Huixin Chen

Isolation and characterization of lipopeptide antibiotics produced by Bacillus subtilis

Aims:  Antibiotics from Bacillus subtilis JA show strong pathogen inhibition ability, which has potential market application; yet, the composition of these antibiotics has not been elucidated. The aim of this paper is to isolate and identify these antibiotics.

Characterization of Fusarium graminearum inhibitory lipopeptide from Bacillus subtilis IB

Bacillus subtilis strain IB exhibiting inhibitory activity against the Fusarium head blight disease fungus Fusarium graminearum was isolated and identified. The major inhibitory compound was purified from the culture broth through anion exchange, hydrophobic interaction, and reverse phase high-performance liquid chromatography (RP-HPLC) steps. It was a 1,463-Da lipopeptide and had an amino acid composition consisting of Ala, Glx, Ile, Orn, Pro, Thr, and Tyr at a molar ratio of 1:3:1:1:1:1:2. Electrospray ionization mass spectrometry/mass spectrometry (ESI MS/MS) analyses of the natural and the ring-opened peptides showed the antagonist was fengycin, a kind of macrolactone molecule with antifungal activity produced by several Bacillus strains. Fluorescence microscopic analysis indicated this peptide permeabilized and disrupted F. graminearum hyphae.

Growth of Hierarchical 3D Mesoporous NiSix/NiCo2O4 Core/Shell Heterostructures on Nickel Foam for Lithium‐Ion Batteries

We demonstrate the facile and well-controlled design and fabrication of heterostructured and hierarchical 3D mesoporous NiSix /NiCo2 O4 core/shell nanowire arrays on nickel foam through a facile chemical vapor deposition (CVD) technique combined with a simple but powerful chemical bath deposition (CBD) technique. The smart hybridization of NiCo2 O4 and NiSix nanostructures results in an intriguing mesoporous hierarchical core/shell nanowire-array architecture. The nanowire arrays demonstrate enhanced electrochemical performance as binder- and conductive-agent-free electrodes for lithium ion batteries (LIBs) with excellent capacity retention and high rate capability on cycling. The electrodes can maintain a high reversible capacity of 1693 mA h g(-1) after 50 cycles at 20 mA g(-1) . Given the outstanding performance and simple, efficient, cost-effective fabrication, we believe that these 3D NiSix /NiCo2 O4 core/shell heterostructured arrays have great potential application in high-performance LIBs.

Harnessing the concurrent reaction dynamics in active Si and Ge to achieve high performance lithium-ion batteries

Advanced composite electrodes containing multiple active components are often used in lithium-ion batteries for practical applications. The performance of such heterogeneous composite electrodes can in principle be enhanced by tailoring the concurrent reaction dynamics in multiple active components for promoting their collective beneficial effects. However, the potential of this design principle has remained uncharted to date. Here we develop a composite anode of Cu/Si/Ge nanowire arrays, where each nanowire consists of a core of Cu segments and a Si/Ge bilayer shell. This unique electrode architecture exhibited a markedly improved electrochemical performance over the reference Cu/Si systems, demonstrating a stable capacity retention (81% after 3000 cycles at 2C) and doubled specific capacity at a rate of 16C (1C = 2 A g−1). By using in situ transmission electron microscopy and electrochemical testing, we unravel a novel reaction mechanism of dynamic co-lithiation/co-delithiation in the active Si and Ge bilayer, which is shown to effectively alleviate the electrochemically induced mechanical degradation and thus greatly enhance the long-cycle stability of the electrode. Our findings offer insights into a rational design of high-performance lithium-ion batteries via exploiting the concurrent reaction dynamics in the multiple active components of composite electrodes.

Approaching the ideal elastic strain limit in silicon nanowires

Single-crystalline silicon nanowires can be reversibly stretched above 10% elastic strain at room temperature. Achieving high elasticity for silicon (Si) nanowires, one of the most important and versatile building blocks in nanoelectronics, would enable their application in flexible electronics and bio-nano interfaces. We show that vapor-liquid-solid–grown single-crystalline Si nanowires with diameters of ~100 nm can be repeatedly stretched above 10% elastic strain at room temperature, approaching the theoretical elastic limit of silicon (17 to 20%). A few samples even reached ~16% tensile strain, with estimated fracture stress up to ~20 GPa. The deformations were fully reversible and hysteresis-free under loading-unloading tests with varied strain rates, and the failures still occurred in brittle fracture, with no visible sign of plasticity. The ability to achieve this “deep ultra-strength” for Si nanowires can be attributed mainly to their pristine, defect-scarce, nanosized single-crystalline structure and atomically smooth surfaces. This result indicates that semiconductor nanowires could have ultra-large elasticity with tunable band structures for promising “elastic strain engineering” applications.

3D hierarchically porous zinc–nickel–cobalt oxide nanosheets grown on Ni foam as binder-free electrodes for electrochemical energy storage

Three-dimensional (3D) hierarchically porous transition metal oxides, particularly those involving different metal ions of mixed valence states and constructed from interconnected nano-building blocks directly grown on conductive current collectors, are promising electrode candidates for energy storage devices such as Li-ion batteries (LIBs) and supercapacitors (SCs). This study reports a facile and scalable chemical bath deposition process combined with simple calcination for fabricating 3D hierarchically porous Zn–Ni–Co oxide (ZNCO) nanosheet arrays directly grown on Ni foam with robust adhesion. The resulting nanostructures are then evaluated as a binder-free electrode for LIBs and SCs. Given its unique architecture and compositional advantages, the electrode exhibits a reversible capacity of 1131 mA h g−1 after 50 cycles at a current density of 0.2 A g−1, an excellent long-term cycling stability at a high current density of 1 A g−1 for 1000 cycles, and a desirable rate capability when tested as an anode for LIBs. When used for SCs, the electrode demonstrates a high specific capacitance (1728 F g−1 at 1 A g−1), an outstanding rate capability (72% capacitance retention from 1 A g−1 to 50 A g−1), and an excellent cycling stability (capacitance of 1655 F g−1 after 5000 cycles at a current density of 20 A g−1 with 108.6% retention). Overall, the unique 3D hierarchically porous ZNCO nanosheets hold a great promise for constructing high-performance energy storage devices.

