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The phase-transition engineering has shown great potential in designing high-performance energy storage and catalytic materials. Herein, we report the phase transition and selenium vacancy induced by the trace boron doping into CoSe 2 , realizing an enhancement of the performance of supercapacitor. The trace amounts of boron doping (∼ 0.07 wt%) induce the phase-transition from cubic to orthorhombic structures and trigger selenium vacancies in orthorhombic cobalt diselenide (o-CoSe 2). The doped defective cobalt diselenide (o-CoSe 2−x /B) exhibits a high specific capacity of 376.3 mA h g−1 at a current density of 1 A g−1, which is much larger than that of the undoped cubic cobalt diselenide (211.3 mA h g−1) and annealed cubic cobalt diselenide (208.3 mA h g−1). A hybrid supercapacitor assembled using o-CoSe 2−x /B and activated carbon delivers a high energy density of 102.5 W h kg−1 at a power density of 850.4 W kg−1 and maintains an energy density of 34.0 W h kg−1 at 16,767.1 W kg−1. In addition, the device possesses an excellent cycling stability that remains 83.5 % of the initial capacitance after 25,000 cycles at a current density of 10 A g−1. These results demonstrate that the boron is a new efficient dopant that can dramatically improve the supercapacitor performance of CoSe 2 through the structural phase transition and defect engineering. [Display omitted] • Trace amounts of boron induces phase-transition from c-CoSe 2 to o-CoSe 2. • Se vacancies defects arise with the help of boron doping engineering. • The o-CoSe 2−x /B shows the enhanced performance as electrode for supercapacitor. • Providing an efficient dopant for design of CoSe 2 based energy storage materials. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the MnO 2 /three-dimensional carbon nanotubes-graphene nanocomposite was synthesized on Cu foil substrate by chemical vapor deposition and subsequent thermal decomposition of manganese acetyllacetonate precursors. The nanocomposite material was directly used as a binder-free electrode to investigate the supercapacitive performance. The results indicate that the appropriate defects and MnO 2 nanoparticles are introduced simultaneously into the carbon nanotubes-graphene architecture in one-step. The specific capacitance of MnO 2 /three-dimensional carbon nanotubes-graphene/Cu electrode is up to 365 F g−1 at a current density of 1 A g−1 in 1.0 M Na 2 SO 4 solution, which is 9 times higher than that of electrode without MnO 2 modification. After 1000 cycles at 1 A g−1, the capacity retention is still maintained at 97.0%, suggesting potential applications in high-performance energy storage devices. The excellent electrochemical performances of nanocomposite electrode can be attributed to the significantly synergistic effects between the lasting electronic conductivity of three-dimensional carbon nanotubes-graphene/Cu with the appropriate defects and the pseudocapacitance of the MnO 2 nanoparticles. Graphical abstract Image 1 Highlights • MnO 2 /3D CNTs-G/Cu was fabricated as a binder-free electrode using a facile method. •Defects and α-MnO 2 was introduced simultaneously into the 3D CNTs-G/Cu in one-step. •The specific capacitance of MnO 2 /3D CNTs-G/Cu reached 365 F g−1 at 1 A g−1 current. •Synergistic effects of 3D CNTs-G/Cu lasting conductivity and MnO 2 pseudocapacitance. [ABSTRACT FROM AUTHOR]

• Utilizing the well-designed Ni 2 CoS 4 @ZIF-67 precursor as self-sacrificing templates. • Constructing the porous α-Ni(Co)S@NiCoO 2 composites with core–shell like structure. • Novel combination of Ni-Co-S and Ni-Co-O shows outstanding capacitive performance. As inspired by the surging demand for high performance energy storage systems, researchers have been designing and exploring advanced electrode materials exhibiting higher energy and power densities. In this study, a novel combination of nickel-cobalt sulfide and oxide was reported for high performance supercapacitors. The porous α-Ni(Co)S@NiCoO 2 composites with core–shell structure were derived from the well-designed precursor with Ni 2 CoS 4 and ZIF-67 serving as the self-sacrificing templates through a two-step calcination process at elevated temperatures. Such a heterostructure exhibited an ultra-high specific capacity of 502.4 mA h g–1 at a current density of 1 A g–1, which was attributed to the unique porous core–shell structure and the ingenious combination of bimetallic sulfide and oxide. Furthermore, a hybrid supercapacitor based on the α-Ni(Co)S@NiCoO 2 composite and commercial activated carbon achieved a high energy density of 82.4 Wh kg–1 at a power density of 847.5 W kg–1. The prominent electrochemical performance exhibited by the α-Ni(Co)S@NiCoO 2 heterostructure in this study was demonstrated to be promising to practically serve as advanced electrode materials in supercapacitors. [ABSTRACT FROM AUTHOR]

• The CNTs/NiCo 2 S 4 hybrids with three kinds of interfaces were designed and prepared. • Supercapacitive properties of CNTs/NiCo 2 S 4 were improved by interface regulation. • An aqueous asymmetric supercapacitor was successfully assembled and evaluated. • An CNT:Ni@NiCo 2 S 4 //AC device showed excellent electrochemical energy storage. Integrating metal sulfides with carbon materials is considered as one of effective approaches to meet the demand of high-performance electrochemical energy storage materials. In this paper, we emphasize the critical role of interface between NiCo 2 S 4 and CNTs for supercapacitive performance of the hybrid structures. The CNTs/NiCo 2 S 4 nanocomposites with three kinds of interfaces are prepared using a one-step hydrothermal method by adding the pristine CNTs, surface-oxidized CNTs and nickel-coated CNTs, respectively. Benefiting from the unique nickel interface structure that adequately realizes the effective utilization of the conductive CNTs owing to the homogeneous dispersion of CNTs throughout the matrix as well as the strong interface adhesion by a bridging role, the CNTs:Ni@NiCo 2 S 4 nanocomposite exhibits a high specific capacity of 224.0 mAh g−1 at a current density of 1 A g−1. An asymmetric supercapacitor assembled by the CNTs:Ni@NiCo 2 S 4 nanocomposite and activated carbon as positive electrode and negative electrode, respectively, exhibits a high energy density of 60.7 Wh kg−1 at a power density of 800 W kg−1 and an excellent cycling stability of 88% capacitance retention after 10,000 cycles at 10 A g−1. This work described herein provides a new strategy for development of high-performance energy storage materials. [ABSTRACT FROM AUTHOR]