Functional groups distributed on carbon nanotube surfaces using vacuum plasma for the high-capacitance supercapacitor electrode

The excellent mechanical stability and electrochemical reactivity of activated carbon nanostructures has resulted in their wide use as an electrode material for the energy storage device. The method of activation generally uses a solution process using a strong acid or a strong base, which makes it difficult to control the degree of activation, and has limitations in using harmful chemicals. In this work, a method of fabricating activated carbon nanotubes in which heterogeneous element-based functional groups are finely controlled in a carbon structure using a vacuum plasma process is proposed. The type of functional group introduced into the carbon structure was adjusted by varying the type of plasma gas (O₂, NH₃, or C₄F₈), while the amount of functional group was changed through the exposure power. Carbon nanotubes with oxygen-related functional groups showed a large active surface area (141.66 m² g⁻¹) and volume of micropores than in the other cases (NH₃ and C₄F₈), to promote the rapid adsorption/desorption of ions, thereby offering excellent energy storage performance. The carbon nanotube into which oxygen is introduced was applied as an electrode material for a symmetrical two-electrode supercapacitor device to have a specific capacitance of 284 F g⁻¹, and excellent rate capability and cycle stability of 95.1% after 5000 cycles.

Activated carbon nanotubes in which the degree and type of the functional group is finely adjusted by the vacuum plasma process exhibit high energy storage capacity.