A high-performance asymmetric supercapacitor designed with a three-dimensional interconnected porous carbon framework and sphere-like nickel nitride nanosheets

Article abstract of DOI:10.1039/c9nj02509j

To achieve high-energy density of supercapacitors and maintain their intrinsic high power density, the operating voltage should be extended by assembling high specific capacitance electrode materials into an asymmetric supercapacitor (ASC) device. Herein, an ASC was assembled based on a three-dimensional (3D) interconnected porous carbon framework (PRPC-1K) as a negative electrode and 3D sphere-like nickel nitride (Ni₃N) nanosheets as a positive electrode in an aqueous KOH electrolyte. The PRPC-1K was prepared by a simple activation process with biomass poplar root as the carbon precursor, and the Ni₃N nanosheets were successfully synthesized via a simple low-temperature hydrothermal and further urea-assisted nitridation process. Due to the unique structures and high capacitive performances of these materials, the Ni₃N//PRPC-1K ASC assembled based on these two materials achieved the high energy density of 30.9 W h kg^-1 at the high power density of 412 W kg^-1 and acceptable electrochemical cycling stability with an 81% retention after 5000 cycles.

Full text of DOI:10.1039/c9nj02509j

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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
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High-Performance Asymmetric Supercapacitor Designed with
Three-Dimensional Interconnected Porous Carbon Framework
and Sphere-like Nickel Nitride Nanosheets
Received 00th January 20xx,
Accepted 00th January 20xx
‡
a
‡a
b
a
a
a
a
Hui Peng, * Xiuwen Dai, Kanjun Sun, Xuan Xie, Fei Wang, Guofu Ma,* and Ziqiang Lei
DOI: 10.1039/x0xx00000x
To achieve the high energy density of supercapacitor and maintain their intrinsic high power density, it usually extend the
operating voltage by assembling high specific capacitance electrode materials into an asymmetric supercapacitor (ASC)
device. Herein, an ASC is assembled based on three-dimensional (3D) interconnected porous carbon framework (PRPC-1K)
www.rsc.org/
as negative electrode and 3D sphere-like nickel nitride (Ni
The PRPC-1K is prepared by a simple activation process with biomass poplar root as carbon precursor, and the Ni
nanosheets are successfully synthesized via a simple low temperature hydrothermal and further urea-assisted nitridation
3
N) nanosheets as positive electrode in aqueous KOH electrolyte.
3
N
process. In virtue of their unique structures and high capacitive performance, the Ni
3
N//PRPC-1K ASC assembled based on
-1
-1
these two materials achieved a high energy density of 30.9 Wh kg at a high power density of 412 W kg , and acceptable
electrochemical cycling stability with 81% retention after 5000 cycles.
materials and faradaic-type (high energy output) positive
materials, thus the high power density and high energy density
of the device can be realized simultaneously.
Carbon materials, ranging from activated carbon,[5,6] carbon
nanotubes,[7] carbon aerogel,[8] graphene,[9,10] and biomass
derived porous carbons,[11-16] have attracted the attention of
1. Introduction
Supercapacitors, because of its superior power density, long
lifetime and short charging time, have attracted widely attention
as one of the most promising devices for electrical energy
storage.[1,2] However, it has been recently discovered that the
supercapacitors have serious deficiencies of low energy density
E) and high cost. According to the equation of E =1/2 CV , the
device capacitance (C) and operating voltage (V) are the
determinants of high energy density in supercapacitors. The
device capacitance of a supercapacitor mainly depends on the
inherent properties of electrode materials, including special
micromorphology (e.g., 2D nanosheets and 3D network), good
electronic conductivity, high cycle stabilities, and existence of
multiple redox status and so on. In addition, designing the
aqueous asymmetric supercapacitor (ASC) is an effective way
for extending the operating voltage, since it could utilize the
working potential of two different electrodes in the same
aqueous electrolytes.[2-4] ASC is usually assembled based on
carbon-based capacitive-type (high power output) negative
researchers due to their high specific surface area, high
electronic conductivity, good chemical stability and long
cycling life.[17-19] Among those carbon materials, biomass
2
(
derived porous carbons are the most potential candidates for
supercapacitor electrode materials on account of their easy
preparation, renewability, low cost and eco-friendliness.[1,5,9] To
fabricate the biomass-based carbon materials with a developed
porous structure and large specific surface area, the activators
2
such as KOH, ZnCl , etc., are usually employed because they
can generally create abundant mesopore structures in biomass
carbon materials.[11] Especially, the 3D interconnected porous
carbon framework can provide continuous conductive network
for electron transport and a fully interconnected hierarchical
porosity for ion transport.[20] This inspires us to study the 3D
interconnected porous carbon nanomaterials made from
biomass-based carbon precursor with regular pore structure
naturally as advanced electrode materials for energy storage
aKey Laboratory of Eco-Environment-Related Polymer Materials of Ministry of
Education, Key Laboratory of Polymer Materials of Gansu Province, College of
Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou applications. We expect that the poplar root with abundant
30070, China.
