Enhancing the Lithium Storage Performance of the Nb2O5 Anode via Synergistic Engineering of Phase and Cu Doping.

Nb2O5 has been viewed as a promising anode material for lithium-ion batteries by virtue of its appropriate redox potential and high theoretical capacity. However, it suffers from poor electric conductivity and low ion diffusivity. Herein, we demonstrate the controllable fabrication of Cu-doped Nb2O5 with orthorhombic (T-Nb2O5) and monoclinic (H-Nb2O5) phases through annealing the solvothermally presynthesized Nb2O5 precursor under different temperatures in air, and the Cu doping amount can be readily controlled by the concentration of the precursor solution, whose effect on the lithium storage behaviors of the Cu-doped Nb2O5 is thoroughly investigated. H-Nb2O5 shows obvious redox peaks (Nb5+/Nb4+ and Nb4+/Nb3+) with much higher capacity and better cycling stability than those for the widely investigated T-Nb2O5. When introducing appropriate Cu doping, the optimized H-Cu0.1-Nb2O5 electrode shows greatly enhanced conductivity and lower diffusion barrier as revealed by the theoretical calculations and electrochemical characterizations, delivering a high reversible capacity of 203.6 mAh g-1 and a high capacity retention of 140.8 mAh g-1 after 5000 cycles at 1 A g-1, with a high initial Coulombic efficiency of 91% and a high rate capacity of 144.2 mAh g-1 at 4 A g-1. As a demonstration for full-cell application, the H-Cu0.1-Nb2O5||LiFePO4 cell displays good cycling performance, exhibiting a reversible capacity of 135 mAh g-1 after 200 cycles at 0.2 A g-1. More importantly, this work offers a new synthesis protocol of the monoclinic Nb2O5 phase with high capacity retention and improved reaction kinetics.

Vapor-phase derived ultra-fine Bismuth nanoparticles embedded in carbon nanotube networks as anodes for sodium and potassium ion batteries.

Bismuth (Bi) is a promising material as the anode for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to its characteristics such as reasonable price and high theoretical volumetric capacity (3800 mAh cm-3). Nevertheless, considerable drawbacks have hindered the practical applications of Bi, including its relatively low electrical conductivity and inevitable volumetric change during the alloying/dealloying processes. To solve these problems, we proposed a novel design:Bi nanoparticles were synthesized via a single-step low-pressure vapor-phase reaction and embedded onto the surfaces of multi-walled carbon nanotubes (MWCNTs). After being vaporized at 650℃ and 10-5 Pa, Bi nanoparticles less than 10 nm were uniformly distributed in the three-dimensional (3D) MWCNT networks to form a Bi/MWNTs composite. In this unique design, the nanostructured Bi can reduce the risk of structural rupture during cycling, and the structure of the MWCMT network is beneficial in shortening the electron/ion transport path. In addition, MWCNTs can improve the overall conductivity of the Bi/MWCNTs composite and prevent particle aggregation, thus improving the cycling stability and rate performance. As an anode material for SIB, the Bi/MWCNTs composite has demonstrated excellent fast charging performance with a reversible capacity of 254 mAh/g at 20 A/g. A capacity of 221mAhg-1 after cycling at 10 A/g for 8000 cycles has also been achieved for SIB. As an anode material for PIB, the Bi/MWCNTs composite has delivered excellent rate performances with a reversible capacity of 251 mAh/g at 20 A/g. A specific capacity of 270mAhg-1 after cycling at 1Ag-1 for 5000 cycles has also been achieved for PIB.

Ultrahigh Temperature Lead-Free Film Capacitors via Strain and Dielectric Constant Double Gradient Design.

With the development of miniaturization, lightweight and integration of electronic devices, the demand for high-temperature dielectric capacitors is becoming urgent. Nevertheless, the breakdown strength and polarization are deteriorated at high temperatures due to the thermal energy assisting the electron transport and impeding the dipole alignment. Here, a structure of capacitor with double gradients of dielectric constant gradient and strain gradient is designed to achieve high breakdown strength, high working temperature, and high energy storage density simultaneously. It is found that the designed structure of BaHf0.17 Ti0.83 O3 /1mol% SiO2 doped BaZr0.35 Ti0.65 O3 /0.85BaTiO3 -0.15Bi(Mg0.5 Zr0.5 )O3 exhibits excellent energy storage performance. The energy storage density of 127.3 J cm-3 with an energy storage efficiency of 79.6% is realized in the up-sequence multilayer with period N = 2 at room temperature. Moreover, when the working temperature varies from -100 to 200 °C, the energy storage density of the N = 4 capacitor keeps stably at 84.62 J cm-3 with an energy storage efficiency 78.42% at 6.86 MV cm-1 . All these properties promise great potential applications of the designed multilayer capacitors with the double gradients in harsh environments, and the design principle can be applicable to other systems to boost working temperature.

