alam2020.pdf

Ceramics International 47 (2021) 11220–11230
Available online 30 December 2020
0272-8842/© 2021 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Nickel-manganese phosphate: An efficient battery-grade electrode for
supercapattery devices
Shahid Alam, Muhammad Zahir Iqbal *
Nanotechnology Research Laboratory, Faculty of Engineering Sciences, GIK Institute of Engineering Sciences and Technology, Topi, 23640, Khyber Pakhtunkhwa,
Pakistan
A R T I C L E I N F O
Keywords:
Binary composites
Supercapattery
Energy storage
Charge storage mechanism
Specific energy
A B S T R A C T
This study investigates the charge storage mechanism in binary metal phosphates of NiMn(PO4)2 synthesized
through sono-chemical method. We studied the surface morphology and elemental analysis through SEM and
EDX analysis. From electrochemical measurements, the NiMn(PO4)2 demonstrates a high Qs of 678 Cg-1
at 0.4 Ag-
1
. The supercapattery device is fabricated by considering NiMn(PO4)2 as a positive and AC as a negative elec
trode. Also, we noticed effective cyclic stability of 99.2% after 5000 GCD cycles revealing a high specific energy
of 63.8 Whkg− 1
and a maximum specific power of 11892 Wkg-1
. Furthermore, the impact of capacitive and
diffusive contributions to the total capacity of the device is studied by employing Dunn’s model. Moreover,
power law is employed to calculate the b values for the device; the trend of b value ranges from 0.723 to 0.785
confirming the hybrid nature for the device. The contribution of electrostatic (capacitive) and Faradaic (diffu
sive) charge storage mechanism amplify the overall energy storage performance of the device. Such features of
NiMn(PO4)2 can offer a unique platform to further investigate new electrode materials for energy storage
devices.
1. Introduction
The increasing environmental pollution, elevated cost of energy re
sources, and depletion of fossil fuels increase the demand for renewable
energy resources [1,2]. Among the renewable energy resources, wind
and solar energy are the most favorable sources [3,4]. However, the
dependency of solar and wind energy on weather and sunlight is the
major hindrance in the continuant supply of energy [5,6]. The most
frequently used devices for energy storage applications are super
capacitors, conventional capacitors, batteries and fuel cells etc. [7–11].
In batteries, electrochemical reactions such as Faradaic reactions are
accountable for energy storage. In spite of having very high energy
density, the low power density of batteries limits their practical appli
cations when a high power is required [12,13]. Among these energy
storage systems, the electrochemical supercapacitors (SCs) have fasci
nated the researchers across the globe [14–16]. The distinctive features
of supercapacitors like high specific power and specific energy, excellent
life cycle stability, rapid charge discharge process, and above all the
environment friendly nature make them the most favorable devices for
storing energy efficiently [17]. Based on the charge storage process, SCs
are categorized as electric double layer and pseudocapacitor [18–21].
The EDLCs store charges through an electrostatic process and carbona
ceous materials are used as electrode material in EDLCs [22,23]. On the
other hand, the redox faradaic reactions are involved in the pseudoca
pacitors. The metal oxides and conducting polymers are used as elec
trode material in pseudocapacitors [24–26]. In contrast, the battery
grade materials possess high specific energy due to redox faradaic re
actions. The charge storage in battery type materials take place on aid of
redox faradaic reactions.
Although, the energy storage mechanism in batteries and pseudo
capacitors is almost the same (based on faradaic reaction) but they
possess different electrochemical signatures. In order to get the
maximum advantage the supercapacitor (high specific power) and bat
tery (high specific energy) can be combined in a single asymmetric de
vice termed as supercapattery. The supercapattery can give the
combined features of supercapacitor and battery i-e high power and high
specific energy along with good life cycle stability. This supercapattery
with versatile future can be the best alternative to both supercapacitors
and batteries. In the fabrication of supercapattery various battery grade
materials are utilized in positive electrode. The role of this battery type
electrode is to enhance the specific energy of the device. To obtain an
optimum electrochemical performance by a supercapattery high
* Corresponding author.
E-mail address: zahir.upc@gmail.com (M.Z. Iqbal).
Contents lists available at ScienceDirect
Ceramics International
journal homepage: www.elsevier.com/locate/ceramint
https://doi.org/10.1016/j.ceramint.2020.12.247
Received 13 November 2020; Received in revised form 22 December 2020; Accepted 24 December 2020

11221
performance battery grade material is required. It must have high ionic
conductivity, good redox active nature and high specific surface area.
Furthermore, the stable nature of the electrode is also an important
factor as the battery type electrode possess fewer electrochemical sta
bility due to excessive redox reactions. So, the optimization of efficient
battery grade electrode material with flashing electrochemical perfor
mance like superior specific capacity and high stable nature is needed to
be addressed.
So far, various types of electrode materials like metal oxides, phos
phates, sulfides, and conducting polymers have been used in super
capattery device. Recently, the conducting polymers (CPs) are found as
profitable electrode material for energy storage devices [27–29]. Apart
from the excellent conductivity of CPs, the poor capacity retention and
cyclic stability limit their scope in supercapattery devices [30].
Whereas, metal oxides like ruthenium, iron, and cobalt oxide arise as
useful electrode material for energy storage devices [16,31]. These
materials have a high surface to volume ratio and aggregate when used
in their pure form. The electroactive sites in the material reduce due to
aggregation and it results in dwindling specific capacity [31]. On the
other hand, various metal phosphates like nickel, manganese, and cobalt
phosphates have indicated good conductivity and environment friendly
nature [32,33]. Therefore, due to the fast ion transport mechanism,
these metal phosphates are found to be suitable electrode material for
supercapacitor applications. Nevertheless, the optimization of electrical
conductivity, bandgap, structural flexibility, and carrier mobility are
some of the critical issues need to be solved [32,34,35]. To address these
issues, the use of various nano heterostructures could be the possible
choice. The formation of redox active sites and defects in grain bound
aries of heterostructure result in high ionic conductivity, short diffusion
path and enhanced redox activity. Therefore, extensive research has
been made for the utilization of doped heterostructures of metal phos
phates as battery grade electrode material for hybrid energy storage
devices [35–40]. Jikui et al. [41] utilized 2D porous Co3O4 nano-sheet as
battery grade electrode synthesized via direct hydrothermal method.
