Study On The Electrochemical Performance Of Modified Porous Carbon Electrode Materials And Modified Polyaniline As Redox Additives In Supercapacitors

Supercapacitors are a new type of energy storage device different from traditional batteries,which have the advantages of high charging efficiency,slow discharge rate,good cycle stability,green and environmental protection.The physical and chemical properties of electrode materials will affect the electrochemical performance of supercapacitors greatly.Therefore,how to select and prepare electrode materials is needed to develop super capacitors suitable for a certain situation.Carbon material,as the most widely distributed earth resource in natural environment,has the characteristics of easy access,high conductivity,high specific surface area and strong chemical stability.It is the most commonly used electrode material,but the untreated carbon material is directly used as electrode material,and the specific capacitance measured in common electrolyte is low.The common method is to modify carbon materials or composite with other materials.The process of preparing composite materials is usually complex and the production cost is high.However,the process of modified carbon materials is generally relatively simple,easy to produce and conducive to industrialization.Therefore,this paper deals with the surface modification of commercial activated carbon.Besides electrode materials,the influence of electrolyte on super capacitor can not be ignored.However,due to the limitation of decomposition voltage of water,the voltage window of sulfuric acid electrolyte is narrow.In this paper,polyaniline oxidation-reduction reaction is used as redox additive to increase the voltage window of the system and further improve the electrochemical performance of supercapacitor.However,polyaniline has poor solubility in inorganic acid solution.In order to solve this problem,the introduction of strong polar hydroxyl functional groups in the long chain of polyaniline can improve the solubility of polyaniline,and hydrogen bond is produced by combining with hydrogen ions,which is conducive to fixing free electrons in electrolytes,accelerating the oxidation-reduction reaction of polyaniline,and adding additional pseudo electricity to the system Rong.（1）In view of the modification of carbon materials,oxygen/sulfur functional groups were designed and prepared on the surface of carbon materials.The specific content is to use one-step hydrothermal method to mix hydrogen peroxide（H₂O₂）and sulfuric acid（H₂SO₄）with active carbon materials into the reactor,and then use the pressure generated by hydrogen peroxide decomposition at a certain temperature to"squeeze"oxygen/sulfur atom or functional group into carbon micropores or"attach to"the carbon surface,so as to achieve the goal of high doping oxygen/sulfur.The change of temperature affects the reaction process and changes the decomposition degree of H₂O₂,thus changing the number of oxygen functional groups on the carbon surface.These oxygen functional groups have certain hydrophilicity and are conducive to the effective contact between carbon and electrolyte.Under the constant temperature condition,as a strong oxidizing acid,the change of the dosage will affect the oxidation intensity of the system,and change the number of oxygen functional groups,And increase a certain amount of sulfur functional groups.The results show that the hydrothermal temperature and the amount of H₂SO₄ play an important role in determining the structure and capacitance of carbon materials.At 60℃,the specific capacitance of the modified carbon material（OSC-60-1）is 168 F g^-1 at 1A g^-1 current density,nearly 4 times higher than that of untreated carbon(43 F g^-1),and the stability after 5000cycles is 92%,which is higher than that of untreated nano porous carbon（90%）.The energy density of the modified sample is 5.49 Wh kg^–1 and the power density is 500 W kg^–1.In addition to improving the wettability of carbon materials,the oxygen containing functional groups also produce pseudocapacitors through redox reaction.（2）In view of the modification of polyaniline,hydroxyl groups were introduced into polyaniline chain.The specific content is that in the process of low temperature synthesis of polyaniline,alginate,a kind of organic compound rich in hydroxyl,is added to achieve the purpose of introducing hydroxyl group into the long chain of polyaniline.The structure and electrochemical tests of the Modified Polyaniline were carried out.The results of FTIR and XPS showed that the modified polyaniline was rich in hydroxyl group.The contact angle of the samples was tested,which showed that the hydrophilicity of polyaniline modified by hydroxyl group was greatly improved.The electrochemical test results show that the electrochemical performance of the device is improved significantly after adding the hydroxyl modified polyaniline to sulfuric acid electrolyte.The results of three electrode test show that the specific capacitance of the device increases from 134F g^-1 to 250 F g^-1,which is nearly twice the original one when compared with the electrolyte system without polyaniline.The energy density of the two electrode system was as high as 41.47 Wh kg^–1 when the power density was 500 W kg^-1,while the addition of Polyaniline in 100m L of 1 M H₂SO₄ was only 0.05g.