Xue-Jing Ma

Design and synthesis of CoMoO4–NiMoO4·xH2O bundles with improved electrochemical properties for supercapacitors

CoMoO4–NiMoO4·xH2O bundles with excellent electrochemical behavior were designed and synthesized by a facile strategy. CoMoO4 nanorods were fabricated by a chemical co-precipitation method, and then CoMoO4–NiMoO4·xH2O bundles were prepared by the same method using the CoMoO4 nanorods as the backbone material. A growth mechanism was proposed to explain the formation of the bundles. The composites combine the advantages of the good rate capability of CoMoO4 and the high specific capacitances of NiMoO4·xH2O, showing higher specific capacitances than CoMoO4 and a better rate capability than NiMoO4·xH2O. A maximum specific capacitance of 1039 F g−1 was achieved at a current density of 2.5 mA cm−2, and 72.3% of this value remained at a high current density of 100 mA cm−2. The excellent electrochemical performance makes the composite a promising electrode material for electrochemical capacitors.

Facile synthesis of NiMoO4·xH2O nanorods as a positive electrode material for supercapacitors

NiMoO4·xH2O nanorods with one-dimensional structures and high performances are synthesized by a facile chemical co-precipitation method. A maximum specific capacitance of 1136 F g−1 is achieved at a current density of 5 mA cm−2. The fabricated NiMoO4·xH2O is a good positive electrode material for supercapacitors due to its unique structure and excellent capacitive properties. To enhance the energy density and enlarge the potential window, an asymmetric supercapacitor is assembled using NiMoO4·xH2O as the positive electrode and activated carbon (AC) as the negative electrode in 2 M aqueous KOH electrolyte. It exhibits a high energy density and stable power characteristics. A maximum specific capacitance of 96.7 F g−1 and specific energy of 34.4 W h kg−1 are demonstrated for a cell voltage between 0 and 1.6 V, indicating that the fabrication of an asymmetric supercapacitor is an effective way to enhance the energy density.

Hydrothermal process for the fabrication of CoMoO4·0.9H2O nanorods with excellent electrochemical behavior

A hydrothermal process is developed to fabricate one-dimensional CoMoO4·0.9H2O nanorods with excellent electrochemical behavior. The study puts forward a new research strategy for the application of binary metal oxides based new materials in supercapacitors.

Facile fabrication and perfect cycle stability of 3D NiO@CoMoO4 nanocomposite on Ni foam for supercapacitors

An advanced binder-free electrode for high-performance supercapacitors has been designed by growing a three-dimensional (3D) NiO@CoMoO4 nanocomposite on Ni foam. Such a unique nanocomposite combined separately the advantages of the perfect cycling stability and rate capability of CoMoO4 and the high specific capacitance of NiO. Furthermore, the nanostructure of NiO@CoMoO4 could serve as an “ion reservoir” to store ions of the electrolyte, and give it a higher specific surface area and more active sites. As a result, this electrode exhibited remarkable specific capacitances (848 F g−1 at a current density of 0.5 A g−1), perfect cycle stability (100% of cycle efficiency after 3000 cycles) and excellent electrochemical performance compared to single oxide electrodes. And this work also demonstrates the feasibility of rational design of advanced integrated nanocomposite electrodes for high-performance supercapacitors.

Nickel vanadate and nickel oxide nanohybrid on nickel foam as pseudocapacitive electrodes for electrochemical capacitors

A novel self-supported electrode of nickel vanadate and nickel oxide nanohybrid on nickel foam with excellent pseudocapacitive properties was synthesized using a combination of a hydrothermal strategy and subsequent annealing treatment. The porous nanostructure not only provides a larger surface area for faradic reactions, but also allows the rapid transportation of electrolyte ions for improving rate capability. The electrode demonstrates outstanding capacitance, satisfying rate capability and good cycling stability, showing the coupling effects of nickel vanadate and nickel oxide. In this case, the electrode has an energy density of 46 W h kg−1 at a power density of 101 W kg−1, demonstrating the importance and great potential of nickel vanadate in the development of energy storage systems.

