Construction Of Two-dimensional Proton Transfer Channels In Graphene Oxide Membranes And Enhancement Of Their Performance

Global environmental pollution and energy shortage are becoming more and more serious,making the development of new clean energy urgent.Proton exchange membrane fuel cells have shown great potential to solve the above problems due to their advantages such as cleanliness and high efficiency.The proton exchange membrane is the core component of the fuel cell,and its performance determines the energy conversion efficiency of the entire device.Construction of well-defined nanochannels bearing abundant ion exchange sites is recognized as efficient strategy to enhance ion transport in membranes.In this study,graphene oxide(GO)was utilized as the building block for proton transfer channels,and intercalators were introduced into GO interlaters.The d-spacing,water absorption,and functional groups of the membranes could be effectively controlled by designing the phycical and chemical properties of the intercalators.Moreover,the continuity and regularity of the proton transfer channels were improved,achieving high proton conductivity,high structure and performance stability of GO membrane.The research results are listed as follows:(1)Synergistic manipulation of physical and chemical microenvironments to intensify proton conduction of GO membranes.GO/SC[n]A membranes with sulfonated calixarene(SC[n]A)as intercalation were prepared by vacuum assisted self-assembly.The SC[n]A with ultrahigh IEC_w(5.37 mmol g^-1)imported high density of sulfonic acid groups to proton transfer channels.Moreover,rigid frameworks of SC[8]A could support the adjacent GO nanosheets robustly,and then enhance the mechanical properties of GO/SC[8]A membranes with covalent corsslinking.We designed three SC[n]As(n=4,6,8)with the same IEC_w but different sizes as intercalators to adjust the d-spacing of the GO membrane,thereby optimizing the water environment inside the proton transfer channels.As a result,the d-spacing of GO/SC[4]A,GO/SC[6]A and GO/SC[8]A membranes were 1.63,1.72,1.82 nm,respectively.Based on collaboratively optimized physical and chemical microenvironment of the proton transfer channels,these membranes exhibited increasing proton conductivity in the order of GO/SC[4]A<GO/SC[6]A<GO/SC[8]A.The GO/SC[8]A-30%membrane exhibited the highest proton conductivity of 327.0 mS cm^-1 at 80 ^oC,100%RH,which was 2.9 times higher than GO membrane.(2)The manipulation of chemical microenvironment to intensify proton conduction of GO membranes.GO/SL membranes with sulfonated lignin(SL)as intercalation were prepared by vacuum assisted self-assembly.SL has a three-dimensional network structure,which could widen the interlayer distance of GO nanosheets and strengthen the mechanical properties of GO/SL membranes.The abandunt sulfonic acid groups and ether bonds of SL could serve as proton donors and acceptors,respectively,which provided abundant proton transfer sites and constructed a continuous hydrogen bonding network,improving the proton conductivity of the GO/SL membranes under high and low RH.Based on optimized chemical microenvironment of the proton transfer channels,the GO/SL-100%membrane exhibited the highest proton conductivities of 346 mS cm^-1 at 80 ^oC and 100%RH,which was 3.0 times higher than that of GO membrane.In summary,from the perspective of rational selection and design of intercalators,we further enhanced the regularity and continuity of proton transfer channels by modulating the molecular structure and the type or number of functional groups of intercalators.In addition,the apply of intercalation method to precisely control the physical/chemical properties of the interlayer channels of GO or other two-dimensional materials not only enables the rapid transfer of ions,but also shows important potential in molecular separation processes of precise sizes.