Abstract
A simple and scalable process has been developed for synthesizing spinel NiCo 2 O 4 nanocrystals through a thermal decomposition method. The introduction of hexadecyltrimethylammonium bromide (CTAB, (C 16 H 33 )N(CH 3 ) 3 Br) into precursor solutions significantly enhances the homogeneity and porosity of spinel NiCo 2 O 4 . The porosity and high specific surface area of NiCo 2 O 4 preserves the brilliant pseudo-capacitive performances due to providing smooth paths for electrolyte penetration and ion diffusion into inner active sites. Morphologies and microstructures of the active materials are examined by transmission electron microscopic (TEM) and X-ray diffraction (XRD) analyses. Thermogravimetric analysis (TGA) is used to evaluate the thermal properties of precursor solutions. The electrochemical performances of NiCo 2 O 4 are systematically characterized by cyclic voltammetry and charge-discharge tests. Asymmetric supercapacitors are assembled with these brilliant binary oxides as the positive electrode and activated carbon as the negative electrode. The highly porous NiCo 2 O 4 exhibits superior capacitive performances, i.e., high specific capacitance (764 F g -1 at 2 mV s -1 ) and long cycle life. © 2013 Elsevier B.V. All rights reserved.