关键词: 活性炭, 含磷基团, 孔隙结构, 赝电容, 超级电容器

Abstract:

Different kinds of phosphorus-containing activated carbons were prepared by phosphoric acid activation of lignocellulosic precursor and modification with H₃PO₄. Elemental analysis, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption were employed to analyze the elemental content, surface chemistry, and pore structures of the activated carbons. The electrochemical properties of the carbon materials were characterized for their application as supercapacitors in KOH and H₂SO₄ electrolytes using galvanostatic charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopic analyses. A statistical analysis by an intercept-free multiple linear regression method was employed to investigate the factors that influence the specific capacitance of activated carbon electrodes. In addition, a three-electrode cell setup was used to analyze the cause of the phosphorus contribution on capacitance. The results show that phosphorus increases the specific capacitance of activated carbons by the introduction of pseudo-capacitance; the activated carbon with phosphorus content of 5.88% (w) exhibits a specific capacitance of 185 F·g^-1 at 0.1 A·g^-1. The statistical analysis showed that mesopores facilitate an access of electrolyte ions to the surface of micropores. The pores in the width ranges of 1.10-1.61 nm, 2.12-2.43 nm and 3.94 -4.37 nm benefit the formation of the electric double layer in 6 mol·L^-1 KOH electrolyte; the pores with sizes of 0.67-0.72 nm have a positive effect in 1 mol·L^-1 H₂SO₄ electrolyte.

Key words: Activated carbon, Phosphorus functional group, Pore structure, Pseudo-capacitance, Supercapacitor