property of hybrid membrane.Manipulating the amount of functional groups on PQD could regulate the ability of acid-base pair on accepting/donating protons,benfitting for the construction of low energy barrier interfacial channel.The proton conductivity of hybrid membrane reached 138.2 mS cm-1.The assembled fuel cell attains maximum power density and current density of 119.5 mW cm-2 and 495.3 mA cm-2,respectively.Importanely,the abundant-NH/-NH2 groups on PQD could generate strong electrostatic interactions with-SO3H groups on SPEEK,thus worked as cross-linkers,affording high DS SPEEK membrane(DS=93.7%)excellent dimensional stability.To verify the generality of in-situ molecular-level hybridization,CS membrane without nanophase separated structure was also selected and utilized to prepared hybrid membranes.The CS based hybrid membranes also achieved highly enhanced proton conduction property and dimensional stability.Through the above three studies,proton conduction channels with high efficiency were condstructed in hybrid membrane through hybridization strategy.The construction of these interfacial transfer channels efficiently improved the proton conductivity and hydrogen fuel cell performances.The formation mechanism of interfacial transfer channel and its effect on proton transfer as well as the relevant proton transfer mechanism were also investigated.These findings may provide guidance for the development of high-performance proton conduction materials.