The supercapattery device was assembled by using Co3O4 nano-sheets
and AC. The device yields a maximum energy density of 22.49
Whkg− 1
at corresponding power of 800 Wkg-1
with an excellent cyclic
stability of 91.8% after 10,000 GCD cycles. Similarly, Xiaoying et al.
[42] has made composite of battery type MnCoO4 with AC and utilized it
as electrode material for supercapattery device. The composite yields a
maximum specific capacity of 443.5 Cg-1
at 0.5 Ag-1
. Wang et al. [43]
utilize magnesium cobaltite micro flowers (MgCo2O) as battery type
electrode material for supercapattery device. The electrode demonstrate
a maximum specific capacity of 313.3 Cg-1
at 1 Ag-1
in three electrode
assembly. The electrode also demonstrate a cyclic stability of 74.5%
after 5000 cycles. Anjon et al. [44] utilized Urchin-like NiO nanosphere
synthesized via microwave assisted hydrothermal technique as elec
trode material for supercapacitor and batteries. The material is utilized
as anode in lithium ion batteries and it exhibited a specific capacity of
1027 mAhg− 1
and also delivers a specific capacitance of 736 Fg-1
when
used as electrode in supercapacitor. Mirghni et al. synthesized NiCo
(PO4)3/GF based heterocomposite for hybrid supercapacitor. The
fabricated device yields specific energy of 34.8 Whkg− 1
and specific
power of 377 Wkg-1
at 0.5 Ag-1
[45]. Cobalt phosphates are excessively
utilized as electrode material in high performance SC devices. Chen et al.
reported the nano-flower shaped CoP electrode for high performance SC
exhibiting a maximum capacitance of 418 Fg-1
at 1 Ag-1
[46]. The spe
cific energy and specific power are observed to be 8.8 Whkg− 1
and 6
Wkg-1
, respectively, with good cyclic durability of 97% for 6000 cycles.
Furthermore, J. Zhao et al. performed the hydrothermal synthesis of
ammonium nickel phosphate hydrate and used it for supercapacitor
applications [47]; a maximum capacitance of 1072 Fg-1
at 1.5 Ag-1
in
three cell assembly and the device showed a good cyclic stability of 95%
after 3000 GCD cycles. Liu et al. fabricated a mixed metal phosphate
composite by using a microwave synthesis technique [48]. The electrode
displayed the highest capacitance of 828 Fg-1
at 1 Ag-1
with 81.3%
capacitance retention after 3000 cycles.
Here, we synthesized nickel-manganese phosphate via sono-
chemical method as a working electrode in supercapattery devices.
The binary composites are made by mixing Mn and Ni in equal ratios and
calcined at 400 ◦
C to test for energy storage applications. Electro
chemical measurements like CV, GCD, and EIS are performed in three-
electrode assembly; an electrode with the best electrochemical perfor
mance was used in supercapattery device. Our device comprised of
NiMn(PO4)2 and activated carbon as positive and negative electrodes,
respectively. This asymmetric device is tested in two electrode assembly.
The electrochemical results reveal high specific energy of 64.2 Whkg− 1
and a maximum specific power of 11,896 Wkg-1
. Besides, the device
exhibits an outstanding cyclic stability of 99.2% after 5000 GCD cycles.
2. Experimental setup
2.1. Materials
Manganese Chloride (MnCl2).4H₂O, Nickel chloride (NiCl2)⋅2H₂O),
and disodium hydrogen phosphate (Na2HPO4), are acquired from the
Sigma. Potassium hydroxide (KOH), activated carbon (AC), N-methyl-2-
2pyrolidone (NMP), polyvanylidene fluoride (PVDF) and acetylene
black, were also bought from Sigma.
2.2. Synthesis of Ni(PO4)2 and Mn(PO4)2 nanoparticles
Ni(PO4)2 nanoparticles were synthesized via sonochemical method
followed via calcination. Firstly 25 ml solution of 0.05 M (NiCl2)⋅2H₂O)
is made in DI water and placed under probe sonicator. Afterward, 25 ml
solution of 5 M Na2HPO4 is dropwise added in above mentioned solution
and sonicated for 45 min. A light greenish colloidal solution is formed.
The power of sonication waves is 950 W and amplitude is kept at 40%.
The synthesized material is collected by centrifugation process and
washed several times with DI water and acetone. The obtained material
is then dried at 60 ◦
C overnight and calcined at 400 ◦
C for 4 h. The Mn
(PO4)2 nanoparticles are synthesized by adopting a similar procedure
and (MnCl2).4H₂O is used as a precursor.
2.3. Synthesis of Ni-Mn(PO4)2 binary composites
The binary composite of Ni-Mn(PO4)2 is made under probe sonicat
ion by doping (MnCl2).4H₂O in (NiCl2)⋅2H₂O) solution. Initially 0.05 M
of (NiCl2)⋅2H₂O) is melted in 15 ml of DI water. After that, 0.0125 M of
(MnCl2).4H₂O is dissolved in 10 ml DI water and dropwise added in the
above solution under constant starring. The mixed solution is then
subjected to prob sonicator and 25 ml solution of 0.75 M Na2HPO4 is
added dropwise in the previous solution under probe sonication. The
sonication is performed for 45 min until the colloidal solution is formed.
The obtained nanoparticles are collected washed and dried overnight as
discussed in the case of (NiCl2)⋅2H₂O). The binary composite is also
calcined at 400 ◦
C for 4 h. The composite is symbolized as NiMn(PO4)2
(see Fig. 1).
