Enhanced cycling stability of hierarchical NiCo2S4@Ni(OH)2@PPy core–shell nanotube arrays for aqueous asymmetric supercapacitors

Abstract

In this article, a novel electrode of NiCo₂S₄@Ni(OH)₂@polypyrrole nanotube arrays supported on nickel foam is fabricated through a facile method. Due to the superior electronic conductivity of the shell material polypyrrole (PPy) and the high pseudocapacitance of Ni(OH)₂ together with the short ion transport pathway of NiCo₂S₄ nanotube arrays, the obtained core–shell NiCo₂S₄@Ni(OH)₂@PPy shows an enhanced pseudocapacitive performance of about 9.1125 F cm⁻² at a current density of 5 mA cm⁻², which is nearly three times higher than that of the pristine NiCo₂S₄ sample (3.1875 F cm⁻²). The kinetic analysis reveals the diffusion controlled faradaic characteristic of NiCo₂S₄@Ni(OH)₂@PPy (43.57% capacitive contribution). Moreover, an asymmetric supercapacitor is successfully assembled with NiCo₂S₄@Ni(OH)₂@PPy as the positive electrode and active carbon (AC) as the negative electrode. The NiCo₂S₄@Ni(OH)₂@PPy//AC device exhibits a relatively high energy density of 34.67 W h kg⁻¹ at a power density of 120.127 W kg⁻¹ and excellent cycling performance (about 98.87% capacitance retention over 30 000 cycles). The results show that the NiCo₂S₄@Ni(OH)₂@PPy core–shell nanotube array is a promising electrode material for high performance supercapacitor applications.