7 research outputs found
Copper-Nanoparticle-Induced Porous Si/Cu Composite Films as an Anode for Lithium Ion Batteries
āWelcome-matā-like
porous Si/Cu composite amorphous films are fabricated by applying
the predeposited Cu-nanoparticle-assembled film as the growth direction
template for the subsequent deposition of a Si active layer with the
cluster beam deposition technique. When used as the binder-free anodes
for lithium ion batteries, the acquired single-layer porous Si/Cu
composite film exhibits a large reversible capacity of 3124 mA h g<sup>ā1</sup> after 1000 cycles at 1 A g<sup>ā1</sup>. Even
when cycled at 20 A g<sup>ā1</sup> for 450 cycles, the porous
Si/Cu composite film still delivers a decent reversible capacity of
2086 mA h g<sup>ā1</sup>. Also, multilayer porous Si/Cu composite
films are synthesized through layer-by-layer sputtering and exhibit
outstanding cyclability and relatively high specific capacity and
initial Coulombic efficiency irrespective of increasing the layer
number from two to four layers. The reasons for the excellent electrochemical
properties of single-layer and multilayer porous Si/Cu composite films
are discussed in detail
Electrostatic Assembly of Sandwich-like Ag-C@ZnO-C@AgāC Hybrid Hollow Microspheres with Excellent High-Rate Lithium Storage Properties
Herein,
we introduce a facile electrostatic attraction approach to produce
zincāsilver
citrate hollow microspheres, followed by thermal heating treatment
in argon to ingeniously synthesize sandwich-like Ag-C@ZnO-C@Ag-C hybrid
hollow microspheres. The 3D carbon conductive framework in the hybrids
derives from the <i>in situ</i> carbonation of carboxylate
acid groups in zincāsilver citrate hollow microspheres during
heating treatment, and the continuous and homogeneous Ag nanoparticles
on the outer and inner surfaces of hybrid hollow microspheres endow
the shells with the sandwiched configuration (Ag-C@ZnO-C@Ag-C). When
applied as the anode materials for lithium ion batteries, the fabricated
hybrid hollow microspheres with sandwich-like shells reveal a very
large reversible capacity of 1670 mAh g<sup>ā1</sup> after
200 cycles at a current density of 0.2 A g<sup>ā1</sup>. Even
at the very large current densities of 1.6 and 10.0 A g<sup>ā1</sup>, the high specific capacities of about 1063 and 526 mAh g<sup>ā1</sup> can be retained, respectively. The greatly enhanced electrochemical
properties of Ag-C@ZnO-C@Ag-C hybrid microspheres are attributed to
their special structural features such as the hollow structures, the
sandwich-like shells, and the nanometer-sized building blocks
Template-Free Synthesis of Amorphous Double-Shelled ZincāCobalt Citrate Hollow Microspheres and Their Transformation to Crystalline ZnCo<sub>2</sub>O<sub>4</sub> Microspheres
A novel and facile approach was developed
for the fabrication of amorphous double-shelled zincācobalt
citrate hollow microspheres and crystalline double-shelled ZnCo<sub>2</sub>O<sub>4</sub> hollow microspheres. In this approach, amorphous
double-shelled zincācobalt citrate hollow microspheres were
prepared through a simple route and with an aging process at 70 Ā°C.
The combining inward and outward Ostwald ripening processes are adopted
to account for the formation of these double-shelled architectures.
The double-shelled ZnCo<sub>2</sub>O<sub>4</sub> hollow microspheres
can be prepared via the perfect morphology inheritance of the double-shelled
zincācobalt citrate hollow microspheres, by calcination at
500 Ā°C for 2 h. The resultant double-shelled ZnCo<sub>2</sub>O<sub>4</sub> hollow microspheres manifest a large reversible capacity,
superior cycling stability, and good rate capability
Shape-Selective Formation of Monodisperse Copper Nanospheres and Nanocubes via Disproportionation Reaction Route and Their Optical Properties
Synthesis
of stable and monodisperse Cu nanocrystals of controlled
morphology has been a long-standing challenge. In this Article, we
report a facile disproportionation reaction approach for the synthesis
of such nanocrystals in organic solvents. Either spherical or cubic
shapes can be produced, depending on conditions. The typical Cu nanospheres
are single crystals with a size of 23.4 Ā± 1.5 nm, and can self-assemble
into three-dimensional (3D) nanocrystal superlattices with a large
scale. By manipulating the chemical additives, monodisperse Cu nanocubes
with tailorable sizes have also been obtained. The probable formation
mechanism of these Cu nanocrystals is discussed. The narrow size distribution
results in strong surface plasmon resonance (SPR) peaks even though
the resonance is located in the interband transition region. Double
SPR peaks are observed in the extinction spectra for the Cu nanocubes
with relative large sizes. Theoretical simulation of the extinction
spectra indicates that the SPR band located at longer wavelengths
is caused by assembly of Cu nanocubes into more complex structures.