3. Results and discussion
3.1. Surface morphology and material composition
The structural morphology and phase purity of the synthesized
nanoparticles are studied by using XRD technique. Fig. 2 demonstrates
the XRD pattern of all the synthesized samples. The obtained pattern
corresponds to Ni(PO4)2 (JCPD, card no. 038–1473) [34,35]. The two
humps appeared between 2θ angle of 21–35 affirms the amorphous
nature of Ni(PO4)2 [29]. Similarly the small diffraction peaks are
observed corresponds to Mn(PO4)2 (JCPD, card no. 03–0426) [36]. The
low intensity of peaks and small humps in the XRD pattern attributes to
the amorphous nature of synthesized materials [29]. The obtained
S. Alam and M.Z. Iqbal

11222
diffraction pattern is in well agreement with the report literature of
nickel and manganese phosphate [29,30,36,37]. The surface
morphology of all the synthesized NiMn(PO4)2 based binary nano
composites is studied by employing SEM analysis. Fig. 3 (a) represents
the SEM image of the composites which indicates the formation of NiMn
(PO4)2 nanoflakes. Furthermore, the elemental composition of the
composite is also investigated by performing energy-dispersive X-ray
spectroscopy (EDX). The EDX of the NiMn(PO4)2 nanoflakes is demon
strated in Fig. 3(b–c). The observed peaks of EDX affirm the existence of
Ni, Mn, P, O, Cl, and C elements which reveals the formation of binary
metallic phosphate. There is no impurity peak observed in EDX which
confirms the purity of synthesized material.
3.2. Electrochemical performance
3.2.1. Cyclic voltammetry
The CV measurements are performed to investigate the electro
chemical performance of the synthesized materials in three electrode
assembly. The Pt wire and Hg/HgO are used as counter and reference
electrodes respectively. Measurements are performed in a potential
window range of 0.6 V and 1 M KOH is used as an electrolyte. The CV
curves of all three electrodes at various scan rates are demonstrated in
Fig. 4(a–c). The prominent oxidation and reduction peaks are observed
in the voltammograms indicates the occurrence of redox faradaic re
actions which affirms the battery-grade nature of the tested electrode
materials [49]. It can be noticed that the peak current increases with
increasing scan rates. The oxidation peaks in the CV curve for NiPO4
shifts towards higher potential at higher scan rates due to the unavail
ability of electrolyte ions inside the electrode material. Whereas, the
binary nanocomposites exhibit more prominent redox peaks at high scan
rate reflects its better rate capability and good electrochemical perfor
mance compared to other samples. Fig. 4 (d) represents the CV curves of
all three samples at 3 mVs− 1
. It can be noticed that the CV curve of bi
nary composite demonstrates a higher peak current and maximum area
under the curve. The specific capacity of the tested materials is calcu
lated from the CV curves by using the following expression:
Qs =
1
vm
∫
Vf
Vi
I × V dV (1)
In the above equation, Qs represents specific capacity (Cg− 1
), V de
notes the scan rate (mVs− 1
), m symbolizes the mass of electrode mate
rial, whereas, the integral part of the equation implies the area under the
curve. The binary composite i-e NiMn(PO4)2 exhibits maximum Qs value
of 788 Cg-1
at 3 mVs− 1
and also shown good rate capability compare to
pristine Ni(PO4)2 and Mn(PO4)2. To investigate the different wt % of Mn
in Ni the CV curves for all the samples at 3, 30 and 50 mVs− 1
are per
formed as demonstrated in Fig. 5(a–c). The result reveals that the sample
with 75% Ni and 25% Mn demonstrates maximum area under the curve
and high specific capacity compare to other samples. The trend of Qs
with scan rates is demonstrated in Fig. 5(d). It can be observed that the
Ni0.75Mn0.25(PO4)2 depicts maximum Qs value.
3.2.2. GCD measurements
The charge storage performance of the synthesized nanocomposites
is further investigated by performing GCD measurements in three elec
trode assembly. The measurements are performed in a PW range of
0–0.6 and 1 M KOH is used as an electrolyte. The Pt wire and Hg/Hgo are
used as counter and reference electrode respectively. Fig. 6(a–b) dem
onstrates the discharging curves of all three samples at different current
densities. The non-linearity of discharging curves indicates the battery-
grade nature of synthesized materials as noticed in CV measurements.
The energy storage performance of each electrode is investigated by
calculating the specific capacity by using the following equation [49].
Fig. 1. Schematic illustration of sonochamical synthesis of binary metallic phosphates and washing drying and calcination process.
Fig. 2. XRD pattern of Ni(PO4)2, Mn(PO4)2, and NiMn(PO4)2.

11223
Qs =
I × Δt
m
(2)
In the above equation, I denotes the total current, Δt represents the
discharging time and m is the mass of the working electrode. From the
above equation it can be perceived that the electrode which possess
maximum discharging time will have high specific capacity. In Fig. 6 (b)
it can be observed that the binary composite of NiMn(PO4)2 exhibit
maximum discharging time compare to other two samples hence, yields
a highest specific capacity of 678 Cg-1
at 0.4 Ag-1
. To ratify the optimum
electrode material the GCD is performed at 1 Ag− 1
for the composite with
50% and 75% Mn doping as demonstrated in Fig. 7 (a). It can be
observed that the Ni75Mn25(PO4)2 indicates best electrochemical per
formance with maximum capacity of 570 Cg-1
at 1 Ag-1
. Fig. 7 (b)
demonstrates the trend of Qs with current densities for all the samples.
The result reveals that 25 wt % Mn in Ni yields best electrochemical
performance.
The trend of Qs for all the samples w.r.t scan rates and current density
is illustrated in Fig. 5(a–b). The maximum Qs value has been measured
for binary composites from both CV and GCD measurements. It can be
observed from Fig. 8(a–b) that the Qs value decreases by increasing the
scan rate and current densities. This is because at lower scan rate and
current value the ions move steadily in the electrolyte and get enough
time to interact with electrode material, also the maximum redox sites
are available and complete redox reaction can be performed which re
sults in maximum Qs at low scan rate and current density values. In
contrast, at the elevated scan rates and current density values the ions
move rapidly and did not get enough time to perform the complete redox
reaction thus results in low Qs value at higher scan rates. The maximum
electrochemical performance of NiMn(PO2)4 can be explained from CV
curves for all the samples. Fig. 3(f) demonstrates the comparison of CV
curves for all the samples at 3 mVs− 1
. The pure Ni(PO2)4 has the
maximum value of redox oxidation state at 0.54V while Mn(PO2)4 has
the maximum oxidation redox peak at 0.46V. The composite comprising
of 25% Mn and 75% of Ni holds a broader redox oxidation peak that
incorporates the maximum redox oxidation potential of both Ni and Mn
whereas, the peak current is almost similar to Ni(PO2)4 which in result
enhances the overall electrochemical performance of composite
compare to all other samples. From the comparison of all three elec
trodes it can be concluded that the binary composite of NiMn(PO4)2
demonstrates maximum Qs value and also possess good rate capability as
seen in Fig. 8(a–b).
