37 research outputs found
Marine Corrosion Protective Coatings of Hexagonal Boron Nitride Thin Films on Stainless Steel
Recently, two-dimensional, layered
materials such as graphene and hexagonal boron nitride (h-BN) have
been identified as interesting materials for a range of applications.
Here, we demonstrate the corrosion prevention applications of h-BN
in marine coatings. The performance of h-BN/polymer hybrid coatings,
applied on stainless steel, were evaluated using electrochemical techniques
in simulated seawater media [marine media]. h-BN/polymer coating shows
an efficient corrosion protection with a low corrosion current density
of 5.14 × 10<sup>–8</sup> A/cm<sup>2</sup> and corrosion
rate of 1.19 × 10<sup>–3</sup> mm/year and it is attributed
to the hydrofobic, inert and dielectric nature of boron nitride. The
results indicated that the stainless steel with coatings exhibited
improved corrosion resistance. Electrochemical impedance spectroscopy
and potentiodynamic analysis were used to propose a mechanism for
the increased corrosion resistance of h-BN coatings
Bottom-up Approach toward Single-Crystalline VO<sub>2</sub>‑Graphene Ribbons as Cathodes for Ultrafast Lithium Storage
Although lithium ion batteries have
gained commercial success owing
to their high energy density, they lack suitable electrodes capable
of rapid charging and discharging to enable a high power density critical
for broad applications. Here, we demonstrate a simple bottom-up approach
toward single crystalline vanadium oxide (VO<sub>2</sub>) ribbons
with graphene layers. The unique structure of VO<sub>2</sub>-graphene
ribbons thus provides the right combination of electrode properties
and could enable the design of high-power lithium ion batteries. As
a consequence, a high reversible capacity and ultrafast charging and
discharging capability is achieved with these ribbons as cathodes
for lithium storage. A full charge or discharge is capable in 20 s.
More remarkably, the resulting electrodes retain more than 90% of
the initial capacity after cycling more than 1000 times at an ultrahigh
rate of 190C, providing the best reported rate performance for cathodes
in lithium ion batteries to date
Functionalized Multilayered Graphene Platform for Urea Sensor
Multilayered graphene (MLG) is an interesting material for electrochemical sensing and biosensing because of its very large 2D electrical conductivity and large surface area. We propose a less toxic, reproducible, and easy method for producing functionalized multilayer graphene from multiwalled carbon nanotubes (MWCNTs) in mass scale using only concentrated H<sub>2</sub>SO<sub>4</sub>/HNO<sub>3</sub>. Electron microscopy results show the MLG formation, whereas FTIR and XPS data suggest its carboxylic and hydroxyl-functionalized nature. We utilize this functionalized MLG for the fabrication of a novel amperometric urea biosensor. This biosensor shows linearity of 10–100 mg dL<sup>–1</sup>, sensitivity of 5.43 μA mg<sup>–1</sup> dL cm<sup>–2</sup>, lower detection limit of 3.9 mg dL<sup>–1</sup>, and response time of 10 s. Our results suggest that MLG is a promising material for electrochemical biosensing applications
Synthesis and Photoresponse of Large GaSe Atomic Layers
We report the direct growth of large,
atomically thin GaSe single
crystals on insulating substrates by vapor phase mass transport. A
correlation is identified between the number of layers and a Raman
shift and intensity change. We found obvious contrast of the resistance
of the material in the dark and when illuminated with visible light.
In the photoconductivity measurement we observed a low dark current.