College of Chemistry and Environmental Science, Lanzhou City University, Lanzhou
30070, China.
Corresponding authors: penghui@nwnu.edu.cn (H. Peng), magf@nwnu.edu.cn (G.
Ma).
These authors contributed equally to this work. They should thus be considered
7
porous structure naturally from carbon framework structures
will likely reveal some interesting features and properties.
Recently, transition metal nitrides have attracted increasing
attention and are more and more widely for used as lithium ion
battery and supercapacitor electrodes on account of their low
b
7
‡
co-first authors.
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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cost, superior energy densities and corrosion resistance.[21-24] filtrate became neutrality. Finally, the obtained carbon was
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DOI: 10.1039/C9NJ02509J
o
However, the specific capacitance of most metal nitrides is dried in a vacuum oven at 60 C for 12 h. The resulting carbon
relatively small due to the high electrical resistance, and materials prepared at weight ratio of KOH/carbon precursor of
volume changes caused by corresponding reactions.[25] Nickel 1 and 2 were named as PRPC-1K and PRPC-2K, respectively.
compounds are widely studied in faradaic-type materials
because of their high theoretical capacity, low cost, and mixing KOH was directly carbonized at 800 C for 2 h at
reversible redox reaction. Similarly, nickel nitride has also been heating rate of 5 C min , and the obtained carbon material is
developed as electrode materials for supercapacitors. For labeled as PRPC.
3
instance, Yu et al. reported the tiny Ni N nanoparticles firmly
For comparison purpose, the carbon precursor without
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.3 Synthesis of 3D sphere -like Ni
The Ni N nanosheets are successfully synthesized via a
simple low temperature hydrothermal and further urea-assisted
nitridation process. In a typical synthesis, NiCl ·6H O (0.0285
3
N nanosheets
fastened to graphene sheets and used as electrodes in
supercapacitors, which had high specific capacitance of 2087.5
3
-1
-1 [26]
F g at 1 A g . Prasad et al. prepared the 3D nanorhombus
Ni N thin films and used in supercapacitor electrodes, which
the specific capacitance is 285 F g at a scan rate of 10 mV s
We should note that the synthesis of nickel nitride
2
2
3
-
1
-
g, 1.2 mmol) and urea (0.0720 g, 1.5 mmol) were dissolved in
distilled water (80 mL). After sonication for at least 30 minutes,
the solution was transferred to Teflon-lined stainless steel
autoclave (100 mL) and heated to 150 °C for 3 hours in an oven
and then cooled it down to room temperature. The nickel
compound precursor (Ni(OH) ·0.75H O) was washed with
2 2
water, ethanol for several times and dried in an oven at 60 °C
for 12 h.
1.[27]
materials generally contains complicated steps and strenuous.
To achieve the high energy density of supercapacitor and
maintain their intrinsic high power density, here, a novel
asymmetric supercapacitor is designed by utilizing 3D
interconnected framework of porous carbon (PRPC-1K) as
negative electrodes and 3D sphere-like nickel nitride (Ni
nanosheets as positive electrodes. The 3D sphere-like Ni
nanosheets was synthesized via simple hydrothermal and
subsequent nitriding Ni precursors (Ni(OH) 0.75H O) method,
and the PRPC-1K was obtained by a KOH activation method
from poplar root as carbon precursor. The assembled
asymmetric supercapacitor (Ni
energy density and electrochemical stabilities. These findings
imply that Ni N//PRPC-1K ACS may be promising for the
future use in the energy storage systems.
