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Abstract: Herein, a flexible method is designed to engineer nitrogen‐doped carbon materials (NC) with different functional and structural specialties involving N‐doping level, graphitization, and surface area via tuning the carbonization temperature of the pre‐prepared zeolitic imidazolate framework‐8 (ZIF‐8 ) crystals. With the aim to unveil the effect of these features on the electrochemical performance of sulfur cathode, these samples are evaluated as sulfur host and comprehensively investigated. NC‐800 (800 °C, 10.45%N, 1032.4 m2 g−1) exhibits the best electrochemical capability comparing with NC‐700 (700 °C, 16.59%N, 891.4 m2 g−1) and NC‐900 (900 °C, 7.59%N, 987.6 m2 g−1). High surface area and N‐doping can work together to well increase the capacity of sulfur cathode, thanks to the improved transportation of charge carriers and effective anchoring of active sulfur, while the latter specialty just makes sulfur cathode have decent capacity in case of low surface area. Graphitization and quaternary nitrogen favorably improve the electric conductivity of the electrode, empowering the improvement of discharge capacity initially and rendering the good cyclability cooperatively relying on the effective immobilization of active materials. The related results suggest the significance of rational design of carbon maxtrix for sulfur to improve the performance of Li‐S batteries. [ABSTRACT FROM AUTHOR]

Chalcogenide micro/nanocomposite structures have been attracting worldwide attention due to prospective applications in photocatalytic hydrogen production. Well-defined micro/nanostructures with pronounced properties are of extraordinary importance. Herein, a facile one-pot method for the synthesis of monodisperse, size-controllable CdS core-shell and CdS@Zn xCd1− xS core-double shell submicrospheres, which were engineered with respect to structure and size, is reported. CdS core-shell submicrospheres with different sizes were selectively prepared for the first time. The growth mechanism was investigated in detail by monitoring the time-dependent morphology of intermediates by TEM. By introduction of a zinc precursor in the synthetic system, CdS@Zn xCd1− xS core-double shell submicrospheres were obtained by cation exchange of CdS with zinc ions, with a process of diffusion of CdS towards the outside and transformation of Zn xCd1− xS crystallites. The H2 evolution rate over CdS@CdxZn1− xS (5.17 mmol h−1 g−1) is 12.3 times that of CdS core-shell structures (0.42 mmol h−1 g−1) under visible light, owing to the efficient charge separation, as demonstrated by electrochemical impedance and transient-state time-resolved photoluminescence spectroscopy. Furthermore, CdS@Zn xCd1− xS core-double shell structures exhibited excellent stability over 20 h of hydrogen production. [ABSTRACT FROM AUTHOR]

In this paper, an extended Stöber method has been developed to fabricate a Ni2+-polydopamine (PDA) complex coated on Co3[Co(CN)6]2@SiO2 composites. After one-step carbonization involving the heat treatment of a Prussian blue analogue (PBA) of Co3[Co(CN)6]2 cores and the PDA-Ni2+ shell under a nitrogen atmosphere, homogeneous Co@SiO2@C/Ni submicrorattles were synthesized. Notably, the silica interlayer played a vital role in the formation of such Co@SiO2@C/Ni submicrorattle structures. Without the protection of SiO2, Co–Ni@C composites were obtained instead and aggregated seriously due to sintering at high temperature. While with the silica layer as the spacer, the obtained Co@SiO2@C/Ni composites were not only well dispersed in the solution, but could also be adjusted in terms of the size and density of Ni nanoparticles (NPs) on the surface. Moreover, the size of core Co and surficial Ni NPs can be facilely modulated via changing the calcination temperature, which can effectively control the catalytic performance of the as-prepared nanocomposites. The as-prepared Co@SiO2@C/Ni submicrorattles were employed as the reaction catalyst for the reduction of 4-nitrophenol (4-NP), and exhibit both superior catalytic activity and cycling stability to Co@SiO2 and Co–Ni@C composites. [ABSTRACT FROM AUTHOR]