The synthesis procedure that we report here is expected to foster
systematic investigations on the physical properties and self-assembly
of Cu nanocrystals with shape and size singularity for their potential
applications in photonic and nanoelectronic devices
Enhanced Microwave Absorption Properties by Tuning Cation Deficiency of Perovskite Oxides of Two-Dimensional LaFeO<sub>3</sub>/C Composite in XāBand
Development
of microwave absorption materials with tunable thickness and bandwidth
is particularly urgent for practical applications but remains a great
challenge. Here, two-dimensional nanocomposites consisting of perovskite
oxides (LaFeO<sub>3</sub>) and amorphous carbon were successfully
obtained through a one pot with heating treatment using sodium chloride
as a hard template. The tunable absorption properties were realized
by introducing A-site cation deficiency in LaFeO<sub>3</sub> perovskite.
Among the A-site cation-deficient perovskites, La<sub>0.62</sub>FeO<sub>3</sub>/C (L<sub>0.62</sub>FOC) has the best microwave absorption
properties in which the maximum absorption is ā26.6 dB at 9.8
GHz with a thickness of 2.94 mm and the bandwidth range almost covers
all X-band. The main reason affecting the microwave absorption performance
was derived from the A-site cation deficiency which induced more dipoles
polarization loss. This work proposes a promising method to tune the
microwave absorption performance via introducing deficiency in a crystal
lattice
Facile Preparation of Well-Dispersed CeO<sub>2</sub>āZnO Composite Hollow Microspheres with Enhanced Catalytic Activity for CO Oxidation
In
this article, well-dispersed CeO<sub>2</sub>āZnO composite
hollow microspheres have been fabricated through a simple chemical
reaction followed by annealing treatment. Amorphous zincācerium
citrate hollow microspheres were first synthesized by dispersing zinc
citrate hollow microspheres into cerium nitrate solution and then
aging at room temperature for 1 h. By calcining the as-produced zincācerium
citrate hollow microspheres at 500 Ā°C for 2 h, CeO<sub>2</sub>āZnO composite hollow microspheres with homogeneous composition
distribution could be harvested for the first time. The resulting
CeO<sub>2</sub>āZnO composite hollow microspheres exhibit enhanced
activity for CO oxidation compared with CeO<sub>2</sub> and ZnO, which
is due to well-dispersed small CeO<sub>2</sub> particles on the surface
of ZnO hollow microspheres and strong interaction between CeO<sub>2</sub> and ZnO. Moreover, when Au nanoparticles are deposited on
the surface of the CeO<sub>2</sub>āZnO composite hollow microspheres,
the full CO conversion temperature of the as-produced 1.0 wt % AuāCeO<sub>2</sub>āZnO composites reduces from 300 to 60 Ā°C in comparison
with CeO<sub>2</sub>āZnO composites. The significantly improved
catalytic activity may be ascribed to the strong synergistic interplay
between Au nanoparticles and CeO<sub>2</sub>āZnO composites
High-Performance NaāO<sub>2</sub> Batteries Enabled by Oriented NaO<sub>2</sub> Nanowires as Discharge Products
NaāO<sub>2</sub> batteries are emerging rechargeable batteries
due to their high theoretical energy density and abundant resources,
but they suffer from sluggish kinetics due to the formation of large-size
discharge products with cubic or irregular particle shapes. Here,
we report the unique growth of discharge products of NaO<sub>2</sub> nanowires inside NaāO<sub>2</sub> batteries that significantly
boosts the performance of NaāO<sub>2</sub> batteries. For this
purpose, a high-spin Co<sub>3</sub>O<sub>4</sub> electrocatalyst was
synthesized via the high-temperature oxidation of pure cobalt nanoparticles
in an external magnetic field. The discharge products of NaO<sub>2</sub> nanowires are 10ā20 nm in diameter and ā¼10 Ī¼m
in length, characteristics that provide facile pathways for electron
and ion transfer. With these nanowires, NaāO<sub>2</sub> batteries
have surpassed 400 cycles with a fixed capacity of 1000 mA h g<sup>ā1</sup>, an ultra-low over-potential of ā¼60 mV during
charging, and near-zero over-potential during discharging. This strategy
not only provides a unique way to control the morphology of discharge
products to achieve high-performance NaāO<sub>2</sub> batteries
but also opens up the opportunity to explore growing nanowires in
novel conditions