3
N)
N
To prepare 3D sphere-like Ni
3
N nanosheets, the above as-
prepared Ni(OH) ·0.75H O (100 mg) and urea (2.0 g) were put
3
2
2
at two separate porcelain boat and placed into the tube furnace
with urea at the upstream side of the furnace. After that, the
2
2
o
-1
sample was heated to 350 C with a heating rate of 2 °C min
and then stayed at this temperature for 3 h under static N
atmosphere. Finally, the furnace was cooled to room
temperature naturally to obtain the Ni N material. For
comparison purposes, the NiO was synthesized in the same way
as that for Ni N except without urea and under the air condition.
2
3
N//PRPC-1K) achieved a high
3
3
3
2
. Experimental section
3
. Results and discussion
2
.1. Materials
3.1 The structure of the negative electrode and its
electrochemical performance.
Poplar roots (the poplar grown in Gansu province of China),
Nickel (Ⅱ) chloride hexahydrate (NiCl ·6H O), urea and
2 2
potassium hydroxide (KOH) are purchased from Sinopharm
Chemical Reagent Co., Ltd., Shanghai, China. All the chemical
reagents were in analytical grade and without further
purification before used.
Poplar is a very ordinary plant that grows in many parts of
the world, the poplar roots (PRs) possess an abundant 3D
porous structure naturally. However, those PRs usually have no
commercial value and will cause the environment pressure. In
order to make the PRs have high added value, here, 3D
interconnected PRs-based porous carbon (PRPC-1K) was
prepared by pyrolysis of PRs using KOH as activating agent.
Fig. 1a illustrates the preparation procedure for PRPC-1K.
2.2 Synthesis of 3D poplar roots-based interconnected porous
carbon framework
Briefly, the poplar roots were thoroughly washed with
distilled water several times and dried in an oven at 60 C. The Briefly, the low-cost and abundant natural poplar roots were cut
cleaned poplar roots were first pre-carbonized at 500 C for 2 h into pieces and pre-carbonized under a nitrogen atmosphere.
at heating rate of 5 C min in a continuous slowly flowing N
atmosphere. Then, the obtained carbon materials were mixed with KOH and further activated and carbonized at 800 C for 2
with KOH in different proportions (ratio of KOH/carbon h under a nitrogen atmosphere to prepare the 3D hierarchical
precursor = 1 and 2) in 30 mL distilled water and followed by PRPC-1K with numerous nanopores. Fig. 1b shows the SEM
evaporation step at 60 C until the formation of solid precursor images of PRPC direct carbonized without KOH activation
mixture. Then, the mixture was activated and carbonized at 800 step, where the cross-linked 3D honeycomb porous morphology
o
o
o
-1
2
Then, the obtained pre-carbonized carbon materials were mixed
o
o
o
o
-1
C for 2 h at heating rate of 5 C min in a continuous slowly is clearly observed. Moreover, it can be seen that multistage
flowing N atmosphere. The resulting mixture product was macroporous and hole channels (30-60 mm) are surrounded by
2
washed with 2 M HCl solution to remove the inorganic salts numerous small hole channels (5-10 mm), indicating the co-
and then thoroughly washed with distilled water until the exist of numerous macroporous and mesopores structure in
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PRPC. Fig. 1c and 1d show the SEM images of PRPC-1K and pressure of 0.1-0.9 P/P
0
, suggesting the presence of abundant
View Article Online
PRPC-2K, respectively, showing that the unique honeycomb mesoporous and macroporous structureDs.OIT: 1h0e.10d39e/tCai9lNeJd02B50E9TJ
porous structure of poplar roots is still retained after activation surface area and pore structure parameters of the as-prepared
by different levels of KOH. Fig. 1e and 1f show the cross- PRPC, PRPC-1K, and PRPC-2K samples are shown in Table
sectional view and magnified top-view SEM image of PRPC- S1. The specific surface area of the PRPC, PRPC-1K and
1
K, respectively. From the cross-sectional view, we can PRPC-2K materials measured by the Brunauer-Emmett-Teller
2
-1
observe that the channels are aligned straight through from top (BET) method are 17.8, 710.7 and 268.7 m g , respectively.
