活性炭表面改性对其比电容及储能机理的影响

采用熔融Na2S对活性炭表面进行改性，通过循环伏安测试了活性炭的比电容，并通过FT-IR, BET, EIS和电泳实验分析了比电容变化的原因及其储能机理。研究发现，以10%的硫酸钠溶液为电解质，活性炭经Na2S 1000℃热处理1 h后的比电容由44.6 F/g提升至80.8 F/g，所增加的比电容主要来自于双电层电容，部分来自于氧化还原赝电容(占总电容的5.6%)。通过向电解质溶液中添加37 mmol/L的FeCl3，比电容提高至103 F/g (赝电容占12.6%)，但并不稳定，后期有下降的趋势。如果向电解质溶液添加30 mmol/L的K3Fe(CN)6]，则比电容提升到了126 F/g，并且非常稳定、甚至有继续缓慢增加的趋势。活性炭经Na2S热处理后，储能机理由单纯的双电层物理储能变为双电层物理&化学储能+氧化还原赝电容储能。

Effect of surface modification of activated carbon on its specific capacitance and mechanism of energy storage

The surface of activated carbon was modified by melted sodium sulfide and its specific capacitance was evaluated by the cyclic voltammetry experimental data. The reason for specific capacitance changed with this treatment and the mechanism of energy storage were investigated by FT-IR, BET, EIS, and electrophoresis experiments. The results showed that the specific capacitance of activated carbon in 10% sodium sulfate electrolyte solution was elevated from 44.6 F/g to 80.8 F/g after treated with sodium sulfide at 1000℃ for 1 h. The increment of specific capacitance mainly came from double-layer capacitance and secondarily from redox pseudocapacitance (the ratio of pseudocapacitance to total capacitance was only 5.6%). After adding 37 mmol/L ferric chlorides in the electrolyte solution, the specific capacitance was further elevated to 103 F/g, in which the proportion of pseudocapacitance capacitance to total capacitance amounted to 12.6%. However, the capacitance value was unstable and decreased gradually during subsequent cycles, which may be caused by the electronegativity of the activated carbon surface. It had been verified by the electrophoresis experiment that the surface of activated carbon after heat treatment by sodium sulfide was positively charged. The law of same charge mutual repulsion lead to unstable adsorption of Fe3+ on the surface of activated carbon. However, if 30 mmol/L K3Fe(CN)6] was added in the electrolyte solution, the specific capacitance was promoted to 126 F/g and kept stable, even slightly and slowly increased during subsequent cycles. The cyclic voltammetry curve showed that the specific capacitance at this time still mainly came from the double-layer and the EIS experiment confirms that the charge exchange resistance was dramatically reduced when the Fe(CN)6]3– anion appeared in the electrolyte solution. According to the shape of the CV curve and the results of EIS, FT-IR and BET, it can be concluded that the energy-storage mechanism of activated carbon changed from physical double-layer to physical and chemical double-layer together with redox pseudocapacitance after treated by sodium sulfide.