Ling-Bin Kong

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.

Asymmetric Supercapacitor Based on Loose-Packed Cobalt Hydroxide Nanoflake Materials and Activated Carbon

Cobalt hydroxide nanoflakes with a maximum specific capacitance of 735 F/g are successfully synthesized by a facile chemical precipitation method. To enhance energy density, an asymmetric-type pseudo/electric double-layer capacitor is considered where Co(OH) 2 nanoflakes and activated carbon act as the positive and negative electrodes, respectively. The electrochemical properties of the two electrodes and the asymmetric supercapacitor are investigated in 2 M KOH aqueous electrolyte. Values for the maximum specific capacitance of 72.4 F/g and specific energy of 92.7 Wh/kg are demonstrated for a cell voltage between 0 and 1.6 V. By using the nanoflake Co(OH) 2 electrode, the asymmetric supercapacitor exhibits high energy density and stable power characteristics. The hybrid supercapacitor also exhibited a good electrochemical stability with 93.2% of the initial capacitance over consecutive 1000 cycle numbers.

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.

Cobalt vanadate as highly active, stable, noble metal-free oxygen evolution electrocatalyst

Water splitting, to produce hydrogen and oxygen, has long been considered to be a desirable option for the storage of electrical energy. The catalysts for oxygen evolution reactions (OER) are very important in this process. Herein, we have synthesized Co3V2O8 nanoparticles by a simple and cost-effective technique, which have low crystallinity and large specific surface area (122.8 m2 g−1). Because of the low crystallinity, large specific surface area and suitable pore size, Co3V2O8 nanoparticles yielded an electrocatalytic OER current density of up to 429.7 mA cm−2 at 2.05 V vs. RHE and low OER over potentials of 359 mV (at 10 mA cm−2) and 497 mV (at 100 mA cm−2). In addition, the OER stability of the Co3V2O8 catalyst was very excellent, and the current density at 2.05 V was reduced by just 7.3% after galvanostatic OER measurement at 10 mA cm−2 for 3 h. This work demonstrates that binary metal oxides Co3V2O8 is a highly active and stable oxygen evolution electrocatalyst that can potentially replace expensive noble metal-based anode catalysts for electrochemical water splitting to generate hydrogen fuels.

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.

Waste paper based activated carbon monolith as electrode materials for high performance electric double-layer capacitors

A surface modified carbon monolith (m-CM) was successfully synthesized by carbonization of a waste paper precursor, followed by a simple surface modification with a HNO3 solution. The morphology, pore structure, and surface functional groups of the as-obtained m-CM are characterized by scanning electron microscopy (SEM), N2 adsorption–desorption measurements, and Fourier transform infrared spectroscopy (FT-IR), respectively. The electrochemical properties are investigated by cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS). After surface modification, the surface hydrophilicity and the electrical conductivity of the m-CM is increased by introducing functional groups and dissolution of the impurities, thus the electrochemical performances of the m-CM are significantly improved. A high gravimetric capacitance (Cm) and volumetric capacitance (Cv) of 232 F g−1 and 36.7 F cm−3 is obtained at a current density of 5 mA cm−2 in 2 M KOH electrolyte, respectively. Based on the above investigation, such a treatment could be a promising method to convert organic waste to high-performance carbon electrode materials for electric double-layer capacitors.

An Approach to Preparing Ni-P with Different Phases for Use as Supercapacitor Electrode Materials.

Herein, we describe a simple two-step approach to prepare nickel phosphide with different phases, such as Ni2 P and Ni5 P4 , to explain the influence of material microstructure and electrical conductivity on electrochemical performance. In this approach, we first prepared a Ni-P precursor through a ball milling process, then controlled the synthesis of either Ni2 P or Ni5 P4 by the annealing method. The as-prepared Ni2 P and Ni5 P4 are investigated as supercapacitor electrode materials for potential energy storage applications. The Ni2 P exhibits a high specific capacitance of 843.25 F g(-1) , whereas the specific capacitance of Ni5 P4 is 801.5 F g(-1) . Ni2 P possesses better cycle stability and rate capability than Ni5 P4 . In addition, the Fe2 O3 //Ni2 P supercapacitor displays a high energy density of 35.5 Wh kg(-1) at a power density of 400 W kg(-1) and long cycle stability with a specific capacitance retention rate of 96 % after 1000 cycles, whereas the Fe2 O3 //Ni5 P4 supercapacitor exhibits a high energy density of 29.8 Wh kg(-1) at a power density of 400 W kg(-1) and a specific capacitance retention rate of 86 % after 1000 cycles.

An Asymmetric Supercapacitor with Both Ultra-High Gravimetric and Volumetric Energy Density Based on 3D Ni(OH)2/MnO2@Carbon Nanotube and Activated Polyaniline-Derived Carbon

Development of a supercapacitor device with both high gravimetric and volumetric energy density is one of the most important requirements for their practical application in energy storage/conversion systems. Currently, improvement of the gravimetric/volumetric energy density of a supercapacitor is restricted by the insufficient utilization of positive materials at high loading density and the inferior capacitive behavior of negative electrodes. To solve these problems, we elaborately designed and prepared a 3D core-shell structured Ni(OH)2/MnO2@carbon nanotube (CNT) composite via a facile solvothermal process by using the thermal chemical vapor deposition grown-CNTs as support. Owing to the superiorities of core-shell architecture in improving the service efficiency of pseudocapacitive materials at high loading density, the prepared Ni(OH)2/MnO2@CNT electrode demonstrated a high capacitance value of 2648 F g-1 (1 A g-1) at a high loading density of 6.52 mg cm-2. Coupled with high-performance activated polyaniline-derived carbon (APDC, 400 F g-1 at 1 A g-1), the assembled Ni(OH)2/MnO2@CNT//APDC asymmetric device delivered both high gravimetric and volumetric energy density (126.4 Wh kg-1 and 10.9 mWh cm-3, respectively), together with superb rate performance and cycling lifetime. Moreover, we demonstrate an effective approach for building a high-performance supercapacitor with high gravimetric/volumetric energy density.

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.