Sulfur-doped carbon nanotubes with hierarchical micro/mesopores for high performance pseudocapacitive supercapacitors.

Increasing the specific surface area and the amount of doping heteroatoms is an effective means to improve the electrochemical properties of carbon nanotubes (CNTs). The usual activation method makes it difficult for the retention of the heteroatoms while enlarging the specific surface area, and it can be found from literatures that specific surface area and S-content of carbon-based electrode materials are mutually exclusive. Here, CNTs with high specific surface area and sulfur content are constructed by simple activation of sulfonated polymer nanotubes with KHCO3, and the excellent electrochemical performance can be explained by the following points: first, KHCO3can be decomposed into K2CO3, CO2and H2O during the activation process. The synergistic action of physical activation (CO2and H2O) and chemical activation (K2CO3) equips the electrode material with high specific surface area of 1840 m2g-1and hierarchical micro/mesopores, which is beneficial to its double-layer capacitance. Second, compared with reported porous CNTs prepared by chemical activation (KOH) or physical activation (CO2or H2O), the mild activator KHCO3makes the sulfur content at a high level of 4.6 at%, which is very advantageous for high pseudocapacitance performance.