Search

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]

[Display omitted] • Boron-containing metal-free catalysts (BC 4 N and BC 6 N 2) as efficient cathode materials of lithium-sulfur batteries. • BC 4 N and BC 6 N 2 possess stronger trapping capability for LiPs/S 8 than previously reported metal-free catalysts and perform even better than some metal-containing catalysts. • BC 4 N exhibits superior catalytic performance for Li 2 S decomposition with low energy barrier (0.8 eV) • Crystalline phase BC 4 N and BC 6 N 2 containing high density and homogeneous distribution of active boron sites could overcome the challenges faced by other carbon-based metal-free catalysts obtained via doping strategy. Lithium-sulfur (Li-S) batteries are considered as ideal next-generation energy storage devices, the commercial applications of them are hindered by their inherent drawbacks of shuttle effect and sluggish conversion among lithium polysulfides (LiPs). To tackle these issues, significant research efforts have been devoted to designing high-performance metal-based catalysts implemented in the sulfur cathodes, which however face the challenges of source scarcity and cycling instability. Here, based on first-principles calculations, we investigated our previously predicted two-dimensional (2D) metal-free boron-containing catalysts of BC 4 N and BC 6 N 2 and found that they possess strong trapping capability for LiPs adsorption energy as low as −6.41 eV beneficial for suppressing shuttle effect. Moreover, BC 4 N exhibits even superior catalytic performances toward the redox of sulfur, which can be evidenced by the low free energy change of the rate determining step of reduction reaction and small energy barrier of 0.80 eV for Li 2 S decomposition, outperforming most previously reported metal-based catalysts. Our research can pave a new way for designing new 2D metal-free catalysts in Li-S batteries, which highlights the importance of boron atoms in suppressing shuttle effect and catalyzing sulfur redox. [ABSTRACT FROM AUTHOR]