30 research outputs found
Flexible and Stackable Laser-Induced Graphene Supercapacitors
In
this paper, we demonstrate that by simple laser induction, commercial
polyimide films can be readily transformed into porous graphene for
the fabrication of flexible, solid-state supercapacitors. Two different
solid-state electrolyte supercapacitors are described, namely vertically
stacked graphene supercapacitors and in-plane graphene microsupercapacitors,
each with enhanced electrochemical performance, cyclability, and flexibility.
Devices with a solid-state polymeric electrolyte exhibit areal capacitance
of >9 mF/cm<sup>2</sup> at a current density of 0.02 mA/cm<sup>2</sup>, more than twice that of conventional aqueous electrolytes.
Moreover, laser induction on both sides of polyimide sheets enables
the fabrication of vertically stacked supercapacitors to multiply
its electrochemical performance while preserving device flexibility
Functionalized Low Defect Graphene Nanoribbons and Polyurethane Composite Film for Improved Gas Barrier and Mechanical Performances
Nanocomposite of Polyaniline Nanorods Grown on Graphene Nanoribbons for Highly Capacitive Pseudocapacitors
A facile
and cost-effective approach to the fabrication of a nanocomposite
material of polyaniline (PANI) and graphene nanoribbons (GNRs) has
been developed. The morphology of the composite was characterized
by scanning electron microscopy, transmission electron microscopy,
X-ray photoelectron microscopy, and X-ray diffraction analysis. The
resulting composite has a high specific capacitance of 340 F/g and
stable cycling performance with 90% capacitance retention over 4200
cycles. The high performance of the composite results from the synergistic
combination of electrically conductive GNRs and highly capacitive
PANI. The method developed here is practical for large-scale development
of pseudocapacitor electrodes for energy storage
Functionalized Graphene Nanoribbon Films as a Radiofrequency and Optically Transparent Material
We
report that conductive films made from hexadecylated graphene nanoribbons
(HD-GNRs) can have high transparency to radiofrequency (RF) waves
even at very high incident power density. Nanoscale-thick HD-GNR films
with an area of several square centimeters were found to transmit
up to 390 W (2 × 10<sup>5</sup> W/m<sup>2</sup>) of RF power
with negligible loss, at an RF transmittance of ∼99%. The HD-GNR
films conformed to electromagnetic skin depth theory, which effectively
accounts for the RF transmission. The HD-GNR films also exhibited
sufficient optical transparency for tinted glass applications, with
efficient voltage-induced deicing of surfaces. The dispersion of the
HD-GNRs afforded by their edge functionalization enables spray-, spin-,
or blade-coating on almost any substrate, thus facilitating flexible,
conformal, and large-scale film production. In addition to use in
antennas and radomes where RF transparency is crucial, these capabilities
bode well for the use of the HD-GNR films in automotive and general
glass applications where both optical and RF transparencies are desired
Cobalt Nanoparticles Embedded in Nitrogen-Doped Carbon for the Hydrogen Evolution Reaction
There
is great interest in renewable and sustainable energy research
to develop low-cost, highly efficient, and stable electrocatalysts
as alternatives to replace Pt-based catalysts for the hydrogen evolution
reaction (HER). Though nanoparticles encapsulated in carbon shells
have been widely used to improve the electrode performances in energy
storage devices (e.g., lithium ion batteries), they have attracted
less attention in energy-related electrocatalysis. Here we report
the synthesis of nitrogen-enriched core–shell structured cobalt–carbon
nanoparticles dispersed on graphene sheets and we investigate their
HER performances in both acidic and basic media. These catalysts exhibit
excellent durability and HER activities with onset overpotentials
as low as ∼70 mV in both acidic (0.5 M H<sub>2</sub>SO<sub>4</sub>) and alkaline (0.1 M NaOH) electrolytes, and the overpotentials
needed to deliver 10 mA cm<sup>–2</sup> are determined to be
265 mV in acid and 337 mV in base, further demonstrating their potential
to replace Pt-based catalysts. Control experiments reveal that the
active sites for HER might come from the synergistic effects between
the cobalt nanoparticles and nitrogen-doped carbon
Boron- and Nitrogen-Doped Graphene Quantum Dots/Graphene Hybrid Nanoplatelets as Efficient Electrocatalysts for Oxygen Reduction