to bottom and have many mesopores on them. From the However, the specific surface area and pore volume of PRPC-
magnified top-view SEM image, we can see the pore structure 2K are lower than that of PRPC-1K when increase the weight
around the macroporous more clearly. TEM image (Fig. 1g) of ratio of KOH/carbon precursor from 1 to 2, which may be due
the PRPC-1K further confirms its amorphous feature. It is to the collapse of pores caused by the excessive activation.[1,13]
suggesting that many mesopores and macropores were created Fig. 2b shows the corresponding pore size distributions of
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during the carbonization process.
PRPC, PRPC-1K and PRPC-2K samples. It is found that the
pore size of PRPC, PRPC-1K and PRPC-2K is mainly centered
in the range of 2-10 nm, indicating the existence of superior
mesoporous structures. The PRPC-1K possesses the high
specific surface area and pore volume, which is expected to
display outstanding electrochemical performance as
supercapacitor electrode material.
a
The XRD patterns of PRPC, PRPC-1K and PRPC-2K
samples are shown in Fig. 2c. All samples exhibit two typical
peaks, corresponding to diffractions of (002) and (100),
respectively, indicating typically graphite carbon with an
amorphous structure. The (002) diffraction peak of PRPC-1K
and PRPC-2K samples are slightly larger than that of PRPC,
which may be due to the enhanced graphitic structures in the
samples during the activation process.[1] The Raman spectra of
the PRPC, PRPC-1K and PRPC-2K samples were further
evaluated their graphite carbon structure (Fig. 2d). All the
−
1
samples have the typical D-band (about 1350 cm ) and G-band
about 1610 cm ) peaks, indicating typically graphite carbon
−
1
(
structure.
Fig. 1 (a) Scheme of the scalable preparation for PRPC-1K; SEM images of the (b) PRPC;
(c) PRPC-1K; (d) PRPC-2K; (e) cross-sectional view of PRPC-1K; (f) top-view SEM images
of PRPC-1K; (g) TEM image of the PRPC-1K.
Nitrogen adsorption-desorption isotherms of PRPC, PRPC-
1
K and PRPC-2K illustrate the variety of porosity by KOH
Fig. 2 (a) Nitrogen adsorption-desorption isotherms and (b) pore size distribution
curves of PRPC; PRPC-1K and PRPC-2K samples; (c) XRD patterns and (d) Raman spectra
activation, the results are shown in Fig. 2a. All of the samples
exhibit the type IV isotherm, showing they have a significant of PRPC, PRPC-1K and PRPC-2K samples.
amount of mesopores. It can be seen that the adsorbed volume
of PRPC-1K and PRPC-2K are remarkable larger than that of
PRPC material, indicating carbonized poplar roots by KOH and PRPC-2K electrodes was firstly studied in a three-electrode
activation can improve porosity of carbon. In addition, the system using 2 M KOH aqueous electrolyte. Fig. 3a shows the
PRPC-1K has unambiguous hysteresis loop at the relative typical cyclic voltammetry (CV) curves of all samples obtained
The electrochemical performance of the PRPC, PRPC-1K
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at 50 mV s . The CV curves of PRPC-1K and PRPC-2K three-electrode cell is shown in Fig. 3f. The PRPC-V1ieKw AertlieclcetOronldinee
electrodes show quasi-rectangular shapes, indicating that the shows a good capacitance retention oDfOI8: 190%.103a9f/tCe9rNJ1002,500090J
rapid electrochemical response and typical and typical consecutive charge-discharge cycles, indicating that the PRPC-
electrochemical double layer energy storage characteristics. By 1K electrode has a high electrochemical stability.
comparison, the CV curve of PRPC exhibits a small and
irregular triangular shape, indicating low charge response
caused by the electrolyte ions difficult to diffuse into the
electrode material and thus lead to an ion sieving effect.[28]
PRPC-1K shows the largest electrochemical CV area among
the electrodes, meaning it has the maximum specific
capacitance.
