Guiling Wang

Nanographene-Constructed Carbon Nanofibers Grown on Graphene Sheets by Chemical Vapor Deposition: High-Performance Anode Materials for Lithium Ion Batteries

We report on the fabrication of 3D carbonaceous material composed of 1D carbon nanofibers (CNF) grown on 2D graphene sheets (GNS) via a CVD approach in a fluidized bed reactor. Nanographene-constructed carbon nanofibers contain many cavities, open tips, and graphene platelets with edges exposed, providing more extra space for Li(+) storage. More interestingly, nanochannels consisting of graphene platelets arrange almost perpendicularly to the fiber axis, which is favorable for lithium ion diffusion from different orientations. In addition, 3D interconnected architectures facilitate the collection and transport of electrons during the cycling process. As a result, the CNF/GNS hybrid material shows high reversible capacity (667 mAh/g), high-rate performance, and cycling stability, which is superior to those of pure graphene, natural graphite, and carbon nanotubes. The simple CVD approach offers a new pathway for large-scale production of novel hybrid carbon materials for energy storage.

Facile synthesis of porous (Co, Mn)3O4 nanowires free-standing on a Ni foam and their catalytic performance for H2O2 electroreduction

Porous (Co, Mn)3O4 nanowires freely standing on a Ni foam are synthesized via a template-free growth method, followed by a thermal treatment in air. The nanowires are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. Their catalytic performance in H2O2 electroreduction is evaluated by linear scan voltammetry and chronoamperometry. Results show that a thermal treatment leads to the conversion of solid nanowires of MnCO3 + CoCO3 to porous nanowires of (Co, Mn)3O4via decomposition and reconfiguration, which is identified to be the catalytic active component for H2O2 electroreduction. Nanowires calcined at 300 °C exhibit the highest activity for H2O2 reduction and a current density of 329 mA cm−2 is obtained in 3.0 mol dm−3 KOH + 0.6 mol dm−3 H2O2 at −0.4 V (vs. Ag/AgCl, KCl). The catalytic activity of (Co, Mn)3O4 nanowires is almost twice than that of Co3O4 nanowires. The role of Mn in improving the catalytic activity is proposed and discussed.

Molten salt synthesis of nitrogen doped porous carbon: a new preparation methodology for high-volumetric capacitance electrode materials

To meet the ever-increasing need for high-efficiency energy storage in modern society, porous carbon materials with large surface areas are typically employed for electrical double-layer capacitors to achieve high gravimetric performances. However, their poor volumetric performances come from low packing density and/or high pore volume resulting in poor volumetric capacitance, which would limit their further applications. Here, a novel and one-step molten salt synthesis of a three-dimensional, densely nitrogen-doped porous carbon (NPC) material by using low-cost and eco-friendly tofu as the nitrogen-containing carbon source is proposed. Hierarchically porous carbon with a specific surface area of 1202 m2 g−1 and a high nitrogen content of 4.72 wt% and a bulk density of ∼0.84 g cm−3 is obtained at a carbonation temperature of 750 °C. As the electrode material for a supercapacitor, the NPC electrode shows both ultra-high specific volumetric and gravimetric capacitances of 360 F cm−3 and 418 F g−1 at 1 A g−1 (based on a three-electrode system), respectively, and excellent cycling stability without capacitance loss after 10 000 cycles at a high charge current of 10 A g−1 in KOH electrolyte. Moreover, the as-assembled symmetric supercapacitor exhibits not only an excellent cycling stability with 97% capacitance retention after 10 000 cycles, but also a high volumetric energy density up to 27.68 W h L−1 at a current density of 0.2 A g−1, making this new method highly promising for compact energy storage devices with simultaneous high volumetric/gravimetric energy and power densities.

