Influence of Heat Treatment Temperature on the Structure and Electrochemical Performance of Asphaltene-Based B/N Co-Doped Porous Carbons

B/N co-doped porous carbons have been synthesized by heat treatment at different temperatures using asphaltene from coal liquefaction residue as a carbon precursor, nitric acid as a nitrogen source, H3BO3 as a boron source and a pore-forming agent. The influence of the heat treatment temperature on the porestructure and surface chemical properties was investigated, and the electrochemical performance in relation to the pore-structure and surface chemical properties was discussed. The crystal structure, morphology, porestructure, composition and electrochemical performance were examined using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, element analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), and an electrochemical workstation. The results of these analyses indicated that the crystal structure, pore-structure and surface properties were influenced significantly by the heat treatment process. Increases in the heat treatment temperature led to improvements in the degree of graphitization, as well as gradual increases in the boron content. In contrast, the nitrogen content decreased and the specific surface area and total pore volume increases gradually and then decline. The electrochemical performance was found to be dependent on the pore-structure and suitable surface chemical properties. The sample synthesized at 900 degrees C had a specific surface area of 1103 m(2) . g(-1), pore volume of 0.921 cm(3).g(-1), nitrogen content of 5.256% ( w), boron content of 1.703% ( w), and a maximal specific capacitance of 349 F.g(-1) at 100 mA.g(-1) in 6 mol.L-1 aqueous solution of KOH. The sample subjected to a heat treatment at 1000 degrees C had the best rate capability, with a capacity retention of 75% when the current density increased from 100 mA.g(-1) to 10 A.g(-1).