Preparation And Microstructure Control Of Carbon-based Hydrogen Storage Materials At Atmospheric Pressure

Hydrogen energy is the development direction of new energy in the future.Hydrogen is chemically active at room temperature,and its large-scale storage and transportation has always been a bottleneck in the application and promotion of hydrogen energy.In the overall layout of " 14th Five-Year Plan"of National Key R&D Program,the development of high-density solid hydrogen storage materials is clearly proposed in the key special projects of "Hydrogen Energy Technology" and"High-end Functional and Smart Materials".Among the various existing adsorption hydrogen storage materials,carbon-based hydrogen storage materials are becoming a hotspot in the research of hydrogen storage materials due to their high specific surface area,high safety,light weight and reproducibility.To develop new carbon-based hydrogen storage material at atmospheric pressure,polyacrylonitrile fiber,viscose fiber,and recycled spunlace nonwoven fiber are used as raw materials to carry out the preparation of porous carbon materials such as activated carbon fiber,activated carbon nanofiber,activated carbon fiber with special structure and carbon aerogel.The main research contents of this paper are as follows:(1)Using polyacrylonitrile as raw material,dry-jet wet spinning process and electrostatic spinning technology are used to prepare three kind of fiber precursors,which include polyacrylonitrile nascent fibers with obvious skin-core structure,polyacrylonitrile nascent fibers with inconspicuous skin-core structure and polyacrylonitrile nanofiber.First,based on the difference in the activation difficulty between the skin structure and the core structure in the PAN fiber with obvious skin-core structure,the nitrogen-oxygen co-doped hollow activated carbon fiber(N/O-ACHF)was prepared by phosphoric acid activation technology from the precursor of the polyacrylonitrile nascent fiber with obvious skin-core structure.The prepared N/O-ACHF has a smooth outer wall,densely packed micron-sized macropores(0.31-2.18 ?mm)on the inner wall,and a rich micropore/mesopore structure(0-6 nm).The specific surface area,micropore volume,surface oxygen content and surface nitrogen content of N/O-ACHF are 545.72 m2/g,0.19 cm3/g,15.26 at%and 4.06 at%,respectively.The density of hydrogen storage is 1.35 wt%at 77 K and 1 bar.Secondly,the outer wall macroporous activated carbon fiber(ACF-MaO-1)was developed through sonication-assisted potassium hydroxide activation technology from the PAN nascent fibers with inconspicuous skin-core structure.The specific surface area,micropore volume,surface oxygen content and surface nitrogen content of ACF-MaO-1 are 872.67 m2/g,0.37 cm3/g,12.13 at%and 4.13 at%,respectively,The density of hydrogen storage is 1.75 wt%under 77 K and 1 bar conditions.Aiming at the phenomenon of surface structure peeling during the process of sonication-assisted impregnation and high-temperature activation,two peeling mechanisms of skin dissection peeling mode and layer-by-layer peeling mode were proposed respectively.Finally,from the precursor of PAN nanofiber,activated carbon nano fibers ACNF-1 and ACNF-2 were prepared by sonication-assisted chemical activation process and sonication-assisted physical-chemical combined activation process.The specific surface areas of ACNF-1 and ACNF-2 could reach 1994.03 m2/g and 2007.66 m2/g respectively,and their hydrogen storage density at 77 K and 1 bar are 2.61 wt%and 2.64 wt%,respectively.(2)Using phosphoric acid and zinc chloride as activators,two viscose-based activated carbon fibers of VACF-Pi-1 and VACF-Zn-3 were prepared with viscose fibers used as raw materials respectively.The specific surface area,total pore volume,micropore volume and surface oxygen content of VACF-Pi-1 are 1184.51 m2/g,0.60 cm3/g,0.41 cm3/g and 15.25 at%,respectively.The density of hydrogen storage is 2.19 wt%at 77 K and 1 bar conditions.The specific surface area,total pore volume,micropore volume and ultramicropore volume of VACF-Zn-3 are 1576.17 m2/g,0.70 cm3/g,0.55 cm3/g and 0.20 cm3/g,respectively.The density of hydrogen storage is 2.52 wt%at 77 K,1 bar conditions.Using viscose-based activated carbon fiber as the raw material and hydrochloric acid as the activator,the ultra-micropore structure of viscose-based activated carbon fiber with a pore size of 0.56 nm is accurately controlled by sonication-assisted chemical reactivation technology.When the concentration of hydrochloric acid is 5 wt%,it has the best effect on increasing the ultra-micropore volume at a diameter of 0.56 nm.(3)Using viscose fiber as raw material and phosphoric acid as activator,surface fibrillated schistose activated carbon fiber VACF-FL-2 and surface fibrillated stick-shaped activated carbon fiber VACF-RL-1 were prepared by sonication-assisted phosphoric acid activation treatment after high-temperature carbonization.The fiber surface of VACF-FL-2 is densely covered with petal-like lamella structure,and the ratio of the thickness of the petal-like lamella to the diameter of the uneroded fiber matrix is about 1:3.31.The specific surface area,total pore volume,micropore volume,ultramicropore volume and surface oxygen element of VACF-FL-2 are 1085.77 m2/g,0.45 cm3/g,0.39 cm3/g,0.19 cm3/g and 13.11 at%,respectively.The hydrogen storage density of VACF-FL-2 at 77 K and 1 bar is 2.04 wt%.The rod-like structure on the surface of VACF-RL-1 fiber is distributed in a fluffy state,and its specific surface area,total pore volume,micropore volume and ultramicropore volume are 956.81 m2/g,0.48 cm3/g,0.34 cm3/g and 0.25 cm3/g,respectively.The hydrogen storage density of VACF-FL-2 is 1.97 wt%at 77 K and 1 bar.(4)Based on the "top-down" preparation strategy of carbon aerogel particles,four kinds carbon aerogel particles of PAN-CA-P,PAN-CA-K,VF-CA-K1 and RVF-CA-K1 were prepared from raw materials of PAN nascent fibers,viscose fibers and recycled spunlace nonwovens by sonication-assisted chemical activation technology.The specific surface area,total pore volume,micropore volume and ultramicropore volume of PAN-CA-P are 2732.18 m2/g,1.13 cm3/g,1.01 cm3/g,0.26 cm3/g and 15.25 at%,respectively.The relative content of pores can reach 89.38%,and the hydrogen storage density at 77 K and 1 bar reaches 3.17 wt%.The specific surface area,total pore volume,micropore volume and ultramicropore volume of PAN-CA-K are 2269.33 m2/g,0.98 cm3/g,0.84 cm3/g and 0.22 cm3/g,respectively.The relative content of micropore reaches 89.38%,and the density of hydrogen storage at 77 K and 1 bar reaches 2.98 wt%.The specific surface area,total pore volume,micropore volume and ultramicropore volume of VF-CA-K1 are 1955.48 m2/g,1.03 cm3/g,0.66 cm3/g and 0.25 cm3/g,respectively.The density of hydrogen storage at 77 K,1 bar conditions is 2.62 wt%.The specific surface area,total pore volume,micropore volume and ultramicropore volume of RVF-CA-K1 are 1522.81 m2/g,0.79 cm3/g,0.51 cm3/g and 0.17 cm3/g,respectively.The relative content of micropores is 64.56%,and the hydrogen storage density at 77 K and 1 bar is 2.49 wt%.