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Supercapacitors or electrochemical capacitors, as energy storage devices, require very stable positive electrode materials for useful applications. Although most positive electrodes are based on crystalline mixed-metal hydroxides, their pseudocapacitors usually perform poorly or have a short cycle life. High activities can be achieved with amorphous phases. Methods to produce amorphous materials are also not typically amenable towards mixed-metal compositions. It is demonstrated that electrochemistry in an ambient environment can be used to produce a series of amorphous mixed-metal hydroxides with a homogeneous distribution of metals for use as positive electrode materials in a supercapacitor. The integrated performance of the amorphous ternary mixed-metal hydroxide pseudocapacitor is superior to that of crystalline materials. The amorphous Ni-Co-Fe hydroxide supercapacitor is characterized by a long-term cycling stability that retained 94% of its capacity after 20 000 cycles. This is much higher than the cycle life of crystalline devices. These results show the broad applicability of this methodology towards new electrode materials for high-performance supercapacitors, especially amorphous mixed-metal hydroxides, as advanced electrode materials. [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]