氧化锰表面改性活性炭电极材料的电化学特性

用Mn(NO3)2溶液浸渍-高温热解法对普通活性炭进行表面改性处理以改善其电化学性能. 采用氮气吸附、SEM、XRD等方法研究改性活性炭的比表面积、孔结构、形貌和氧化锰的晶体结构; 用循环伏安、恒流充放电、交流阻抗等电化学方法研究了改性活性炭电极构成的电化学电容器的性能. 结果表明, Mn(NO3)2热解产生的多价态氧化锰有法拉第赝电容效应, 尤其是立方晶形结构的α-Mn2O3, 与活性炭的双电层电容构成了复合电容, 因而改性炭材料的比电容有明显的提高, 其质量比电容达到254 F·g-1, 比未改性炭的165 F·g-1提高了54%. 改性炭电极电化学电容器具有优异的充放电可逆性和稳定性, 而且等效串联电阻较小, 只有0.40 Ω; 经2000次循环的长期测试, 容量保持率几乎达到100%.

Electrochemical Properties of Manganese Oxide Surface-Modified Activated Carbon Electrode Materials

To improve electrochemical properties of activated carbon (AC), a commercial AC was modified by means of soaking in manganese nitrate solution and subsequent pyrolysis. Nitrogen adsorption at 77 K, SEM, and XRD were used to study the surface area, porosity, profile of modified AC, and the crystal structure of deposited manganese oxides. The performance of electrochemical capacitors using the modified AC as electrode materials was investigated by cyclic voltammograms, ac (alternating current) impedance, and constant current charge/discharge. Results showed that manganese oxides, especially α-Mn2O3, produced from the Mn(NO3)2 decomposition had an obvious pseudo-capacitance effect. This effect was coupled with the electrical double layer capacitance of AC to form a complex capacitance so that the specific capacitance of modified AC could be as high as 254 F·g-1 which is 54% higher than that of the unmodified AC. In addition, the tested capacitor with modified AC electrodes showed excellent performance during reversible charge-discharge and also displayed high stability. Its equivalent series resistance was small at 0.40 Ω. After a long termtest of 2000-cycles the capacitance retained nearly 100% of its original value.