Self-supported 3D NiCo-LDH/Gr composite nanosheets array electrode for high-performance supercapacitor

Highlights: • 3D free-standing NiCo-LDH nanosheets are decorated on GF/NF and GW/NF. • The specific capacitance of NiCo-LDH/GF/NF electrode is 2690 F g^-1 at 5 A g⁻¹. • The asymmetric supercapacitor exhibits a high energy density and power density. Graphene film (GF) and graphene nanowall (GW) are first grown on conductive nickel foams (NF) by a chemical vapor deposition (CVD) method. Then the nickel cobalt layered double hydroxides (NiCo-LDHs) nanosheets arrays are directly deposited on the NF, GF/NF and GW/NF by a facile hydrothermal method to form three-dimensional (3D) porous NiCo-LDH/Gr composite electrodes. The electrochemical performance and morphology of the obtained self-supported NiCo-LDH/NF, NiCo-LDH/GF/NF and NiCo-LDH/GW/NF composite electrodes are analyzed and observed. It shows that the NiCo-LDH/GF/NF composite electrode exhibits excellent capacitive properties (2690 F g^-1 at 5 A g⁻¹), which is 2.0 and 1.5 times of that of NiCo-LDH/NF and NiCo-LDH/GW/NF. The outstanding capacity of the NiCo-LDH/GF/NF electrode is ascribed to the numerous channels for rapid electron transport provided by the self-supported and high-quality GF. In addition, an asymmetric supercapacitor (ASC) is fabricated by using NiCo-LDH/GF/NF electrode. The optimized NiCo-LDH/GF/NF//AC device delivers a maximum energy density of 50.2 Wh kg⁻¹, a high power density of 8002 W kg^-1 at 17.6 Wh kg⁻¹, and powers two green light-emitting-diodes for more than 3 min after charging 1 min. Therefore, the NiCo-LDH/Gr/NF composite electrode is a potential candidate in electrochemical energy storage device.