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Activated carbon (AC) prepared by two-stage microwave-induced physical activation of oil palm shell have been coated using electroless plating technique to form nanocomposite material. The composite materials were calcinated at different temperature of 300, 400 and 500°C for one hour. The nanocomposite materials were evaluated as potential electrodes for supercapacitors. Using the composite electrodes in a two-electrode symmetrical capacitor, the properties of the composite electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Results from electrochemical measurements show that the nanocomposite electrodes exhibit superior capacitive performance compared with the AC electrode. The specific capacitance have been found to increase by 85–205% with respect to the AC electrode. In addition, the specific capacitance as well as the energy density were found to reduce with the increment of the calcination temperature. The composite electrode calcinated at 300°C offers the maximum enhancement of 205% in both specific capacitance and energy density.
The signal crayfish (Pacifastacus leniusculus) was introduced to Crater Lake in 1915 and now threatens the local extinction of an endemic salamander, the Mazama newt (Taricha granulosa mazamae). More than a century after their introduction, crayfish have expanded in distribution to occupy nearly 80% of the lakeshore. Although newts remain in uninvaded areas, they are almost entirely absent in crayfish occupied areas. Abundance of benthic macroinvertebrates was dramatically reduced in locations with crayfish compared with areas of the lake where crayfish were absent. Isotopic signatures of newt and crayfish tissue confirm overlap in the diets of the two species and demonstrate their similar position in the Crater Lake food web. Mesocosm experiments conducted with newts and crayfish revealed that crayfish prey directly on newts, displace newts from cover, and generally alter newt behavior. Combined, this evidence suggests that further crayfish expansion likely will cause additional declines in newt abundance and distribution, and could lead to extinction of the unique population of newts in Crater Lake.
Co-doped Li3V2−x Co x (PO4)3/C (x =0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li3V2−x Co x (PO4)3/C (0≤ x ≤0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li3V2−x Co x (PO4)3. XPS studies also revealed that V4+ and V3+ ions were present in the Co2+-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x >0.10. Differential capacity curves of Li3V2−x Co x (PO4)3/C compounds showed that the voltage peaks associated with the extraction of three Li+ ions shifted to higher voltages with an increase in Co content, and when the Co2+-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li3V2(PO4)3 phase. For the Li3V1.85Co0.15(PO4)3/C compound, the initial capacity was 163.3mAh/g (109.4% of the initial capacity of the undoped Li3V2(PO4)3) and 73.4% capacity retention was observed after 50 cycles at a 0.1C charge/discharge rate. The doping of Co2+into V sites should be favorable for the structural stability of Li3V2−x Co x (PO4)3/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li+ extraction/insertion, thus resulting in the improvement of cell cycling ability.
Partial manganese substitution of iron in ferrous carbonate (MnxFe1−xCO3, x = 0, 0.1, 0.2, 0.3) is obtained via a one-step hydrothermal method. The phase structure, morphology, and structural stability are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis, respectively. The results of XRD demonstrate that Mn-doping does not obviously change the phase structure. MnxFe1−xCO3 possesses cockscomb-like and tunnel structures observed by SEM images. Meanwhile, the results of XPS further demonstrate the existence of Fe2+ and Mn2+. Mn-doped FeCO3 samples remarkably improve galvanostatic charge–discharge stability and rate capability as anode materials for lithium-ion batteries because of the synergistic behavior of Fe2+ and Mn2+ with cockscomb-like and tunnel structures. MnxFe1−xCO3 (x = 0.2) as an anode material delivers an initial specific discharge capacity of 2400 mAh g−1 at 200 mA g−1 and 904 mAh g−1 over 100 cycles. Therefore, MnxFe1−xCO3 anode materials are promising for lithium-ion batteries because of their low-cost preparation, environmentally friendly nature, and excellent electrochemical performance.