3.2.3. Electrochemical impedance spectroscopy (EIS)
To investigate the interaction between electrode and electrolyte and
the mechanism of such interactions the EIS is an important technique. It
provides the information about the internal resistance of electrode ma
terial and the resistance between electrode and electrolyte [50]. Fig. 9
demonstrates the EIS spectrum for all the samples performed in three
electrode assembly in a frequency range of 0.1–105
Hz. The x-axis rep
resents the real part of the impedance and the imaginary part is repre
sented on the y-axis. The zoomed part of EIS is shown in the inset of the
figure for better understanding.
The ESR is measured for all the samples from the point of intersection
with the x-axis. The value of ESR signifies the conductivity of the sam
ple. The estimated ESR values for Ni(PO4)2, NiMn(PO4)2, and Mn(PO4)2
are 1.03, 0.95 and 1.63 Ω respectively. The least value of binary com
posite signifies it highest ionic conductivity compared to the other two
samples. Furthermore, the formation of semicircles with a larger
Fig. 3. Structural morphology and material composition of NiMn(PO4)2 (a) SEM analysis and (b–c) EDX spectrum.

11224
diameter at high frequency regime signifies charge transfer resistance
(Rct), the sloppy part at lower frequency region represents hydroxyl ions
(OH) diffusion inside the electrode material which indicates the War
burg impedance (W) [51]. The vertical line for NiMn(PO4)2 represents
its low Warburg impedance. The obtained results from EIS measurement
are in good agreement with the CV and GCD measurements which im
plies the best electrochemical performance of NiMn(PO4)2 compare to
pristine phosphates of both the metals.
4. Supercapattery performance measurement
To energy storage performance of the binary composite is further
investigated by fabricating a supercapattery device via utilizing NiMn
(PO4)2 as a positive electrode and AC as a negative electrode. The device
Fig. 4. CV curves of all three samples at different scan rates in three cell assembly. Fig. 2(a–c) Ni(PO4)2, Mn(PO4)2 and NiMn(PO4)2 respectively. (f) Comparison of
the CV profile of all three samples at 3 mVs− 1
.
Fig. 5. CV curves of all the sample with different wt % of Mn in Ni. (a) at 3 mVs− 1
, (b) 30 mVs− 1
and (c) 50 mVs− 1
. (d) Comparison of Qs with scan rate for all
the samples.

11225
Fig. 6. Discharging curves of all the samples at different current densities in three electrode assembly. (a) Ni(PO4)2 (b) Mn(PO4)2 and (c) NiMn(PO4)2. (d) GCD
curves for all three samples at 0.4Ag-1
.
Fig. 7. (a) Discharging curves of all the samples at different wt % of Mn in Ni at 1 Ag-1
. (b) The trend of Qc for all three samples (Ni(PO4)2, 25% Mn, 50% Mn and
75% and Mn(PO4)2) as a function of different current densities.

11226
was tested in two electrode configuration by keeping 1 M KOH as an
electrolyte. Fig. 10 (a) demonstrates the schematic representation of
supercapattery device. The separate CV curve of both the electrodes are
taken at 10 mVs− 1
in three electrode assembly before the fabrication of
the device and is illustrated in Fig. 10 (b). As per literature, for a sig
nificant increase in energy storage performance of supercapacitors, it
should certainly work at larger potential windows. The maximum PW of
the supercapattery device is optimized by performing the CV measure
ments at various PWs as demonstrated in Fig. 10 (c). The maximum PW
is obtained by combining the PW of NiMn(PO4)2 (0–0.7 V) and AC (− 1
to 0 V). Fig. 10 (d) demonstrates the CV measurements of the super
capattery device at different scan rates ranges from 3 to 100 mVs− 1
. The
rectangular behavior of the CV curve in the voltage range of 0–0.5 V
attributes to the EDLC response due to the adsorption of electrolyte ions
at the electrode-electrolyte interface and originate due to capacitive
electrode (AC in this case). Whereas, beyond 0.5 V the redox peaks are
observed originated due to faradaic reaction contribute to the charge
storage mechanism. It can be noticed that the intensity of the redox
peaks increases as the scan rate increases. The combined effect of
capacitive and battery grade electrode can be observed in the CV curves
from the rectangular part and redox peaks respectively. Furthermore,
the CV curves retain its shape even at high scan rate attributes to the
good rate capability of the device.
To evaluate the energy storage parameters of the device GCD mea
surements are performed for the device in two electrode assembly in a
PW of 0–1.7 V by keeping 1 M KOH as an electrolyte. The discharging
curves of the device are demonstrated in Fig. 10 (e). The symmetric
behavior in the GCD curves is due to the capacitive electrode whereas
the slight hump in the curves depicts the presence of redox reactions due
to battery graded electrode. The energy storage capability like specific
energy and specific power of the device is calculated by using the
following relation:
E =
ΔV × Q
3.6 × 2
(3)
P =
E × 3600
Δtdis
(4)
Here, Q represents the specific capacity, Δt denotes the discharging
time, and ΔV represents the PW. The supercapattery reveals a high
specific energy of 64.2 Whkg− 1
, with corresponding specific power, is
340 Wkg-1
at a current density of 0.4 Ag-1
and a maximum value of
specific power is 11896 Wkg-1
at 14 Ag-1
. The comparison of device
performance with previously reported literature in terms of specific
energy and power is demonstrated in Fig. 10 (f) [52–55]. Furthermore,
the detailed comparison of reported work with oxide and phosphate
based electrode materials is provided in Table 1.
Along with excellent specific energy and power the device exhibits,
outstanding life cycle stability demonstrated in Fig. 11 (a). The device
maintains the capacity retention of 99.2% after 5000 continuous GCD
cycles. The slight enhancement in specific capacity after ~300 cycles,
signifies the stabilization of electrode to their maximum limit. As the
number of cycles increases initially the diffusion of electrolyte ions into
the active material increases which in term improves the redox activ
ities. So, this will results in an upsurge in the charge storage capacity of
the device. The ESR value for the device is calculated before and after
the stability measurement by performing EIS in two electrode assembly
and is represented in Fig. 11 (b). The device demonstrates a very low
ERS of 0.34 Ω before stability measurements. The small diameter
semicircle and vertical line in the EIS spectrum at high frequency region
represent the high conductivity of supercapattery device long with
excellent OH−
diffusion into the material respectively, which affirms the
good capacitive behaviors of device. The ESR of the device is increased
slightly from the initial value to 0.65 Ω due to an increase in the internal
resistance of electrode material and electrolyte due to the continue
charge-discharge process. The increase in Warburg resistance is also
observed through a slight shift of vertical line towards low frequency
region which depicts the loss in capacitive behavior of device after 5000
GCD cycles. The overall trend of the EIS spectrum before and after sta
bility measuring shows good cyclic stability of the device.
