Preparation Of Functionalized Partially Reduced Graphene Oxides And Their Electrochemical Performances

Graphene has extraordinary large BET surface,excellent electrical conductivity,and good chemical stability,which makes it very suitable for use as electrode materials for electric double layer capacitor?EDLC?.However,due to the inevitable aggregation and restack,as well as the relatively low specific capacitance limits its application in supercapacitor.Graphene oxide?GO?contains large amounts of oxygen functional groups on the surface,which can increase the pseudo capacitance of electrode materials by Faraday reactions.But the bad electrical conductivity of GO hinders its utilization as electrode materials.Therefore,in this pape r functionalized partially reduced graphene oxides were prepared through hydrothermal method with GO and organic compounds which contains amino groups.The as-prepared samples have both EDLC capacitance and pseudo capacitance mechanisms.This feature endows materials good electrochemical performance.Specific contents and results are as follows:?1?Organic amine partially reduced graphene oxides have been synthesized under hydrothermal conditions by using very small amounts of 1,4-butanediamine and phenylethylamine as reducing agent,nitrogen sources and morphology modifier.The electrochemical performance of the as-prepared samples was studied.The results show that the samples prepared with small amounts of organic amine have three-dimension network structure and large specific surface area,its pore size increases with the increased amount of organic amine.Therefore,the samples show good EDLC performance,the sample synthesized with 1,4-butanediamine and phenylethylamine exhibit a specific capacitance of 106.4 F g^-1 and 106.6 F g^-1,respectively at 0.3 A g^-1 in 1 M Na₂SO₄ electrolyte.The surface of samples retained a lot of acidic oxygen functional groups and introduced some nitrogen functional groups which are beneficial to enhance the pseudocapacitance,conductivity and wettability of samples.The samples synthesized with 1,4-butanediamine and phenylethylamine exhibit a high specific capacitance of 268.8 Fg^-1 and 264.1 Fg^-1,high energy density of 9.3 Wh kg^-1 and 9.2 Wh kg^-1 at 0.3 A g^-1 in 6 M KOH electrolyte,respectively.They also show good cycle stability along with 101.03% and 101.85% of its initial specific capacitance after 10000 cycles at a current density of 10 A g^-1.?2?Hydroxyl functionalized partially reduced graphene oxides have be en synthesized under hydrothermal conditions by using small amounts p-aminophenol and trometamol.The morphology and pore structure was improved by functionalized with phenolic hydroxyl group and alocholic hydroxyl group.The electrochemical analysis results show that the samples prepared from p-aminophenol has higher hydrophilicity and greater surface area and high conductivity,thus the capacitance performance is better,while alcoholic hydroxyl functionalized samples have more stable pore structure,so it has better cycle stability in 1 M Na₂SO₄ electrolyte.In 6 M KOH electrolyte,the electrochemical analysis results show that the samples functionalized by high chemical activity phenolic hydroxyl exhibit very good specific capacitance performance and higher energy density,the specific capacitance and energy density are up to 284.1 F g^-1 and 9.9 Wh kg^-1 at 0.3 A g^-1 which is greater than current commercial supercapacitors.But its cycle stability is not exceptionally good as charging and discharging test its capacitance continues to decrease.The samples functionalized by stable alocholic hydroxyl group not only have excellent capacitive properties,also have very high rate performance and cycle stability.After 10,000 times of charging and discharging cycles at 10 A g^-1,the specific capacitance and energy density is up to 276.8 F g^-1 and 9.6 Wh kg^-1 at 0.3 A g^-1.?3?Amino acid functionalized partially reduced graphene oxides have been synthesized under hydrothermal conditions by using small amounts of ne utral amino acids?alanine?,acidic amino acids?glutamate?and basic amino acids?lysine?as precursor.Results show that a small amount of neutral amino acids can effectively improve the specific surface area and pore structure of the sample,followed by acidic amino acids,but in alkaline amino acid functionalized samples graphene layers occurred aggregation and restack.Therefore,in 1 M Na₂SO₄ electrolyte alanine functionalized samples have best EDLC performance.During the amino acid Functionalized process a lot of carboxylic functional groups and a small amount of nitrogen-containing functional groups were introduced into the sample surface,meanwhile,a large number of hydroxyl groups were retained.Therefore,the specific capacitance and energy density of alanine functionalized samples are up to 262.8 F g^-1 and 9.1 Wh kg^-1 at 0.3 A g^-1 in 6 M KOH electrolytes.In addition,because of the carboxyl groups of amino acid molecules with strong hydrophilic and good electrochemical stability,different acidities amino acid functionalized samples exhibit good rate performance and cycle stability.