Synthesis of Co(OH)2/CNTs nanocomposite with superior rate capability and cyclic stability for energy storage applications

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Abstract
The good rate capability and longer cyclic performance are the two key features electrochemical capacitors that are highly dependent on the electrochemical stability, structure, electrical conductivity, composition, and nature of the charge storing-mechanism involved by its electrodes. Herein, we fabricated layered Co(OH)2 and their nanocomposite with carbon nanotubes (CNTs, 5%) via a two-step approach for electrochemical applications. The as-prepared nanocomposite based electrode displays good specific capacitance (Cs), negligible capacity fade, and promising rate capability on electrochemical tests via a three-electrode configuration. More precisely, the nanocomposite based electrode showed Cs of 802 Fg−1 at 0.5 Ag−1 and loss just 3.8% of its initial capacitance (at 1st cycle) after 5000 cyclic tests. Furthermore, the nanocomposite electrode lost around 14% of its initial capacitance on increasing the current density from 0.5 to 5 Ag−1 that reveals its novel rate capability. The observed superior electrochemical aptitude of the fabricated nanocomposite is credited to the layered nanoarchitecture of the Co(OH)2 and CNTs matrix. The CNTs-matrix, because of their lower properties, performs multiple roles to improve the supercapacitive performance of the whole composite. Firstly, they accelerate the charge transfer within the nanocomposite matrix due to its higher electrical conductivity. Secondly, they facilitate mass transport due to its hollow structure. Thirdly, they sandwich between the layers of Co(OH)2 and suppress the stacking process. Fourthly, the added CNTs itself act as a capacitive supplement and further improve the specific capacitance of the nanocomposite. Finally, CNTs buffers the whole nanocomposite against the volume expansion during the continuous cyclic tests. The electrochemical and structural stability of Co(OH)2/CNTs sample was also evaluated by EIS and PXRD characterizations after electrochemical tests. The acquired result showed that fabricated nanocomposite has great potential for advanced energy storage applications.