Abstract
A flexible asymmetric supercapacitor (ASC) with high electrochemical performance was constructed using reduced graphene oxide (rGO)-wrapped redox-active metal oxide-based negative and positive electrodes. Thin layered rGO functionality on the positive and the negative electrode surfaces has promoted the feasible surface-active sites and enhances the electrochemical response with a wide operating voltage window. Herein we report the controlled growth of rGO-wrapped tubular FeMoO4 nanofibers (NFs) via electrospinning followed by surface functionalization as a negative electrode. The tubular structure offers the ultrathin-layer decoration of rGO inside and outside of the tubular walls with uniform wrapping. The rGO-wrapped tubular FeMoO4 NF electrode exhibited a high specific capacitance of 135.2 F g−1 in Na2SO4 neutral electrolyte with an excellent rate capability and cycling stability (96.45% in 5000 cycles) at high current density. Meanwhile, the hydrothermally synthesized binder-free rGO/MnO2 nanorods on carbon cloth (rGO-MnO2@CC) were selected as cathode materials due to their high capacitance and high conductivity. Moreover, the ASC device was fabricated using rGO-wrapped FeMoO4 on carbon cloth (rGO-FeMoO4@CC) as the negative electrode and rGO-MnO2@CC as the positive electrode (rGO-FeMoO4@CC/rGO-MnO2@CC). The rationally designed ASC device delivered an excellent energy density of 38.8 W h kg−1 with a wide operating voltage window of 0.0–1.8 V. The hybrid ASC showed excellent cycling stability of 93.37% capacitance retention for 5000 cycles. Thus, the developed rGO-wrapped FeMoO4 nanotubes and MnO2 nanorods are promising hybrid electrode materials for the development of wide-potential ASCs with high energy and power density.
Highlights
Immense interest in the rapid development of portable flexible electronic tools has promoted the need for lightweight and high-performing energy storage devices to meet the requirement for a resilient power supply [1,2]
The design of asymmetric supercapacitors (ASCs) with two different sets of electrode systems has provided an efficient strategy for developing the operating voltage window and providing a high energy density to meet the demands of emerging technology [5]
While intensive efforts directed at ASCs have focused on device structures such as V2O5/carbon [6], MnO2/graphene or carbon [7], Co3O4@C@Ni3S2/activated carbon (AC) [8], MnO2/Fe3O4 [9], MnO2/MoS2 [10], carbon nanotube (CNT)-MnO2/CNT-SnO2 [11], graphene/polypyrrole [12], and graphene–NiOH/graphene [13], most of the assembled supercapacitor devices have been configured with liquid electrolytes
Summary
Immense interest in the rapid development of portable flexible electronic tools has promoted the need for lightweight and high-performing energy storage devices to meet the requirement for a resilient power supply [1,2]. Most of the ASC devices have been configured with pseudocapacitive materials as the positive electrode while carbon-based materials have commonly been used as negative electrodes [5,14]. ASCs using carbon-based negative electrodes have suffered due to the low energy density with a lower capacitance of the activated carbon (AC) in the aqueous electrolytes, especially in neutral conditions. In comparison with the electrode surface features, the flexible electrode has held many advantages along with high flexibility and stability [15]. At this point, the flexible ASCs are expected to attract a huge demand, with their flexibility providing the key to portable energy storage systems
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