Highly conductive carbon nanotube-graphene hybrid yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi-walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT-graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT-graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg-1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high-performance supercapacitors, batteries, high current capable cables, and artificial muscles

Nanostructured carbon electrodes

Supercapacitors are promising energy storage and power output technologies due to their improved energy density, rapid charge-discharge cycle, high cycle efficiency and long cycle life. Free standing poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) / single walled nanotube films have been characterised by scanning electron microscopy, Raman spectroscopy and thermo-gravimetric analysis to understand the physical properties of the films. Films with varying compositions of poly(3,4-ethylenedioxythiophene) / poly(styrene sulfonate) and single walled nanotubes were compared by electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge / discharge to understand their electrochemical properties. A comparison of the results shows that having single walled nanotubes dispersed throughout the polymer matrix increases the capacitance by 65 % and the energy density by a factor of 3 whilst achieving good capacity retention over 1000 cycles. Graphene is sp2 hybridised carbon atoms in a honeycomb crystal lattice, which has attracted a lot of interest in materials science and condensed matter physics research due to its favourable electronic properties, abundance and low cost. Exfoliated graphene oxide which has also been partially reduced has been achieved using microwave irradiation through the use of a conventional microwave that has led to rapid expansion and a marked volume increase of the graphene oxide. This has enabled a porous material to be developed that can serve as a conductive scaffold and support for composite electrode materials. Graphene based materials coupled with transition metal oxides are promising electrode materials in asymmetric supercapacitors owing to their unique properties which include high surface area, good chemical stability, electrical conductivity, abundance, and lower cost profile over time. A composite material consisting of graphene oxide exfoliated with microwave radiation (mw rGO), and manganosite (MnO) is synthesised in order to explore their potential as an electrode material. The composite material was characterised by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) was used to explore the process occurring at the electrode / electrolyte interface. Long term cyclability and stability was investigated using galvanostatic charge / discharge testing. From the resulting analysis, an asymmetric supercapacitor was constructed with the best composite containing 90% MnO- 10% mw rGO (w/w). The device exhibited a capacitance of 0.11 F/cm2 (51.5 F/g by mass) and excellent capacity retention of 82% after 15 000 cycles at a current density of 0.5 A/g. Composites containing CNTs and graphene are materials of particular interest in the energy storage and conversion area due to their favourable properties which can result in unique optical, electrical, magnetic and chemical properties which are substantially different than that of the individual components. It has been shown that the combination of both CNTs and graphene allows an expressway of electron transport from the electrode material to the current collector. The ability of the CNTs to ‘sandwich’ in between the graphene sheets helps to alleviate restacking by acting as a spacer (thus maintaining surface area) while increasing electrical conductivity and mechanical stability. We describe a facile method to develop electrodes of SWNT and exfoliated graphene oxide (mw rGO) with varying weight ratios via sonication, centrifugation and vacuum filtration. These composites are then optimised with the best performing weight ratio to be used in the fabrication of a supercapacitor. Extensive electrochemical testing revealed that the incorporation of SWNTs with mw rGO yielded an electrode material with large specific capacitances. The specific capacitances in all cases exceeded 125 F/g with the optimised / ideal weight ratio of 90% SWNT – 10% mw rGO exceeding 300 F/g. The thickness of the 90% SWNT – 10% mw rGO was optimised with the maximum attainable current per unit area arising at a thickness of 17 microns. Lastly, a device was fabricated that showed excellent reversibility upon current switching from 0.05 A/g up to 4.0 A/g, with a specific capacitance of 80 mF/cm2 and 128 F/g respectively at 0.05 A/g. Long term testing showed excellent stability over 10 000 cycles, with the maximum attainable energy and power density being 5.8 W.h/kg and 1.9 MW/kg

Effect of post-spinning on the electrical and electrochemical properties of wet spun graphene fibre

