Preparation And Supercapacitor Performance Studies Of Hierarchical Porous Carbons

Supercapacitor,a new type of electrochemical energy storage device,is also known as electrochemical capacitor.It not only has some characteristics of traditional capacitors,but includes some characteristics of the battery.This device is separated mainly by two high conductivity electrodes through the electrosolution with moving ions.As the main component of supercapacitors,electrode material is quite of importance,which could be classified as Carbon materials,metal oxides and conductive polymers.The quickening pace of social modernization is obvious to all.How to use a clean and friendly renewable energy storage device will be paid more and more attention by the society,in which the supercapacitor is located in the column of these energy storage devices.Due to the high power density,high charging speed,long service life,excellent adaptability to low temperature,long time placement,high reliability,and so forth,supercapacitor has been widely used in new energy vehicles,rail traffic,energy storage,military and related fields,which means that the development of supercapacitor is prospective.In order to explore the potential application of other materials,the main research contents are as follows:A facile and straightforward carbonization method for fabricating micro-/mesoporous carbons have been implemented by using different citrate salts as porogen and banana peel as the carbon precursor.The formation of porous structure is based on the reaction of alkali and non-alkali organic salts such as citrate salts of potassium and magnesium during the carbonization process.The as-decomposed products contain many inorganic particles?i.e.K₂O or MgO?embedded within the carbon frameworks.These byproducts either acted as activator agent or acted as endotemplate in the formation of porous carbons with diverse pore sizes,which when removed by acid washing,leads to a microporous or mesoporous network.Correspondingly,electrochemical measurements show that the specific capacitance of the carbon materials improved from 59 to 258–273 F/g at 0.1 A/g?The carbon foams for supercapacitor electrode materials,with well-developed pores and doped heteroatoms have always been of great interest.Nevertheless,the preparation of these materials often involves complicated process.In this work,we present a facile method via oil-in-water emulsion method to synthesis N-doped hierarchical porous carbon foams?N-HPCFs?contaning a large specific surface area?1859 m²/g?and high pore volume?0.83 cm³/g?without any templates and traditional activation approach.The unique structure and chemistry resulted from coupled effects of introduction of potassium citrate and a stabilized hydrogen-bonding interaction between carbon precursor resorcinol/formaldehyde?R/F?resol and nitrogen precursor melamine in the presence of cosurfactant ethylene glycol?EG?.As electrodes for supercapacitors,N-HPCFs exhibit a high specific capacitance up to 298 F/g at 1A/g in a three-electrode system using 6 M KOH electrolyte,and good stability with over 93%capacitance retention after 5000 cycles at 10 A/g.Therefore,such a N-doped hierarchical carbon foams are promising high-performance electrode for energy storage devices.A composite of manganese oxide?MnO₂?and hollow carbon sphere?HCS?was fabricated by a facile liquid phase deposition process for supercapacitor electrodes.The C/MnO2 composite had a HCS core and a shell composed of?-MnO₂ nanoflakes.HCS in the composite not only serves as the template for the growth of MnO₂ nanoflakes,but also as the electrically conductive channel for electrochemical performance enchancement.The physicochemical and electrochemical properties of the C/MnO₂ composite were significantly enhanced as compared with those of MnO2 hollow spheres?MnO2,HS?.As the electrode of supercapacitors,it's specific capacitance reached 340 F/g under the current density of 1 A/g in the solution of 1 M Na2SO4,of which the specific capacitance remained90.2%after 1000 cycle numbers,which showed a good electrochemical performance.