Carbon nanotube-nanopipe composite vertical arrays for enhanced electrochemical capacitance

The newly-designed vertical array structure of carbon nanotubes (CNTs) surrounding carbon nanopipes (CNTs@CNPs) was fabricated, which includes the formation of the primary CNP (ca. 200 nm in diameter) arrays in virtue of the anodic aluminum oxide (AAO) membrane template with infiltration of polymer solution containing metal catalyst precursor, followed by carbonization and CVD growth of the secondary CNTs (20 nm in diameter). The secondary CNTs with controllable density/length are grown both inside and outside the primary CNPs, which not only induce the four times increase of the specific surface areas for the samples, but also largely enhance the interconnection between the vertical CNPs for good electric conductance. The unique CNTs@CNPs arrays significantly improve the electrochemical capacitance per unit area with great long-term stability, indicating the promise as new material platform for development of advanced energy-storage devices.