346
R. R. Deshmukh et al.
a template with nanoholes on indium tin oxide (ITO) coated substrate gives ultrahigh
specific capacitance value of 3407 F g
−1 (Yuan et al. 2012).
4.3 Nanotubes for ESS
When nanowires are made hollow, this makes both inner and outer surface areas
available for energy conversion or storage mechanism; making surface area almost
two folds more effective. Thus, nanotube has been widely used electrode material due
to their large surface area to store charges and an efficient pathway to transport charges
in the tubular nanostructures. They can be of carbon like CNT or of metal oxides
like TiO 2 , MnO 2 etc. Nanotubes can be randomly distributed or aligned properly in
arrays like honeycomb structures.
One dimensional CNTs with significant length-to-diameter ratio, in which carbon
atoms are arranged as a hexagonal lattice with each carbon atom surrounded by three
nearest neighboring atoms, to form a special covalent sp
2 carbon bonding. In addition,
CNTs possess unique size-/surface-dependent properties useful for efficient energy
storage (Ganguly et al. 2014). High-purity vertically aligned multiwalled carbon
nanotubes (MWCNTs) gave a high reversible lithium storage capacity of 950 mAh/g
in lithium-ion cells (Wang et al. 2006). By opening or cutting the CNTs, the capacity
can be further increased. SWNTs are prepared by using strong acid to open the
tubes and reducing their length to obtain a reversible capacity of about 700 mAh
g
−1 (Shimoda et al. 2002). TiO 2 nanotubes in Li-ion batteries, exhibited an overall
capacitance of 182 mAh g
−1 at a charge/discharge rate of 80 mAh g
−1 (Liu et al.
2008).
By using electrochemical deposition techniques, Xia et al. synthesized freestanding MnO 2 nanotube arrays on a Pt substrate. They showed that the MnO 2
nanotube array electrode had good capacitive behavior than MnO 2 nanowire array
electrode. The MnO 2 nanotube arrays showed a specific capacitance of 320 F g
−1 ,
which is high as compared to the MnO 2 nanowire array electrode (Xia 2010). Poly
(3, 4-ethylenedioxythiophene) (PEDOT) nanotubes electrode based supercapacitor
gave a high power density of 25 kW kg
−1 at energy density (5.6 Wh kg
−1 ) maintained at 80% (Liu et al. 2008). The TiO 2 nanotubes prepared by anodization for
different durations induced porosity which had an impact on the capacitance value
as 18.3 μF/cm
2 , 19.3 μF/cm
2 , 27.7 μF/cm
2 and 49.9 μF/cm
2 for 10 s, 30 s, 600 s,
and 1800 s, respectively (Endut et al. 2013).
4.4 Core-Shell Structures for ESS
One dimensional nanostructured current collector core can provide a support for
active sites, forming a core-shell 1-D nano material. The fabrication of core–shell
nanostructures of the same or different materials provides stable nanostructured
R. R. Deshmukh et al.
a template with nanoholes on indium tin oxide (ITO) coated substrate gives ultrahigh
specific capacitance value of 3407 F g
−1 (Yuan et al. 2012).
4.3 Nanotubes for ESS
When nanowires are made hollow, this makes both inner and outer surface areas
available for energy conversion or storage mechanism; making surface area almost
two folds more effective. Thus, nanotube has been widely used electrode material due
to their large surface area to store charges and an efficient pathway to transport charges
in the tubular nanostructures. They can be of carbon like CNT or of metal oxides
like TiO 2 , MnO 2 etc. Nanotubes can be randomly distributed or aligned properly in
arrays like honeycomb structures.
One dimensional CNTs with significant length-to-diameter ratio, in which carbon
atoms are arranged as a hexagonal lattice with each carbon atom surrounded by three
nearest neighboring atoms, to form a special covalent sp
2 carbon bonding. In addition,
CNTs possess unique size-/surface-dependent properties useful for efficient energy
storage (Ganguly et al. 2014). High-purity vertically aligned multiwalled carbon
nanotubes (MWCNTs) gave a high reversible lithium storage capacity of 950 mAh/g
in lithium-ion cells (Wang et al. 2006). By opening or cutting the CNTs, the capacity
can be further increased. SWNTs are prepared by using strong acid to open the
tubes and reducing their length to obtain a reversible capacity of about 700 mAh
g
−1 (Shimoda et al. 2002). TiO 2 nanotubes in Li-ion batteries, exhibited an overall
capacitance of 182 mAh g
−1 at a charge/discharge rate of 80 mAh g
−1 (Liu et al.
2008).
By using electrochemical deposition techniques, Xia et al. synthesized freestanding MnO 2 nanotube arrays on a Pt substrate. They showed that the MnO 2
nanotube array electrode had good capacitive behavior than MnO 2 nanowire array
electrode. The MnO 2 nanotube arrays showed a specific capacitance of 320 F g
−1 ,
which is high as compared to the MnO 2 nanowire array electrode (Xia 2010). Poly
(3, 4-ethylenedioxythiophene) (PEDOT) nanotubes electrode based supercapacitor
gave a high power density of 25 kW kg
−1 at energy density (5.6 Wh kg
−1 ) maintained at 80% (Liu et al. 2008). The TiO 2 nanotubes prepared by anodization for
different durations induced porosity which had an impact on the capacitance value
as 18.3 μF/cm
2 , 19.3 μF/cm
2 , 27.7 μF/cm
2 and 49.9 μF/cm
2 for 10 s, 30 s, 600 s,
and 1800 s, respectively (Endut et al. 2013).
4.4 Core-Shell Structures for ESS
One dimensional nanostructured current collector core can provide a support for
active sites, forming a core-shell 1-D nano material. The fabrication of core–shell
nanostructures of the same or different materials provides stable nanostructured