Mesostructured niobium (Nb)-doped TiO2-carbon (Nb-TiO2-C) composites are synthesized by a hydrothermal process for application as anode materials in Li-ion batteries. The composites have a hierarchical porous structure with the Nb-TiO2 nanoparticles homogenously distributed throughout the porous carbon matrix. The Nb content is controlled (0–10 wt%) to investigate its effect on the physico-chemical properties and electrochemical performance of the composite. While the crystalline/surface structure varied with the addition of Nb (d-spacing of TiO2: 0.34–0.36 nm), the morphology of the composite remained unaffected. The electrochemical performance (cycle stability and rate capability) of the Nb-TiO2-C composite anode with 1 wt% Nb doping improved significantly. First, a full cut-off potential (0–2.5 V vs. Li/Li+) of Nb-doped composite anode (1 wt%) provides a higher energy utilization than that of the un-doped TiO2-C anode. Second, Nb-TiO2-C composite anode (1 wt%) exhibits an excellent long-term cycle stability (100% capacity retention, 297 mAh/g at 0.5 C after 100 cycles and 221 mAh/g at 2 C after 500 cycles) and improved rate-capability (192 mAh/g at 5 C), respectively (1 C: 150 mA/g). The superior electrochemical performance of Nb-TiO2-C (1 wt%) could be attributed to the synergistic effect of improved electronic conductivity induced by optimal Nb doping (1 wt%) and lithium-ion penetration (high diffusion kinetics) through unique pore structures.
The effects of conducting carbon additive on the performance of LiCoO2 and LiMn2O4 cathodes in lithium-ion batteries have been investigated. While 2–5wt.% of carbon are adequate for the LiMn2O4 cathode to deliver good rate capability and maintain cyclability, the LiCoO2 cathode requires more carbon (10wt.%) to achieve likewise. The sensitivity of the LiCoO2 electrode for carbon content is particularly pronounced in high rate charging. Cyclic voltammetry and electrochemical impedance spectroscopy measurements indicate that deteriorating particle contacts leading to the incomplete charging of the active materials is the primary cause of material non-performance.
Nano-LiFePO4/C cathode materials have been synthesized by a solid–state reaction method using Tween60-Span60 composite as surfactant and carbon source. The Tween60-Span60 composite surfactants together lead a strong space steric effect, which ensures a high surface energy and reaction kinetic of the precursors. Consequently, it contributes to the formation of uniformly distributed LiFePO4 particles coated with a thin layer of carbon. The unique structured LiFePO4/C cathode materials can deliver high electrochemical capacities of 166, 150.5 and 130.1 mAh g−1 under 0.1 C at 25, 0 and −20 °C, respectively. Moreover, the LiFePO4/C cathode materials demonstrate an excellent rate capability and cycle performance, no discernible specific discharge capacity fading has been observed after over 400 cycles under the rate of 0.1–5 C at 25 °C, or after over 100 cycles under the rate of 0.1–0.5 C at −20 °C.
Novel massif-like Cu x O nanostructure was directly growing on Cu foam via a facile thermal oxidation method in air atmosphere. The massifs are about 5μm in mean diameter and 4μm in mean height, which consist of a large number of nanoparticles with mean size about 100nm. Cu x O nanowires that evolve from the particles locate at the laps of the massifs. Galvanostatic battery testing shows that the Cu x O/Cu electrode exhibits excellent cycle stability and rate capability. The charge and discharge capacities are both 1.8mAhcm−2 after 100 cycles under a discharge/charge rate of 0.35C. After testing at various rates from 0.2 to 12C over 50 cycles, the 5th-cycle discharge capacity can resume well when lowering the discharge/charge rate to 0.2C. The performances are testified due to a novel electrochemical activation effect that induces the reconstruction of porous forest-like morphology in cycling.
Three-dimensional (3D) porous V2O5 and Fe0.1V2O5.15 thin films have been prepared by electrostatic spray deposition technique. X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy are employed to investigate the structures and valence states of the films. Galvanostatic cell cycling, cyclic voltammetry and impedance spectroscopy are used to characterize their electrochemical properties. The Fe0.1V2O5.15 thin film shows much better cycling performance than the non-doped V2O5 thin film. Fe3+ can act as a stabilizing agent in the layered V2O5 and increase the reversibility of the charge and discharge processes towards deeper depth of lithium insertion/extraction. The dissolution of the active material in the electrolyte can also be significantly suppressed in the Fe-doped sample. Nevertheless, the Fe-doping causes a slight decrease in lithium ion diffusion coefficient.
