煤系腐植酸基层次孔炭的制备及电化学性能

Electrochemical performance of hierarchical porous carbons prepared from coal based humic acid

为提高煤炭利用率,以煤系腐植酸为前驱体,KOH为活化剂,在较低碱炭比(≤1)和活化温度(700℃)条件下制备双电层电容器用炭电极材料。利用低温N_2吸附对所制炭材料进行孔结构表征,采用恒流充放电、循环伏安和漏电流测试等手段评价其在3 mol/L KOH中的电化学性能。结果表明,所制炭材料呈现典型的层次阶梯孔径分布,孔径主要分布在0. 5～5. 0 nm,包括0. 5～1. 8 nm微孔和3. 5～4. 6 nm中孔;氧元素含量均超过20%。随着碱炭比升高,相应炭材料含氧量、比表面积、总孔容和微孔孔容逐渐升高,最高分别为26. 67%、878 m^2/g、0. 66 cm^3/g和0. 407 cm^3/g;中孔率先升高后降低,最高为62. 1%。微孔主要是腐植酸在活化过程中挥发分析出和部分含氧官能团热解形成的,高的中孔率主要由于钾的扩孔作用。4种层次孔炭电极材料在3 mol/L KOH电解液中具有良好的充放电可逆性和典型的双电层电容特性,其质量比电容、比电容保持率最高分别达256 F/g、84%,漏电流≤0. 015 m A。各炭材料具有合理的孔径分布,同时含有丰富的含氧官能团,有利于缩短电解质离子在电极材料内部的扩散路径,提高电极材料与电解液的润湿性,降低扩散阻力,是一种理想的双电层电容器用炭电极材料。

In order to improve coal utilization efficiency,hierarchical porous carbon electrode materials( HPCs) for double-layer capacitors was prepared from humic acids by KOH activation at 700 ℃ for 1 hour and lower KOH/carbon ratios( below 1).The oxygen content and pore structure characteristics of as-prepared carbons were performed by elemental analyzer and N2 adsorption apparatus.The electrochemical performances were monitored by galvanostatic charge-discharge,cyclic voltammetry and leak current in a two-electrode system with 3 mol/L KOH solution as the electrolyte,respectively.The results show that the four carbons possess high oxygen content( above 20%) and hierarchical pore size distribution mainly including the micropores from 0.5 nm to 2.0 nm and the mesopores from 3.5 nm to 4.6 nm.With the KOH/carbon ratios increasing,the oxygen content,specific surface area,total pore volume,micropore volume and mesoporosity of the carbons all increase,and can reach at 26.67%,878 m2/g,0.66 cm3/g,0.407 cm3/g and 62.1%,respectively. The micropores are mainly generated from the release and decomposition of volatile and oxygen-containing functional groups during the activation and pyrolysis of humic acid.And the high mesoporosity is mainly due to the pore reaming effect of potassium.The four carbon materials exhibit good charge/discharge reversibility and typical double layer capacitive characteristics,and the specific capacitance and capacity retention ratio can reach up to 256 F/g and 84% with a low leak current less than 0.015 m A.All carbon materials have reasonable pore size distribution and rich oxygen-containing functional groups,which is beneficial to shorten the diffusion path of electrolyte ions in the electrode material,improve the wettability of electrode material and electrolyte and reduce the diffusion resistance,which suggesting that the hierarchical porous carbons are ideal electrode materials for electrochemical capacitors.