Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo₂O₄ In Situ Grown on...

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo₂O₄/rGO/NF) was assembled via an aqueous coprecipitation-hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo₂O₄/rGO/NF composite is featured as thin NiCo₂O₄ nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo₂O₄ nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo₂O₄/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g^-1 (1503.3 C g^-1) at 1 A g^-1, a superior rate performance of 2335.2 F g^-1 at 20 A g^-1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo₂O₄/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg^-1 at a power density of 800 W kg^-1, and the energy density at a peak power density of 20004 W kg^-1 still remained at 48.9 Wh kg^-1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo₂O₄/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas.