Chunli Wang

Metal-Organic Framework Template Synthesis of NiCo2S4@C Encapsulated in Hollow Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage

Owing to its richer redox reaction and remarkable electrical conductivity, bimetallic nickel cobalt sulfide (NiCo2S4) is considered as an advanced electrode material for energy-storage applications. Herein, nanosized NiCo2S4@C encapsulated in a hollow nitrogen-doped carbon cube (NiCo2S4@D-NC) has been fabricated using a core@shell Ni3[Co(CN)6]2@polydopamine (PDA) nanocube as the precursor. In this composite, the NiCo2S4 nanoparticles coated with conformal carbon layers are homogeneously embedded in a 3D high-conduction carbon shell from PDA. Both the inner and the outer carbon coatings are helpful in increasing the electrical conductivity of the electrode materials and prohibit the polysulfide intermediates from dissolving in the electrolyte. When researched as electrode materials for lithium storage, owing to the unique structure with double layers of nitrogen-doped carbon coating, the as-obtained NiCo2S4@D-NC electrode maintains an excellent specific capacity of 480 mAh g-1 at 100 mA g-1 after 100 cycles. Even after 500 cycles at 500 mA g-1, a reversible capacity of 427 mAh g-1 can be achieved, suggesting an excellent rate capability and an ultralong cycling life. This remarkable lithium storage property indicates its potential application for future lithium-ion batteries.

Formation of Mo–Polydopamine Hollow Spheres and Their Conversions to MoO2/C and Mo2C/C for Efficient Electrochemical Energy Storage and Catalyst

Highly uniform hierarchical Mo-polydopamine hollow spheres are synthesized for the first time through a liquid-phase reaction under ambient temperature. A self-assembly mechanism of the hollow structure of Mo-polydopamine precursor is discussed in detail, and a determined theory is proposed in a water-in-oil system. Via different annealing process, these precursors can be converted into hierarchical hollow MoO2 /C and Mo2 C/C composites without any distortion in shape. Owing to the well-organized structure and nanosize particle embedding, the as-prepared hollow spheres exhibit appealing performance both as the anode material for lithium-ion batteries and as the catalyst for hydrogen evolution reaction (HER). Accordingly, MoO2 /C delivers a high reversible capacity of 940 mAh g-1 at 0.1 A g-1 and 775 mAh g-1 at 1 A g-1 with good rate capability and long cycle performance. Moreover, Mo2 C/C also exhibits an enhanced electrocatalytic performance with a low overpotential for HER in both acidic and alkaline conditions, as well as remarkable stability.

Self-Assembly of Hierarchical Ni-Mo-Polydopamine Microflowers and their Conversion to a Ni-Mo2C/C Composite for Water Splitting

With the aim of finding efficient non-noble metal catalysts for water splitting, hierarchical Ni-Mo-polydopamine microflowers (Ni-Mo2 C/C MF) were synthesized through a facile aqueous-phase reaction at room temperature. NiMoO4 nanowires were utilized as both Ni and Mo source; they can complex with dopamine to form a hierarchical structure and affect the scale of the final product. The energy dispersive spectroscopy (EDS) measurement of Ni-Mo2 C/C microflowers (MF) shows a high content of Mo2 C and Ni (>90u2005wtu2009%). For the hydrogen evolution reaction (HER), the Ni-Mo2 C/C MF displays a low overpotential of 99u2005mV at a current density of -10u2005mAu2009cm-2 and a small Tafel slope of 73u2005mVu2009dec-1 in 1.0u2009m KOH. By comparison with Mo2 C/C microspheres (MS), the nanosized Ni-doped particles offer more active sites and enhance the kinetic performance. This facile synthesis strategy is also suitable for preparing other metal-Mo2 C/C composites that can be used in the fields of catalysis and energy conversion.

Large‐Scale Fabrication of Core–Shell Structured C/SnO2 Hollow Spheres as Anode Materials with Improved Lithium Storage Performance

Due to the high theoretical capacity as high as 1494 mAh g-1 , SnO2 is considered as a potential anode material for high-capacity lithium-ion batteries (LIBs). Therefore, the simple but effective method focused on fabrication of SnO2 is imperative. To meet this, a facile and efficient strategy to fabricate core-shell structured C/SnO2 hollow spheres by a solvothermal method is reported. Herein, the solid and hollow structure as well as the carbon content can be controlled. Very importantly, high-yield C/SnO2 spheres can be produced by this method, which suggest potential business applications in LIBs field. Owing to the dual buffer effect of the carbon layer and hollow structures, the core-shell structured C/SnO2 hollow spheres deliver a high reversible discharge capacity of 1007 mAh g-1 at a current density of 100 mA g-1 after 300 cycles and a superior discharge capacity of 915 mAh g-1 at 500 mA g-1 after 500 cycles. Even at a high current density of 1 and 2 A g-1 , the core-shell structured C/SnO2 hollow spheres electrode still exhibits excellent discharge capacity in the long life cycles. Consideration of the superior performance and high yield, the core-shell structured C/SnO2 hollow spheres are of great interest for the next-generation LIBs.

Preparation of a graphitic N-doped multi-walled carbon nanotube composite for lithium–sulfur batteries with long-life and high specific capacity

One of the challenges for lithium–sulfur batteries is a rapid capacity fading owing to the insulating of sulfur and Li2S2/Li2S compounds, the dissolving and consequent shuttling of polysulfide generated as intermediates during charge–discharge processes in the electrolyte. In this work, graphitic N-doped multi-wall carbon nanotube (GN/PNCNTs) composites are synthesized by in situ chemical polymerization and carbonization processes. The nitrogen doping in the GN/PNCNTs composite can effectively enhance chemisorption between sulfur and carbon, which can enable the uniform deposition of discharge products and lead to a high utilization and reversibility of active materials. Because of these technological superiorities, the as-prepared S-GN/PNCNTs cathode with a sulfur content of 60 wt% exhibits high initial specific capacity and excellent cycling stability at up to 600 cycles at 1C. Meanwhile, the rate capacities of the cathode are demonstrated from 0.5C to 6C with a specific capacity of 1178 mA h g−1 (the initial specific capacity) to 586 mA h g−1 (the 60th cycle).

A Kind of Coordination Complex Cement for the Self-Assembly of Superstructure

Not like the macroscopic building materials, the controllable assembly of blocks into superstructure has not been conquered in microscale, especially for the ordinary particles with shape defects and weak surface activities. Here, a facile route of assembling particles into superstructures utilizing Mo-polydopamine complex as the binder and curing agent is established. A side-by-side adsorption and growth mechanism in a water/ethanol system is derived, and the factors influencing the final structures are verified. This system is suitable to assemble superstructures from particles of different shapes such as nanospheres, nanocubes, nanorods, and hollow spheres in the range from 10 to 500 nm in size. And after high temperature and etching treatment, the generated MoO2/N/C frameworks with superpore structures derived from different blocks exhibit a high structural plasticity and potential application as multifunctional carriers for energy storage. Rather than the obtained system, our work assembles superstructures from various building blocks and explores more valuable complex cements for superstructures construction.