Acknowledgements

maximum potential window 0–1.8 V without any degradation. Thus, all electrochemical studies have been done within maximum potential window from 0 to 1.8 V and the CV curves (Figure 7(b)) at different scan rates show relatively rectangular nature without presence of any redox peaks. It clearly indicates that the charge storage mechanism is mainly due to the electric double layer of the device. The CV profiles also remain almost same without any distortion with increasing scan rates, indicating suitable fast charge–discharge property. To study the rate capability of this ASC device, the GCD test at different current densities (1.0, 1.25,

Science,Technology and Advanced Application of Supercapacitors

(Figure 7(c)) show that the discharge time decreases with increasing current density. For practical purpose it is expected that a good supercapacitor device provides high specific capacitance and high energy density. The relationship between specific capacitance vs. current density of the fabricated ASC device shows that the device delivers maximum specific capacitance of 166.7 F g<sup>1</sup> at current density

. The specific capacitance also decreases when current density increases, since diffusion of electrolyte ions and electrons most likely are restricted due to the time constrain. The specific energy and power densities of the ASC have been calculated from the discharge curves at different current densities in the voltage window of 0–1.8 V and the Ragone plot is shown in Figure 7(d). This device delivers offers specific energy density and power density of 75.01 W h kg<sup>1</sup> and

In summary, the electrochemical properties of TiO2-V2O5 and NiMn2O4 composites have been demonstrated. Three dimensional, mesoporous, interlinked tube-like ordered architecture of TiO2-V2O5 nanocomposite offers large surface area which enhances the specific capacitance. The composite offers maximum specific capacitance of 310 F g<sup>1</sup> in 1 M KCl solution at 2 mV s<sup>1</sup> scan rate. It is found out that the maximum capacitance value arises from the contribution of inner active sites of the electrode rather than the outer surface. The NiMn2O4 nanoparticles with 8 nm average diameter show spherical shape with BET sur-

porous structures, which can be utilized to fabricate working electrodes of the electrochemical supercapacitors. The electrodes made of NiMn2O4 nanoparticles possess excellent charge storage characteristics, with specific capacitance of up to 875 F g<sup>1</sup> attainable at a scan rate of 2 mV s<sup>1</sup> in 1.0 M Na2SO4 electrolyte solution. The coexistence of Ni and Mn in the lattice of this binary oxide is seen to have a positive effect on the improvement of electrochemical charge storage capability of the electrodes due to enhanced electronic conductivity. Both these two composites demonstrate excellent device performance. The asymmetric device based on TiO2-V2O5 shows specific capacity of 86 F g<sup>1</sup> at 4.2 A g<sup>1</sup> with

asymmetric device based on NiMn2O4 demonstrates 166.7 F g<sup>1</sup> at current density 1 A g<sup>1</sup> with specific energy density and power density of 75.01 W h kg<sup>1</sup>

composites can be used as the electrodes for future energy storage devices.

the maximum energy density (Ecell) and power density (Pcell) about

columbic efficiency 97.6% indicating that the device is suitable for high-

performance supercapacitor applications in future.

, respectively. The ASC device configuration (Figure 7d) presents a

. The agglomerated spinel nanoparticles generate highly

, respectively. On the other hand the

, respectively. These superior performances ensure that these

) has been performed. The GCD plots

1.50, 1.75, 2.00, 2.25 and 2.50 A g<sup>1</sup>

1Ag<sup>1</sup>

2.25 kW kg<sup>1</sup>

8. Conclusion

face area of 43.6 m<sup>2</sup> g<sup>1</sup>

20.18 W h kg<sup>1</sup> and 5.94 kW kg<sup>1</sup>

and 2.25 kW kg<sup>1</sup>

102

A. Ray (File No.–09/096(0927)/2018-EMR-I) and S. Saha (File No.–09/096 (0898)/2017–EMR-I) wish to thank CSIR, Government of India for financial support. S. Das is thankful to the Department of Science and Technology (DST), Government of India, for providing research support through the 'INSPIRE Faculty Award' (IFA13-PH-71). A. Roy (IF140920) is also thankful to the Department of Science and Technology (DST), INSPIRE, Government of India, for providing research support through the 'INSPIRE Fellowship'.
