Mao-Cheng Liu

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.

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.

Advanced asymmetric supercapacitors based on Ni3(PO4)2@GO and Fe2O3@GO electrodes with high specific capacitance and high energy density

Ni3(PO4)2@GO composites were fabricated via a facile chemical precipitation method. More importantly, it was observed from electrochemical measurements that the obtained Ni3(PO4)2@GO electrode showed a good specific capacitance (1392.59 F g−1 at 0.5 A g−1) and cycling stability (1302 F g−1 retained after 1000 cycles at 1 A g−1). In addition, a high-voltage asymmetric supercapacitor was successfully fabricated using Ni3(PO4)2@GO and Fe2O3@GO as the positive and negative electrodes, respectively. The asymmetric supercapacitor could be cycled reversibly in the high-voltage region of 0–1.6 V and displayed intriguing performances with a maximum specific capacitance of 189 F g−1 at a current density of 0.25 A g−1. Furthermore, the Fe2O3@GO//Ni3(PO4)2@GO asymmetric supercapacitor exhibited a high energy density of 67.2 W h kg−1 and an excellent long cycle-life along with 88% specific capacitance retention after 1000 cycles. The impressive results presented here may pave the way for promising applications in high energy density storage systems.

Facile synthesis of a nickel vanadate/Ni composite and its electrochemical performance as an anode for lithium ion batteries

Ni3V2O8/Ni composites were prepared by a simple one-step hydrothermal route and they showed superior electrochemical performance as anode materials for Li-ion batteries. They had a unique three-dimensional (3D) architecture, in which interlaced Ni3V2O8 nanosheets and nanoflakes were uniformly grown on Ni foam. The Ni3V2O8/Ni composites delivered a discharge capacity of 1626.1 in the initial cycle at a specific current of 200 mA g−1, maintaining 1286.8 mA h g−1 after 100 cycles. After 600 cycles at 1000 mA g−1, the discharge capacity was maintained at 941.3 mA h g−1, and even when the current was 10 A g−1, a discharge capacity of 477.7 mA h g−1 was achieved. The excellent lithium storage performance of the Ni3V2O8/Ni composites could be attributed to their unique 3D architecture, favorable electrochemical reconstruction in cycling and their intimate contact with the Ni foam substrates, which offered fast electrical and ionic transport, provided a sufficient electrode/electrolyte contact area and facilitated accommodation of strain during lithiation/delithiation cycling. In addition, details of the electrochemical reaction process of Ni3V2O8 were carefully investigated to discover the conversion and intercalation reaction routes. Such novel Ni3V2O8/Ni composites might provide insight for the use of metal vanadate as an energy storage material.

Design and synthesis of one-dimensional Co3O4/Co3V2O8 hybrid nanowires with improved Li-storage properties

A new nanostructure of one-dimensional Co3O4/Co3V2O8 hybrid nanowires directly grown on Ti substrates with improved electrochemical Li-storage properties are successfully prepared by a simple hydrothermal strategy. The nanocomposites consist of the primary Co3O4 nanowires acting as the “core” and secondary Co3V2O8 nanocrystals as the “shell” layer, which form one-dimensional tentacle-like nanostructure. When used as potential anodes for lithium ion batteries, the Co3O4/Co3V2O8 hybrid nanowires exhibited an enhanced capacity with high initial discharge capacity of 1677 mA h g−1 at 200 mA g−1 and retained at 1251 mA h g−1 after 200 cycles. Even when the current reached 5000 mA g−1 the electrode can still maintain an average discharge capacity of 807 mA h g−1. The enhanced electrochemical performances are attributed to unique hybrid nanowire architecture and an improved synergistic effect of two electrochemically component, ranking the hybrid nanostructure as a promising electrode material for high-performance energy storage systems.