3
.2 The structure of the positive electrode and its
electrochemical performance.
The 3D nickel nitride (Ni N) nanosheets were synthesized
via a simply hydrothermal reaction and subsequent urea assists
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nitridation process.
Fig. 4 (a, b) SEM image of Ni
HRTEM image of the Ni N nanosheets.
3 3
N nanosheets; (c) TEM image of Ni N nanosheets; (d)
3
The mechanism of annealing reaction follows the equations
1 and 2) below:
(
CO(NH
2
)
2
→ NH
3
↑ + HCNO (Above 160℃)
(1)
6Ni(OH)
2
+ 4NH
3
→ 2Ni N + 12H O + N
3
2
2
(2)
The SEM image of the Ni precursor (Fig. S1a) is presented
3D sphere-like morphology with intertwined nanosheet
subunits. Similarly, the Ni N (Fig. 4a-b) and NiO (Fig. S1b) are
3
-1
-
Fig. 3 (a) CV curves of PRPC, PRPC-1K, andPRPC-2K at 50 mV s ; (b) GCD curves at 1 A g
1;
(c) GCD rate performance PRPC, PRPC-1K, and PRPC-2K; (d) CV curves of PRPC-1K at
various sweep rates; (e) GCD curves of PRPC-1K at various current densities; (f) cyclic also showed uniform 3D sphere-like morphology composed of
stability of PRPC-1K at 1 A g-1 for 10,000 cycles.
intertwined nanosheets, indicating that the original morphology
of nickel precursor was not destroyed by nitridation and
Fig. 3b shows the galvanostatic charge-discharge (GCD) curves
of the PRPC, PRPC-1K and PRPC-2K electrodes at a current
oxidation process. The TEM image further confirmed the 3D
sphere-like structure of the Ni N (Fig. 4c). The lattice spacings
were measured to be 0.23 nm corresponding to the (100) planes
of the hexagonal Ni N (JCPDS Card No. 89-7096) (Fig.4d).
The selected-area electron diffraction (SAED) pattern revealed
that the Ni N is a polycrystal structure with c-axis crystalline
3
-1
density of 0.5 A g . Similarly, PRPC-1K shows the longest
charge-discharge time with the maximum specific capacitance
among the electrodes. Fig. 3c shows the specific capacitance of
all the electrodes at various current densities. Specifically, the
3
3
specific capacitance of PRPC-1K is 170 F g at 0.5 A g-1,
-1
orientation (Fig. 4d).
-1
which is larger than that of PRPC (96 F g ) and PRPC-2K (155
The characterization of crystallographic structure and phase
purity of the samples were analyzed by X-ray powder
diffraction (XRD) measurement. As shown in Fig. S2a, the
-1
F g ). Moreover, PRPC-1K exhibits high capacitance retention
-1
of 68% even at 20 A g , which value is also higher than that of
PRPC and PRPC-2K. The high specific capacitance of PRPC-
1K is results from the hierarchical pore structure with high
specific surface area and large mesopore volume matching with
the aqueous electrolyte ions.[29-31] Fig. 3d shows the typical CV
curves of PRPC-1K at various scan rates. Fig. 3e shows the
charge-discharge profiles of PRPC-1K at different current
densities. The cycling performance of PRPC-1K based on a
diffraction peaks can be well assigned to (Ni(OH)
2 2
·0.75H O)
(
JCPDS No. 38-0715), and Fig. S2b exhibits the counterpart
sample of NiO (JCPDS No. 44-1159). As shown in Fig. 5a, the
diffraction peaks can be mainly assigned to the hexagonal
3
phase of Ni N (JCPDS No. 89-7096), which major diffraction
o
peaks at 38.9°, 41.9°, 44.4 , 58.5°, 70.6°, and 78.4° can be
4
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indexed to the (100), (002), (101), (102), (110), and (103) of NiO electrode, indicating Ni
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N electrode has a larger specific
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planes of the Ni
at 37.2° and 62.9° are ascribe to the corresponding (101) and capacitance of NiO and Ni
3
N phases. Meanwhile, other diffraction peaks capacity than NiO electrode. Fig. 6dDOsIh: o10w.1s039th/Ce9NsJp0e2c5i0f9icJ
N electrodes at various current
3
104) planes of the NiO phases (JCPDS No. 44-1159). The densities. The Ni N electrode exhibits a high specific capacity
3
(
-
1
-1
above results prove that the material is mainly contain the Ni
3
N
of 92.7 mAh g at a current density of 1 A g , which is larger
-
1
-1
and some NiO. Element mapping (Fig. S3a) and Energy than that of NiO (23.8 mAh g at 1 A g ). Fig. S4a shows the
dispersive spectroscopy (EDS, Fig. S3b) were conducted to Nyquist plots of Ni N and NiO. Apparently, the Ni N possesses
analyze the elemental distribution of sample. As shown in Fig. the steeper slope of the curves and the smaller diameter of
S3b, the signals of Ni and N have been detected with a Ni:N semicircle; it means that Ni N has the reduced ion diffusion
N. resistance. As presented in Fig. S4b, the capacity retention of
Ni N is 80% after charging/discharging cycling for 1500
3
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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7
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9
0
1
2
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7
8
9
0
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9
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8
9
0
3
ratio of 3.7, which is higher than the theoretical value of Ni
This deviation may result from the presence of some NiO.
