Owing
to excellent metallic conductivity, hydrophilic surfaces,
and surface redox properties, a two-dimensional (2D) metal carbide
of Ti3C2T
x
-MXene
could serve as a promising pseudocapacitive electrode material for
energy storage devices. Meanwhile, the 2D reduced graphene oxide (rGO)
combining with the hierarchical cubic spinel nickel–cobalt
bimetal oxide (NiCo2O4) nanospikes could control
ion diffusion for charge storage, thereby facilitating the improvement
of the energy density of a supercapacitor. As per the strategy, the
pseudocapacitive 2D Ti3C2T
x
was loaded on a flexible acid-treated carbon fiber (ACF)
backbone to prepare a Ti3C2T
x
/ACF negative electrode by a convenient drop-casting method.
Meanwhile, 2D rGO was deposited on ACF by a simple dip-dry process,
which was further decorated by the spinel NiCo2O4 nanospikes using a hydrothermal method to obtain a NiCo2O4@rGO/ACF positive electrode. The fabricated Ti3C2Tx/ACF electrode exhibited an excellent specific
capacitance of 246.9 F/g (197.5 mF/cm2) at 4 mA/cm2 along with 96.7% capacity retention over 5000 charge/discharge
cycles, whereas the NiCo2O4@rGO/ACF electrode
showed a specific capacitance of 1487 F/g (458.3 mA h/g) at 3 mA/cm2 with a cycling stability of 88.2% over 10 000 charge/discharge
cycles. As a result, a flexible all-solid-state hybrid supercapacitor
(FHSC) device using the pseudocapacitive Ti3C2T
x
/ACF on the negative side with a widespread
voltage window and the battery-type NiCo2O4@rGO/ACF
on the positive side with high electrochemical activity delivered
an excellent volumetric capacitance of 2.32 F/cm3 (141.9
F/g) at a current density of 5 mA/cm2 with a high-energy
density of 44.36 Wh/kg (0.72 mWh/cm3) at a power density
of 985 W/kg (16.13 mW/cm3) along with a cycling stability
of 90.48% over 4500 charge/discharge cycles. Therefore, the pseudocapacitive
2D Ti3C2T
x
/ACF negative
electrode could replace carbon-based electrodes and a combination
of it with the battery-type NiCo2O4@rGO/ACF
positive electrode should be a promising way to step up the energy
density of a supercapacitor.
Combining oxides with bimetallic elements may be an efficient route to modify the electronic distribution for improving the intrinsic activity of electrocatalysts, and further engineering the defect structure and adjusting...
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