As potential high-performance anode materials for Li-ion batteries (LIBs), mesoporous TiNb2O7 (M-TNO) microspheres were synthesized through a facial solvothermal and subsequent calcination process. Due to the reduced charge and ion transfer distances, the M-TNO samples showed smaller charge transfer resistance and faster Li ion diffusion. The void space in the M-TNO can boast the structural stability by buffer the volume change during cycling to result in long cycle life. A high specific capacity of 319 mA h g−1 can be realized in the first cycle at 0.1 C, and the cyclability and kinetics were superior at the electrode in the following cycles. The M-NTO presented outstanding high rate performances at 1 C and 10 C, with a high rate capacity of 155 mA h g−1 and a very slow capacity fading of 0.03% per cycle after 500 cycles at 10 C. Electrochemical measurements indicating that the elevated rate capacity and long cycle life were derived from the more proportion of capacitive capacity, smaller charge transfer resistance and faster Li+ ion diffusion.
Using intermittent X-ray diffraction, an understanding of the time dependence of phase evolution in the electrode materials during lithium extraction can be determined. Phase evolution in both coated and uncoated nano-scale LiFePO4 samples upon chemical delithiation has been investigated by this technique. Different kinetic behaviors are observed in the two samples and the technique helps to understand the delithiation mechanism in the nano-scale LiFePO4 and is able to resolve phase evolution in seconds’ resolution.
The structural information (including the lattice parameters, atomic sites and coordinates (x, y, z)) of Na2VMn2(PO4)3/C has been presented for the first time. It has a monoclinic lattice with the space group of C2/c and cell parameters of a = 12.0494 Å, b = 12.6198 Å, c = 6.5170 Å, β = 114.7°. The valence states of elements and the vibrational modes of Na2VMn2(PO4)3/C are performed by X-ray photoelectron spectroscopy, Raman and FTIR. Furthermore, at 5 mA g−1, Na2VMn2(PO4)3/C as cathode for SIBs shows a reversible discharge capacity of 80.4 mAh g−1. At 20 mA g−1, Na2VMn2(PO4)3/C shows an initial charge capacity of 46.1 mAh g−1 with the capacity retentions of 63.7% after 100 cycles. The poor cycle stability may be attributed to its low intrinsic Na+ diffusion coefficient (D Na+ ) and Jahn-Teller effect during the sodiation/desodiation process.
In resource limited settings non-availability of CD4 count facility at the site could adversely affect the ART roll out programme. Point of care CD4 enumerating equipments can make the CD4 count available at the site of care and improve the patients’ management considerably. This study is aimed at determining the utility of a Point of Care PIMA CD4 analyzer (Alere, Germany) in the field settings in India.
Confirmatory diagnosis of African trypanosomiasis relies on demonstration of parasites in body fluids by bright field microscopy. The parasitaemia in infected patients and animals is usually low, and concentration methods are used to try and increase the chances of seeing parasites. Recently, fluorescence microscopes using light-emitting diodes (LED) have been developed. Since they emit strong light, their use does not require a dark room, making field application a possibility. We have combined LED fluorescence microscopy with lysis of red blood cells (RBC) to improve the sensitivity and speed of detecting trypanosomes. In studies conducted at four centers in Uganda and the Democratic Republic of the Congo, parasitaemic blood was serially diluted and the RBCs lysed using commercial buffer. Samples were then concentrated by centrifugation, and different volumes of the sediment used to make thin and thick smears. Next, these were stained with acridine orange or Giemsa, and examined using an LED microscope under fluorescence or bright light, respectively. Detection of parasites was significantly improved by RBC lysis and concentration, regardless of the staining and microscopy method used. Further improvements were made when smears were prepared using larger volumes of sediment. The best results were obtained with thin smears prepared using 20μl of sediment and stained with acridine orange. The time taken to see the first parasite was dramatically reduced when smears were examined by LED fluorescence microscopy, compared to bright light. LED fluorescence microscopy was found to be easier and requiring less visual effort than bright field microscopy. These studies demonstrate the potential for incremental improvement in detection of Trypanosoma brucei by combining LED fluorescence microscopy with RBC lysis and concentration. The lysis and concentration method may also be useful in sample preparation for other diagnostic tests for trypanosomiasis.
