Preparation And Application Of Nico-BH@TiC/CNF Composites In Supercapacitors

In recent years, the development of renewable and clean energy devices to meet economy and ecologically sustainable development has received considerable attention in the world. Among these energy storage devices, the supercapacitors(SCs) have wide prospect of application due to the unique properties including excellent cycle stability, fast charge and discharge capability and high power density. However, the performances of SCs are limited by the intrinsic characteristic and structure of electrode materials. Therefore, the development of electrode materials with excellent performance is important for the advanced SCs. Carbon materials have aroused wide research because of its large specific surface area, good conductivity and porous structure. Nevertheless, the electrochemical performance of carbon materials is limited due to its energy storage mechanism. Transition metal hydroxides or oxides with high theoretical capacitance have been widely studied as electrode materials. However, their practical application as electrode materials is disadvantageous due to the low conductivity and unstable structure. In order to develop electrode materials with excellent performance, the three-dimensional and flexible titanium carbide–carbon nanofibers(TiC/CNFs) were successfully fabricated through electrospinning and carbonization methods. Moreover, based on TiC/CNFs as matrix material, a flexible NiCo-BH@TiC/CNF composite was successfully fabricated by microwave assisted synthesis method. Meanwhile, we have studied the electrochemical performance of NiCo-BH@TiC/CNF composite. This paper mainly includes the following two parts.1. The flexible and uniform TiC/CNFs were prepared by electrospinning polyacrylonitrile(PAN) nanofibers containing Titanium tetrachloride(TiCl4), Polyacrylonitrile(PAN) and Nickel nitrate(Ni(NO3)2) precursor, followed by thermal treatment. The as-prepared TiC/CNFs possessed electrical conductivity of 25.0 S/cm, which is much higher than the corresponding carbon nanofibers. After 60 bending cycles, the TiC/CNFs have 96% conductivity retention. Even with 200 bending cycles, the TiC/CNFs still exhibited excellent conductivity retention of 40%.2. A flexible hierarchical porous nickel-cobalt binary hydroxide(NiCo-BH) nanosheets and titanium carbide-carbon nanofiber(NiCo-BH@TiC/CNF) composite, based on TiC/CNFs as matrix material, is successfully fabricated by microwave assisted synthesis method. Under optimized conditions, the NiCo-BH@TiC/CNF composite electrodes exhibit excellent specific capacitance, rate capability, and long cycling stability. In particular, the NiCo-BH41@TiC/CNF-based asymmetric supercapacitor has a prominent energy density of 55.93 Wh kg-1 and a high power density of 18300 W kg-1, and exhibits a good stability with 93.3% capacitance retention after 3000 cycles at 5.0 A g-1 current density. These excellent electrochemical performances could be attributed to the effective combination of high electroconductivity of TiC/CNFs, and interconnected porous structure of the NiCo-BH nanosheets. There may be two reasons. The TiC/CNFs act as a conductive interwoven network to improve the conductivity of hybrid electrodes, and as an ideal matrix to hinder NiCo-BH nanosheets from aggregation. The interconnected porous structure improves the diffusion of electrolyte ion by offering numerous passages for the contact of active sites with electrolyte. Therefore, the flexible and free-standing NiCo-BH@TiC/CNF composite is a promising electrode material for supercapacitors.