3
3
cycles.
Fig. 5 (a) XRD pattern of Ni
of Ni N nanosheets.
3
N nanosheets; (b-d) X-ray photoelectron spectroscopy (XPS)
3
Fig. 6 (a) CV curves of Ni
current densities; (c) CV curves of Ni
Ni N and NiO.
3
N at various scan rates; (b) GCD curves of Ni
3
N at various
N and NiO at 10 mV s ; (d) GCD rate performance
X-ray photoelectron spectroscopy (XPS) was carried out to
confirm the existence of this Ni N composition. Elements of
Ni, O, C, N can be found in the XPS survey spectrum (Fig. 5b).
As shown in Fig. 5c, the peaks at 852.6 and 872.3 eV in
spectrum of Ni N nanosheets are attributed to monovalent Ni
3
2p3/2 and Ni 2p , respectively.
-1
3
3
3
3
.3 Electrochemical properties of the as-fabricated
asymmetric supercapacitor
1/2
[21,32]
The two bands at 860.4
In this work, an asymmetric supercapacitors (ASC) have
constructed by utilizing the nickel nitride (Ni N) nanosheets as
3
the positive electrodes and 3D interconnected framework of
porous carbon (PRPC-1K) as negative electrodes. Fig. 7a
N//PRPC-1K ASC. Fig.
N (-0.10 to 0.65 V) and PRPC-
K (-1 to 0 V) electrodes with their corresponding voltage
3/2
and 879.5 eV are ascribed to the satellite peaks of Ni 2p and
1/2
[32]
Ni 2p , respectively. The N 1s peak 400.8 eV can be also
ascribed to the formation of Ni
N (Fig. 5d).[33,35] In addition to
these peaks, the peaks at 855.7 and 878.3eV are assigned to
3
illustrates the conceptual design of Ni
b shows the CV curves of Ni
3
3
NiO, which is generated due to the surface oxidation of Ni
the air.[32,34,35]
Similarly, the electrochemical performance of the Ni N
3
electrode was also first estimated in a three-electrode system
with 2 M KOH electrolyte. Fig. 6a shows the typical CV curves
3
N in
7
1
-1
windows at a scan rate of 10 mV s for comparison.
According to their CV curves, the potential window of the
as-assembled Ni N//PRPC-1K ASC can be extended to 1.65 V
3
of Ni
to 0.65 V. The Ni
various scan rates, manifesting it has typical Faradaic behavior.
Fig. 6b shows the GCD curves of the Ni N electrode at various
3
N at various scan rates in the potential window from -0.1
as the sum of the potential ranges of the positive and negative
electrodes. Fig. 7c shows the CV curves of the ASC at various
scan rates with one pairs of redox peaks, indicating typical
reversible Faradaic behavior. In addition, the almost symmetric
GCD curves (Fig. 7d) indicate the ASC has a high coulombic
efficiency and electrochemical reversibility. Fig. 7e shows the
Ragone plot (energy density vs power density) of the
N//PRPC-1K ASC device, which value was calculated based
N//PRPC-1K
ASC achieved a high energy density of 30.9 Wh kg at a high
3
N electrode shows a pair of redox peaks at
3
current densities. All discharge curves are almost symmetrical
to the corresponding charge curves, suggesting excellent
electrochemical reversible behavior of the electrode material.