Preparation of Few-Layer Porous Graphene by a Soft Mechanical Method with a Short Rolling Transfer Process.

Few-layer porous graphene is a promising material for a variety of fields. However, the synthesis of few-layer porous graphene is a great challenge. Here we report a feasible green path to produce few-layer porous graphene, which was exfoliated from high-pressure graphite balls onto microspheres with rough surfaces by a mild rolling transfer process. Ordinary ball milling equipment was adopted for the low-speed (100 rpm) ball-microsphere rolling transfer process. The rolling time (<10 min) was controlled to obtain porous graphene instead of graphene. The porous graphene on the exfoliating microspheres was then easily dispersed in solution by bath sonication. The product contains very few impure functional groups. The hole size and layer distribution of the few-layer porous graphene have been demonstrated to be 2.37±1.17 nm and 2.4±0.7 layers, respectively, and can be adjusted by redesigning the surface of the microspheres.

Regulating Surface and Grain-Boundary Structures of Ni-Rich Layered Cathodes for Ultrahigh Cycle Stability.

The wide applications of Ni-rich LiNi1- x-y Cox Mny O2 cathodes are severely limited by capacity fading and voltage fading during the cycling process resulting from the pulverization of particles, interfacial side reactions, and phase transformation. The canonical surface modification approach can improve the stability to a certain extent; however, it fails to resolve the key bottlenecks. The preparation of Li(Ni0.4 Co0.2 Mn0.4 )1- x Tix O2 on the surface of LiNi0.8 Co0.1 Mn0.1 O2 particles with a coprecipitation method is reported. After sintering, Ti diffuses into the interior and mainly distributes along surface and grain boundaries. A strong surface and grain boundary strengthening are simultaneously achieved. The pristine particles are fully pulverized into first particles due to mechanical instability and high strains, which results in serious capacity fading. In contrast, the strong surface and the grain boundary strengthening can maintain the structural integrity, and therefore significantly improve the cycle stability. A general and simple strategy for the design of high-performance Ni-rich LiNi1- x - y Cox Mny O2 cathode is provided and is applicable to surface modification and grain-boundary regulation of other advanced cathodes for batteries.

Changing the Phosphorus Allotrope from a Square Columnar Structure to a Planar Zigzag Nanoribbon by Increasing the Diameter of Carbon Nanotube Nanoreactors.

Elemental phosphorus nanostructures are notorious for a large number of allotropes, which limits their usefulness as semiconductors. To limit this structural diversity, we synthesize selectively quasi-1D phosphorus nanostructures inside carbon nanotubes (CNTs) that act both as stable templates and nanoreactors. Whereas zigzag phosphorus nanoribbons form preferably in CNTs with an inner diameter exceeding 1.4 nm, a previously unknown square columnar structure of phosphorus is observed to form inside narrower nanotubes. Our findings are supported by electron microscopy and Raman spectroscopy observations as well as ab initio density functional theory calculations. Our computational results suggest that square columnar structures form preferably in CNTs with an inner diameter around 1.0 nm, whereas black phosphorus nanoribbons form preferably inside CNTs with a 4.1 nm inner diameter, with zigzag nanoribbons energetically favored over armchair nanoribbons. Our theoretical predictions agree with the experimental findings.

Mesoporous gold nanoparticles for photothermal controlled anticancer drug delivery.

Aim: To realize the transit and release of cancer drug exactly as well as high drug loading ratio, we reported a biocompatible and temperature responsive controlled drug delivery system based on 3D mesoporous structured Au networks. Materials & methods: Here, we filled the hollow interiors of Au networks with a phase-change material so that the drug release was easily regulated by controlling the temperature only. Results: Thanks to the high near-infrared reflectance absorbance and mesoporous structure, the Au-PEG + lauric acid/doxorubicin system showed a strong photothermal conversion efficiency, high drug-loading ratio (54.2% for doxorubicin) and controlled drug release. Conclusion: This system revealed great advantages in photothermal therapy and chemotherapy, offering an obvious synergistic effect in cancer treatment.

A general soft-enveloping strategy in the templating synthesis of mesoporous metal nanostructures.

