Hydrothermal growth of 3D graphene on nickel foam as a substrate of nickel-cobalt-sulfur for high-performance supercapacitors

Abstract

A facile and efficient one-step hydrothermal approach is presented to prepare a three-dimensional graphene-nanosheets/nickel foam (3D NF/G) substrate for pseudocapacitive materials to utilize its high specific surface area and short ion channel lengths. Scanning electron microscope (SEM) observation shows thin graphene nanosheets (∼10 nm) are assembled into 3D porous architectures and uniformly deposited on NF for the NF/G substrate obtained under addition of KOH at low graphene oxide (GO) concentration. Raman and X-ray photoelectron spectroscopy (XPS) analysis further shows the homogenous dispersion of GO in the solution increases reducibility of graphene and avoids agglomeration of nanosheets during the hydrothermal process, which accelerate the graphene nanosheets self-assemble into 3D interconnected structures on NF. Furthermore, flower-like Ni-Co-S nanosheets was then deposited on NF/G substrate by electrodeposition to form NF/G/Ni-Co-S composite, in which 3D graphene can guarantee the high utilization of electroactive species and favorable reaction kinetics. The as-synthesized electrode shows greatly improved electrochemical performances with an ultrahigh specific capacitance of 2526 F g−1 at a current density of 2 A g−1 and of 1916 F g−1 even at a current density of 10 A g−1. Additionally, it also exhibits superior cycle stability by retaining 77.0% of its original state after 2000 cycles at high current density of 20 A g−1, indicating promising applications as an efficient electrode for supercapacitors.