羰基、羧基和羟基表面官能团对碳纳米管电容量的影响

分别采用混酸、空气、硝酸和高锰酸钾对碳纳米管进行氧化处理,以在其表面引入官能团,进而研究了表面官能团对碳纳米管电化学性能的影响.X-射线光电子谱分析表明:混酸氧化处理引入的官能团主要为羰基和羧基;空气氧化使碳纳米管表面链接较多的羟基,但羰基和羧基的含量最少;而硝酸处理和高锰酸钾处理引入了中等数量的羰基和羧基.经四种处理方法所得碳纳米管具有相近的比表面积和孔结构.通过比较它们的比电容发现:羰基和羧基贡献了最多的准电容,尤其羰基含量与碳纳米管的电容量呈正比关系;而羟基主要增强了双层电容,并未引入明显的准法拉第容量.由于羰基和羧基比羟基具有更低的电荷传递电阻,有利于快速的法拉第反应,从而引入准电容.

The effect of carbonyl, carboxyl and hydroxyl groups on the capacitance of carbon nanotubes

Concentrated H2SO4 :HNO3 mixed acids, air, nitric acid and potassium permanganate were used to oxidize carbon nanotubes (CNTs) to introduce surface functional groups (SFGs) and the effects of the type and amount of SFGs on the electrochemical properties of CNT supercapacitors were investigated. XPS analysis shows that the mixed acid oxidation produces carbonyl ( CcO ) and the carboxyl ( O-C=O ) groups, the air oxidation results in hydroxyl and the smallest amount of carbonyl and carboxyl groups, and both the nitric acid and potassium permanganate treatments result in a moderate amount of carbonyl and carboxyl groups. It was found that the specific surface area and pore structures of the four samples are similar and carbonyl and carboxyl groups contribute the most to pseudo-capacitance through a Faradic reaction. In particular, the carbonyl group has a proportional relationship to the capacitance of CNTs. However, the hydroxyl group does not lead to an obvious increase of pseudo-capacitance, but can increase the electric double layer capacitance. The carbonyl and the carboxyl groups are advantageous for fast Faradic reactions to introduce pseudo-capacitance, owing to their lower charge transfer resistance than that of the hydroxyl group.