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Production cost, capacitance, and electrode materials safety are the key factors to be concerned about for supercapacitors. In this work, a type of carbon nanosheets was produced through the carbonization of tripotassium citrate monohydrate and nitric acidification. Subsequently, a well-designed manganese dioxide/carbon nanosheets composite was synthesized through hydrothermal treating. The carbon nanosheets served as the substrate for growing the manganese dioxide, regulating its distribution, and preventing it from inhomogeneous dimensions and severe agglomeration. Many manganese dioxide nanosheets grew vertically on the numerous functional groups generated on the surface of the carbon nanosheets during acidification. The synergistic combination of carbon nanosheets and manganese dioxide tailors the electrochemical performance of the composite, which benefits from the excellent conductivity and stability of carbon nanosheets. The carbon nanosheets derived from tripotassium citrate monohydrate are conducive to the remarkable performance of manganese dioxide/carbon nanosheets electrode. Finally, an asymmetric supercapacitor with active carbon as the cathode and manganese dioxide/carbon nanosheets as the anode was assembled, achieving an outstanding energy density of 54.68 Wh·kg−1 and remarkable power density of 6399.2 W·kg−1 superior to conventional lead-acid batteries. After 10000 charge-discharge cycles, the device retained 75.3% of the initial capacitance, showing good cycle stability. Two assembled asymmetric supercapacitors in series charged for 3 min could power a yellow light emitting diode with an operating voltage of 2 V for 2 min. This study may provide valuable insights for applying carbon materials and manganese dioxide in the energy storage field.

As a new energy-storage device, a supercapacitor has attracted great attention, but its low power density limits its wide application. The key to develop high-performance supercapacitors is to find...

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.