Grace Wee

Synthesis and electrochemical properties of electrospun V2O5 nanofibers as supercapacitor electrodes

Vanadium pentoxide (V2O5) nanofibers (VNF) were synthesized through a simple electrospinning method, and their application as supercapacitor electrodes demonstrated. The effect of annealing temperature on the microstructure and morphology of VNF was investigated systematically through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) surface area measurements. Electrochemical properties of the synthesized products as electrodes in a supercapacitor device were studied using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy in aqueous electrolyte of different pH and also in an organic electrolyte. The highest specific capacitance was achieved for VNF annealed at 400 °C, which yielded 190 F g−1 in aqueous electrolyte (2 M KCl) and 250 F g−1 in organic electrolyte (1 M LiClO4 in PC) with promising energy density of 5 Wh kg−1 and 78 Wh kg−1 respectively.

The facile synthesis of hierarchical porous flower-like NiCo2O4 with superior lithium storage properties

In this work, we demonstrate the facile fabrication of 3-dimensional (3D) hierarchical porous flower-like NiCo2O4 and its application as an anode material in high-performance lithium ion batteries (LIBs). The uniform flower-like NiCo2O4 is built from porous nanoplates with thicknesses of approximately 25 nm. A detailed investigation reveals that PVP plays an important role, not only in controlling the formation of the delicate hierarchical flower-like structure, but also in creating the uniform pores of each nanoplate. Furthermore, a possible formation mechanism for this unique structure is proposed based on the experimental results. As a virtue of its beneficial structural features, the as-prepared NiCo2O4 exhibits an enhanced lithium storage capacity and excellent cycling stability (∼939 mA h g−1 at 100 mA g−1 after 60 cycles). This remarkable electrochemical performance can be attributed to the hierarchical structure and sufficient void space within the surface of the nanoplates, which effectively increases the contact area between the active materials and the electrolyte, reducing the Li+ diffusion pathway and buffering the volume change during cycling.

Electrospun Porous NiCo2O4 Nanotubes as Advanced Electrodes for Electrochemical Capacitors

Novel, porous NiCo2O4 nanotubes (NCO-NTs) are prepared by a single-spinneret electrospinning technique followed by calcination in air. The obtained NCO-NTs display a one-dimensional architecture with a porous structure and hollow interiors. The effect of precursor concentration on the morphologies of the products is investigated. Due to their unique structure, the prepared NCO-NT electrode exhibits a high specific capacitance (1647 F g(-1) at 1 A g(-1)), excellent rate capability (77.3 % capacity retention at 25 A g(-1)), and outstanding cycling stability (6.4 % loss after 3000 cycles), which indicates it has great potential for high-performance electrochemical capacitors. The desirable enhanced capacitive performance of NCO-NTs can be attributed to the relatively large specific surface area of these porous and hollow one-dimensional nanostructures.

Printable photo-supercapacitor using single-walled carbon nanotubes

A printable, all solid-state photo-supercapacitor (PSC) incorporating both organic photovoltaic (OPV) and supercapacitor (SC) functions has been demonstrated utilizing a single-walled carbon nanotube network, enabling a thinner (< 0.6 mm) and lighter (< 1 g) device architecture, which leads to a 43% reduction in device internal resistance as compared to external wire connected OPVs and SCs.

Bifunctional carbon nanotube networks for supercapacitors

Highly conducting and porous carbon nanotube (CNT) networks are used as the sole electron conducting material in supercapacitors. The high conductivity of CNT networks and the high surface area allow the replacement of both the metallic current collector and the active material that forms one side of the electrochemical double layer. The combination of both functions in one single layer leads to lightweight charge storage devices that can be manufactured using simple and cheap room temperature methods. The authors have demonstrated that the specific capacitance of such CNT electrodes is comparable to that of other carbon electrodes.

Particle Size Effect of Silver Nanoparticles Decorated Single Walled Carbon Nanotube Electrode for Supercapacitors

Well dispersed silver nanoparticles AgNPs of different sizes 1–13 nm on single walled carbon nanotubes SWCNTs were synthesized by a facile room-temperature deposition–precipitation process. The morphology and microstructure of samples examined by the transmission electron microscopy showed a monodispersed silver particle decorated SWCNT of 2 wt % as determined by the Rietveld phase analysis of powder X-ray diffraction patterns. The chemical state of silver determined from the binding energies of high resolution Ag 3d peaks from X-ray photoelectron spectroscopy revealed a silver Ag 0 oxidation state. Electrochemical properties were studied using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance studies. Silver decorated SWCNTs demonstrated to be effective bifunctional charge collectors and active electrode materials for a supercapacitor, exhibiting a higher specific capacitance 106 F g �1

Electrospun hierarchical CaCo2O4 nanofibers with excellent lithium storage properties.

Hierarchical CaCo2O4 nanofibers (denoted as CCO-NFs) with a unique hierarchical structure have been prepared by a facile electrospinning method and subsequent calcination in air. The as-prepared CCO-NFs are composed of well-defined ultrathin nanoplates that arrange themselves in an oriented manner to form one-dimensional (1D) hierarchical structures. The controllable formation process and possible formation mechanism are also discussed. Moreover, as a demonstration of the functional properties of such hierarchical architecture, the 1D hierarchical CCO-NFs were investigated as materials for lithium-ion batteries (LIBs) anode; they not only delivers a high reversible capacity of 650 mAh g(-1) at a current of 100 mA g(-1) and with 99.6% capacity retention over 60 cycles, but they also show excellent rate capability with respect to counterpart nanoplates-in-nanofibers and nanoplates. The high specific surface areas as well as the unique feature of hierarchical structures are probably responsible for the enhanced electrochemical performance. Considering their facile preparation and good lithium storage properties, 1D hierarchical CCO-NFs will hold promise in practical LIBs.

A Polyoxovanadate as an Advanced Electrode Material for Supercapacitors

Polyoxovanadate Na(6)V(10)O(28) is investigated for the first time as electrode material for supercapacitors (SCs). The electrochemical properties of Na(6)V(10)O(28) electrodes are studied in Li(+) -containing organic electrolyte (1 M LiClO(4) in propylene carbonate) by galvanostatic charge/discharge and cyclic voltammetry in a three-electrode configuration. Na(6)V(10)O(28) electrodes exhibit high specific capacitances of up to 354 F g(-1). An asymmetric SC with activated carbon as positive electrode and Na(6)V(10)O(28) as negative electrode is fabricated and exhibits a high energy density of 73 Wh kg(-1) with a power density of 312 W kg(-1), which successfully demonstrates that Na(6)V(10)O(28) is a promising electrode material for high-energy SC applications.