5. The charge storage mechanism in supercapattery
The analysis of Dunn and his co-workers is utilized at various sweep
rates. The quantitative assessment of capacitive and diffusive contri
butions in the total capacity of the fabricated devices can be calculated
[56].
i(V)=k1v + k2v 1/2
(5)
Fig. 8. The trend of Qc for all three samples as a function of different (a) scan rate, (b) current densities.
Fig. 9. EIS spectrum of all the samples in three cell assembly within a fre
quency range of 0.1–100 KHz. Inset displays the zoom in vision of EIS curves.

11227
In Eq. (5), the output current for a definite potential is represented by
i(V), v indicates the scan rate and the expressions k1v are capacitive
currents (adsorption of charges results in surface controlled) and k2v1/2
are diffusive currents (diffusion-controlled owing to redox reactions).
Fig. 12(a–f) displayed statistical analysis at different sweep rates for
distinctive separation of currents owing to the surface plus diffusion-
controlled processes.
To the entire capacity of supercapattery, the capacitive contribution
is obtained to be 40% at 3 mVs− 1
scan rate Fig. 12 (a), and diffusive
contribution is found to be dominant at scan rate of 3 mVs− 1
because the
ions get enough time to ample the redox relations at lower scan rates
thus, the charge storage takes place on the aid of battery grade electrode.
An upsurge in the capacitive contribution is observed as the scan rate is
increased and it found to be 78% at 100 mVs− 1
because at high scan rate
the ions didn’t get sufficient time to complete the redox reaction and the
charge storage contribution is dominant for capacitive electrode at
elevated scan rates as seen in bar plot Fig. 12 (b). The above analysis
confirms the hybrid nature of the device as the charge storage contri
bution takes place through both capacitive and battery graded
electrodes.
Furthermore, the power law is applied for the theoretical investiga
tion of the electrochemical performance of the hybrid device. The
following equation demonstrates the power law by defining the relation
between scan rate ‘I’ and current density ‘v’. [57,58].
i = avb
(6)
ln(i) = ln(k) + bln(v) (7)
here, k and b are the adjustable parameters. The exponent of power b is
used to investigate the charge storage mechanism of device. The value of
the b should be equal to 1 for the ideal supercapacitor demonstrates non-
diffusive charge storage whereas, for the batteries, b should be equal to
0.5 depicts the diffusion-controlled charge storage process. Thus, the
value of b lies between 0 and 1 demonstrates the mechanism of charge
storage in supercapattery device [59–61]. Fig. 13 demonstrates the
graph between the log of scan rates for voltages and log of I from 0.8 to
1.35 V. The value of b obtained through linear fitting and lies in the
range of 0.72–0.76 lies exactly in between the range of batteries and SCs.
The range of b values suggested the presence of a both capacitive and
diffusive mechanism for the charge storage process in supercapattery
device. Thus, the results reveal that the fabricated supercapattery device
comprising of binary metal phosphates provides a route towards the
development of efficient and cost-effective energy storage system.
6. Conclusion
We synthesized NiMn(PO4)2 by sono-chemical method; a facile and
cost-effective approach. The surface morphology and elemental analysis
Fig. 10. (a) Schematic illustration of supercapattery device. (b) CV profile of NiMn(PO4)2 and AC at 30 mVs− 1
in three cell assembly. (c) CV measurement of the
device at different PW’s in two cell assembly. (d) CV curves of the supercapattery device at various scan rates in two electrode configuration. (e) Discharging curves
of the fabricated device at various current densities in two cell assembly. (f) Ragone plot represents the comparative study of this work with previously re
ported literature.
Table 1
Comparison of our work with previously reported literature.
S.
no
Electrode
material
Max. Energy density
(Whkg− 1
)
Max. Power density
(Wkg− 1
)
Ref
1. Co3(PO4)2
nanoflakes
43.2 5800 [62]
2. MWCNT-Co3O4-
Ag
16.5 297.5 [63]
3. Sol-gel Co3O4 40 742 [64]
4. CoMoO4 18.89 106 [65]
5. TiO2/RGO 54.3 420.4 [66]
6. Co3(PO4)
2.8H2O
29.2 4687 [67]
7. Ni3(PO4)2-
Ag3PO4
32.4 399.5 [68]
8 Ni-Zn Phosphate 33.7 824.9 [69]
9 NICoP 36 4000 [70]
10 NiCoP 56 5333 [71]
11 Sr3P2/PANI 28.9 5100 [72]
12 This Work 63.8 11,892 This
work

11228
of the samples were examined through SEM and EDX. The nanoflakes
like morphology was observed. From electrochemical measurements,
the NiMn(PO4)2 demonstrated a high Qs of 678 Cg-1
at 0.4 Ag-1
, which
was used as anode in supercapattery device. Our device exhibited an
outstanding cyclic stability of 99.2% after 5000 GCD cycles, high spe
cific energy of 63.8 Whkg− 1
and a maximum specific power of 11,892
Wkg-1
. The impact of capacitive and diffusive contributions in the total
capacity is studied by employing Dunn’s model. Moreover, the hybrid
nature of device was approved from power law thereby presenting the
trend from 0.723 to 0.785. In conclusion, the contribution of electro
static (capacitive) and Faradaic (diffusive) charge storage mechanism
amplifies the overall energy storage performance of the device.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgment
This work is supported by Higher Education Commission (HEC) of
Pakistan under the National Research Program for Universities (NRPU)
with Project No. 5544/KPK/NRPU/R&D/HEC/2016.
References
[1] C. Azar, K. Lindgren, B.A. Andersson, Global energy scenarios meeting stringent
CO2 constraints—cost-effective fuel choices in the transportation sector, Energy
Pol. 31 (2003) 961–976.