One-step synthesis of copper compounds on copper foil and their supercapacitive performance

Nanowire-like Cu(OH)2 arrays, microflower-like CuO standing on Cu(OH)2 nanowires and hierarchical CuO microflowers are directly synthesized via a simple and cost-effective liquid–solid reaction. The specific capacitance of Cu(OH)2, CuO/Cu(OH)2 and CuO are 511.5, 78.44 and 30.36 F g−1, respectively, at a current density of 5 mA cm−2. Therefore, the Cu(OH)2/Cu-foil electrode displays the best supercapacitive performance. The capacitance retention reaches up to 83% after 5000 charge/discharge cycles with the columbic efficiency of ∼98%. More importantly, the nanowire Cu(OH)2 transformed into stable nanosheet CuO after about 600 constant current charge–discharge cycles. Additionally, we fabricate an asymmetric supercapacitor with nanowire Cu(OH)2/Cu-foil as a positive electrode, activated carbon (AC) as a negative electrode and 6 mol dm−3 KOH as electrolyte, which exhibits an energy density of 18.3 W h kg−1 at a power density of 326 W kg−1.

Preparation of porous cadmium sulphide on nickel foam: a novel electrode material with excellent supercapacitor performance

Large surface area, high electrical conductivity, and abundant channels have been recognized to favor faradic capacitors, but their realization at the same time by a facile preparation process is still a great challenge. Here, we synthesized porous cadmium sulphide freely standing on nickel foam (CdS/NF) via a one-step hydrothermal method which possesses high specific capacitance, good rate capability and outstanding cycling stability. The CdS/NF microspheres present pores with a mean size of ∼3 nm, resulting in fast diffusion of ions, facile transportation of electrons and high activity, which make great synergistic contributions to reversible redox reactions. In the resulting supercapacitors, a specific capacitance of 909 F g−1 is achieved at a current density of 2 mA cm−2 with excellent rate capability that 88% of the original capacitance is retained at 50 mA cm−2. After 5000 charge–discharge cycles at current densities as large as 50 mA cm−2, 104% of initial capacitance is maintained. Finally, asymmetric supercapacitors with a high energy density of 28 W h kg−1 at a power density of 160 W kg−1 were obtained.

Preparation of Au nanodendrites supported on carbon fiber cloth and its catalytic performance to H2O2 electroreduction and electrooxidation

Well-defined Au dendrites supported on carbon fiber cloth are successfully prepared by potential pulse electrodeposition without additives or surfactants. The electrode (D-Au/CFC) is characterized by transmission electron microscopy, scanning electron microscopy and X-ray diffractometry. H2O2 electroreduction in H2SO4 and electrooxidation in KOH solution on the dendritic Au electrode are studied by linear sweep voltammetry and chronoamperometry. The D-Au/CFC electrode exhibits much higher catalytic activity and remarkably improved utilization of Au than Au nanoparticles prepared by the same method for both H2O2 electroreduction and electrooxidation owing to its unique open dendritic structure. The H2O2 electroreduction in H2SO4 solution exhibits much larger overpotentials than the H2O2 electrooxidation in KOH solution on the D-Au/CFC electrode. A high DPPFC performance using it both as the anode and cathode exhibits an open circuit voltage as high as ∼0.8 V and the peak power density can reach 14 mW cm−2 at 20 °C.

Electrodeposition of Pd nanoparticles on C@TiO2 nanoarrays: 3D electrode for the direct oxidation of NaBH4

A newly designed and fabricated electrode with three-dimensional structures is reported. The electrode consists of a conducting nanoarray substrate and Pd nanoparticles. The substrate is an array of TiO2 nanowires with a carbon coating layer prepared via a thermal evaporation method. Pd nanoparticles were electro-deposited on the substrate surfaces by the potentiostatic pulse method. The morphology of the electrode is observed by scanning electron microscopy and transmission electron microscopy, and its structure is analyzed using an X-ray diffractometer. The catalytic performance is evaluated by cyclic voltammetry and chronoamperometry. The electrode exhibited excellent catalytic performance for NaBH4 electro-oxidation. The current density for NaBH4 electro-oxidation at the electrode reported in this work (524 mA mg−1) is about 5 times of that at conventional Pd/C (100 mA mg−1). This enhanced performance is likely to be due to the improved mass transport of NaBH4, good electronic conductivity and high Pd utilization of the electrode.