The scarcity and high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has limited the commercial and scalable use of fuel cells. Heteroatom-doped nanocarbon materials have been demonstrated to be efficient alternative catalysts for ORR. Here, graphene quantum dots, synthesized from inexpensive and earth-abundant anthracite coal, were self-assembled on graphene by hydrothermal treatment to form hybrid nanoplatelets that were then codoped with nitrogen and boron by high-temperature annealing. This hybrid material combined the advantages of both components, such as abundant edges and doping sites, high electrical conductivity, and high surface area, which makes the resulting materials excellent oxygen reduction electrocatalysts with activity even higher than that of commercial Pt/C in alkaline media
Enhanced Cycling Stability of Lithium Sulfur Batteries Using Sulfur–Polyaniline–Graphene Nanoribbon Composite Cathodes
A hierarchical
nanocomposite material of graphene nanoribbons combined
with polyaniline and sulfur using an inexpensive, simple method has
been developed. The resulting composite, characterized by scanning
electron microscopy, transmission electron microscopy, X-ray photoelectron
microscopy, and X-ray diffraction analysis, has a good rate performance
and excellent cycling stability. The synergistic combination of electrically
conductive graphene nanoribbons, polyaniline, and sulfur produces
a composite with high performance. The method developed here is practical
for the large-scale development of cathode materials for lithium sulfur
batteries
Rebar graphene
As the cylindrical sp2-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics, and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, such as graphene, are still absent. Here, we demonstrate the successful synthesis of CNT-toughened graphene by simply annealing functionalized CNTs on Cu foils without needing to introduce extraneous carbon sources. The CNTs act as reinforcing bar (rebar), toughening the graphene through both π–π stacking domains and covalent bonding where the CNTs partially unzip and form a seamless 2D conjoined hybrid as revealed by aberration-corrected scanning transmission electron microscopy analysis. This is termed rebar graphene. Rebar graphene can be free-standing on water and transferred onto target substrates without needing a polymer-coating due to the rebar effects of the CNTs. The utility of rebar graphene sheets as flexible all-carbon transparent electrodes is demonstrated. The in-plane marriage of 1D nanotubes and 2D layered materials might herald an electrical and mechanical union that extends beyond carbon chemistry
Asphalt-Derived High Surface Area Activated Porous Carbons for Carbon Dioxide Capture
Research activity toward the development
of new sorbents for carbon
dioxide (CO<sub>2</sub>) capture have been increasing quickly. Despite
the variety of existing materials with high surface areas and high
CO<sub>2</sub> uptake performances, the cost of the materials remains
a dominant factor in slowing their industrial applications. Here we
report preparation and CO<sub>2</sub> uptake performance of microporous
carbon materials synthesized from asphalt, a very inexpensive carbon
source. Carbonization of asphalt with potassium hydroxide (KOH) at
high temperatures (>600 °C) yields porous carbon materials
(<b>A-PC</b>) with high surface areas of up to 2780 m<sup>2</sup> g<sup>–1</sup> and high CO<sub>2</sub> uptake performance
of 21
mmol g<sup>–1</sup> or 93 wt % at 30 bar and 25 °C. Furthermore,
nitrogen doping and reduction with hydrogen yields active N-doped
materials (<b>A-NPC</b> and <b>A-rNPC</b>) containing
up to 9.3% nitrogen, making them nucleophilic porous carbons with
further increase in the Brunauer–Emmett–Teller (BET)
surface areas up to 2860 m<sup>2</sup> g<sup>–1</sup> for <b>A-NPC</b> and CO<sub>2</sub> uptake to 26 mmol g<sup>–1</sup> or 114 wt % at 30 bar and 25 °C for <b>A-rNPC</b>. This
is the highest reported CO<sub>2</sub> uptake among the family of
the activated porous carbonaceous materials. Thus, the porous carbon
materials from asphalt have excellent properties for reversibly capturing
CO<sub>2</sub> at the well-head during the extraction of natural gas,
a naturally occurring high pressure source of CO<sub>2</sub>. Through
a pressure swing sorption process, when the asphalt-derived material
is returned to 1 bar, the CO<sub>2</sub> is released, thereby rendering
a reversible capture medium that is highly efficient yet very inexpensive