Design Of Two-dimension Lamellar Membrane Channel Structure And Intensification Of Proton Conduction

Proton exchange membrane(PEM)serves as the heart of hydrogen fuel cell,whose proton conductivity and stability determine the performance and lifetime of the fuel cell.Thus,it is an urgent need to design and prepare PEM with high proton conduction and stability for the development of hydrogen fuel cell technology.Two-dimensional lamellar membranes are promising for ion or molecule transfer and separation,due to its long-range regular nanochannels,strong chemical stability,and ease of ultrathin.However,the current lamellar membranes as PEMs usually have some problems,such as low proton conductivity,severe transfer anisotropy,and poor structural stability.In response to the above problems,this paper focuses on the relationship between the membrane-channel microstructure and proton conduction as well as stability.Polydopamine-modified graphene oxide(DGO)nanosheets,Nafion,and polymer-like quantum dots(PQD)were chosen as basic material.By optimizing the arrangement of interlayer proton carriers and constructing sheet-dot-framework(SDF)structure,the new method and strategy for enhancing membrane proton conduction and structural stability is proposed,in hope of offering some guidance to the design and applications of high-performance proton conduction materials.The details were summarized as follows:(1)Optimize the arrangement of proton carriers for intensification of membrane proton conduction and stability.The Nafion intercalated DGO membrane(ND-D)was prepared,and the strategy of "thermal rearrangement-electrostatic induction" was further proposed to control the orderly arrangement of interlayers sulfonic acid carriers.Combining the results of experiments and molecular dynamics simulations,the specific process mechanism of carrier rearrangement is interpreted.Heating promotes the movement of the Nafion segments.meanwhile,based on the electrostatic interaction between the sulfonic acid groups and the amino groups on the surface of the nanosheet,the sulfonic acid groups are enriched on the surface of the nanosheet,forming abundant acid-base pair transfer interface channels.The results show the horizontal and vertical conductivities of heat-treatment membranes at 130 ℃(ND-D-130)increase 86.3% and127.8% in comparison to ND-D membrane and its transfer anisotropy coefficient decreases to 11.9.Furthermore,the stronger electrostatic interaction is formed between the amino groups on the surface of the nanosheets and the enrichment of sulfonic acid groups,which greatly improves the structural stability of the membrane.Compared with the ND-D membrane,the ND-D-130 membrane has a 115% increase in interlayer force.(2)Construct sheet-dot-framework structure for intensification of membrane proton conduction and stability.Two kinds of precursors(citric acid and diethylenetriamine)were uniformly intercalated into the interlayers of the DGO membrane,then in situ convert into PQD and cross-link with the adjacent DGO nanosheets through the in situ microwave-assisted polycondensation method to produce SDF membrane.Conductive PQDs work as bridges for efficient cross-layer proton conduction and thus afford significantly enhanced vertical proton conductivity and reduced transfer anisotropy.Specifically,the vertical conductivity of the SDF-4 membrane increases over 10 times higher than that of the DGO membrane at 80 ℃ and 100% RH,while the transfer anisotropy coefficient decreases to 2.5.This then permits a 208% and 216%improvement in maximum power density and current density of hydrogen fuel cell.Importantly,the ordered covalent framework offers outstanding structural and operational stability,with a certain potential in practical applications.