The Studies On Preparation And Supercapacitive Behaviors Of Hierarchically Porous Carbons Electrode Material

Electrochemical capacitors （ECs）, named supercapacitors or ultracapacitors andpsuedocapacitors, are specific and new-style devices by combining traditionalcapacitors and batteries for energy stores and conversion. ECs have gained asignificant amount of interest and attention because they have various advantages, forexamples fast charge/discharge, long-time cycle life, low internal resistance and highpower density. It is well known that the key of development of ECs depends upon thedevelopment of the electrode material with high performance. Currently, the mostimportant electrode materials for ECs are carbons with high specific surface areas.What’s more, hierarchical porous carbons are extensively investigated due to theirsimple process, controllable pore size and kinds of pore structures. In this paper,hierarchically porous carbons （HPCs） are prepared by sol-gel self-assembly processwith nickel oxide and surfactant as the dual template. Furthermore, the effects ofsurfactant template concentration, activated methods and aqueous electrolytes onphysical properties and electrochemical performance of HPCs are discussed.Various hierarchically porous carbons are prepared by adjusting initial mass ratioof nickel nitrate and surfactant. The morphologies of HPCs are characterizated byField emission scanning electron microscope （FE-SEM） and so on. And the specificsurface areas and pore size distribution are measured by nitrogenadsorption–desorption isotherm at77K. The results show the as-prepared porouscarbons with micro-meso-macro structures. The porous carbons （marked with HPCs-3）with the most excellent electrochemical performance are obtained when the initialmass ratio of nickel nitrate and surfactant is4:4, and the highest specific surface areasof HPCs-3is689m²g^-1. The highest specific capacitance of HPCs-3electrode fromCV is272F g^-1at the scan rate of1mV s^-1in6.0mol L^-1KOH electrolyte.The HPCs with initial mass ratio of nickel nitrate and surfactant of4:4areactivated by HNO₃and ZnCl2, and the effects of activated methods on physicalproperties and electrochemical performance of HPCs are discussed. The results showthe specific surface areas of the activated HPCs are improved. Compared to the HPCs,the HPCs-ZnCl2have more oxygen functional groups, while the HPCs-HNO₃indicatehigher oxygen and nitrogen groups. The electrochemical behaviors of the modifiedHPCs are improved. What’s more, the HPCs activated by HNO₃have the mostexcellent properties with the highest specific capacitance, the most stable cycle life and the smallest equivalent series resistance （ESR）.The HPCs with initial mass ratio of nickel nitrate and surfactant of4:4andactivated by HNO₃are used as the electrode material of supercapacitor. Theelectrochemical performances of supercapacitor in2.0mol L^-1（NH4）2SO4,2.0mol L^-1Na2SO4,0.5mol L^-1H₂SO₄and6.0mol L^-1KOH aquous electrolytes are discussed.The results display that supercapacitor in6.0mol L^-1KOH electrolyte exhibits thebest excellent electrochemical preporties. What’s more, the cycle life tests reveal thatsupercapacitors in various aqueous electrolytes have good stability in the voltagerange of0.0¹.0V and0.0¹.2V, especially the specific capacitance of thesupercapacitor in6.0mol L^-1KOH stabilized nearly at a fixed value after5000cycles.Furthermore, the ESR of supercapacitor in6.0mol L^-1KOH calculated fromgalvanostatic charge/discharge is low of2.83Ω.