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As an emerging energy storage device, supercapacitor is widely investigated owing to its excellent capability, quick charge-discharge and tremendous cycle life. The operation potential window, energy density and mass loading of supercapacitor must be taken into deep consideration for its practical application. In this work, an outstanding electrode based on CFF@V2O5 nanosheets was prepared. Then a free-standing asymmetric supercapacitor with CFF@V2O5 composite as positive electrode and CFF@AC as negative electrode was assembled. Owing to the functional groups produced on CFF after the activation, V2O5 nanosheets was immobilized. The composite exhibits remarkable specific capabilities of 1465 mF cm−2 (492 F g−1). The energy density of the assembled free-standing asymmetric supercapacitor achieves 0.928 mWh cm−3 when the power density is 17.5 mW cm−3. After 6000 charging-discharging cycles as under normal, bended and anti-bended conditions for respective 2000 cycles, the device retains 89.7% of the initial capacitance, exhibiting fascinating cycle stabilization. Finally, two devices linked series can lighten a LED of 1.8 V for 2 min after charging for 2.5 min, which is inspiring for the practical application and production of self-supporting asymmetric supercapacitors.

In this work, novel silver nanoparticles supported on amino-functionalized peeled-watermelon-like silica-coated magnetic catalysts (Fe3O4@SiO2-NH2-Ag) were successfully synthesized for the catalytic reduction of 4-nitrophenol (4-NP) in wastewater. The Fe3O4 nanoparticles were further coated with silica forming a structure similar to peeled watermelon to improve the stability of magnetic Fe3O4 and inhibit their aggregation. Furthermore, surface modification of Fe3O4@SiO2 particles with amino groups was used for the immobilization of silver nanoparticles. As a result, the Fe3O4@SiO2-NH2-Ag (10%) exhibits excellent catalytic activity to reduce 4-NP, which obtained the first-best reaction rate constant of 0.026 s−1. Besides, the Fe3O4@SiO2-NH2-Ag could be easily recovered under an external magnetic field and was reused for 25 catalytic cycles without a significant decline in catalytic activity. The related catalytic mechanism of the reaction was discussed. Overall, the excellent magnetic recyclable nature and immortal catalytic activity make Fe3O4@SiO2-NH2-Ag a very promising material for practical use.

As a typical flexible electrode substrate, carbon cloth (CC) has high flexibility but compromised capacitance performance. In this work, CuS nanoflake arrays with enhanced pseudocapacitance property are loaded on the surface of CC via a one-step solvothermal method. CuS nanoflakes provide the electroactive sites required for faradaic redox reaction, while the channels between the nanoflake arrays play a vital role to improve the efficiency of charges transportation. Benefit from the favorable microstructure, CuS/CC-4 demonstrates the specific capacity of 213.8 C g−1 at 0.49 A g−1 (436.5 mF cm−2 at 1 mA cm−2), and maintains 75.1% of initial capacitance after 5000 cycles. Furthermore, a quasi-solid-state asymmetric flexible supercapacitor (AFSC) is assembled with the voltage window of 1.6 V, which delivers the energy density of 0.027 mWh cm−2 and exhibits outstanding cycle stability of 86.4% after 5000 cycles at a high current density of 5 mA cm−2. This work provides insights into the integrated electrode containing the merits of flexibility, lightweight and satisfying electrochemical performance, and revealing its promising application prospects in flexible energy storage devices.

At present, it is still a challenge for developing hybrid supercapacitors with outstanding electrochemical performance. Herein, a step-by-step approach was tailored to fabricate a novel electrode material as nickel-vanadium layered double hydroxide (NiV-LDH)@Co2NiO4 nano-coral arrays anchored on nickel foam. Thanks to the three-dimensional interconnected nanostructure, the electrode fully immersed in electrolyte participates in faradaic redox reaction, which promotes the transfer of ions and charges, leading to the enhancement of electrochemical performance. The optimal NiV-LDH@Co2NiO4/NF (nickel foam) exhibits 1381.8 C g−1 at 1 A g−1, which is the best among the prepared samples (compared with NiV-LDH/NF and Co2NiO4/NF). Benefitting from the coral-like interconnect morphology, NiV-LDH@Co2NiO4/NF retains 79.8% of the initial capacity after 5000 cycles at 5 A g−1. Besides, NiV-LDH@Co2NiO4/NF and activated carbon (AC) act as positive and negative electrodes, assembling a hybrid asymmetric supercapacitor, which delivers an ideal energy density of 68.7 W h kg−1 at a power density of 878.6 W kg−1 and leaves 88.6% of specific capacity remaining after 5000 cycles. To evaluate the practical application of NiV-LDH@Co2NiO4/NF//AC, two devices are connected in series and acted as a continuous energy supply for a 2.2 V LED light.

Rapid developing flexible electronics, such as flexible screens, sensors and wearable devices, make them forward to invent portable and flexible energy storage systems. Flexible supercapacitors possess quick charge-discharge, high power density, environmentally friendly and flexible characteristics, which highly cater to the growing market demands. In supercapacitors, electrolyte is one of the key factors affecting their performance. Herein, we demonstrate that a self-assembly Mn3O4/carbon cloth (Mn3O4/CC) electrode is synthesized successfully by a two-step hydrothermal method. In a three electrodes system, the Mn3O4/CC electrode is tested in Na2SO4 and KOH respectively. The results reveal that Mn3O4/CC exhibits higher specific capacitance (555 mF cm−2 at 1 mA cm−2) and lower internal resistance in KOH. On the other hand, it expresses nearly no loss in the cycle stability test (99% retention after 2000 cycles) in Na2SO4. The all-solid-state asymmetric supercapacitor presents a maximum energy density reaching 25 μWh cm−2 with a power density of 0.64 mW cm−2. It also presents ultra-high flexibility (bending and twisting for 200 times) and superior cycling performance (99.3% after 2000 cycles). Hence, the Mn3O4/CC electrode is of great prospect in the application of flexible electronic devices.