There is an urgent need for electroactive materials that exhibit high electrochemical performance and mechanically-compliant properties while also retaining high strength and durability. Single graphene sheets have a large electroactive surface area and excellent electrical properties. However, to transfer the excellent mechanical and physical properties of individual graphene to macrostructures for practical application remains a challenge. Herein we demonstrate the effect of carbon nanotubes and/or conducting polymer on electrical and electrochemical properties of graphene fibres. The hybrid graphene/carbon nanotube/poly(3,4-ethylenedioxythiophene) fiber possessed significantly higher electrical conductivity (over 400 S cm-1) compared to a graphene fiber. This value is ≈500% higher than the reduced graphene oxide fiber. The graphene fibers show impressive electrochemical responses with a specific capacitance in excess of 499 F cm-3 at the scan rate of 5 mV S-1. This was significantly enhanced for hybrid graphene/CNT/PEDOT fiber by ≈221% compared to graphene fibre at the scan rate of 1000 mV s-1

Nano-carbon electrodes for thermal energy harvesting

Thermogalvanic cells are capable of converting waste heat (generated as a by-product of almost all human activity) to electricity. These devices may alleviate the problems associated with the use of fossil fuels to meet the world\u27s current demand for energy. This review discusses the developments in thermogalvanic systems attained through the use of nano-carbons as the electrode materials. Advances in cell design and electrode configuration that improve performance of these thermo converters and make them applicable in a variety of environments are also summarized. It is the aim of this review to act as a channel for further developments in thermogalvanic cell design and electrode engineering

High strain stretchable solid electrolytes

Wearable electronic devices that can be integrated seamlessly into clothing for monitoring and feedback need to be not only flexible, but also stretchable with low stiffness. Currently there are few solid electrolytes that are sufficiently stretchable for wearable electronic devices. Here we report stretchable solid electrolytes that can be elastically stretched more than 500% of their original length with ionic conductivities as high as 7 x 10(-5) S cm(-1) and tensile breaking strengths larger than 1.5 MPa. These solid electrolytes consist of poly(methyl methacrylate) chemical networks solvated by an electrochemically stable ionic liquid. A stretchable supercapacitor was demonstrated by coating a stretchable solid electrolyte with carbon nanotube electrodes

Nano-carbon electrodes for thermal energy harvesting

Thermogalvanic cells are capable of converting waste heat (generated as a by-product of almost all human activity) to electricity. These devices may alleviate the problems associated with the use of fossil fuels to meet the world\u27s current demand for energy. This review discusses the developments in thermogalvanic systems attained through the use of nano-carbons as the electrode materials. Advances in cell design and electrode configuration that improve performance of these thermo converters and make them applicable in a variety of environments are also summarized. It is the aim of this review to act as a channel for further developments in thermogalvanic cell design and electrode engineering

Electrochemical investigation of carbon nanotube nanoweb architecture in biological media

The as-synthesised carbon nanotube nanoweb modified carbon fibre paper (CNT-NW/CFP) was investigated to study the effect of surface protein adsorption in electrochemical activities using immunoglobulin G (IgG) and human serum albumin (HSA). Detail chemical characterisation was carried out using 125I radiolabeling, cyclic voltammetry and electrochemical impedance spectroscopy. Both HSA and IgG were adsorbed onto the electrode at levels of approximately 120 mg/m2. Cyclic voltammetry indicated that the surface-adsorbed protein had a detrimental effect on oxidation/reduction of ferri/ferricyanide whilst EIS spectra revealed a slight increase in impedance and decrease in capacitance

Manganosite-microwave exfoliated graphene oxide composites for asymmetric supercapacitor device applications

Graphene based materials coupled with transition metal oxides are promising electrode materials in asymmetric supercapacitors owing to their unique properties which include high surface area, good chemical stability, electrical conductivity, abundance, and lower cost profile over time. In this paper a composite material consisting of graphene oxide exfoliated with microwave radiation (mw rGO), and manganosite (MnO) is synthesised in order to explore their potential as an electrode material. The composite material was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to explore the process occurring at the electrode/electrolyte interface. Long term cyclability and stability were investigated using galvanostatic charge/discharge testing. From the resulting analysis, an asymmetric supercapacitor was constructed with the best composite containing 90% MnO–10% mw rGO (w/w). The device exhibited a capacitance of 0.11 F/cm2 (51.5 F/g by mass) and excellent capacity retention of 82% after 15,000 cycles at a current density of 0.5 A/g