Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 23
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nanoscale ; 12(7): 4320-4327, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-32043511

RESUMO

Non-uniformity of switching parameters, e.g., switching voltage and resistances of the high resistance state and low resistance state, could obstruct the practical application of electrochemical metallization cells. Higher switching voltages are also undesirable in terms of power consumption. The non-uniformity is usually related to the number of conductive filaments (CFs) and their degree of dissolution during the RESET process. The number of CFs can be ideally reduced to one by decreasing the device area. However, the degree and location of the dissolution of CFs are difficult to control. Here, we introduce a SiO2/Ta2O5 heterojunction to control the dissolution of CFs, in which the growth direction and the shape of CFs are controlled by the SiO2 layer, while the dissolution of CFs is controlled in the ultrathin Ta2O5 layer. Transmission electron microscopy analysis clearly suggested that the formation/dissolution of CFs occurs in the ultrathin Ta2O5 layer, resulting in low voltage operation (<0.3 V) with high stability and uniformity (Vset distributes in the range smaller than 0.1 V and Vreset distributes in the range smaller than 0.08 V).

2.
Small ; 15(40): e1902363, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31419025

RESUMO

Lithium-sulfur batteries (LSBs) have shown great potential for application in high-density energy storage systems. However, the performance of LSBs is hindered by the shuttle effect and sluggish reaction kinetics of lithium polysulfides (LiPSs). Herein, heterostructual Nb2 O5 nanocrystals/reduced graphene oxide (Nb2 O5 /RGO) composites are introduced into LSBs through separator modification for boosting the electrochemical performance. The Nb2 O5 /RGO heterostructures are designed as chemical trappers and conversion accelerators of LiPSs. Originating from the strong chemical interactions between Nb2 O5 and LiPSs as well as the superior catalytic nature of Nb2 O5 , the Nb2 O5 /RGO nanocomposite possesses high trapping efficiency and efficient electrocatalytic activity to long-chain LiPSs. The effective regulation of LiPSs conversion enables the LSBs enhanced redox kinetics and suppressed shuttle effect. Moreover, the Nb2 O5 /RGO nanocomposite has abundant sulfophilic sites and defective interfaces, which are beneficial for the nucleation and growth of Li2 S, as evidenced by analysis of the cycled separators. As a result, LSBs with the Nb2 O5 /RGO-modified separators exhibit excellent rate capability (816 mAh g-1 at 3 A g-1 ) and cyclic performance (628 mAh g-1 after 500 cycles). Remarkably, high specific capacity and stable cycling performance are demonstrated even at an elevated temperature of 50 °C or with higher sulfur loadings.

3.
Nanoscale Res Lett ; 13(1): 236, 2018 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-30112714

RESUMO

In this paper, we introduce hemiellipsoid- and inverted hemiellipsoid-modified semiconductor nanowire (NW) optical structures, and present a systematic investigation on light management of the corresponding arrays based on GaAs. It is found that the modification makes well utilization of light scattering and antireflection, thus leading to excellent light confinement with limited effective thickness. For example, 90% and 95% of the incident photons with the energy larger than the bandgap energy can be trapped by the inverted hemiellipsoid-modified NW arrays with the effective thicknesses of only ~ 180 and 270 nm, respectively. Moreover, excellent light confinement can be achieved in a broad range of the modification height. Compared to the corresponding array without top modification, spatial distribution of the photo-generated carriers is expanded, facilitating carrier collection especially for the planar pn junction configuration. Further investigation indicates that these composite nanostructures possess excellent omnidirectional light confinement, which is expected for advanced solar absorbers.

4.
Dalton Trans ; 47(33): 11503-11511, 2018 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-30074035

RESUMO

Owing to a lack of electroactive sites and poor conductivity, Co oxides/hydroxides nanosheet network electrodes usually show low experimental capacity, hardly meeting the demand for high energy density needed for an asymmetric supercapacitor. Herein, we demonstrate a surface capacity enhancement of a 3D cobalt oxides/hydroxides nanosheet network cathode through a simple cyclic voltammetry electro-deposition method. By optimizing the electro-deposition parameters, the as-prepared Co oxides/hydroxides nanosheet network electrode delivers a significantly high capacity of 427 C g-1 at the current density of 1 A g-1 and excellent rate ability of 79.8% at the current density of 10 A g-1, as well as outstanding cycling life. A detailed voltammetric analysis using the power-law relationship and Trasatti's method shows that both the large surface area, high pore volume and polycrystalline nature contribute to the enhancement of the surface capacity. In addition, the assembled asymmetric all-solid-state supercapacitor also presents a volume energy density of 2.78 mW h cm-3 at a power density of 14 mW cm-3 and excellent cycling stability. In addition, our prepared asymmetric supercapacitor shows super flexibility and was used to light up a heart-shaped logo. This work may provide valuable insights into the design and fabrication of electrode materials with improved capacity and rate ability.

