Facile synthesis and characterization of Au-Cu, Pt-Cu nanotubes by sacrificial template method

Bimetallic nanotubes with noble metals have already shown more versatile performances than single-metallic nanotubes. However, most of the current methods to prepare bimetallic nanotubes are based on existed hard template, which could not be easily removed after the formation of bimetallic nanotubes. It is still a challenge for synthesizing bimetallic nanotubes without the template removing subsequently. In this research, we developed a novel method to prepare noble metal-copper (Cu) bimetallic nanotubes with Cu nanowires as the sacrificial template. The aqueous solutions with chloroauric acid or palladium chloride were used to bring displacement reaction with Cu nanowires. The simultaneous alloying effect and Kirkendall effect result in hollow nanostructures. The Cu nanowire was converted to a bimetallic hollow with Au-Cu or Pt-Cu alloy nanotubes. This facile method could achieve large-scale preparation of bimetallic nanotubes with noble metals. Furthermore, this alloy nanotube shows superior electrochemical catalytic performance than single-metallic nanoparticles. (C) 2014 Elsevier Ltd. All rights reserved

Single-walled carbon nanotube embedded porous carbon nanofiber with enhanced electrochemical capacitive performance

Active carbon nanofibers (CNFs) with porous structure show highly electrochemical double-layer capacitance for supercapacitors because of their large specific area. However, their poor crystallization induced the low conductivity, which could largely limit the electrochemical performance of the porous CNFs. In this research, porous CNFs with single-walled carbon nanotubes (SWCNTs) were prepared by electrospinning and high temperature carbonization. The introduction of SWCNTs into porous CNFs could largely enhance the conductivity of the porous CNF nanotextiles, thus the electrochemical performance of the composite nanotextile was largely enhanced. The specific capacitance of the composite could achieve 417 F/g at a current density of 0.5 A/g, and keep 193 F/g at the high current density of 10 A/g. Furthermore its specific capacitance could keep 96% after 2000 cycles of charge/discharge at the current density of 10 A/g. This nanotextile could be a promising candidate for the binder-free and filler-free electrodes of high-performance supercapacitors. (C) 2015 Elsevier B.V. All rights reserved

Hierarchical carbon nanotube/alpha-Ni(OH)(2) nanosheet composite paper with enhanced electrochemical capacitance

<span lang="EN-US" style="font-family: &quot;Calibri&quot;,&quot;sans-serif&quot;; font-size: 10.5pt; mso-bidi-font-size: 11.0pt; mso-ascii-theme-font: minor-latin; mso-fareast-font-family: 宋体; mso-fareast-theme-font: minor-fareast; mso-hansi-theme-font: minor-latin; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-bidi-theme-font: minor-bidi; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><font color="#000000">Carbon nanotube (CNT)/alpha-Ni(OH)(2) composite paper based on CNT paper was prepared by a facile chemical bath deposition (CBD) method. alpha-Ni(OH)(2) nanosheets were vertically grown on individual CNTs in CNT paper to form hierarchical nanowires. The loading mass of alpha-Ni(OH)(2) in the composite paper could be 66 wt%. Thus the composite paper showed much higher specific surface area than that of pristine CNT paper. This novel structure brings the composite paper an electrochemical capacitance high to 1144 F/g at the current density of 0.5 A/g, and maintains 585 F/g at 10 A/g. This composite paper could be a promising candidate for the electrodes of high-performance supercapacitors. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.</font></span

Graphene-Patched CNT/MnO2 Nanocomposite Papers for the Electrode of High-Performance Flexible Asymmetric Supercapacitors

