33 research outputs found
A Multifunctional Protein Coating for Self-Assembled Porous Nanostructured Electrodes
Creation
of three-dimensional (3D) porous nanostructured electrodes
with controlled conductive pathways for both ions and electrons is
becoming an increasingly important strategy and is particularly of
great interest for the development of high-performance energy storage
devices. In this article, we report a facile and environmentally friendly
self-assembly approach to fabricating advanced 3D nanostructured electrodes.
The self-assembly
is simply realized via formation of a multifunctional protein coating
on the surface of electrode nanoparticles by using a denatured soy
protein derived from the abundantly prevalent soybean plant. It is
found that the denatured protein coating plays three roles simultaneously:
as a surfactant for the dispersion of electrode nanoparticles, an
ion-conductive coating for the active materials, and a binder for
the final electrode. More importantly, it is interestingly found that
being a unique surfactant, the surface protein coating enables the
self-assembly behavior of the electrode nanoparticles during the evaporation
of aqueous dispersion, which finally results in 3D porous nanostructured
electrodes. In comparison with the most classic binder, polyĀ(vinylidene
fluoride), the advantages of the 3D nanostructured electrode in terms
of electrochemical properties (capacity and rate capability) are demonstrated.
This study provides an environmentally friendly and cost-effective
self-assembly strategy for fabrication of advanced nanostructured
electrodes using electrode nanoparticles as the building block
Charge Transport Properties in TiO<sub>2</sub> Network with Different Particle Sizes for Dye Sensitized Solar Cells
The charge transport properties in the TiO<sub>2</sub> nanoparticle networks with the different TiO<sub>2</sub> nanoparticle
sizes were investigated by means of electrochemical impedance spectroscopy
(EIS) with consideration of morphological aspects of mesoporous TiO<sub>2</sub> network including particle size (<i>d</i><sub>p</sub>), coordination number (<i>N</i><sub>n</sub>), neck diameter
(<i>d</i><sub>n</sub>), and effective surface area (<i>S</i><sub>e</sub>). The morphological analysis of the network
revealed that the particle size and surface area would be factors
exerting an impact on the charge transport properties, while the coordination
number and neck diameter seemed to be consistent with the nanoparticle
size. As a result, the electron transport along with the TiO<sub>2</sub> network was predominantly affected by the particle size in terms
of the mean free path; the bigger particle size provides both long
travel distance and less collision chance with the boundary. Surface
area seems to exert a strong influence on the recombination when it
is in contact with an electrolyte, suggesting that pore size distribution
determining penetration of an electrolyte has to be considered in
terms of the effective surface area (<i>S</i><sub>e</sub>). Due to the low transport resistance, high recombination resistance,
and low chemical capacitance, the largest particle showed the longest
diffusion length (<i>L</i><sub>n</sub>). However, the highest
efficiency observed in 15 nm TiO<sub>2</sub> nanoparticle photoanode
indicated that the compensating characteristics of the morphological
factors of the network for light harvesting efficiency (LHE) (surface
area) and charge collection efficiency (Ī·<sub>c</sub>, particle
size) should be balanced in designing a nanostructured network for
high performance DSCs
Elucidating the Role of Defects for Electrochemical Intercalation in Sodium Vanadium Oxide
Na<sub>1.25+<i>x</i></sub>V<sub>3</sub>O<sub>8</sub> (with <i>x</i> < 0, = 0, and > 0) was synthesized via a wet chemical
route involving the reduction of V<sub>2</sub>O<sub>5</sub> in oxalic
acid and NaNO<sub>3</sub> followed by calcination. It was possible
to control the sodium composition in the final product by adjusting
the amount of sodium precursor added during synthesis. It was revealed
that deficient and excessive sodium contents, with respect to the
ideal stoichiometry, are accommodated or compensated by the respective
generation of oxygen vacancies and partial transition metal reduction,
or cation disordering. When examined as NIB electrode material, the superior performance
of the cation disordered material with excessive sodium was clearly
demonstrated, with more than 50% higher storage capacity and superior
rate capacity and cyclic stability. The formation of oxygen vacancies
initially seemed promising but was coupled with stability issues and
capacity fading upon further cycling. The disparity in electrochemical
performance was attributed to variations in the electronic distribution
as promoted through Naāion interactions and the direct influence
of such on the oxygen framework (sublattice); these factors were determined
to have significant impact on the migration energy and diffusion barriers
Polyol-Mediated Solvothermal Synthesis and Electrochemical Performance of Nanostructured V<sub>2</sub>O<sub>5</sub> Hollow Microspheres
Hollow vanadyl glycolate nanostructured microspheres
were synthesized
via a highly scalable and template-free polyol-induced solvothermal
process. Subsequent calcination transformed the precursor material
into vanadium pentoxide, a well-studied transition metal oxide. The
vanadyl glycolate nanoparticles were synthesized through a self-seeding
process and then aggregated around N<sub>2</sub> microbubbles formed
during the reaction that acted as āquasi-micellesā due
to the large polarization discrepancy between nitrogen and water.
