Regulation Of Graphene Oxide Assembly Behavior And Study Of Its Membrane Barrier And Sensing Performance

Hydrogen,as an efficient and environmentally friendly energy carrier,represents a crucial direction in the future global energy technology revolution.The development of safe,efficient,and cost-effective hydrogen storage technologies is imperative for the advancement of hydrogen energy.In recent years,high-pressure hydrogen storage technologies using composite pressure vessels have rapidly progressed due to advantages such as short gas loading and unloading times,as well as scaled storage and transportation.Among these,lightweight fourth and fifth-generation carbon fiber/epoxy resin（EP）composite material pressure vessels have emerged as hotspots in high-pressure hydrogen storage research.Researchers have focused on optimizing pressure vessel structures and enhancing composite material performance,yet research on the hydrogen gas barrier properties and health monitoring aspects of pressure vessel composites remains relatively limited.This study,based on the molecular structure of graphene oxide（GO）featuring coexistence of graphitic and oxidized regions,achieved controlled assembly of nanosheets through precise modulation of GO intra-and intermolecular conformation during its assembly stages in liquid,gel,and solid phases.This enabled the establishment of methods for preparing and modulating the performance of GO-based membranes tailored for applications in hydrogen gas（H₂）barrier and high-pressure sensing.By conducting foundational research on the gas barrier and structural health monitoring aspects of GO-based membranes in composite pressure vessels,theoretical frameworks and practical guidance were provided for designing and enhancing the multifunctionality of composite material layers in high-performance hydrogen storage tanks.The main achievements are as follows:（1）Small-sized GO（SGO:average nanosheet diameter of 5μm）and large-sized GO（LGO:average nanosheet diameter of 20μm）were separately assembled into membranes（SGOm and LGOm,respectively）using vacuum filtration.Micro-and nano-scale structural analyses and performance characterizations were conducted to elucidate the principles of uneven capillary force distribution resulting from the coexistence of graphitic and oxidized regions in molecular structure and the influence mechanism of GO/water micro-interface density on the aligned assembly of nanosheets.Results demonstrated that LGOm exhibited a more ordered alignment structure and gas permeability three orders of magnitude lower than that of SGOm,demonstrating significant assembly advantages in extending gas diffusion pathways.Furthermore,to further optimize the orientation assembly behavior of GO nanosheets and enhance the gas barrier performance of GO-based membranes,highly crystalline graphene oxide nanosheets（HGO）were introduced into LGO,and reduced GO membranes（GM）were prepared through thorough reduction treatment.By precisely controlling the ratio of HGO and LGO,the internal orientation structure of the GM was effectively optimized,thereby providing a more tortuous diffusion path for gas molecules.Moreover,the reduction treatment led to a decrease in the interlayer spacing of GM from 0.77 nm to 0.36nm,further narrowing the diffusion channels for gas molecules.Moreover,the reduction treatment led to a decrease in the interlayer spacing of GM from 0.77nm to 0.36 nm,further narrowing the diffusion channels for gas molecules.Gas barrier test results showed that GM reduced the gas permeability of nitrogen（N₂）,carbon dioxide（CO₂）,and hydrogen（H₂）to 0.90,1.15,and 9.87cm³·mm/（m²·d·atm）respectively,with the barrier ability to H₂ improved by 1.2times compared to LGOm（2）Based on molecular patch engineering strategy,polyethyleneimine（PEI）was introduced between GO nanosheets to achieve dual structural optimization of GO assembly behavior through both non-covalent and covalent interactions.This resulted in the preparation of GO membranes（PGOm）with high H₂ barrier properties.Density functional theory（DFT）calculations revealed the extension mechanism of liquid-phase GO nanosheet conformation due to hydrogen bonding.Combined with microstructure and mechanical performance,this elucidated the contribution mechanism of covalent interactions to nanosheet array orientation alignment.Based on the dual barrier mechanism in parallel and perpendicular directions,PGOm exhibited an extremely low H₂ gas permeability(P_H2).Even at a high temperature of 80°C,P_H2 was only 2.6 cm³·mm/（m²·d·atm）,achieving a significant improvement in H₂ barrier performance.Moreover,the ultra-fast infiltration of EP by PGOm showcased its enormous potential in enhancing the gas tightness of EP.PGOm-enhanced EP laminated composites demonstrated significantly superior structural advantages in H₂ barrier performance compared to nanofilled composites,with H₂ gas transport rate（H₂GTR）reduced to 2.5 cm³/（m²·d·atm）,achieving a remarkable improvement in barrier performance by 151 times.（3）Incorporating HGO between layers of three-dimensional（3D）crumpled GO nanosheets（CGO）,utilizingπ-πconjugated interactions established by the graphite structure to form"rivets,"transferred the 3D conformation of CGO to assembled membranes,successfully preparing hierarchically porous microstructure GO membrane（PGM）.This resolved the issue of nanosheet 3D conformation collapse caused by capillary force.The PGM-assembled flexible pressure sensors achieved ultra-high pressure sensing within the range of 2000 k Pa and exhibited excellent high-pressure cycling and high-temperature stability.The structure-sensitivity relationship of the internal chemical structures and sensing sensitivity of PGM flexible pressure sensors was elucidated,combining X-ray photoelectron spectroscopy characterization and DFT calculations.Finite element simulations have clarified a two-step deformation mechanism involving low-modulus micron-scale pores and high-modulus nano-scale pores.As the internal nanosheets of the PGM transition from point-plane contact to plane-plane contact,the sensor achieved high sensitivity,with 1.1 k Pa?1within a 600 k Pa pressure range and 0.7 k Pa?1within a 2000 k Pa pressure range.Therefore,PGM flexible pressure sensors can accurately monitor the inflation/deflation processes of pressure vessel models at different pressures and frequencies,demonstrating excellent cycling stability.Moreover,PGM flexible pressure sensors extended to human sensing research effectively captured human activity signals,including minor local movements such as bending and stretching of fingers,elbows,and knees,as well as major movements such as walking,running,and jumping.