Interfacial nitrogen stabilizes carbon-coated mesoporous silicon particle anodes

We report for the first time that the dehydrogenation process of PAN was suppressed and the silicon oxide of the MSP surface was reduced during annealing in Ar + H2. Consequently, the remaining –NH bonds of the carbon chain can interact with the fresh amorphous Si on the surface of the MSPs to form a Si–N–C layer, which improves the adhesion between Si and C and serves as a stable electrolyte blocking layer. In addition, based on micron-sized MSPs, the structural stability of the electrode is dramatically enhanced through in situ formation of Si nanocrystals of less than 5 nm. The low Li+ diffusion kinetics of the Si–N–C layer and self limiting inhomogeneous lithiation in MSPs jointly create unlithiated Si nanocrystals, acting as supporting frames to prevent pulverization of the anode material. Our nitriding MSP anode has exhibited for the first time a 100% capacity retention (394 mA h g−1) after 2000 cycles (10 cycles each at 0.1, 0.5, 1, 2, and 1 and then 1950 cycles at 0.5 A g−1) and a 100% capacity retention at 0.1 A g−1 (540 mA h g−1) after 400 cycles. Thus, our work proposes a novel avenue to engineer battery materials with large volume changes.

Graphene-Encapsulated Nanosheet-Assembled Zinc–Nickel–Cobalt Oxide Microspheres for Enhanced Lithium Storage

The appropriate combination of hierarchical transition-metal oxide (TMO) micro-/nanostructures constructed from porous nanobuilding blocks with graphene sheets (GNS) in a core/shell geometry is highly desirable for high-performance lithium-ion batteries (LIBs). A facile and scalable process for the fabrication of 3D hierarchical porous zinc-nickel-cobalt oxide (ZNCO) microspheres constructed from porous ultrathin nanosheets encapsulated by GNS to form a core/shell geometry is reported for improved electrochemical performance of the TMOs as an anode in LIBs. By virtue of their intriguing structural features, the produced ZNCO/GNS core/shell hybrids exhibit an outstanding reversible capacity of 1015 mA h g(-1) at 0.1 C after 50 cycles. Even at a high rate of 1 C, a stable capacity as high as 420 mA h g(-1) could be maintained after 900 cycles, which suggested their great potential as efficient electrodes for high-performance LIBs.

Synergistically reinforced lithium storage performance of in situ chemically grown silicon@silicon oxide core–shell nanowires on three-dimensional conductive graphitic scaffolds

The silicon material is the most promising candidate for developing new-generation lithium-ion batteries with high energy and power output. However, there remains a significant challenge due to poor electrical conductivity and pulverization of the silicon based anode during cycles. Aiming to solve these problems, in this work we fabricate a novel 3D composite architecture made of a Si@SiOx core–shell nanowire array grown on a 3D graphitic foam (Si CNW–3D GF) substrate by a well-designed multiple-step approach. The prepared Si CNW–3D GF composite shows the integrated advantages for high-performance lithium ion batteries, including its light weight, open macroporosity, high conductivity, high Si NW loading, excellent flexibility as well as SiOx buffer layers. As a result, the Si CNW–3D GF composite exhibits excellent performance such as high reversible lithium storage capacity (3603 mA h g−1 at a current density of 840 mA g−1), excellent cycling performance (up to 100 cycles) and superior rate capability (2299 mA h g−1 at 4200 mA g−1 and 1206 mA h g−1 at 8400 mA g−1), which is 2 times that of the Si CNW electrode where Si CNWs were grown directly on a stainless steel current collector without the presence of 3D GF.

Carbon-coated Si micrometer particles binding to reduced graphene oxide for a stable high-capacity lithium-ion battery anode

Micrometer Si (MSi) particles are an attractive alternative as high energy-density lithium-ion battery anodes. To maintain the structural integrity and resolve the electrical conduction problem of MSi-based anodes, we propose novel MSi/C/reduced graphene oxide (RGO) through simple ball milling liquid polyacrylonitrile (PAN) with MSi and graphene oxide nanosheets, followed by thermal reduction. This structure capitalizes on the interaction of MSi and carbonized PAN with RGO sheets to provide a robust microarchitecture. The mechanical integrity of the in situ formed porous configuration can be dramatically improved by manipulating the size of unreacted Si nanocrystals. In addition, the Si–N–C layer serves as an electrolyte blocking layer, which helps to build a stable SEI layer and results in a high initial coulombic efficiency of 91.7%. Furthermore, the RGO binding to MSi/C acts as a flexible buffer during galvanostatic cycling, allowing microparticles to expand and fractured nanoparticles to anchor, while retaining electrical connectivity at both the particle and electrode levels. As a result, this hierarchical structure exhibits a superior reversible capacity of 1572 mA h g−1 with no capacity loss for 160 cycles at 0.2 A g−1 and over 628 mA h g−1 for 1000 cycles at 2 A g−1.