Multiwall carbon nanotube@mesoporous carbon with core-shell configuration: a well-designed composite-structure toward electrochemical capacitor application

Abstract

Based on the desired electrical conductivity and high specific-surface-area for carbon-based electrodes, herein, we have designed and synthesized uniform multiwall carbon nanotube@mesoporous carbon (MWNT@mesoC) composites with core-shell configuration by combining sol–gel methods and nanocasting. Pristine MWNTs after acid treatment were first coated with uniform mesostructured silica shells to obtain the MWNT@mesoporous silica (MWNT@mesoS) composite using cationic surfactant cetyltrimethyl ammonium bromide (CTAB) as a template. Then, furfural alcohol (carbon source) and oxalic acid (catalyst) were impregnated into the template-free MWNT@mesoS composite and followed by carbonization. The removal of silica led to the replacement of the mesoC shells decorated on the surface of MWNTs. The obtained composite materials retain the one-dimension (1-D) tubular structure and three-dimension (3-D) entangled framework as the original MWNTs. Micro/nanostructure exploration demonstrates that each MWNT is uniformly coated by the mesoC shell with short-pore-length (∼15 nm), which contributes above 300 m² g⁻¹ to specific surface areas purely from bimodal-mesopores (3.9/8.9 nm in diameter). The MWNT@mesoC composite shows greatly increased specific capacitance from 9.0 to 48.4 F g⁻¹ and 6.8 to 60.2 F g⁻¹ in 1.0 M (C₂H₅)₄NBF₄ and 6.0 M KOH, good rate performance with ∼60% maintenance of the initial capacitance at the current density of 20 A g⁻¹ and high cyclability (94% after 1000 cycles).