ZnWO4 hierarchical hexangular microstars (HHMs) composed of crossed microplatelets were synthesized by a two-step hydrothermal reaction without using any surfactants. The homogeneous HHMs were characterized by TEM/SEM and XRD to reveal the structural features and crystallographic phase. On the basis of the analysis of the time-dependent evolution of ZnWO4 HHMs, a mechanism of in-situ formation and crystallographic fusion, wherein the morphology, components, and phase changed, is proposed to explain the formation process of 3D hexagonal structures. Furthermore, calcined ZnWO4 HHMs were evaluated as anode material for lithium-ion batteries, and exhibited better rate capabilities and cycling performance than the as-synthesized material. This can be attributed to the stabilized and highly crystalline structure as well as the synergic and interfacial effects between different metal ions, which relieve the volume change during the charge/discharge process and provide more active sites for lithium-ion storage. The synthetic method and growth mechanism could be applied to design and synthesize other hierarchical structures. [ABSTRACT FROM AUTHOR]

The exploration of inexpensive, facile, and large-scale methods to prepare carbon scaffolds for high sulfur loadings is crucial for the advancement of Li-S batteries (LSBs). Herein, the authors report a new nitrogen and oxygen in situ dual-doped nonporous carbonaceous material (NONPCM) that is composed of a myriad of graphene-analogous particles. Importantly, NONPCM could be fabricated on a kilogram scale via inexpensive and green hydrothermal-carbonization-combined methods. Many active sites on the NONPCM surface are accessible for the efficient surface-chemistry confinement of guest sulfur and its discharge product; this confinement is exclusive of physical entrapment, considering the low surface area. Electrochemical examination demonstrates excellent cycle stability and rate performance of the NONPCM (K)/S composite, even with a sulfur loading of 80 or 90 wt%. Hence, the scaffolds for LSBs exhibit potential for industrialization through further optimization and expansion of the present synthesis. [ABSTRACT FROM AUTHOR]

Although the preparation of hierarchical structures of transition-metal oxides (TMOs) has been intensively studied in recent years, it is still a great challenge to synthesize hierarchical multicomponent TMOs. Herein, we report a versatile method to fabricate three-component TMOs, namely MnO2@NiO/NiMoO4 nanowires@nanosheets hierarchical porous composite structures (HPCSs). Through a combination of a chemical-solution-based route and subsequent calcination, the as-prepared MnOOH@NiMo precursor is topotactically transformed to MnO2@NiO/NiMoO4 HPCSs without notable structural variation. Ultrathin NiO/NiMoO4 nanosheets become interconnected into a honeycomb analogue with plentiful mesopores. Comparative results demonstrate the vital role of hexamethylenetetramine (HMT), and the solvent system in the formation of the MnOOH@NiMo precursor. When examined as electrode materials for electrochemical capacitors, MnO2@NiO/NiMoO4 HPCSs, with an areal mass loading as high as 5 mg cm−2, deliver a specific capacitance of 918 F g−1 at a current density of 1.0 A g−1 and maintain good cycling stability, which displays better electrochemical performance than electrodes composed of a single component. Note that a high-voltage asymmetric supercapacitor is configured with MnO2@NiO/NiMoO4 HPCSs (still as high as 2 mg cm−2) against activated carbon, and exhibits outstanding cycling stability with a high energy density of 26.5 Wh kg−1 and a power density of 401 W kg−1. These analytical and experimental results clearly confirm the advantages of distinctive 3D multicomponent hierarchical architectures for engineering high-performance electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Transition-metal oxides are considered promising anode materials for lithium-ion batteries (LIBs). However, their application is limited because of huge volume changes and poor conductivity during the discharge/charge process. To this end, integration of different active components into an assemblage poses a potential solution. To gain better structural and synthetic control, the integration should be executed in a stepwise manner. In this paper, a versatile strategy to obtain C@Fe3O4@C hollow sandwiched composite structures was explored. Starting from Fe2O3 nanotubes, a RF (resorcinol-formaldehyde resins) layer was sequentially applied outside to form RF@Fe2O3@RF structures, which were calcined to realize carbonization and finalize the C@Fe3O4@C sandwiched structures. To the best of our knowledge, this is the first study on the preparation of a novel Fe3O4/carbon-based nanocomposite. Upon using as an anode material for LIBs, the C@Fe3O4@C hollow sandwiched structures displayed high reversible capacity and good rate performance. The discharge capacity was maintained at 593 mA h g-1 after 350 cycles at a current density of 1000 mA g-1, which is better than that of Fe2O3 nanotubes (discharge capacity of 140 mA h g-1 after 80 cycles at 500 mA g-1). The improved electrochemical performance was attributed to the unique hollow sandwiched composite structure and good electrical conductivity. [ABSTRACT FROM AUTHOR]