Nickel Sulfide Nanoparticles Synthesized by Microwave-assisted Method as Promising Supercapacitor Electrodes: An Experimental and Computational Study

As an energy storage system, pseudocapacitors aim to combine the high power density with the high energy density, because their performance is mainly determined by surface reactions and structures. In this work, NiS nanoparticles are synthesized by microwave-assisted method and used as pseudocapacitor electrode. The NiS electro-active material demonstrates excellent electrochemical performance with high specific capacitance (845 F g(-1) at current densities of 1 A g(-1)), low resistance and excellent cycling stability. To reveal the original reasons of the excellent performance, first-principles density functional theory (DFT) calculations are performed to provide atomic insight on how the electrolyte interacts with NiS nanoparticles electrode. According to the results, two sites are found energy suitable for absorbing hydroxyls on the Ni-terminal surface and have the electron transfer between hydroxyls and Ni atom, which reveals the position of the redox reaction. The density of the states of NiS (0 0 1) surface exhibits metallic, giving an explanation for low resistance and high rate capacitance. The NiS nanoparticles show their potential for pseudocapacitor materials and the atomic insight provides guidance for understanding and improving the performance of the NiS electrode materials. (C) 2015 Elsevier Ltd. All rights reserved.