Fig. 6c shows the typical CV curves of NiO and Ni
electrodes obtained at 10 mV s . Both the NiO and Ni
3
N
N
Ni
3
-
1
3
on GCD data (Fig. 7d). It is shows that the Ni
3
electrodes are show a pair of redox peaks. However, the
electrochemical active area of Ni N electrode is larger than that
-
1
3
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J. Name., 2013, 00, 1-3 | 5
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power density of 412 W kg and still remains energy density of In summary, 3D interconnected framework of pVoierowuAsrticcleaOrbnloinne
5.4 Wh kg-1 at high power density of 4173.7 W kg-1. (PRPC-1K) with unique honeycomb poroDuOsI:s1t0r.u10c3tu9/rCe9aNnJd02h50ig9hJ
Furthermore, the maximum energy density of Ni N//PRPC-1K specific surface area was successfully synthesized by a simple
1
3
ASC is remarkable higher than most symmetrical activation process with biomass poplar root as carbon
-
supercapacitors such as FTMAC-4//FTMAC-4 (18.14 Wh kg precursor, which is further used as negative electrode material
1)
,[1] N,S-PCNs1-1//N,S-PCNs1-1 (21.0 Wh kg ), BDHSC- for supercapacitor that exhibits high specific capacitance of 170
-1
[7]
-1
[30]
-1
-1
1
//BDHSC-1 (20 Wh kg ), and even higher than that of the F g at 0.5 A g . In addition, the uniform 3D sphere-like Ni
3
N
previously reported some ASC (Table S2), such as composed of intertwined nanosheets units was prepared via a
PCNS@VNNP//NiO (16 Wh kg ),
CNS/VNNPs (29.5 Wh kg ). Ni/VN//N1-xV O
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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7
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9
0
1
2
3
4
5
6
7
8
9
0
-1 [36]
Ni(OH)
2
//N- simple low temperature hydrothermal and further urea-assisted
(23.3 Wh kg- nitridation process, which further used as positive electrode
-
1 [37]
x 2
1)
,
[38]
Co(OH)
2
//VN (22 Wh kg-1),[39] Ni-Co oxide//AC (12 Wh material for supercapacitor that exhibits high specific capacity
-1
[40]
-1
-1
kg ).
analysis of the Ni
There is apparent semicircle in the high-frequency range and a assembled based on these two materials achieved a high energy
Electrochemical impedance spectroscopy (EIS) of 92.7 mAh g at 1 A g . In virtue of their unique structures
3
N//PRPC-1K ASC was shown in Fig. S5, and high capacitive performance, the Ni N//PRPC-1K ASC
3
-1
-1
sloping line in the low-frequency region in the EIS density of 30.9 Wh kg at a high power density of 412 W kg ,
spectrogram, representing low bulk resistance (R =1.94), low and acceptable electrochemical cycling stability 81% retention
charge transfer resistance (Rct=1.48) and significant capacitance after 5000 cycles. Such hybridized ACS presented here aims at
behavior, respectively. The sloping curve is greater than 45 in lowing fabricating cost and high specific capacitance materials
low frequency region indicates the ideal capacitive behavior of for practical applications. These findings imply that
s
o
the device. As presented in Fig. 7f, there is a high capacitance Ni
retention of 81% achieved after long-term the energy storage systems.
charging/discharging cycling for 5000 cycles, showing that the
Ni N//PRPC-1K ASC displays excellent cycling stability.
3
N//PRPC-1K ACS may be promising for the future use in
a
3
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge the National Science Foundation of
China (21664012, 21703173, 51863019), the program for
Changjiang Scholars and Innovative Research Team in
University (IRT15R56), Basic Scientific Research Innovation
Team Project of Gansu Province (1606RJIA324), University
Scientific Research Innovation Team of Gansu Province
(
2017C-04).
Notes and references
1
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