Preparation And Electrochemical Performance Of Humic Acid Based Hierarchical Porous Carbon Materials

Supercapacitors, also called electrochemical capacitors, are regarded as a bridge between batteries and conventional dielectric capacitors. Electrode materials are the key factors determining the electrochemical performence of supercapacitors. In this paper, hierarchical porous carbons(HPCs), a highly textured carbon material, are prepared by a simple one-step activation derived from humic acid with a ratio of KOH as the activation agent under certain temperature.HPCs obtained by activation of humic acid are rich in oxygen-containing functional groups, which allow the formation and uniform anchoring of fine MnO2 via strong chemical interactions between the functional groups of HPCs and the nanomaterials.The effect of activation process on the pore structure of HPCs was systematically investigated by SEM, TEM, XRD, N2 adsorption/desorption, etc. The activation process of humic acid and the formation mechanism of pore structure of as-obtained carbon HPCs were discussed in detail. The electrochemical performance and energy storage mechanism of HPCs were also investigated.Humic acid based HPCs show high performance for supercapacitors possessing of the optimized capacitance of 189 F g-1 in 3 M KOH and 118 F g-1 in 1 M Et4NBF4/PC with high capacitive retention and cyclic stability, which can be attributed to the staged pore size distribution.Growth of MnO2 nanospots on the HPCs was achieved via reduction of aqueous KMnO4 solution by ethanol in the presence of HPCs at room temperature. HPCs/MnO2 composites still maintain hierarchical porous structure, yielding an electrode showing excellent electrochemical performance with improved capacitance.