Intercalation-pseudocapacitance hybrid anode for high rate and energy lithium-ion capacitors

Existing rechargeable batteries not only fail to meet the demand for high power applications but also cause heavy metal pollution.Li-ion capacitors(LICs),which can achieve higher charging speeds and energy densities than supercapacitors,have attracted extensive attention.Nevertheless,sluggish Li-ion diffusion of the battery-type anode results in limited rate performance of LICs.Herein,highperformance LICs using both battery and capacitor type Mn_(2)V_(2)O_(7)-graphene(MVO-G)anodes and hempstem-derivated activated carbon(HSAC)cathodes with a large surface area are first reported.In addition to high pseudocapacitance,the MVO-G possesses the advantage of fast Li^(+)storage performance making it a suitable choice for advanced LIC anodes.Graphene is employed to enhance overall conductivity and cycling stability leading to enhanced energy storage.The MVO-G//HSAC LICs exhibit a high energy density of 148.1 Wh kg^(-1) at a power density of 150 W kg^(-1) and 25 Wh kg^(-1) even at15 k W kg^(-1).More importantly,the MVO-G//HSAC LICs also show excellent cycling stability of 90%after15,000 cycles,which is expected for high performance energy storage systems.

Hardness of Mn_2V_2O_7 thin films and its influential factors

Mn2V2O7 thin films were deposited onto amorphous glass substrates using a chemical bath deposition method and different deposition time. X-ray diffraction （XRD） analysis was used to define the structure of the films. Their roughness, thickness, and surface properties were evaluated through atomic force microscopy （AFM）. The hardness of the films was measured using a nanohardness tester The film thickness, average grain size, and roughness were positively correlated with each other. These three parameters were observed to increase with the deposition time. The film thickness and average grain size were inversely correlated with the hardness and rough- ness. In addition, the number of crystallites per unit area and the dislocation density were observed to be positively correlated with the hardness and roughness. This study was designed to elucidate and formalize the underlying reasons for these relationships.

A Pt/MnV_(2)O_(6) nanocomposite for the borohydride oxidation reaction

Problems associated with carbon support corrosion under operating fuel cell conditions require the identification of alternative supports for platinum-based nanosized electrocatalysts.Platinum supported on manganese vanadate(Pt/MnV_(2)O_(6))was prepared by microwave irradiation method and characterized using X-ray diffraction,Fourier-transform infrared spectroscopy,X-ray photoelectron spectroscopy,scanning electron microscopy with energy dispersive spectroscopy,and transmission electron microscopy.The borohydride oxidation reaction(BOR)on Pt/MnV_(2)O_(6) was studied in highly alkaline media using voltammetry,chronoamperometry,and electrochemical impedance spectroscopy.BOR electrocatalytic activity of Pt/MnV_(2)O_(6) was also compared with that of commercial Pt/C(46 wt%Pt)electrocatalyst.The apparent activation energy of BOR at Pt/MnV_(2)O_(6) was estimated to be 32 k J mol^(-1) and the order of reaction to be 0.51,indicating that borohydride hydrolysis proceeds in parallel with its oxidation.Long-term stability of Pt/MnV_(2)O_(6) under BOR typical conditions was observed.A laboratory-scale direct borohydride fuel cell assembled with a Pt/MnV_(2)O_(6) anode reached a specific power of 274 W g^(-1).Experimental results on Pt/MnV_(2)O_(6) were complemented by DFT calculations,which indicated good adherence of Pt to MnV_(2)O_(6),beneficial for electrocatalyst stability.