5.
Small ; : e1801836, 2018 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-29971944

RESUMO

Dual carbon-based potassium dual ion batteries (K-DCBs) have recently attracted ever-increasing attention owing to the potential advantages of high performance-to-cost ratio, good safety, and environmental friendliness. However, the reported K-DCBs still cannot simultaneously meet the requirements of high capacity, long cycling stability, and low cost, which are necessary for practical applications. In this study, a K-DCB with good comprehensive performance including capacity, cycling stability, medium discharge voltage, and energy density is developed by introducing the optimal cathode and anode materials, i.e., KS6 and natural graphite, respectively. An initial capacity of ≈54.6 mAh g-1 and 92.5% capacity retention after 400 cycles can be delivered in a wide voltage window of 2.4-5.4 V at the current density of 100 mA g-1 . A high medium discharge voltage around 4.2 V and an energy density up to 158.3 Wh kg-1 are meanwhile delivered by the K-DCB. In addition, the working mechanism of the devices is understood in detail. It is believed that valuable contributions to the electrochemical performance improvement of the related devices toward practical applications can be provided by this study.

6.
Small ; 13(45)2017 12.
Artigo em Inglês | MEDLINE | ID: mdl-29024532

RESUMO

To satisfy the increasing energy demands of portable electronics, electric vehicles, and miniaturized energy storage devices, improvements to lithium-ion batteries (LIBs) are required to provide higher energy/power densities and longer cycle lives. Group IVA element (Si, Ge, Sn)-based alloying/dealloying anodes are promising candidates for use as electrodes in next-generation LIBs owing to their extremely high gravimetric and volumetric capacities, low working voltages, and natural abundances. However, due to the violent volume changes that occur during lithium-ion insertion/extraction and the formation of an unstable solid electrolyte interface, the use of Group IVA element-based anodes in commercial LIBs is still a great challenge. Evaluating the electrochemical performance of an anode in a full-cell configuration is a key step in investigating the possible application of the active material in LIBs. In this regard, the recent progress and important approaches to overcoming and alleviating the drawbacks of Group IVA element-based anode materials are reviewed, such as the severe volume variations during cycling and the relatively brittle electrode/electrolyte interface in full-cell LIBs. Finally, perspectives and future challenges in achieving the practical application of Group IVA element-based anodes in high-energy and high-power-density LIB systems are proposed.

7.
Opt Lett ; 42(19): 3928-3931, 2017 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-28957163

RESUMO

In this Letter, a light management structure composed of wedge-shaped semiconductor nanowall arrays is introduced. Theoretical investigation based on gallium arsenide (GaAs) indicates that a 1000 nm high array (wall base width/array periodicity: 500 nm) with an effective thickness of only 500 nm can deliver a maximum photocurrent density (Jph) of ∼29.0 mA/cm2 at AM1.5G illumination. (For an ideal absorber with the same bandgap, the corresponding value is ∼32.0 mA/cm2.) However, Jph of a 1500 nm thick flat GaAs film is only ∼19.2 mA/cm2 at the same illumination condition. The wedge-shaped nanowall arrays meanwhile exhibit good omnidirectional light confinement. At the incident angle of 60°, Jph of the aforementioned nanowall array is ∼12.7 mA/cm2, and the corresponding value for an ideal absorber is ∼16.0 mA/cm2. Considering the simple structure and excellent light confinement in a broad range of the system parameters, including array periodicity, the nanowall height, and the incident angle of light, the wedge-shaped semiconductor nanowall arrays provide a valuable platform for fabricating the related high performance-to-cost semiconductor optoelectronic devices.

8.
Sci Rep ; 7(1): 822, 2017 04 11.
Artigo em Inglês | MEDLINE | ID: mdl-28400573

RESUMO

A time-decay resistive switching memory using a 3D vertical Pt/Ta2O5-x/W device architecture is demonstrated, in which horizontal W electrodes were fabricated, and vertical Pt electrodes was formed at the sidewall after oxide was deposited. Unlike conventional resistive switching, which usually form a conductive filament connect two electrodes, a weak conductive filament was formed from bottom electrode W to near top electrode Pt. The memory can be recovered with a time scale when the electrical stimulation is removed. However, different decay behaviors were observed in one decay curve, including rapid decay and slow decay processes. This can be a good simulation of different stages of forgetting. By a combination of the current decay fitting and the conductive analysis, the rapid decay and slow decay processes correspond to ion diffusion and electron detrapping, respectively.

