ZIF-8-Templated Hollow Cubelike Si/SiO₂@C Nanocomposites for Superior Lithium Storage Performance

Silicon-based anodes are of particular interest for the application of next generation large-capacity lithium-ion batteries (LIBs) because of their natural abundance and ultrahigh theoretical lithium storage ability. However, the huge volume expansion and inferior cyclic stability severely limit their practical applications. To address this challenge, herein, hollow cubelike hybrid composites consisting of a Si/SiO2 cross-link covered by a carbon layer (Si/SiO2@C) have been rationally synthesized through a facile zeolitic imidazolate framework template method. Within hybrid composites, the porous Si/SiO2 cross-link with an internal void can effectively mitigate volume changes and facilitate fast channels for Li+ during the charge–discharge process while the coated carbon layer not only can improve the electrical conductivity of the composites but also guarantees the structural integrity. As expected, the hollow Si/SiO2@C composite electrode has outstanding electrochemical properties including excellent reversible capacity (1280 mAh g–1 at 500 mA g–1 after cycled for 200 times) and superior rate performance (782 and 660 mAh g–1 at current densities of 3.2 and 6.4 A g–1, respectively). Considering the convenient preparation and naturally abundant of composites as well as their excellent electrochemical performance, the hollow Si/SiO2@C may hold great promise as advanced electrodes for next-generation LIBs

Growth of SiC Nanowires from NiSi Solution

We present a simple melt solution strategy for the growth of high-yield SiC nanowires out of NiSi solution. The growth temperature and base vacuum before filling argon during the reaction are found to have a significant effect on the morphology of the product growth. Taking into consideration the action of Ni in the NiSi melt and the possible participation of a tiny amount of oxygen, the formation of SiC nanowires is discussed by a combination of the solid−liquid−solid reaction for nucleation and the vapor−liquid−solid process for nanowire growth. The nanowires were also investigated with Raman spectroscopy. Such a simple and economical method may be extended to synthesize other one-dimensional nanostructures

A Practical Nonflammable Na₄B₃₆H₃₄-Based Hydroborate Electrolyte for High-Voltage All-Solid-State Sodium Batteries

High-voltage solid electrolytes (SEs) are highly desired for the development of safe and high-energy-density all-solid-state batteries (ASSBs). Herein, a nonflammable conjuncto-hydroborate of Na4B36H34 is developed with a wide electrochemical stability window (ESW) of up to 6.9 V. Density functional theory calculations reveal an enlarged Na-ion diffusion pathway and fast dynamics of [B36H34]4–, contributing to the fast Na+ conduction in Na4B36H34. Remarkably, the mixed-anion Na4B36H34-7Na2B12H12 SE demonstrates high ionic conductivity (1.02 × 10–3 S cm–1), wide ESW (5.5 V), high Na+ transference number (0.97), low electronic conductivity, low density (1.1709 g cm–3), good compressibility, decent mechanical strength, nonflammability, and solubility. Moreover, the Na/Na4B36H34-7Na2B12H12/Na symmetrical cell can maintain long-term cyclability over 200 h at 0.1 mA cm–2. In addition, a 4.5 V high-voltage Na3V2(PO4)2O2F/Na battery with good cycling stability was fabricated using Na4B36H34-7Na2B12H12 as SE. The proposed Na4B36H34-based hydroborate electrolyte turns out to be a promising SE candidate for the practical application of high-voltage and high-energy-density ASSBs

Porous Spinel Zn_<i>x</i>Co_3–<i>x</i>O₄ Hollow Polyhedra Templated for High-Rate Lithium-Ion Batteries

Nanostructured metal oxides with both anisotropic texture and hollow structures have attracted considerable attention with respect to improved electrochemical energy storage and enhanced catalytic activity. While synthetic strategies for the preparation of binary metal oxide hollow structures are well-established, the rational design and fabrication of complex ternary metal oxide with nonspherical hollow features is still a challenge. Herein, we report a simple and scalable strategy to fabricate highly symmetric porous ternary Zn_<i>x</i>Co_3–<i>x</i>O₄ hollow polyhedra composed of nanosized building blocks, which involves a morphology-inherited and thermolysis-induced transformation of heterobimetallic zeolitic imidazolate frameworks. When tested as anode materials for lithium-ion batteries, these hollow polyhedra have exhibited excellent electrochemical performance with high reversible capacity, excellent cycling stability, and good rate capability

Growth of Tapered SiC Nanowires on Flexible Carbon Fabric: Toward Field Emission Applications

Tapered silicon carbide (SiC) nanowires were directly grown on the surface of flexible carbon fabric by a chemical vapor deposition process. The products were systemically characterized by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electronic diffraction, and energy-dispersive X-ray spectroscopy. The results revealed that the tapered nanowires were of single crystalline β-SiC phase with the growth direction along [111] and had a feature of zigzag faceting over the wire surfaces. Such faceting was created by a quasi-periodic placement of twinning boundaries along the wire axis, which can be explained by surface energy minimization during the growth process. Based on the characterizations and thermodynamics analysis, the Fe-assisted vapor–liquid–solid (VLS) growth mechanism of tapered SiC nanowires was discussed. Furthermore, field emission measurements showed a very low turn-on field at 1.2 V μm^–1 and a high field-enhancement factor of 3368. This study shows that SiC nanowires on carbon fabric have potential applications in electronic devices and flat panel displays

In Situ Formation of Cobalt Nitrides/Graphitic Carbon Composites as Efficient Bifunctional Electrocatalysts for Overall Water Splitting

Developing cost-effective and highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great interest for overall water splitting but still remains a challenging issue. Herein, a self-template route is employed to fabricate a unique hybrid composite constructed by encapsulating cobalt nitride (Co_5.47N) nanoparticles within three-dimensional (3D) N-doped porous carbon (Co_5.47N NP@N-PC) polyhedra, which can be served as a highly active bifunctional electrocatalyst. To afford a current density of 10 mA cm^–2, the as-fabricated Co_5.47N NP@N-PC only requires overpotentials as low as 149 and 248 mV for HER and OER, respectively. Moreover, an electrolyzer with Co_5.47N NP@N-PC electrodes as both the cathode and anode catalyst in alkaline solutions can drive a current density of 10 mA cm^–2 at a cell voltage of only 1.62 V, superior to that of the Pt/IrO₂ couple. The excellent electrocatalytic activity of Co_5.47N NP@N-PC can be mainly ascribed to the high inherent conductivity and rich nitrogen vacancies of the Co_5.47N lattice, the electronic modulation of the N-doped carbon toward Co_5.47N, and the hierarchically porous structure design

Dual carbon-hosted Co-N3 enabling unusual reaction pathway for efficient oxygen reduction reaction

Single-atom cobalt-nitrogen-carbon (Co-N-C) has emerged as one of the most promising electrocatalysts for the oxygen reduction reaction (ORR) as it has the utmost atomic utilization efficiency and may avoid possible Fenton reactions. Herein, we report dual carbon-supported single-atom cobalt with the unusual Co-N coordination number of three (Co-N3-C) as an efficient catalyst for the ORR. The combination of experiments and density functional theory calculations reveal that the Co-N3-C would experience an activation process and be favorable to lowering the energy barriers of the intermediates, leading to accelerated reaction kinetics. The as-prepared Co-N3-C catalyst exhibited unprecedented ORR activity with a half-wave potential of 0.891 V versus reversible hydrogen electrode and outstanding stability under alkaline conditions, not only outperforming the previously reported Co-based catalysts but also surpassing state-of-the-art Pt/C catalyst. The current work may provide a new insight into the engineering of the single-atom coordination environment to improve the catalytic activity