[2] S. Jacobsson, A. Johnson, The diffusion of renewable energy technology: an
analytical framework and key issues for research, Energy Pol. 28 (2000) 625–640.
[3] E.V. Mc Garrigle, J.P. Deane, P.G. Leahy, How much wind energy will be curtailed
on the 2020 Irish power system? Renew. Energy 55 (2013) 544–553.
[4] M.Z. Iqbal, S. Alam, M.M. Faisal, S. Khan, Recent advancement in the performance
of solar cells by incorporating transition metal dichalcogenides as counter
electrode and photoabsorber, Int. J. Energy Res. 43 (2019) 3058–3079.
[5] V. Khare, S. Nema, P. Baredar, Solar–wind hybrid renewable energy system: a
review, Renew. Sustain. Energy Rev. 58 (2016) 23–33.
[6] A. Evans, V. Strezov, T.J. Evans, Assessment of sustainability indicators for
renewable energy technologies, Renew. Sustain. Energy Rev. 13 (2009)
1082–1088.
Fig. 11. Life cycle stability test of supercapattery device for 5000 GCD cycles. (b) EIS measurements of the device before and after the stability test.
Fig. 12. (a) The pink region depicts the capacitive contribution of at scan rates of 3 mVs− 1
. The light bluish portion is the experimental CV curves at these scan rates
represents diffusive contribution. (b) Bar plot represents the total capacitive and diffusive contribution at different scan rates. (For interpretation of the references to
colour in this figure legend, the reader is referred to the Web version of this article.)
Fig. 13. Log of peak current and scan rates at constant voltages to calculate the
b values of the device.

11229
[7] D. Jain, S. Hashmi, A. Kaur, Surfactant assisted polyaniline nanofibres—reduced
graphene oxide (SPG) composite as electrode material for supercapacitors with
high rate performance, Electrochim. Acta 222 (2016) 570–579.
[8] R. Kötz, M. Carlen, Principles and applications of electrochemical capacitors,
Electrochim. Acta 45 (2000) 2483–2498.
[9] H.M. Singh, A.K. Pathak, K. Chopra, V. Tyagi, S. Anand, R. Kothari, Microbial fuel
cells: a sustainable solution for bioelectricity generation and wastewater treatment,
Biofuels 10 (2019) 11–31.
[10] J. Liu, Z. Bao, Y. Cui, E.J. Dufek, J.B. Goodenough, P. Khalifah, Q. Li, B.Y. Liaw,
P. Liu, A. Manthiram, Pathways for practical high-energy long-cycling lithium
metal batteries, Nature Energy 4 (2019) 180–186.
[11] Y. Qian, S. Lu, F. Gao, Preparation of MnO 2/graphene composite as electrode
material for supercapacitors, J. Mater. Sci. 46 (2011) 3517–3522.
[12] S. Senthilkumar, R.K. Selvan, Fabrication and performance studies of a cable-type
flexible asymmetric supercapacitor, Phys. Chem. Chem. Phys. 16 (2014)
15692–15698.
[13] H. Mi, X. Zhang, S. An, X. Ye, S. Yang, Microwave-assisted synthesis and
electrochemical capacitance of polyaniline/multi-wall carbon nanotubes
composite, Electrochem. Commun. 9 (2007) 2859–2862.
[14] A. González, E. Goikolea, J.A. Barrena, R. Mysyk, Review on supercapacitors:
technologies and materials, Renew. Sustain. Energy Rev. 58 (2016) 1189–1206.
[15] M. Zhi, C. Xiang, J. Li, M. Li, N. Wu, Nanostructured carbon–metal oxide composite
electrodes for supercapacitors: a review, Nanoscale 5 (2013) 72–88.
[16] G. Wang, L. Zhang, J. Zhang, A review of electrode materials for electrochemical
supercapacitors, Chem. Soc. Rev. 41 (2012) 797–828.
[17] M. Salanne, B. Rotenberg, K. Naoi, K. Kaneko, P.-L. Taberna, C.P. Grey, B. Dunn,
P. Simon, Efficient storage mechanisms for building better supercapacitors, Nature
Energy 1 (2016) 1–10.
[18] J.R. Miller, P. Simon, Electrochemical capacitors for energy management, Sci.
Magazine 321 (2008) 651–652.
[19] S. Trasatti, P. Kurzweil, Electrochemical supercapacitors as versatile energy stores,
Platin. Met. Rev. 38 (1994) 46–56.
[20] P. Simon, Y. Gogotsi, B. Dunn, Where do batteries end and supercapacitors begin?
Science 343 (2014) 1210–1211.
[21] A. Shukla, S. Sampath, K. Vijayamohanan, Electrochemical supercapacitors: energy
storage beyond batteries, Curr. Sci. Bangalore 79 (2000) 1656–1661.
[22] L. Hao, X. Li, L. Zhi, Carbonaceous electrode materials for supercapacitors, Adv.
Mater. 25 (2013) 3899–3904.
[23] Z. Chen, S. Ye, S.D. Evans, Y. Ge, Z. Zhu, Y. Tu, X. Yang, Confined assembly of
hollow carbon spheres in carbonaceous nanotube: a spheres-in-tube carbon
nanostructure with hierarchical porosity for high-performance supercapacitor,
Small 14 (2018), 1704015.
[24] Y. Jiang, J. Liu, Definitions of pseudocapacitive materials: a brief review, Energy
Environ. Mater. 2 (2019) 30–37.
[25] V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate
electrochemical energy storage, Energy Environ. Sci. 7 (2014) 1597–1614.
[26] M.Z. Iqbal, S. Alam, A.M. Afzal, M.J. Iqbal, K. Yaqoob, M.A Kamran, M.R.A. Karim,
T. Alherbi, Binary composites of strontium oxide/polyaniline for high performance
supercapattery devices, Solid State Ionics 347 (2020) 115276.
[27] Z.S. Iro, C. Subramani, S. Dash, A brief review on electrode materials for
supercapacitor, Int. J. Electrochem. Sci 11 (2016) 10628–10643.
[28] L. Fu, Q. Qu, R. Holze, V.V. Kondratiev, Y. Wu, Composites of metal oxides and
intrinsically conducting polymers as supercapacitor electrode materials: the best of
both worlds? J. Mater. Chem. 7 (2019) 14937–14970.
