6 research outputs found
Hydrothermal Growth of Hierarchical Ni<sub>3</sub>S<sub>2</sub> and Co<sub>3</sub>S<sub>4</sub> on a Reduced Graphene Oxide Hydrogel@Ni Foam: A High-Energy-Density Aqueous Asymmetric Supercapacitor
Ni
foam@reduced graphene oxide (rGO) hydrogel–Ni<sub>3</sub>S<sub>2</sub> and Ni foam@rGO hydrogel–Co<sub>3</sub>S<sub>4</sub> composites have been successfully synthesized with the aid of a
two-step hydrothermal protocol, where the rGO hydrogel is sandwiched
between the metal sulfide and Ni foam substrate. Sonochemical deposition
of exfoliated rGO on Ni foam with subsequent hydrothermal treatment
results in the formation of a rGO-hydrogel-coated Ni foam. Then second-time
hydrothermal treatment of the dried Ni@rGO substrate with corresponding
metal nitrate and sodium sulfide results in individual uniform growth
of porous Ni<sub>3</sub>S<sub>2</sub> nanorods and a Co<sub>3</sub>S<sub>4</sub> self-assembled nanosheet on a Ni@rGO substrate. Both
Ni@rGO–Ni<sub>3</sub>S<sub>2</sub> and Ni@rGO–Co<sub>3</sub>S<sub>4</sub> have been electrochemically characterized in
a 6 M KOH electrolyte, exhibiting high specific capacitance values
of 987.8 and 1369 F/g, respectively, at 1.5 A/g accompanied by the
respective outstanding cycle stability of 97.9% and 96.6% at 12 A/g
over 3000 charge–discharge cycles. An advanced aqueous asymmetric
(AAS) supercapacitor has been fabricated by exploiting the as-prepared
Ni@rGO–Co<sub>3</sub>S<sub>4</sub> as a positive electrode
and Ni@rGO–Ni<sub>3</sub>S<sub>2</sub> as a negative electrode.
The as-fabricated AAS has shown promising energy densities of 55.16
and 24.84 Wh/kg at high power densities of 975 and 13000 W/kg, respectively,
along with an excellent cycle stability of 96.2% specific capacitance
retention over 3000 charge–discharge cycles at 12 A/g. The
enhanced specific capacitance, stupendous cycle stability, elevated
energy density, and a power density as an AAS of these electrode materials
indicate that it could be a potential candidate in the field of supercapacitors
Preparation of CTAB-Assisted Hexagonal Platelet Co(OH)<sub>2</sub>/Graphene Hybrid Composite as Efficient Supercapacitor Electrode Material
In
this paper, our work deals with the preparation of cetyl trimethylammonium
bromide (CTAB)-assisted hexagonal platelet β CoÂ(OH)<sub>2</sub> via a simple hydrothermal process and its graphene-based hybrid
composite with improved electrochemical properties. The prepared materials
were successfully characterized by FTIR, XRD, FESEM, TEM, and TGA
analysis. The materials were subjected to electrochemical analysis
by a three electrode system in a 6 M KOH electrolyte in terms of a
cyclic voltammetry, cyclic charge–discharge, and electrochemical
impedance study. The CTAB-assisted CoÂ(OH)<sub>2</sub> with hexagonal
architecture exhibited the highest specific capacitance of 312 F/g
at a 2 mV/s scan rate and 285 F/g at a 2 A/g constant discharge current
density. The high utility of pseudocapacitive CoÂ(OH)<sub>2</sub> is
achieved only in its graphene-based hybrid composite, which responded
with specific capacitance of 532 F/g at a 2A/g current density and
a 94% specific capacitance retention over 500 charge discharge cycles
Decorating Graphene Oxide with Ionic Liquid Nanodroplets: An Approach Leading to Energy-Dense, High-Voltage Supercapacitors
A major
stumbling block in the development of high energy density
graphene-based supercapacitors has been maintaining high ion-accessible
surface area combined with high electrode density. Herein, we develop
an ionic liquid (IL)–surfactant microemulsion system that is
found to facilitate the spontaneous adsorption of IL-filled micelles
onto graphene oxide (GO). This adsorption distributes the IL over
all available surface area and provides an aqueous formulation that
can be slurry cast onto current collectors, leaving behind a dense
nanocomposite film of GO/IL/surfactant. By removing the surfactant
and reducing the GO through a low-temperature (360 °C) heat treatment,
the IL plays a dual role of spacer and electrolyte. We study the effect
of IL content and operating temperature on the performance, demonstrating
a record high gravimetric capacitance (302 F/g at 1 A/g) for 80 wt
% IL composites. At 60 wt % IL, combined high capacitance and bulk
density (0.76 g/cm<sup>3</sup>), yields one of the highest volumetric