The proposed formation mechanism provides a firm understanding of
the processes leading to the observed hollow microsphere morphology.
The thermally treated material was tested as a cathode for lithium-ion
battery and showed excellent cycle stability and high rate performance.
The exceptional electrochemical performance was attributed to the
relatively thin-walled structure that ensured fast phase penetration
between the electrolyte and active material and shortened lithium-ion
migration distance. The prolonged cycling stability is ascribed to
the inherent morphological void that can readily accommodate volume
expansion and contraction upon cycling
General Strategy for Designing CoreāShell Nanostructured Materials for High-Power Lithium Ion Batteries
Because of its extreme safety and outstanding cycle life,
Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> has been regarded as one
of the
most promising anode materials for next-generation high-power lithium-ion
batteries. Nevertheless, Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> suffers from poor electronic conductivity. Here, we develop a novel
strategy for the fabrication of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub>/carbon coreāshell electrodes using metal oxyacetyl
acetonate as titania and single-source carbon. Importantly, this novel
approach is simple and general, with which we have successfully produce
nanosized particles of an olivine-type LiMPO<sub>4</sub> (M = Fe,
Mn, and Co) core with a uniform carbon shell, one of the leading cathode
materials for lithium-ion batteries. Metal acetylacetonates first
decompose with carbon coating the particles, which is followed by
a solid state reaction in the limited reaction area inside the carbon
shell to produce the LTO/C (LMPO<sub>4</sub>/C) coreāshell
nanostructure. The optimum design of the coreāshell nanostructures
permits fast kinetics for both transported Li<sup>+</sup> ions and
electrons, enabling high-power performance
Design and Tailoring of a Three-Dimensional TiO<sub>2</sub>āGrapheneāCarbon Nanotube Nanocomposite for Fast Lithium Storage
Nanocrystalline TiO<sub>2</sub> grown on conducting graphene
nanosheets (GNS) and multiwalled carbon nanotubes (CNTs) via a solution-based
method to form a three-dimensional (3D) hierarchical structure for
fast lithium storage. CNTs in the unique hybrid nanostructure not
only prevent the restacking of GNS to increase the basal spacing between
graphene sheets but also provides an additional electron-transport
path besides the graphene layer underneath of TiO<sub>2</sub> nanomaterials,
increasing the electrolyte/electrode contact area and facilitating
transportation of the electrolyte ion and electron into the inner
region of the electrode. Such a 3D TiO<sub>2</sub>āGNSāCNT
nanocomposite had a large specific surface area of 291.2 m<sup>2</sup> g<sup>ā1</sup> and exhibited ultrahigh rate capability and
good cycling properties at high rates
Surface Engineering of Quantum Dots for Remarkably High Detectivity Photodetectors
Ternary
alloyed CdSe<sub><i>x</i></sub>Te<sub>1ā<i>x</i></sub> colloidal QDs trap-passivated by iodide-based ligands
(TBAI) are developed as building blocks for UVāNIR photodetectors.