[29] M. Alzaid, M.Z. Iqbal, S. Alam, et al., Binary composites of nickel-manganese
phosphates for supercapattery devices, J. Energy Storage 33 (2021) 102020.
[30] H. Fu, Z.-j. Du, W. Zou, H.-q. Li, C. Zhang, Carbon nanotube reinforced polypyrrole
nanowire network as a high-performance supercapacitor electrode, J. Mater.
Chem. 1 (2013) 14943–14950.
[31] J. Iqbal, A. Numan, M.O. Ansari, P.R. Jagadish, R. Jafer, S. Bashir, S. Mohamad,
K. Ramesh, S. Ramesh, Facile synthesis of ternary nanocomposite of polypyrrole
incorporated with cobalt oxide and silver nanoparticles for high performance
supercapattery, Electrochim. Acta (2020), 136313.
[32] X. Wang, H.-M. Kim, Y. Xiao, Y.-K. Sun, Nanostructured metal phosphide-based
materials for electrochemical energy storage, J. Mater. Chem. 4 (2016)
14915–14931.
[33] M.Z. Iqbal, J Khan, Optimization of cobalt-manganese binary sulfide for high
performance supercapattery devices, Electrochimica Acta 368 (2021) 137529.
[34] M. Sun, H. Liu, J. Qu, J. Li, Earth-rich transition metal phosphide for energy
conversion and storage, Adv. Energy Mater. 6 (2016), 1600087.
[35] R. Bendi, V. Kumar, V. Bhavanasi, K. Parida, P.S. Lee, Metal organic framework-
derived metal phosphates as electrode materials for supercapacitors, Adv. Energy
Mater. 6 (2016), 1501833.
[36] S. Sahoo, R. Mondal, D.J. Late, C.S. Rout, Electrodeposited nickel cobalt
manganese based mixed sulfide nanosheets for high performance supercapacitor
application, Microporous Mesoporous Mater. 244 (2017) 101–108.
[37] S.H. Kazemi, B. Hosseinzadeh, H. Kazemi, M.A. Kiani, S. Hajati, Facile synthesis of
mixed metal–organic frameworks: electrode materials for supercapacitors with
excellent areal capacitance and operational stability, ACS Appl. Mater. Interfaces
10 (2018) 23063–23073.
[38] N. Padmanathan, H. Shao, K.M. Razeeb, Multifunctional nickel phosphate nano/
microflakes 3D electrode for electrochemical energy storage, nonenzymatic
glucose, and sweat pH sensors, ACS Appl. Mater. Interfaces 10 (2018) 8599–8610.
[39] N. Padmanathan, H. Shao, D. McNulty, C. O’Dwyer, K.M. Razeeb, Hierarchical
NiO–In 2 O 3 microflower (3D)/nanorod (1D) hetero-architecture as a
supercapattery electrode with excellent cyclic stability, J. Mater. Chem. 4 (2016)
4820–4830.
[40] N. Padmanathan, H. Shao, K.M. Razeeb, Honeycomb micro/nano-architecture of
stable β-NiMoO4 electrode/catalyst for sustainable energy storage and conversion
devices, Int. J. Hydrogen Energy 45 (2020) 30911–30923.
[41] J. Zhu, B. Huang, C. Zhao, H. Xu, S. Wang, Y. Chen, L. Xie, L. Chen, Benzoic acid-
assisted substrate-free synthesis of ultrathin nanosheets assembled two-
dimensional porous Co3O4 thin sheets with 3D hierarchical micro-/nano-
structures and enhanced performance as battery-type materials for
supercapacitors, Electrochim. Acta 313 (2019) 194–204.
[42] X. Hu, H. Nan, M. Liu, S. Liu, T. An, H. Tian, Battery-like MnCo2O4 electrode
materials combined with active carbon for hybrid supercapacitors, Electrochim.
Acta 306 (2019) 599–609.
[43] Y. Wang, S. Li, J. Sun, Y. Zhang, H. Chen, C. Xu, Simple solvothermal synthesis of
magnesium cobaltite microflowers as a battery grade material with high
electrochemical performances, Ceram. Int. 45 (2019) 14642–14651.
[44] A.K. Mondal, D. Su, Y. Wang, S. Chen, Q. Liu, G. Wang, Microwave hydrothermal
synthesis of urchin-like NiO nanospheres as electrode materials for lithium-ion
batteries and supercapacitors with enhanced electrochemical performances,
J. Alloys Compd. 582 (2014) 522–527.
[45] A.J. Rockinson-Szapkiw, J. Courduff, K. Carter, D. Bennett, Electronic versus
traditional print textbooks: a comparison study on the influence of university
students’ learning, Comput. Educ. 63 (2013) 259–266.
[46] X. Chen, M. Cheng, D. Chen, R. Wang, Shape-controlled synthesis of Co2P
nanostructures and their application in supercapacitors, ACS Appl. Mater.
Interfaces 8 (2016) 3892–3900.
[47] J. Zhao, H. Pang, J. Deng, Y. Ma, B. Yan, X. Li, S. Li, J. Chen, W. Wang, Mesoporous
uniform ammonium nickel phosphate hydrate nanostructures as high performance
electrode materials for supercapacitors, CrystEngComm 15 (2013) 5950–5955.
[48] M. Liu, N. Shang, X. Zhang, S. Gao, C. Wang, Z. Wang, Microwave synthesis of
sodium nickel-cobalt phosphates as high-performance electrode materials for
supercapacitors, J. Alloys Compd. 791 (2019) 929–935.
[49] M.Z. Iqbal, A. Khan, A. Numan, S.S. Haider, J. Iqbal, Ultrasonication-assisted
synthesis of novel strontium based mixed phase structures for supercapattery
devices, Ultrason. Sonochem. 59 (2019), 104736.
[50] A.E. Elkholy, F.E.-T. Heakal, N.K. Allam, A facile electrosynthesis approach of
amorphous Mn-Co-Fe ternary hydroxides as binder-free active electrode materials
for high-performance supercapacitors, Electrochim. Acta 296 (2019) 59–68.
[51] M.Z. Iqbal, J. Khan, H.T.A. Awan, et al., Cobalt–manganese-zinc ternary phosphate
for high performance supercapattery devices, Dalton Transaction 49 (2020)
16715–16727.
