Synthesis of flower-like NiCo
2
O
4
via chronopotentiometric technique
and its application as electrode materials for high-performance
supercapacitors
Majid Mirzaee, Changiz Dehghanian
*
University of Tehran, College of Engineering, School of Metallurgy and Materials Engineering, P.O. Box 11155-4563, Iran
article info
Article history:
Received 18 June 2018
Received in revised form
19 August 2018
Accepted 20 August 2018
Keywords:
NiCo
2
O
4
Electrochemical method
Chronopotentiometry
Nanoflower
Supercapacitor
abstract
In this paper by a two-step method including electrodeposition and thermal treatment, flower-like ar-
rays of NiCo
2
O
4
were grown on electrochemically reduced graphene oxide (ERGO) on nickel-nickel oxide
foam (NieNiO foam) current collectors. The crystalline structure, morphology and the electrochemical
performance of NiCo
2
O
4
were manipulated by varying the electrodeposition current density. The results
showed that the NiCo
2
O
4
electrodeposited at a current density of 3.0 mA/cm
2
had the highest surface
area equivalent to 98.3 m
2
/g. Using the combination of smart NiCo
2
O
4
and ERGO, the synergistic effect
strategy was created. Based on the results of galvanostatic charge and discharge (GCD), an extraordinary
specific capacitance of 2489 F/g was obtained at a current density of 1 A/g. Also, 94% of specific capac-
itance was maintained at a current density of 20 A/g after 4000 cycles. The resultant electrode provided a
new insight into the development of next-generation supercapacitor with high power and energy
densities.
© 2018 Elsevier Ltd. All rights reserved.
1. Introduction
Undoubtedly, the greatest challenge facing today's modern so-
ciety is the development of alternative energy storage systems due
to ecological concerns emerged. Increasing concerns about the
environment and the need for energy efficient energy storage de-
vices led to research in this area. One of the ideal energy storage
devices is supercapacitors that can be applied to a wide range of
applications such as smart grid and electrical vehicles, due to high
energy and high power density and excellent cycle stability [1,2]. In
the development of high-performance supercapacitors, electrode
materials play an essential role. The use of nickel oxides (NiO) and
cobalt oxide (Co
3
O
4
) was limited due to poor electrical conductivity
and low energy density. NiCo
2
O
4
has better electrochemical per-
formance and higher electrical conductivity than pure nickel and
cobalt oxide [3]. NiCO
2
O
4
is a p-type semiconductor with 2.1 eV
which was good electrical conductivity and multiple oxidation
states. In charge and discharge processes, Co
2þ
/Co
3þ
and Ni
2þ
/Ni
3þ
valency changes are commonly observed, and their peaks generally
overlap in cyclic voltammetric curves [4]. NiCo
2
O
4
not only contain
double layer capacitance but also include high pseudocapacitance
(its pseudocapacitance usually is 10e100 times higher than that of
double layer capacitance), therefore, the double layer capacitor for
these electrodes in the CV plots is very small to be seen. It was
observed that the capacitance was increased after several hundred
cycles, which attributed to a unique morphology and activation
processes [5]. NiCo
2
O
4
synthesis methods are divided into three
categories: sol gel, hydrothermal and electrodeposition method.
The sol-gel method provides high-purity nanoparticles, homoge-
neity and porosity [6]. In the hydrothermal process, the particle size
can also be controlled by adjusting parameters such as tempera-
ture, type and concentration of auxiliary material [7]. The electro-
deposition process has many distinct advantages over other
methods. With this method, NiCo
2
O
4
spinel can be electro-
deposited on a variety of substrates, including carbon fiber and
nickel foam. The combination of this spinel with carbon materials
produces tremendous synergistic effects. By adjusting the solution
concentration, solution pH, and applied potential or current den-
sity, an optimal morphologies for energy storage applications can
be achieved. The NiCo
2
O
4
spinel deposition process comprises the
following subdivisions: (1) the formation of solvent preform; (2)
the simultaneous electrical deposition of nanoparticles; and (3)
thermal decomposition. The presence of this compound, along with
the graphene, exhibits unique specific capacitance and optimal
cycle performance [3,8,9].
* Corresponding author.
E-mail addresses: majidmirzaee7@gmail.com (M. Mirzaee), cdehghan@ut.ac.ir
(C. Dehghanian).
Contents lists available at ScienceDirect
Materials Today Energy
journal homepage: www.journals.elsevier.com/materials-today-energy/
https://doi.org/10.1016/j.mtener.2018.08.011
2468-6069/© 2018 Elsevier Ltd. All rights reserved.
Materials Today Energy 10 (2018) 68e80