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A self-template method is developed for hierarchically yolk-shelled NiCo 2 O 4 spheres (YS-NiCo 2 O 4 ) through a controlled hydrolysis process and followed by a thermal annealing treatment. The yolk-shelled NiCo 2 O 4 spheres possess out-shell consisting of hundreds of ultrathin sheets with 3–5 nm in thickness and solid yolk composing of a large number of nanoparticles. The YS-NiCo 2 O 4 generates a large specific surface area of 169.6 m 2 g −1 . Benefit from the large specific surface area and rich oxygen vacancy, the as-fabricated YS-NiCo 2 O 4 as electrode materials for supercapacitor exhibits high specific capacitance of 835.7 F g −1 at 0.5 A g −1 , an enhanced rate capability and excellent electrochemical stability with 93% retention after 10,000 cycles even at 10 A g −1 . Moreover, a hybrid supercapacitor combined with YS-NiCo 2 O 4 and graphene shows a high energy density of 34.7 Wh kg −1 at the power density of 395.0 W kg −1 at 0.5 A g −1 , even at 20 A g −1 , the hybrid supercapacitor still delivers the energy density of about 12.1 Wh kg −1 and the power density of 11697 W kg −1 . The desirable performance of yolk-shelled NiCo 2 O 4 suggests it to be a promising material as supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Porous NiCo 2 S 4 nanosheets derived from bimetallic MOFs directly grow on a conductive substrate as a binder-free electrode. The unique open-structure NiCo 2 S 4 with porosity facilitates the diffusion of electrolyte and possess abundant electroactive sites, which presents a high specific capacity and long-term cycling stability. An assembled hybrid capacitor exhibits the practical performance of high energy density and excellent cycling property. • The porous NiCo 2 S 4 nanosheet arrays derived from bimetallic Metal-organic frameworks derivatives are prepared. • The effect of NiCo 2 S 4 morphology on electrochemical performance and reaction mechanism are discussed. • A hybrid supercapacitor device exhibits high energy density and superior cycling stability. Recently, metal-organic frameworks (MOFs) derived materials in the form of bulk powders with attractive chemical and structural properties show broad application in electrochemical energy storage. Bimetallic materials-based MOFs usually show better electrochemical properties than that of monometallic derivatives, while achieving the bimetallic MOFs-derived materials on current collector as a binder-free electrode is still a challenge. Here we report a new approach to directly obtain a binder-free electrode of bimetallic MOFs-derived NiCo 2 S 4 nanosheet arrays on nickel foam (NF) substrate. The porous NiCo 2 S 4 nanosheet arrays providing fast electrolyte permeation and rich electrochemical active sites, show an excellent specific capacity of 1354.4 C g−1, high rate performance, and outstanding cycling stability of 82.6% retention after 10,000 cycles. A hybrid supercapacitor assembled with the as-obtained binder-free electrode as a cathode and active carbon as an anode, exhibits high energy density of 49.1 Wh kg−1 at a power density of 375 W kg−1 and superior cycling stability of 94.5% retention after 10,000 cycles. These results offer a novel and general approach to construct binder-free electrode materials with advanced performance for the portable and practical energy storage device. [ABSTRACT FROM AUTHOR]