[52] C.C. Lee, F.S. Omar, A. Numan, N. Duraisamy, K. Ramesh, S. Ramesh, An enhanced
performance of hybrid supercapacitor based on polyaniline-manganese phosphate
binary composite, J. Solid State Electrochem. 21 (2017) 3205–3213.
[53] P.M. Junais, M. Athika, G. Govindaraj, P. Elumalai, Supercapattery performances
of nanostructured cerium oxide synthesized using polymer soft-template, J. Energy
Storage 28 (2020), 101241.
[54] F.S. Omar, A. Numan, S. Bashir, N. Duraisamy, R. Vikneswaran, Y.-L. Loo,
K. Ramesh, S. Ramesh, Enhancing rate capability of amorphous nickel phosphate
supercapattery electrode via composition with crystalline silver phosphate,
[55] R. Ding, L. Qi, M. Jia, H. Wang, Facile and large-scale chemical synthesis of highly
porous secondary submicron/micron-sized NiCo2O4 materials for high-
performance aqueous hybrid AC-NiCo2O4 electrochemical capacitors,
[56] M.Z. Iqbal, S.S. Haider, S. Siddique, M.R.A. Karim, S. Zakar, M. Tayyab, M.
M. Faisal, M. Sulman, A. Khan, M. Baghayeri, Capacitive and diffusion-controlled
mechanism of strontium oxide based symmetric and asymmetric devices, J. Energy
Storage 27 (2020), 101056.
[57] M. Sathiya, A. Prakash, K. Ramesha, J.M. Tarascon, A.K. Shukla, V2O5-anchored
carbon nanotubes for enhanced electrochemical energy storage, J. Am. Chem. Soc.
133 (2011) 16291–16299.
[58] H. Yin, C. Song, Y. Wang, S. Li, M. Zeng, Z. Zhang, Z. Zhu, K. Yu, Influence of
morphologies and pseudocapacitive contributions for charge storage in V2O5
micro/nano-structures, Electrochim. Acta 111 (2013) 762–770.
[59] M. Shi, C. Yang, C. Yan, J. Jiang, Y. Liu, Z. Sun, W. Shi, G. Jian, Z. Guo, J.-H. Ahn,
Boosting ion dynamics through superwettable leaf-like film based on porous gC 3 N
4 nanosheets for ionogel supercapacitors, NPG Asia Mater. 11 (2019) 1–11.
[60] F. Bahmani, S.H. Kazemi, Y. Wu, L. Liu, Y. Xu, Y. Lei, CuMnO2-reduced graphene
oxide nanocomposite as a free-standing electrode for high-performance
supercapacitors, Chem. Eng. J. 375 (2019), 121966.
[61] J. Zhou, J. Yu, L. Shi, Z. Wang, H. Liu, B. Yang, C. Li, C. Zhu, J. Xu, A conductive
and highly deformable all-pseudocapacitive composite paper as supercapacitor
electrode with improved areal and volumetric capacitance, Small 14 (2018),
1803786.
[62] H. Shao, N. Padmanathan, D. McNulty, C. O’Dwyer, K.M. Razeeb, Cobalt
phosphate-based supercapattery as alternative power source for implantable
medical devices, ACS Appl. Energy Mater. 2 (2018) 569–578.
[63] J. Iqbal, A. Numan, S. Rafique, R. Jafer, S. Mohamad, K. Ramesh, S. Ramesh, High
performance supercapattery incorporating ternary nanocomposite of multiwalled
carbon nanotubes decorated with Co3O4 nanograins and silver nanoparticles as
electrode material, Electrochim. Acta 278 (2018) 72–82.
[64] V.S. Devi, M. Athika, E. Duraisamy, A. Prasath, A.S. Sharma, P. Elumalai, Facile
sol-gel derived nanostructured spinel Co3O4 as electrode material for high-
performance supercapattery and lithium-ion storage, J. Energy Storage 25 (2019),
100815.

11230
[65] B. Saravanakumar, X. Wang, W. Zhang, L. Xing, W. Li, Holey two dimensional
manganese cobalt oxide nanosheets as a high-performance electrode for
supercapattery, Chem. Eng. J. 373 (2019) 547–555.
[66] I. Heng, F.W. Low, C.W. Lai, J.C. Juan, N. Amin, S.K. Tiong, High performance
supercapattery with rGO/TiO2 nanocomposites anode and activated carbon
cathode, J. Alloys Compd. 796 (2019) 13–24.
[67] H. Shao, N. Padmanathan, D. McNulty, C. O′
Dwyer, K.M. Razeeb, ACS Appl.
Mater. Interfaces 8 (2016), 28592.
[68] E.A. de Souza, M.J. Giz, G.A. Camara, E. Antolini, R.R. Passos, Ethanol electro-
oxidation on partially alloyed Pt-Sn-Rh/C catalysts, Electrochim. Acta 147 (2014)
483–489.
[69] X. Li, X. Xiao, Q. Li, J. Wei, H. Xue, H. Pang, Metal (M= Co, Ni) phosphate based
materials for high-performance supercapacitors, Inorganic Chem. Front. 5 (2018)
11–28.
[70] S. Surendran, S. Shanmugapriya, A. Sivanantham, S. Shanmugam, R. Kalai Selvan,
Electrospun carbon nanofibers encapsulated with NiCoP: a multifunctional
electrode for supercapattery and oxygen reduction, oxygen evolution, and
hydrogen evolution reactions, Adv. Energy Mater. 8 (2018), 1800555.
[71] S. Surendran, S. Shanmugapriya, P. Zhu, C. Yan, R.H. Vignesh, Y.S. Lee, X. Zhang,
R.K. Selvan, Hydrothermally synthesised NiCoP nanostructures and electrospun N-
doped carbon nanofiber as multifunctional potential electrode for hybrid water
electrolyser and supercapatteries, Electrochim. Acta 296 (2019) 1083–1094.
[72] M.Z. Iqbal, M.M. Faisal, S.R. Ali, A.M. Afzal, M.R.A. Karim, M.A. Kamran,
T. Alharbi, Strontium phosphide-polyaniline composites for high performance
supercapattery devices, Ceram. Int. 46 (8) (2020) 10203–10214.

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