9.
Beilstein J Nanotechnol ; 8: 222-228, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28243560

RESUMO

Heavy-phosphorus-doped silicon anodes were fabricated on CuO nanorods for application in high power lithium-ion batteries. Since the conductivity of lithiated CuO is significantly better than that of CuO, after the first discharge, the voltage cut-off window was then set to the range covering only the discharge-charge range of Si. Thus, the CuO core was in situ lithiated and acts merely as the electronic conductor in the following cycles. The Si anode presented herein exhibited a capacity of 990 mAh/g at the rate of 9 A/g after 100 cycles. The anode also presented a stable rate performance even at a current density as high as 20 A/g.

10.
Nanomicro Lett ; 9(4): 38, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-30393733

RESUMO

In this study, the effect of reduced graphene oxide (rGO) on interconnected Co3O4 nanosheets and the improved supercapacitive behaviors is reported. By optimizing the experimental parameters, we achieved a specific capacitance of ~1016.4 F g-1 for the Co3O4/rGO/NF (nickel foam) system at a current density of 1 A g-1. However, the Co3O4/NF structure without rGO only delivers a specific capacitance of ~520.0 F g-1 at the same current density. The stability test demonstrates that Co3O4/rGO/NF retains ~95.5% of the initial capacitance value even after 3000 charge-discharge cycles at a high current density of 7 A g-1. Further investigation reveals that capacitance improvement for the Co3O4/rGO/NF structure is mainly because of a higher specific surface area (~87.8 m2 g-1) and a more optimal mesoporous size (4-15 nm) compared to the corresponding values of 67.1 m2 g-1 and 6-25 nm, respectively, for the Co3O4/NF structure. rGO and the thinner Co3O4 nanosheets benefit from the strain relaxation during the charge and discharge processes, improving the cycling stability of Co3O4/rGO/NF.

11.
Beilstein J Nanotechnol ; 7: 1289-1295, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27826503

RESUMO

A novel network of spindle-like carbon nanofibers was fabricated via a simplified synthesis involving electrospinning followed by preoxidation in air and postcarbonization in Ar. Not only was the as-obtained carbon network comprised of beads of spindle-like nanofibers but the cubic MnO phase and N elements were successfully anchored into the amorphous carbon matrix. When directly used as a binder-free anode for lithium-ion batteries, the network showed excellent electrochemical performance with high capacity, good rate capacity and reliable cycling stability. Under a current density of 0.2 A g-1, it delivered a high reversible capacity of 875.5 mAh g-1 after 200 cycles and 1005.5 mAh g-1 after 250 cycles with a significant coulombic efficiency of 99.5%.

12.
ACS Nano ; 9(2): 1858-67, 2015 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-25629917

RESUMO

Germanium is a highly promising anode material for lithium-ion batteries as a consequence of its large theoretical specific capacity, good electrical conductivity, and fast lithium ion diffusivity. In this work, Co3O4 nanowire array fabricated on nickel foam was designed as a nanostructured current collector for Ge anode. By limiting the voltage cutoff window in an appropriate range, the obtained Ge anode exhibits excellent lithium storage performance in half- and full-cells, which can be mainly attributed to the designed nanostructured current collector with good conductivity, enough buffering space for the volume change, and shortened ionic transport length. More importantly, the assembled Ge/LiCoO2 full-cell shows a high energy density of 475 Wh/kg and a high power density of 6587 W/kg. A high capacity of 1184 mA h g(-1) for Ge anode was maintained at a current density of 5000 mA g(-1) after 150 cycles.

13.
ACS Appl Mater Interfaces ; 6(22): 20334-9, 2014 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-25379677

RESUMO

N-doped amorphous carbon coated Fe3O4/SnO2 coaxial nanofibers were prepared via a facile approach. The core composite nanofibers were first made by electrospinning technology, then the shells were conformally coated using the chemical bath deposition and subsequent carbonization with polydopamine as a carbon source. When applied as a binder-free self-supported anode for lithium ion batteries, the coaxial nanofibers displayed an enhanced electrochemical storage capacity and excellent rate performance. The morphology of the interwoven nanofibers was maintained even after the rate cycle test. The superior electrochemical performance originates in the structural stability of the N-doped amorphous carbon shells formed by carbonizing polydopamine.

14.
Chem Commun (Camb) ; 50(66): 9361-4, 2014 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-25005328

RESUMO

A Ni3S2 nanotube array has been synthesized on Ni foam using a template-free hydrothermal method. The Ni foam acts as both the reactant and support. The resulting architecture as an electrode for lithium ion batteries benefits from the unique morphology and exhibits excellent electrochemical performance with high capacity, long cycle life and superior rate capability.