MnO2 has been widely studied as the pseudocapactive electrode material of high-performance super. capacitors for its large operating voltage, low cost, and environmental friendliness. However, it suffers from low conductivity and being hardly handle as the electrodes of supercapacitors especially with flexibility, which largely limit its electrochemical performance and application. Herein, we report a novel ternary composite paper composed of reduced graphene sheet (GR)-patched carbon nanotube (CNT)/MnO2, which has controllable structures and prominent electrochemical properties for a flexible electrode of the supercapacitor. The composite paper was prepared by electrochemical deposition of MnO2 on a flexible CNT paper and further adsorption of GR on its surface to enhance the surface conductivity of the electrode and prohibit MnO2 nanospheres from detaching with the electrode. The presence of GR was found remarkably effective in enhancing the initial electrochemical capacitance of the composite paper from 280 F/g to 486.6 F/g. Furthermore, it ensures the stability of the capacitance after a long period of charge/discharge cycles. A flexible CNT/polyaniline/CNT/MnO2/GR asymmetric supercapacitor was assembled with this composite paper as an electrode and aqueous electrolyte gel as the separator. Its operating voltage reached 1.6 V, with an energy density at 24.8 Wh/kg. Such a composite structure derived from a multiscale assembly can offer not only a robust scaffold loading MnO2 nanospheres but also a conductive network for efficient ionic and electronic transport; thus, it is potentially promising as a novel electrode architecture for high-performance flexible energy storage devices

Rational control on floating catalysts for the growth of carbon nanotube assemblies: From vertically aligned carbon nanotube arrays to carbon nanotube films

Floating catalyst chemical vapor deposition (FCCVD) has been widely used for the growth of various carbon nanotube (CNT) macrostructures, mainly including vertically aligned CNT (VACNT) arrays and none-woven CNT films. However, it is still unclear for the reason why these CNT macrostructures with largely different morphologies were received via the similar method. In this research, it revealed that the growth temperature largely affected the nucleation status of floating catalysts and thus controlled the morphologies of CNT macrostructures from VACNT arrays to none-woven CNT films. In low temperatures (below 800 degrees C), VACNTs were grown by bottom-up mechanism with several CNTs, but not one individual from bottom to up along the array height direction. Furthermore, VACNT arrays were only grown on some substrates that can induce iron atoms aggregating to catalyst particles with a suitable size. When increasing the growth temperature higher than 800 degrees C, more catalyst particles were nucleated in the gas flow, which induced the formation of none-woven CNT films composed of thin CNTs (single-walled CNTs and double-walled CNTs). This research was significative for understanding CNT growth mechanism via FCCVD process and the synthesis of different CNT macrostructures by this strategy. (C) 2015 Elsevier B.V. All rights reserved

Carbon Nanotube/Graphene Hybrid Nanostructures and Their Application in Supercapacitors

In this paper, we review the preparation methods of carbon nanotube (CNT)/graphene composite materials for the electrode of supercapacitors, and introduce the developments of CNT/graphene/pseudocapacitive material ternary composite materials with highly electrochemical performance. The rational designed CNT/graphene composite nanostructures could largely utilize the characteristics of carbon nanomaterials for electrochemical double-large supercapacitors, such as large specific area, high conductivity and befitting porous structure, and also achieve large mass loading of pseudo-capacitive materials with high dispersion for pseudocapacitors. As a result, these composite materials are promising candidates for the electrode materials of high-performance supercapacitors with high capacitance, excellent rate performance and long lifetime

Hierarchical CNT@NiCo2O4 core-shell hybrid nanostructure for high-performance supercapacitors

<span lang="EN-US" style="background: yellow; font-family: &quot;Calibri&quot;,&quot;sans-serif&quot;; font-size: 10.5pt; mso-bidi-font-size: 11.0pt; mso-ascii-theme-font: minor-latin; mso-fareast-font-family: 宋体; mso-fareast-theme-font: minor-fareast; mso-hansi-theme-font: minor-latin; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-bidi-theme-font: minor-bidi; mso-highlight: yellow; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><font color="#000000">The mass integration of electrochemically active materials on nanosized conductive fillers is a promising strategy to achieve an ideal electrode structure for energy storage devices. In this research, a one-dimensional CNT@NiCo2O4 nanosheet core-shell structural nanocable was constructed by a facile chemical co-deposition route combined with post-calcination in air. The subsequent thermal treatment led to the transformation of the hydroxide nanosheet precursor to NiCo2O4 nanosheets, during which process the overall morphology and structure were well retained. By selecting CNTs as conductive support for ultra-thin NiCo2O4 nanosheets, a high-performance electrode for supercapacitors was obtained. Notably, the as-prepared CNT@NiCo2O4 nanocables have a high capacitance of 1038 F g(-1) at a current density of 0.5 A g(-1). Furthermore, the specific capacitance of the product was almost 100% retained after 1000 cycles, which indicates excellent structural and cycling stability. More importantly, a relatively high mass loading of active materials on CNTs was also achieved, making the practical application of such electrode materials possible. Consequently, this CNT@NiCo2O4 nanocable is a promising electrode for high-performance supercapacitors.</font></span