capacitances (218 F/cm<sup>3</sup>, at 1 A/g) ever reported for a
high-voltage IL-based supercapacitor. While achieving promising rate
performance and cycle-life, the approach also eliminates the long
and costly electrolyte imbibition step of cell assembly as the electrolyte
is cast directly with the electrode material
Preparation of CTAB-Assisted Hexagonal Platelet Co(OH)<sub>2</sub>/Graphene Hybrid Composite as Efficient Supercapacitor Electrode Material
In
this paper, our work deals with the preparation of cetyl trimethylammonium
bromide (CTAB)-assisted hexagonal platelet β CoÂ(OH)<sub>2</sub> via a simple hydrothermal process and its graphene-based hybrid
composite with improved electrochemical properties. The prepared materials
were successfully characterized by FTIR, XRD, FESEM, TEM, and TGA
analysis. The materials were subjected to electrochemical analysis
by a three electrode system in a 6 M KOH electrolyte in terms of a
cyclic voltammetry, cyclic charge–discharge, and electrochemical
impedance study. The CTAB-assisted CoÂ(OH)<sub>2</sub> with hexagonal
architecture exhibited the highest specific capacitance of 312 F/g
at a 2 mV/s scan rate and 285 F/g at a 2 A/g constant discharge current
density. The high utility of pseudocapacitive CoÂ(OH)<sub>2</sub> is
achieved only in its graphene-based hybrid composite, which responded
with specific capacitance of 532 F/g at a 2A/g current density and
a 94% specific capacitance retention over 500 charge discharge cycles
Solid State Flexible Asymmetric Supercapacitor Based on Carbon Fiber Supported Hierarchical Co(OH)<sub><i>x</i></sub>CO<sub>3</sub> and Ni(OH)<sub>2</sub>
Conducting
flexible carbon fiber (CF) cloth was used as a substrate
for the hydrothermal growth of nickel hydroxide (NiÂ(OH)<sub>2</sub>) and cobalt hydroxy carbonate [CoÂ(OH)<sub><i>x</i></sub>CO<sub>3</sub>] with unique hierarchical flowery architecture and
then was used as a flexible supercapacitor electrode. In a three-electrode
configuration in 6 M KOH aqueous electrolyte, the CF–NiÂ(OH)<sub>2</sub> and CF–CoÂ(OH)<sub><i>x</i></sub>CO<sub>3</sub> electrode showed the maximum specific capacitance of 789 F/g and
550 F/g, respectively, at 2A/g current accompanied by outstanding
cycle stability by retaining 99.9% and 99.5% specific capacitance
over 1500 consecutive charge–discharge cycles at 5 A/g. However,
the low cell voltage (0.4 V) restricted the respective specific energy
to 4.38 and 3.05 Wh/kg at a specific power of 100 W/kg. To overcome
the issue, two solid state flexible asymmetric supercapacitors were
fabricated using the CF–NiÂ(OH)<sub>2</sub> and CF–CoÂ(OH)<sub><i>x</i></sub>CO<sub>3</sub> as the anode and sonochemically
deposited CNT over carbon fiber as the cathode material in PVA-KOH
gel electrolyte. The as-fabricated flexible supercapacitors CF–NiÂ(OH)<sub>2</sub>//CF–CNT and CF–CoÂ(OH)<sub><i>x</i></sub>CO<sub>3</sub>//CF–CNT were able to deliver high specific
energy of 41.1 and 33.48 Wh/kg, respectively, at high specific power
of 1.4 kW/kg accompanied by excellent cycle stability (retaining 98%
and 97.6% specific capacitance, respectively, over 3000 charge–discharge
cycle at 5 A/g)
High Energy Density All Solid State Asymmetric Pseudocapacitors Based on Free Standing Reduced Graphene Oxide-Co<sub>3</sub>O<sub>4</sub> Composite Aerogel Electrodes
Modern flexible consumer
electronics require efficient energy storage devices with flexible
free-standing electrodes. We report a simple and cost-effective route
to a graphene-based composite aerogel encapsulating metal oxide nanoparticles
for high energy density, free-standing, binder-free flexible pseudocapacitive
electrodes. Hydrothermally synthesized Co<sub>3</sub>O<sub>4</sub> nanoparticles are successfully housed inside the microporous graphene
aerogel network during the room temperature interfacial gelation at
the Zn surface. The resultant three-dimensional (3D) rGO-Co<sub>3</sub>O<sub>4</sub> composite aerogel shows mesoporous quasiparallel layer
stack morphology with a high loading of Co<sub>3</sub>O<sub>4</sub>, which offers numerous channels for ion transport and a 3D interconnected
network for high electrical conductivity. All solid state asymmetric
pseudocapacitors employing the composite aerogel electrodes have demonstrated
high areal energy density of 35.92 ÎĽWh/cm<sup>2</sup> and power
density of 17.79 mW/cm<sup>2</sup> accompanied by excellent cycle
life