16.
ACS Appl Mater Interfaces ; 6(1): 648-54, 2014 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-24320600

RESUMO

Carbon-wrapped Fe3O4 nanoparticle films on nickel foam were simply prepared by a hydrothermal synthesis with sucrose as a precursor of subsequent carbonization. The as-prepared samples were directly used as binder-free anodes for lithium-ion batteries which exhibited enhanced rate performance and excellent cyclability. A reversible capacity of 543 mA h g(-1) was delivered at a current density as high as 10 C after more than 2000 cycles. The superior electrochemical performance can be attributed to the formation of a thin carbon layer which constructs a 3D network structure enwrapping the nanosized Fe3O4 particles. Such an architecture can facilitate the electron transfer and accommodate the volume change of the active materials during discharge/charge cycling.

17.
Phys Chem Chem Phys ; 15(24): 9924-30, 2013 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-23673428

RESUMO

We report a facile and reproducible synthesis of nanostructured Ni3S2 films by a hydrothermal route with Ni foam as the precursor reactant and substrate. The synthetic mechanism was examined by investigating the dependence of the films' crystal morphologies on the hydrothermal duration, and uniform nanostructured Ni3S2 films with a porous carpet-like morphology were synthesized on the substrates. The architectures were used as cathodes for lithium ion batteries (LIBs), and their electrochemical performances were evaluated as a function of the film thickness. The first discharge and charge capacities were 596 and 466 mA h g(-1) for the electrode with an optimal film thickness and a higher reversible capacity of 421 mA h g(-1) was obtained after 60 cycles at a current density of 50 mA g(-1). The simplicity of the synthetic methodology and the better electrochemical performance make the synthesized Ni3S2 films a promising cathode material for next-generation LIBs.

18.
Nanoscale ; 5(7): 3037-42, 2013 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-23462740

RESUMO

Porous NiO-ZnO hybrid nanofibers were prepared by a single-nozzle electrospinning technique combined with subsequent heating treatment. The resultant nanofibers are composed of interconnected primary nanocrystals and numerous nanopores with heterostructures between NiO and ZnO. Such characteristics of the structure can lead to excellent electrochemical performances when the nanofiber was evaluated as an anode material for lithium-ion batteries. The porous NiO-ZnO nanofiber electrode delivers a high discharge capacity of 949 mA h g(-1) after 120 cycles at 0.2 A g(-1), and maintains around 707 mA h g(-1) at a current density as high as 3.2 A g(-1). Even after cycling at high rates, the electrode still retains a high discharge capacity of up to 1185 mA h g(-1) at 0.2 A g(-1).

19.
Nanoscale ; 5(5): 1917-21, 2013 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-23354412

RESUMO

Three-dimensional (3D) nanoporous architectures can provide efficient and rapid pathways for Li-ion and electron transport as well as short solid-state diffusion lengths in lithium ion batteries (LIBs). In this work, 3D nanoporous copper-supported cuprous oxide was successfully fabricated by low-cost selective etching of an electron-beam melted Cu(50)Al(50) alloy and subsequent in situ thermal oxidation. The architecture was used as an anode in lithium ion batteries. In the first cycle, the sample delivered an extremely high lithium storage capacity of about 2.35 mA h cm(-2). A high reversible capacity of 1.45 mA h cm(-2) was achieved after 120 cycles. This work develops a promising approach to building reliable 3D nanostructured electrodes for high-performance lithium ion batteries.


Assuntos
Cobre/química , Fontes de Energia Elétrica , Lítio/química , Nanoporos/ultraestrutura , Técnicas Eletroquímicas , Eletrodos , Íons/química , Oxirredução , Temperatura
20.
J Colloid Interface Sci ; 354(1): 76-81, 2011 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-21084095

RESUMO

A simple method was developed to prepare highly water-soluble nanocrystal powders of magnetic iron oxides with different oxidation degree from magnetite (Fe(3)O(4)) to maghemite (γ-Fe(2)O(3)) coated with gluconic acid (GLA). X-ray diffraction and transmission electron microscopy measurements show that the products have a narrow size distribution, and the cores are inverse spinel iron oxides and completely crystallized. Vibrating sample magnetometry measurements reveal that all the samples exhibit superparamagnetic behavior at room temperature. Fourier transform infrared (FTIR) and Raman spectra were used to identify the products. It is shown that GLA molecules are immobilized on the nanoparticle surface by chemical bonding and the carboxyl is asymmetrically bound to the surface iron atom, and the vacancies in the γ-Fe(2)O(3) cores are disordered. Compared with FTIR, Raman spectrum analysis is a rapid, simple, and accurate method for identifying inverse spinel iron oxides. The chemical stability and the high solubility of the products are explained in terms of the proposed coordination modes of the surface iron atom with GLA.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA