Carbon nanotubes (CNTs) are an excellent electrode material for capacitive deionization (CDI), due to their excellent electronic conductivity and outstanding chemical/physical stability. Their powder form and easy aggregation, however, have greatly limited their practical CDI performance. Aiming to address this issue, the authors report a freestanding CNT film which was fabricated by floating-catalyst chemical vapor deposition, as a binder-free electrode for CDI. By simply adjusting the pyrrole content in the precursor, the morphology of the resulting CNT film can be tuned to meet the requirements of CDI. In the presence of 2 wt.% pyrrole, the CNT film with a mesoporous structure exhibited a large specific surface area of 198 m2/g and an increased electric double-layer capacity (40 F/g), which is more than two times as large as that of the pristine CNT film. Due to these merits, the electrosorption capacity for sodium chloride (NaCl) of the CNT film electrode (11·39 mg/g) has been greatly improved compared with that of the pristine CNT film (4·52 mg/g), showing a good potential for large-scale practical CDI.

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As new and alternative energy storage devices to batteries and traditional capacitors, supercapacitors exhibit both high power and high energy density as well as good cycle life. NiCo2S4, a spinel‐structured transition metal sulfide with a high specific capacity, is considered to be a promising electrode material for supercapacitors with great application potential. However, the poor electrical conductivity of NiCo2S4 results in poor rate and cycle performance of the material, which limits its practical application. In this work, we design a composite by loading NiCo2S4 on the surface of carbon nanotubes (CNTs) to enhance the conductivity. The best‐performing CNTs@NiCo2S4 electrode materials were obtained after the optimized heat‐treatment of CNTs@SiO2 precursors. At a current density of 1 A g−1, the CNTs@NiCo2S4 composite exhibits a specific capacity of 216.4 mAh g−1 and a capacity retention of 75 % after 2000 cycles. Even at a high current density of 5 A g−1, the capacity can still retain 87 % of that under 1 A g−1. It is demonstrated that the electrochemical performance of NiCo2S4 can be effectively boosted by combining with conductive CNTs.

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