A sandwich-type three-dimensional layered double hydroxide nanosheet array/graphene composite: fabrication and high supercapacitor performance

In this study, we have developed, for the first time, a facile in situ growth process to prepare a hierarchical three-dimensional (3D) composite composed of graphene layers with layered double hydroxide (LDH) nanosheet arrays grown on both sides. The fabrication process involves coating AlOOH colloids onto the graphene surfaces and the subsequent in situ growth of layered NiAl-LDH nanosheet arrays on the surfaces of graphene sheets via a hydrothermal process. It is found that the NiAl-LDH nanosheet arrays grow perpendicularly and uniformly on both sides of the graphene sheets, constructing a hierarchical 3D nanocomposite with an interesting sandwich structure. This uniquely structured composite has a large specific surface area (184.7 m(2) g(-1)) and typical mesoporous characteristics, which are favorable for achieving high pseudocapacitance performance. Our results reveal that the composite has a specific capacitance of 1329 F g(-1) at a current density of 3.57 A g(-1), and the specific capacitance still remains as high as 851 F g(-1) even when the current density is increased to 17.86 A g(-1). The specific capacitance remains at 91% (823 F g(-1)) after 500 cycles at 15.30 A g(-1) compared with 74% for pure Ni/Al-LDH. The in situ growth method may pave a way to design and fabricate diverse LDH/graphene composites with interesting structures for potential application in supercapacitors and other fields.