In situ growth of Ni-Co-S nanosheet arrays on rGO decorated Ni foam toward high-performance supercapacitors

Electrodes for supercapacitors (SCs) with excellent capacity and rate performance have always been in high demand. Herein, Ni-Co-S nanosheet arrays were successfully anchored on reduced graphene oxide (rGO) covered Ni foam (denoted as Ni-Co-S-rGO/NF-1) by consecutive electrochemical methods and high-performance positive electrode material for SCs was obtained. It was worth mentioning that there were two innovations in this preparation: the first one was that synchronous electroreduction and electrodeposition of graphene oxide (GO) resulted in rGO tightly wrapped Ni foam (denoted as rGO/NF), which enhanced the electroconductibility of the substrate and achieved outstanding rate performance; the second one was that a two-step combination approach composed of cyclic voltammetry (CV) technique and potentiostatic technique was adopted to deposit Ni-Co-S nanosheet arrays, which ensured both higher specific capacity and relatively robust growth of Ni-Co-S on rGO/NF. On account of a synergistic effect of the Ni-Co-S and rGO as well as the unique thin sheet-like nanostructure, the as-prepared electrode revealed excellent supercapacitor properties, including higher specific capacity of 976 C g(-1) at current density of 1 A g(-1), impressive rate capability with 86.4 % retention at 60 A g(-1), and long-term stability of 82.2 % capacity retention after 10,000 cycles. An asymmetric supercapacitor fabricated by the Ni-Co-S-rGO/NF-1 and activated carbon exhibited a maximum energy density of 27 Wh kg(-1) at the power density of 801 W kg(-1), and a power density of 8115 W kg(-1) at the energy density of 11.0 Wh kg(-1). The excellent performance of the Ni-Co-S-rGO/NF-1 electrode suggests that it could be the hopeful electrode materials for energy storage devices.