Oxygen Evolution Assisted Fabrication of Highly Loaded Carbon Nanotube/MnO2 Hybrid Films for High-Performance Flexible Pseudosupercapacitors

To date, it has been a great challenge to design high-performance flexible energy storage devices for sufficient loading of redox species in the electrode assemblies, with well-maintained mechanical robustness and enhanced electron/ionic transport during charge/discharge cycles. An electrochemical activation strategy is demonstrated for the facile regeneration of carbon nanotube (CNT) film prepared via floating catalyst chemical vapor deposition strategy into a flexible, robust, and highly conductive hydrogel-like film, which is promising as electrode matrix for efficient loading of redox species and the fabrication of high-performance flexible pseudosupercapacitors. The strong and conductive CNT films can be effectively expanded and activated by electrochemical anodic oxygen evolution reaction, presenting greatly enhanced internal space and surface wettability with well-maintained strength, flexibility, and conductivity. The as-formed hydrogel-like film is quite favorable for electrochemical deposition of manganese dioxide (MnO2) with loading mass up to 93 wt% and electrode capacitance kept around 300 F g(-1) (areal capacitance of 1.2 F cm(-2)). This hybrid film was further used to assemble a flexible symmetric pseudosupercapacitor without using any other current collectors and conductive additives. The assembled flexible supercapacitors exhibited good rate performance, with the areal capacitance of more than 300 mF cm(-2), much superior to other reported MnO2 based flexible thin-film supercapacitors

Boosting Electrocatalytic Performances of Palladium Nanoparticles by Coupling with Metallic Single-Walled Carbon Nanotubes

Noble metal catalysts are core materials for many energy conversion and storage technologies such as fuel cell and hydrogen storage, while the performances of the noble metals depend critically on the nature of support materials. Herein, for the first time, we report the use of sorted high-purity metallic (m-) and semiconducting (s-) single-walled carbon nanotubes (SWNTs) as support materials for a typical noble metal catalyst, Pd, which has been believed to have strong interactions with SWNTs. Our results clearly suggest that electrocatalytic performances of the noble metals/SWNTs hybrid system, specifically in hydrogen electrosorption and formic acid electrooxidation, exhibit strongly sensitive dependence with respect to the electronic type of SWNT supports. Pd nanoparticles on m-SWNTs demonstrate much enhanced electrocatalytic activities compared with those on s-SWNTs or unsorted-SWNTs. Our in-depth mechanism studies indicate that the m-SWNTs in the nanocomposite tend to provide more effective charge-transfer interfaces with Pd nanoparticles, more likely leading to higher electron densities on Pd nanoparticles to boost their catalytic performance. The present study provides a novel window onto the design and synthesis of new feasible electrocatalyst system for efficient energy conversion and storage

Electrochemical conversion of Ni-2(OH)(2)CO3 into Ni(OH)(2) hierarchical nanostructures loaded on a carbon nanotube paper with high electrochemical energy storage performance

Large-diameter carbon nanotube (CNT) paper was used as a porous and conductive template to obtain vertically aligned Ni-2(OH)(2)CO3 nanowire array shells, which could be further converted into highly active Ni(OH)(2) nanosheets by a cyclic voltammetry strategy. The as-prepared hierarchical nanostructure showed superior electrochemical performance for the electrodes of supercapacitors