Coaxial nickel cobalt selenide/nitrogen-doped carbon nanotube array as a three-dimensional self-supported electrode for electrochemical energy storage.

Herein, we propose a one-step urea pyrolysis method for preparing a nitrogen-doped carbon nanotube array grown on carbon fiber paper, which is demonstrated as a three-dimensional scaffold for constructing a nickel cobalt selenide-based coaxial array structure. Thanks to the large surface area, interconnected porous structure, high mass loading, as well as fast electron/ion transport pathway of the coaxial array structure, the nickel cobalt selenide/nitrogen-doped carbon nanotube electrode exhibits over 7 times higher areal capacity than that directly grown on carbon fiber paper, and better rate capability. The cell assembled by a nickel cobalt selenide/nitrogen-doped carbon nanotube positive electrode and an iron oxyhydroxide/nitrogen-doped carbon nanotube negative electrode delivers a volumetric capacity of up to 22.5 C cm (6.2 mA h cm) at 4 mA cm and retains around 86% of the initial capacity even after 10 000 cycles at 10 mA cm. A volumetric energy density of up to 4.9 mW h cm and a maximum power density of 208.1 mW cm are achieved, and is comparable to, if not better than, those of similar energy storage devices reported previously.