Improved wettability and enhanced ionic transport in highly porous CNT sponge.

We investigated the effect of an electric treatment on the wettability of aqueous solution on carbon nanotubes (CNT) and ion transport behaviors in superhydrophobic porous carbon nanotube sponges (CNTS). This electric activation treatment where an electric voltage was applied across highly porous CNT sponge induced an electrowetting effect. This effect significantly reduced interfacial tensions between CNT sidewalls and aqueous liquids. Meanwhile, polar functional groups were also introduced on CNTs. Both electrowetting effect and polar functional groups greatly improved the wettability of aqueous solutions on CNT sidewalls. After the electric treatment, we observed a dramatic increase in the overall rate of ion flow across porous CNT sponges. The formation of solution channels during the electric treatment is responsible for the enhanced ionic transport in porous CNT sponges. The overall rate of ion flow increased with the increases in electric treatment time and voltage. The crucial role of electric treatment parameters in the ion transport provides a new strategy for precisely controlling the ion transport across CNT sponges by tuning electric treatment time or voltage. Importantly, the good wettability of aqueous solution on CNT sidewalls greatly increased the effective surface area of CNT sponges and thus significantly improved the performance of CNTS-based supercapacitors after the electric treatment.