VO2: from negative electrode material to symmetric electrochemical capacitor

A novel negative electrode material of 3D irregular ellipsoidal VO2 with excellent pseudocapacitive properties is synthesized via a simple heat treatment method. The structural analysis and morphological features show the stable morphological basis of this material, which can favor electron transportation and electroactive species diffusion. The VO2 displays an excellent specific capacitance of 548 F g−1 at a current density of 0.5 A g−1, a wide potential window of −1.0 V to 1.0 V, an excellent energy density of 194.8 W h kg−1 at a power density of 400.5 W kg−1, and a rapidly reversible redox Faraday response. In addition, a VO2//VO2 symmetric supercapacitor has been assembled with a high potential window of 1.6 V, higher than traditional carbon-based cells. As a result, the VO2//VO2 symmetric supercapacitor can deliver a specific capacitance of 60 F g−1 at a current density of 0.25 A g−1 with a good energy density (21.3 W h kg−1 at a power density of 207.2 W kg−1) and stable power characteristics, which demonstrate the excellent performance of the VO2//VO2 symmetric supercapacitor and the great potential of using a VO2 electrode as the negative and/or positive electrodes for supercapacitors with a high comprehensive performance.

NiMoO4-modified MnO2 hybrid nanostructures on nickel foam: electrochemical performance and supercapacitor applications

A novel self-supported electrode of NiMoO4-modified MnO2 hybrid nanostructures on nickel foam has been designed and synthesized using a combination of hydrothermal syntheses. Based on the morphology, a possible mechanism that the surface modification of NiMoO4 not only prevents the MnO2 from dissolving in an alkaline electrolyte of KOH but also improves the capacity is proposed. Therefore, this electrode manifests a satisfying capacitance of 2525 F g−1 (within a potential range of −0.2–0.6 V at a current density of 0.5 A g−1), outstanding rate capability and excellent cycling stability. The reason that the hybrid NiMoO4-modified MnO2 electrode has excellent comprehensive performance is not only the coupling effect which between NiMoO4 and MnO2 but also the semiconductor surface recombination effect which improved the electrical conductivity. Moreover, an asymmetric supercapacitor has been assembled, where the hybrid NiMoO4-modified MnO2 and activated carbon act as the positive and negative electrodes, respectively, and a maximum specific capacitance of 135 F g−1 is demonstrated within a cell voltage between 0 and 1.6 V at a current density of 0.5 A g−1; thus, the supercapacitor exhibits a high energy density and stable power characteristics.

Fabrication of 3D Co3O4–Ni3(VO4)2 heterostructured nanorods on nickel foam possessing improved electrochemical properties for supercapacitor electrodes

Three-dimensional (3D) Co3O4–Ni3(VO4)2 heterostructured nanorods on nickel foam with excellent electrochemical behavior were synthesized by a facile strategy. A growth mechanism was proposed to explain the formation of the composite. The composite combined separately the advantages of the good rate capability of Co3O4 and the high specific capacitances of Ni3(VO4)2, and showed higher specific capacitances than Co3O4 and better rate capability than Ni3(VO4)2. A maximum specific capacitance of 1401 F g−1 and energy density of 31.2 Wh kg−1 were achieved at a current density of 0.5 A g−1, and 70.3% of this value was retained at a high current density of 8 A g−1. After 1000 cycles, 98.3% and 90.9% was retained at 0.5 A g−1 and 8 A g−1, respectively. The excellent electrochemical performance renders the composite a promising electrode for supercapacitors.

Electrochemical performance in alkaline and neutral electrolytes of a manganese phosphate material possessing a broad potential window

An underlying electrode material of manganese phosphate has been designed and synthesized, possessing wide potential windows (−0.9–0.7 V in neutral and −0.5–0.6 V in alkaline electrolyte), satisfying specific capacitances (203 F g−1 in neutral and 194 F g−1 in alkaline electrolyte), outstanding rate capabilities and excellent cycling stabilities. The morphological characteristics and electrochemical analyses indicate that the layered crystal structure offers many nano-paths and improves the diffusion of electrolyte ions, which can noticeably promote electrochemical performance. Furthermore, a Mn3(PO4)2//AC asymmetric supercapacitor and a Mn3(PO4)2//Mn3(PO4)2 symmetric supercapacitor have been assembled at a cell voltage between 0 and 1.6 V, and exhibit excellent electrochemical stabilities and stable energy and power characteristics, which reveal that this manganese phosphate material is promising for electrochemical energy storage applications.

A Novel Capacitive Negative Electrode Material of Fe3N

A capacitive negative electrode material of Fe3N has been synthesized via a simple precursor ammoniation treatment. Electrochemical measure shows that the electrode exhibits a specific capacitance of 270F⋅g−1 at a current density of 0.5A⋅g−1 in 6M KOH, 66% of the initial value remains at a specific current density of 5A⋅g−1. Capacitance retention after 5000 cycles is about 61.5% of the initial capacitance. The electrochemical performance is relatively great in comparison with the literature reports of some Fe-based compounds. Because of the low cost and simple preparation method of Fe3N, the material is promising in electrochemical capacitive energy storage applications.