Both the few surface traps and high loading of QDs are obtained by
in situ ligand exchange with TBAI. The device is sensitive to a broad
wavelength range covering the UVāNIR region (300ā850
nm), showing an excellent photoresponsivity of 53 mA/W, a fast response
time of āŖ0.02s, and remarkably high detectivity values of 8
Ć 10<sup>13</sup> Jones at 450 nm and 1 Ć 10<sup>13</sup> Jones at 800 nm without an external bias voltage. Such performance
is superior to what has been reported earlier for QD-based photodetectors.
The photodetector exhibits excellent stability, keeping 98% of photoelectric
responsivity after 2 months of illumination in air even without encapsulation.
In addition, the semitransparent device is successfully fabricated
using a Ag nanowires/polyimide transparent substrate. Such self-powered
photodetectors with fast response speed and a stable, broad-band response
are expected to function under a broad range of environmental conditions
Salami-like Electrospun Si Nanoparticle-ITO Composite Nanofibers with Internal Conductive Pathways for use as Anodes for Li-Ion Batteries
We report novel salami-like coreāsheath
composites consisting
of Si nanoparticle assemblies coated with indium tin oxide (ITO) sheath
layers that are synthesized via coelectrospinning. Coreāsheath
structured Si nanoparticles (NPs) in static ITO allow robust microstructures
to accommodate for mechanical stress induced by the repeated cyclical
volume changes of Si NPs. Conductive ITO sheaths can provide bulk
conduction paths for electrons. Distinct Si NP-based core structures,
in which the ITO phase coexists uniformly with electrochemically active
Si NPs, are capable of facilitating rapid charge transfer as well.
These engineered composites enabled the production of high-performance
anodes with an excellent capacity retention of 95.5% (677 and 1523
mAh g<sup>ā1,</sup> which are based on the total weight of
Si-ITO fibers and Si NPs only, respectively), and an outstanding rate
capability with a retention of 75.3% from 1 to 12 C. The cycling performance
and rate capability of coreāsheath-structured Si NP-ITO are
characterized in terms of charge-transfer kinetics
Novel Photoanode for Dye-Sensitized Solar Cells with Enhanced Light-Harvesting and Electron-Collection Efficiency
A novel
photoanode structure modified by porous flowerlike CeO<sub>2</sub> microspheres as a scattering layer with a thin TiO<sub>2</sub> film
deposited by atomic layer deposition (ALD) is prepared to achieve
a significantly enhanced performance of dye-sensitized solar cells
(DSSCs). The light scattering capability of the photoanode with the
porous CeO<sub>2</sub> microsphere layer is considerably improved.
The interconnection of particles and electrical contact between bilayer
and conducting substrate is further enhanced by an ALD-deposited TiO<sub>2</sub> film, which effectively reduces the electron recombination
and facilitates electron transport and thus enhances the charge collection
efficiency of DSSCs. As a result, the overall efficiency of the obtained
TiO<sub>2</sub>āCeO<sub>2</sub>-based cells reaches 9.86%,
which is 31% higher than that of the DSSCs with a conventional TiO<sub>2</sub> photoanode
Continuous Size Tuning of Monodispersed ZnO Nanoparticles and Its Size Effect on the Performance of Perovskite Solar Cells
ZnO has been demonstrated
to be a promising candidate to fabricate
high efficiency perovskite solar cells (PSCs) in terms of its better
electron extraction and transport properties. However, the inability
of synthesis of ZnO nanoparticles (NPs) with minimal surface defects
and agglomeration remains a great challenge hindering the fabrication
of highly efficient PSCs. In this work, highly crystalline and agglomeration-free
ZnO NPs with controlled size were synthesized through a facile solvothermal
method. Such ZnO NPs were applied in the fabrication of meso-structured
PSCs. The solar cells with ā¼40 nm ZnO NPs exhibit the highest
power conversion efficiency (PCE) of 15.92%. Steady-state and time-resolved
photoluminescence measurements revealed the faster injection and lower
charge recombination at the interface of ā¼40 nm ZnO NPs and
perovskite, resulting in significantly enhanced <i>J</i><sub>SC</sub> and <i>V</i><sub>OC</sub>