Diameter Dependent Doping of Single-Walled Carbon Nanotube Used as Electrical Double Layer Capacitor Electrode

The present study investigated the carrier doping in relation to the size and surface characteristics of SWCNTs of different sizes and structures, used as electrical double layer capacitor electrodes, employing several different electrolytes (NaI, NaCl, NaBr, and TEMABF(4)). The results of the study showed that the electrode capacitance goes through an abrupt increase in the form of two step-like humps on both sides of the open-circuit potential, giving the cyclic voltammogram the shape of a dumbbell. This dumbbell shape was obtained regardless of the electrolyte utilized. However, the distance between the humps on the voltammogram seemed to inversely correlate with the diameter of the SWCNTs utilized as the capacitor electrode. The results show that the increase in capacitance is connected with the charge carrier doping that correlates with the electronic structure of the SWCNTs, which in turn depends on the diameter of the tube utilized as the electrode material.