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Polyaniline (PANI) nanowire arrays have been prepared for the first time using Na5V12O32 nanowires as a sacrificial template. Fourier-transformed infrared spectroscopy and energy-dispersive X-ray spectroscopy were used to characterize the as-prepared PANI nanowire arrays. Further, the electrochemical properties of the PANI nanowire arrays for lithium-ion batteries were investigated with cyclic voltammetry, galvanostatic charge-discharge experiment, and rate performance. It delivered a high discharge capacity of 119.79 mA h g−1 after 100 cycles between 2.0 and 4.0 V at 30 mA g−1. [ABSTRACT FROM AUTHOR]

Polypyrrole (PPy) nanofibers have been prepared for the first time using FeO hollow nanofibers as a sacrificial template, and characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrum, and Raman spectroscopy. The results show that pyrrole was uniformly polymerized around the FeO and the FeO was subsequently removed thoroughly with HCl. The electrochemical properties of the PPy nanofibers for lithium battery were investigated with cyclic voltammetry, galvanostatic charge-discharge test, and rate performance. The as-prepared PPy nanofibers composed by nanoparticles exhibited with good rate performance, which delivered a high discharge capacity of 98 mA h g after 50 cycles between 2.0 and 3.8 V at 30 mA g. [ABSTRACT FROM AUTHOR]

Abstract: A small external magnetic field of 0.072T was reported to significantly influence the specific capacitances of the supercapacitor with magnetic carbon - metal (iron, cobalt or nickel) oxides microtubular nanocomposite fabrics as flexible electrodes. The decorated metal oxide species and annealing method (microwave-assisted vs. conventional tubular annealing) were discovered to play important roles in the increase or decrease of the capacitance. All the electrodes demonstrated excellent cycling retention performances, for example, upto ~350% for nickel oxide doped carbon nanocomposite electrodes. The corresponding mechanism for the magnetic field influence on the capacitance has been interpreted in term of a synergistic effect of three internal resistances, solution resistance in electrolyte solution, charge transfer resistance at electrode/electrolyte interface and leakage resistance in electric double layer region. The applied magnetic field is able to change the solution resistance due to the magnetohydrodynamic phenomena as well as the electrode resistance (directly corresponds to charge transfer resistance) by the magnetoresistance (MR) behavior. [Copyright &y& Elsevier]

A facile and scalable strategy, based on a hydrothermal route, has been applied to fabricate potassium vanadate (KVO) nanowires on Ti fabric. The morphology, crystal structure, chemical composition of the prepared sample are tested and presented in detail. When tested as cathode materials for lithium-ion batteries, the flexible KVO electrode has a high reversible capacity of 270 mAh g −1 at a current density of 100 mA g −1 after 300 cycles. Furthermore, the KVO delivers outstanding rate behavior, even at 960 mA g −1 , a reversible capacity as high as 214.1 mAh g −1 can be retained. The superior electrochemical performance suggests that the KVO nanowires on Ti fabric can be as a potential cathode candidate for flexible rechargeable lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Lithium vanadate nanowires have been electrodeposited onto a titanium (Ti) foil by a direct current electrodeposition without template. The morphology, crystal structure, and the effects of deposition voltage, temperature and time on the prepared samples were tested and presented. The as-prepared lithium vanadate nanowires/Ti composite can be used as electrode for lithium-ion battery. Electrochemical measurements showed that the electrode displayed a specific discharge capacitance as high as 235.1 mAh g −1 after 100 cycles at a current density of 30 mA g −1 . This research provides a new pathway to explore high tap density vanadates nanowires on metals with enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

Use of hybridized transition-metal oxides nanostructures with a shell coating show promise for improving the electrochemical performance of sodium-ion batteries. Herein, a novel type of designed sodium vanadate @ polypyrrole (Na 5 V 12 O 32 @PPy) nanocomposites with a synergetic core-shell structure was fabricated using sequential hydrothermal and electrodeposition methods. When the Na 5 V 12 O 32 @PPy nanocomposites were employed as a cathode, the assembled sodium-ion batteries exhibited a high reversible discharge capacity of 213 mAh g −1 at a current density of 30 mA g −1 , high rate performance (133 mAh g −1 at 480 mA g −1 ) and superior cycling performance (202 mAh g −1 at 100 mA g −1 after 100 cycles with a capacity retention of 94%). By contrast, the cycling behavior of this novel material proved to be much better than the naked Na 5 V 12 O 32 nanowires. This research provides a new pathway to explore cathode materials for sodium-ion battery with enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

Abstract: This study aims to improve the performance of proton exchange membrane fuel cells (PEMFCs) using carbon nanotubes as scaffolds to support nanocatalyst for power generation over prolonged time periods, compared to the current designs. The carbon nanotubes are prepared using chemical vapor deposition and decorated by platinum nanoparticles (Pt-NPs) using an amphiphilic approach. The PEMFC devices are then constructed using these aligned carbon nanotubes (ACNTs) decorated with Pt-NPs as the cathode. The electrochemical analyses of the PEMFC devices indicate the maximum power density reaches to 860mWcm−2 and current density reaches 3200mAcm−2 at 0.2V, respectively, when O2 is introduced into cathode. Importantly, the Pt usage was decreased to less than 0.2mgcm−2, determined by X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy as complimentary tools. Electron microscopic analyses are employed to understand the morphology of Pt-ACNT catalyst (with diameter of 4–15nm and length from 8 to 20μm), which affects PEMFC performance and durability. The Pt-ACNT arrays exhibit unique alignment, which allows for rapid gas diffusion and chemisorption on the catalyst surfaces. [Copyright &y& Elsevier]

Abstract: Degradation behaviors of polymer electrolyte membrane fuel cell (PEMFC) in high current density region were investigated under Freeze/Thaw cycles. Different dehumidification scenarios namely hot purge, cold purge and no purge were adopted for comparison. Micrographs from scanning electron microscopy proved little change in catalyst-coated membrane (CCM) integrity, no delamination or segregation occurred after many freeze/thaw cycles. Cyclic Voltammetry (CV) measurement revealed reduction in electrochemical active surface area of CCM. The observed performance decay in the high current density region was mainly attributed to the increased interface contact resistance and degraded electric and gas coupling characteristics at interfaces between CCM and GDL in this paper. Meanwhile, the performance degradation under low current densities (for example 400mAcm−2 or even lower) was mainly ascribed to the degraded characteristics of catalyst layers referring to CCM as cyclic voltammetry indicated. Proper dehumidification through gas purging is effective to maintain stable preference under subzero temperature. [Copyright &y& Elsevier]