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 degrees C, followed by CO2-acitvation at 900 degrees C 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.