Preparation Of Carbon Materials Based On Discarded Cannabis Stems And Research On Electrochemical Sodium Storage And Supercapacitor Performance

Biomass materials have the advantages of abundant species,wide distribution,low cost and renewability.Moreover,biomass materials are rich in carbon,which is a kind of good carbon source materials.The hemp stems become waste after the valuable components were extracted.If the residual tetrahydrocannabinol in the hemp stem is not recycled,it may cause the spread and abuse of drugs.Therefore,in this paper,the carbon materials were prepared by high temperature carbonization and other procedures with the hemp stems as carbon source.The structure,morphology,element composition,electrochemical sodium storage and supercapacitive performance were studied.The main research contents as follows:(1)Firstly,waste hemp stems were used as carbon sources,and four hemp stems based carbon materials(C-500,C-600,C-700 and C-800)were prepared by high temperatures carbonization(500?,600?,700?and 800?),and the effects of carbonization temperature were studied to the structure,elemental composition and electrochemical sodium storage properties of the materials.The results show that,with the increase of carbonization temperature,the crystal plane spacing and structural defects decrease grad ually,while the graphitization degree and electrical conductivity increase gradually,in which C-600 showed the best electrochemical sodium storage performance.The first discharge specific capacity was594.6 m Ah?g^-1 at 0.05 A?g^-1 cycle charge/discharge,and the reversible discharge specific capacity was 253.6 m Ah?g^-1.The reversible discharge specific capacity of 128.6 m Ah?g^-1 still maintained even at 1.0 A?g^-1 for 1000 cycles,which obviously higher than the sodium storage performance of the other three carbon anodes.It may be due to C-600 carbon material had moderate interplanar spacing,structural defects and conductivity.(2)Secondly,the waste hemp stems were used as carbon sources,and the porous activated carbon materials were prepared by hydrothermal carbonization,KOH activation and vacuum high temperature carbonization.The effects of different ratios of carbon to alkali on the morphology,microstructure,specific surface area and supercapacitor properties of the composites were studied,and the ratios of carbon to alkali were 1:0,1:1 and 1:2,the samples were labeled as AC-0,AC-1 and AC-2,respectively.The results showed that with the decrease of the ratio for carbon to alkali,the carbon material gradually transforms from irregular solid particles to porous structure.In addition,residual oxygen-containing functional groups have increased,and sulfur elements are lost in the form of soluble KHS.The specific surface area of AC-2 is 1409.1 m²?g^-1,which is obviously higher than 709.5 m²?g^-1 of AC-0 and 998.3 m²?g^-1 of AC-1.Accordingly,the reversible discharge specific capacity of AC-2 was 224.6 F?g^-1 at 0.5A?g^-1 cycle charge/discharge,which higher than 122.7 F?g^-1 of AC-0 and 149.2 F?g^-1 of AC-1,and also showed better cycle stability,which were mainly due to its larger specific surface area,more oxygen-containing functional groups and more active sites.