Preparation of binder-free CuO/Cu2O/Cu composites: a novel electrode material for supercapacitor applications

Cuprous(I) oxide (Cu2O) carries high theoretical specific capacitance (2247.6 F g−1), however, the amount of research about the supercapacitive performance of Cu2O is relatively small compared with other transition metal oxides. A composite of metal and metal oxide could improve the electrochemical performance efficiently. In this work, the results of XRD and XPS demonstrate that CuO/Cu2O/Cu is prepared successfully via a facile, eco-friendly, one-step template-free growth process. SEM figures show that cubic CuO/Cu2O/Cu uniformly and densely covers a skeleton of nickel foam. The binder-free CuO/Cu2O/Cu electrode exhibits excellent supercapacitive performance with a high specific capacitance of 878 F g−1 at a current density of 5 mA cm−2 (1.67 A g−1), when the current density is enlarged ten times (50 mA cm−2 (16.7 A g−1)), the specific capacitance still remains at 545 F g−1. Furthermore, we have first successfully constructed a CuO/Cu2O/Cu//AC asymmetric supercapacitor, which can achieve an energy density of 42 W h kg−1 at a power density of 0.44 kW kg−1. The good electrochemical performance and simple accessibility prove that the as-prepared CuO/Cu2O/Cu/NF electrode has a potential application in electrochemical capacitors.

Facile preparation of three-dimensional Ni(OH)2/Ni foam anode with low cost and its application in a direct urea fuel cell

Three-dimensional Ni(OH)2/Ni foam electrodes with low cost are simply fabricated via a template-free growth method and employed as efficient anodes for a direct urea–hydrogen peroxide fuel cell (DUPFC). The surface morphologies of Ni(OH)2 catalysts on the electrodes can be easily controlled by altering the reaction temperatures. The nano-sheet (NS) Ni(OH)2/Ni foam electrode exhibits highest catalytic activity towards urea electro-oxidation among the four electrodes. The oxidation current density of the NS Ni(OH)2/Ni foam electrode reaches 337 mA cm−2 at 0.45 V (vs. Ag/AgCl) with a low onset oxidation potential in 0.6 mol L−1 urea and 5 mol L−1 KOH solutions. The DUPFC using NS Ni(OH)2/Ni foam anode shows an open circuit voltage of 0.86 V and high peak power density of 19.7 mW cm−2 and 28.8 mW cm−2 at 20 °C and 50 °C, respectively, which is much higher than the performance of direct urea fuel cells reported previously. The outstanding cell performance using a cheap NS Ni(OH)2/Ni foam anode indicates DUPFC is a promising new type of fuel cell.

(LiFePO4-AC)/Li4Ti5O12 hybrid supercapacitor: The effect of LiFePO4 content on its performance

Composites of LiFePO4 and activated carbon (LFP-AC) were prepared by a ball milling method. Their morphologies were investigated by scanning electronic microscopy and energy dispersive spectroscopy. Hybrid supercapacitors were assembled using the LFP-AC composites as the positive electrode and Li4Ti5O12 as the negative electrode (LFP-AC/Li4Ti5O12). Effects of the positive electrode composition (ratio of LiFePO4 to AC) on the performance of LFP-AC/Li4Ti5O12 were investigated via constant current charge-discharge tests. The results demonstrated that the specific capacity and the specific power of the LFP-AC/Li4Ti5O12 hybrid supercapacitor significantly depend upon the content of LiFePO4 in the LFP-AC positive electrode. At 0.5 A g−1 charge-discharge current, the specific capacity of the LFP-AC/Li4Ti5O12 with 30 wt. % LiFePO4 and 70 wt. % AC in the positive electrode is 42% higher than that of AC/Li4Ti5O12, and the two supercapacitors have the same specific power. After 500 charge-discharge cycles at 1.0 A g...