The on–off ratio measured with a 405 nm at 0.5 mW/mm<sup>2</sup> light source is in the order of 10<sup>3</sup>; the photoresponsivity
is 17 mA/W, and the quantum efficiency is 5.2%, suggesting possibility
for photodetector and sensor applications. The photocurrent spectrum
of few-layer GaSe shows an intense blue shift of the excitation edge
and expanded band gap compared with bulk material
Nitrogen-Doped Graphene with Pyridinic Dominance as a Highly Active and Stable Electrocatalyst for Oxygen Reduction
The nitrogen-doped graphene (NG)
with dominance of the pyridinic-N
configuration is synthesized via a straightforward process including
chemical vapor deposition (CVD) growth of graphene and postdoping
with a solid nitrogen precursor of graphitic C<sub>3</sub>N<sub>4</sub> at elevated temperature. The NG fabricated from CVD-grown graphene
contains a high N content up to 6.5 at. % when postdoped at 800 °C
but maintains high crystalline quality of graphene. The obtained NG
exhibits high activity, long-standing stability, and outstanding crossover
resistance for electrocatalysis of oxygen reduction reaction (ORR)
in alkaline medium. The NG treated at 800 °C shows the best ORR
performance. Further study of the dependence of ORR activity on different
N functional groups in these metal-free NG electrodes provides deeper
insights into the origin of ORR activity. Our results reveal that
the pyridinic-N tends to be the most active N functional group to
facilitate ORR at low overpotential via a four-electron pathway
Bottom-up Approach toward Single-Crystalline VO<sub>2</sub>‑Graphene Ribbons as Cathodes for Ultrafast Lithium Storage
Although lithium ion batteries have
gained commercial success owing
to their high energy density, they lack suitable electrodes capable
of rapid charging and discharging to enable a high power density critical
for broad applications. Here, we demonstrate a simple bottom-up approach
toward single crystalline vanadium oxide (VO<sub>2</sub>) ribbons
with graphene layers. The unique structure of VO<sub>2</sub>-graphene
ribbons thus provides the right combination of electrode properties
and could enable the design of high-power lithium ion batteries. As
a consequence, a high reversible capacity and ultrafast charging and
discharging capability is achieved with these ribbons as cathodes
for lithium storage. A full charge or discharge is capable in 20 s.
More remarkably, the resulting electrodes retain more than 90% of
the initial capacity after cycling more than 1000 times at an ultrahigh
rate of 190C, providing the best reported rate performance for cathodes
in lithium ion batteries to date
Anisotropically Functionalized Carbon Nanotube Array Based Hygroscopic Scaffolds
Creating
ordered microstructures with hydrophobic and hydrophilic moieties
that enable the collection and storage of small water droplets from
the atmosphere, mimicking structures that exist in insects, such as
the Stenocara beetle, which live in environments with limited amounts
of water. Inspired by this approach, vertically aligned multiwalled
carbon nanotube forests (NTFs) are asymmetrically end-functionalized
to create hygroscopic scaffolds for water harvesting and storage from
atmospheric air. One side of the NTF is made hydrophilic, which captures
water from the atmosphere, and the other side is made superhydrophobic,
which prevents water from escaping and the forest from collapsing.
To understand how water penetrates into the NTF, the fundamentals
of water/NTF surface interaction are discussed
Strain Rate Dependent Shear Plasticity in Graphite Oxide
Graphene
oxide film is made of stacked graphene layers with chemical
functionalities, and we report that plasticity in the film can be
engineered by strain rate tuning. The deformation behavior and plasticity
of such functionalized layered systems is dominated by shear slip
between individual layers and interaction between functional groups.
Stress–strain behavior and theoretical models suggest that
the deformation is strongly strain rate dependent and undergoes brittle
to ductile transition with decreasing strain rate
Defects Engineered Monolayer MoS<sub>2</sub> for Improved Hydrogen Evolution Reaction
MoS<sub>2</sub> is a promising and
low-cost material for electrochemical hydrogen production due to its
high activity and stability during the reaction. However, the efficiency
of hydrogen production is limited by the amount of active sites, for
example, edges, in MoS<sub>2</sub>. Here, we demonstrate that oxygen
plasma exposure and hydrogen treatment on pristine monolayer MoS<sub>2</sub> could introduce more active sites via the formation of defects
within the monolayer, leading to a high density of exposed edges and
a significant improvement of the hydrogen evolution activity. These
as-fabricated defects are characterized at the scale from macroscopic
continuum to discrete atoms. Our work represents a facile method to
increase the hydrogen production in electrochemical reaction of MoS<sub>2</sub> via defect engineering, and helps to understand the catalytic
properties of MoS<sub>2</sub>
Ballistic Fracturing of Carbon Nanotubes
Advanced materials with multifunctional
capabilities and high resistance to hypervelocity impact are of great
interest to the designers of aerospace structures. Carbon nanotubes
(CNTs) with their lightweight and high strength properties are alternative
to metals and/or metallic alloys conventionally used in aerospace
applications. Here we report a detailed study on the ballistic fracturing
of CNTs for different velocity ranges. Our results show that the highly
energetic impacts cause bond breakage and carbon atom rehybridizations,
and sometimes extensive structural reconstructions were also observed.
Experimental observations show the formation of nanoribbons, nanodiamonds,
and covalently interconnected nanostructures, depending on impact
conditions. Fully atomistic reactive molecular dynamics simulations
were also carried out in order to gain further insights into the mechanism
behind the transformation of CNTs. The simulations show that the velocity
and relative orientation of the multiple colliding nanotubes are critical
to determine the impact outcome