Metal species have a relatively high mobility inside mesoporous silica; thus, it is difficult to introduce the metal precursors into silica mesopores and suppress the migration of metal species during a reduction process. Therefore, until now, the controlled growth of metal nanocrystals in a confined space, i.e., mesoporous channels, has been very challenging. Here, by using a soft-enveloping reaction at the interfaces of the solid, liquid, and solution phases, we successfully control the growth of metallic nanocrystals inside a mesoporous silica template. Diverse monodispersed nanostructures with well-defined sizes and shapes, including Ag nanowires, 3D mesoporous Au, AuAg alloys, Pt networks, and Au nanoparticle superlattices are successfully obtained. The 3D mesoporous AuAg networks exhibit enhanced catalytic activities in an electrochemical methanol oxidation reaction. The current soft-enveloping synthetic strategy offers a robust approach to synthesize diverse mesoporous metal nanostructures that can be utilized in catalysis, optics, and biomedicine applications.

In Situ Probing of the Particle-Mediated Mechanism of WO3 -Networked Structures Grown inside Confined Mesoporous Channels.

Nanocasting, using ordered mesoporous silica or carbon as a hard template, has enormous potential for preparing novel mesoporous materials with new structures and compositions. Although a variety of mesoporous materials have been synthesized in recent years, the growth mechanism of nanostructures in a confined space, such as mesoporous channels, is not well understood, which hampers the controlled synthesis and further application of mesoporous materials. Here, the nucleation and growth of WO3 -networked mesostructures within an ordered mesoporous matrix, using an in situ transmission electron microscopy heating technique and in situ synchrotron small-angle X-ray scattering spectroscopy, are probed. It is found that the formation of WO3 mesostructures involves a particle-mediated transformation and coalescence mechanism. The liquid-like particle-mediated aggregation and mesoscale transformation process can occur in ≈10 nm confined mesoporous channels, which is completely unexpected. The detailed mechanistic study will be of great help for experimental design and to exploit a variety of mesoporous materials for diverse applications, such as catalysis, absorption, separation, energy storage, biomedicine, and nanooptics.

Pseudo-topotactic conversion of carbon nanotubes to T-carbon nanowires under picosecond laser irradiation in methanol.

Pseudo-topotactic conversion of carbon nanotubes into one-dimensional carbon nanowires is a challenging but feasible path to obtain desired diameters and morphologies. Here, a previously predicted but experimentally unobserved carbon allotrope, T-carbon, has been produced from pseudo-topotactic conversion of a multi-walled carbon nanotube suspension in methanol by picosecond pulsed-laser irradiation. The as-grown T-carbon nanowires have the same diameter distribution as pristine carbon nanotubes, and have been characterized by high-resolution transmission electron microscopy, fast Fourier transform, electron energy loss, ultraviolet-visible, and photoluminescence spectroscopies to possess a diamond-like lattice, where each carbon is replaced by a carbon tetrahedron, and a lattice constant of 7.80 Å. The change in entropy from carbon nanotubes to T-carbon reveals the phase transformation to be first order in nature. The computed electronic band structures and projected density of states are in good agreement with the optical absorption and photoluminescence spectra of the T-carbon nanowires.T-carbon is a previously predicted but so far unobserved allotrope of carbon, with a crystal structure similar to diamond, but with each atomic lattice position replaced by a carbon tetrahedron. Here, the authors produce T-carbon nanowires via laser-irradiating a suspension of carbon nanotubes in methanol.

Assembly of Ring-Shaped Phosphorus within Carbon Nanotube Nanoreactors.

A phosphorus allotrope that has not been observed so far, ring-shaped phosphorus consisting of alternate P8 and P2 structural units, has been assembled inside multi-walled carbon nanotube nanoreactors with inner diameters of 5-8 nm by a chemical vapor transport and reaction of red phosphorus at 500 °C. The ring-shaped nanostructures with surrounding graphene walls are stable under ambient conditions. The nanostructures were characterized by high-resolution transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy.

Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction.

The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium:tungsten=1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are ~1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.

The Faraday rotation angle of Ni nanowire arrays: its dependence on photon energy and nanowire size.

The magneto-optical properties of Ni nanowire arrays embedded in anodic aluminum oxide templates are studied, for a selection of photon energies, as a function of their diameter and length for the first time. This was achieved by the determination of Stokes parameters of the transmitted light. The magneto-optical response is found to differ considerably from that of the bulk material. At all photon energies studied, a linear association of the Faraday rotation angle with nanowire length has been observed; moreover, a proportional relationship between rotation angle per unit length and nanowire diameter has also been also observed, consistent with our earlier work on Fe and Co nanowires. The relationship between the Faraday rotation angle per unit length with different nanowire diameters and photon energy has been found to exhibit clear spectroscopic structure.