采用磷酸活化和磷酸改性制备了不同种类的含磷活性炭,采用元素分析、X射线光电子能谱(XPS)和氮气吸附等手段分析了活性炭的元素含量、表面化学性质和孔隙结构,采用恒电流充放电、循环伏安和交流阻抗分别考察了活性炭在KOH和H2SO4电解质溶液中作为超级电容器电极材料的电化学性能,采用自由截距多元线性回归拟合统计分析研究了活性炭电极比电容量的影响因素,应用三电极体系分析了磷元素对活性炭电化学性能的影响机理。研究结果表明,活性炭掺杂的磷引入了赝电容,提高了活性炭电极的比电容量,磷元素含量为5.88%(w)的活性炭的比电容量在0.1 A·g-1下达到185 F·g-1。统计分析结果显示,活性炭的中孔有利于电解质离子向微孔内的扩散。在6 mol·L-1 KOH电解质溶液中,孔径在1.10-1.61 nm、2.12-2.43nm及3.94-4.37 nm范围内是电解质离子在活性炭孔隙内部形成双电层的主要场所;在1 mol·L-1 H2SO4电解质溶液中,孔径在0.67-0.72 nm范围内有利于双电层电容的形成。
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