电解液离子与炭电极双电层电容的关系

以酚醛树脂基纳米孔玻态炭(NPGC)为电极, 通过微分电容伏安曲线的测试, 研究了水相体系电解液离子与多孔炭电极双电层电容的关系. 结果表明, 稀溶液中, 多孔炭电极的微分电容曲线在零电荷点(PZC)处呈现凹点, 电容降低, 双电层电容受扩散层的影响显著；若孔径小, 离子内扩散阻力大, 电容下降更为迅速, 扩散层对双电层电容的影响增大. 而增大炭材料的孔径或电解液浓度, 可明显减弱甚至消除扩散层对电容的影响. 炭电极的单位面积微分电容高, 仅表明孔表面利用率高, 如欲获得高的电容量, 还要有大的比表面积. 离子水化对炭电极的电容产生不利影响, 选用大离子和增大炭材料的孔径, 可有效降低离子水化对炭电极电容性能的影响.

Relationship between Electrolyte Ion and Double-layer Capacitance of Carbon Electrode

Nanoporous glassy carbons(NPGCs) with different pore structures were prepared from phenolic-resin by carbonization at 600 ℃, followed by CO₂-acitvation at 900 ℃ for different times. Specific surface areas and characteristic pore sizes obtained from gas adsorption isotherms were correlated with ion electroadsorption at the electrical double layer obtained from the data of specific capacitance (CV). Results show that in dilute aqueous solution, there is no ion electroadsorption in the minimum region of CV curves of carbon electrode, which should be close to the point of zero charge (PZC), leading to remarkable diffusion of electrical double layer and a decrease in capacitance. Further, the smaller the pore sizes of carbon electrodes, the more diffusible electrical double layer is, resulting in a sharp decrease in capacitance. But, the effect of diffusible double-layer on double layer capacitance is reduced and even eliminated through increasing pore sizes of carbon electrodes or electrolyte concentration. The high specific capacitance of unit surface area of carbon electrodes merely indicates a high utilization ratio of specific surface area. Only with high capacitance of unit area and large specific surface area, can carbon electrode have high double-layer capacity. Hydration of ion has bad influences on double-layer capacitance of carbon electrode, which can be reduced effectively by selecting large ion or increasing pore size of carbon electrode.