In response to the global warming issue, energy storage has
become a huge challenge to the global power systems. Recently, a
lot of efforts have been undertaken to develop new energy storage
devices like supercapacitors, which can provide high energy
density than conventional capacitors and high power density than
batteries [1]. There are two energy storage mechanisms for
supercapacitors: (i). Electric double layer capacitors, wherein
energy storage arises mainly from the separation of ionic charges
at the interfaces between electrodes and electrolyte solution [2].
(ii). Pseudocapacitors uses transition metal oxides and conducting
polymers, which undergoes reversible faradic reactions [3]. As well
known, ruthenium oxide (RuO2) exhibits a high pseudocapacitance,
but its high cost and environmental harmfulness leads to the
limit of its practical applications in supercapacitors [4]. Hence the
development of new materials at low cost for supercapacitors is
still a challenge and needs to be addressed. In recent days,
considerable efforts have been devoted by researchers to develop
alternative electrode materials like MnO2 [5], NiO [6], Co3O4 [7]
and SnO2 [8], etc.
Among the various metal oxide nanomaterials, SnO2 based
nanomaterials have attracted a considerable attention as a
promising electrode material for supercapacitors due to its low
cost and high power density. SnO2 has potential applications in
various
fields like sensors [9] and solar cells [10]. Especially, SnO2
appears to be a promising electrode material for energy storage
devices like lithium ion batteries and supercapacitors due to its
superior electrochemical performance [11]. Though SnO2 gives
better response towards specific capacitance of supercapacitors, it
is still limited to practicality due to the poor transportation of the
electrolyte ions within the SnO2 matrix and its poor electrical
conductivity. Various reports have demonstrated that the carbon
based materials like carbon nanotube and graphene enhance the
electronic conductivity of metal oxides. In recent years, one atomthick
layered crystalline with honeycomb structure of sp2-bonded
carbon called graphene is a good candidate for supercapacitor
electrode material due to its superior electrical conductivity
(106 S cm2) [12], high surface area (2630 m2 g1) [13] and high
thermal conductivity (5000 Wm1K1) [14]. In addition, it can
minimize the contact resistance between the electrode and current
collector, unlike the case of carbon nanotube [15]. Graphene is an
ideal carbon electrode material for electric double layer