An electrochemical polymerization and characterization is reported on a series of eight dicarbazole-type conducting polymers with different attached functional groups. The influence of the electronic character of the subgroup on the ionic conductivity properties of the polymers was examined. Impedance spectroscopy measurements were used to set the ionic chemical diffusion coefficients, D, in the polymer matrix at a variety of doping levels, for each of the polydicarbazoles. We relate D dependency with potential to morphological and electronic processes in the polymer occurring during oxidation. By combination of cyclic voltammetry and impedance spectroscopy for part of the series we reveal that the diffusion of ions in the matrix is easier in polymers were the functional group is highly electron-attracting.
Metal nanoparticles (MNPs) are essential catalyst components in electrochemical energy conversion and storage devices, including fuel cells, Li-air batteries and water-splitting systems. Syntheses of monodisperse MNPs with controlled sizes, shapes and structures is key to fully harvesting their catalytic capabilities. This review first outlines the fundamentals of the synthesis of monodisperse MNPs by organic solution phase reactions. It then summaries common strategies applied to tailor MNP size, shape and structure. The review further highlights recent advances of using MNPs as efficient catalysts to catalyze some representative reactions that related to energy conversions, including oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, methanol/formic acid oxidation reaction, and oxygen evolution reaction.
Large format Li-ion cells were used to study the mechanical responses of single cells of thickness 6.5 mm and stacks of three cells under compressive loading. Various sequences of increasing depth indentations were carried out using a 1.0 inch (25.4 mm) diameter steel ball with steel plate as a rigid support surface. The indentation depths were between 0.025″ and 0.250″ with main indentation increments tests of 0.025″ steps. Increment steps of 0.100″ and 0.005″ were used to pinpoint the onset of internal-short that occurred between 0.245″ and 0.250″. The indented cells were disassembled and inspected for internal damage. Load vs. time curves were compared with the developed computer models. Separator thinning leading to the short circuit was simulated using both isotropic and anisotropic mechanical properties. Our study show that separators behave differently when tested as a single layer vs. a stack in a typical pouch cell. The collective responses of the multiple layers must be taken into account in failure analysis. A model that resolves the details of the individual internal cell components was able to simulate the internal deformation of the large format cells and the onset of failure assumed to coincide with the onset of internal short circuit.
The model formulation, development process, and experimental validation of a new vehicle powertrain simulator called LFM (Light, Fast, and Modifiable) are presented. The existing powertrain simulators were reviewed and it was concluded that there is a need for a new, easily modifiable simulation platform that will be flexible and sufficiently robust to address a variety of hybrid vehicle platforms. First, the structure and operating principle of the LFM simulator are presented, followed by a discussion of the subsystems and input/output parameters. Finally, a validation exercise is presented in which the simulator's inputs were specified to represent the University of Delaware's fuel cell hybrid transit vehicle and “driven” using an actual drive cycle acquired from it. Good agreement between the output of the simulator and the physical data acquired by the vehicle's on-board sensors indicates that the simulator constitutes a powerful and reliable design tool.
Our study focused on number transcoding in children. It investigated how 9-year-olds with and without arithmetical disabilities wrote Arabic digits after they had heard them as number words. Planning time before writing each digit was registered. Analyses revealed that the two groups differed not only in arithmetical abilities but also in verbal and reading abilities. Children with arithmetical disabilities were overall slower in planning Arabic digits than were control children with normal arithmetical abilities. In addition, they showed a number size effect for numbers smaller than 10, suggesting a semantically mediated route in number processing. Control children did not need more planning time for large numbers (e.g., 8) than for small numbers (e.g., 3), suggesting a direct nonsemantic route. For both two- and three-digit numbers, both groups of children showed a number size effect, although the effect was smaller each time for control children. The presence of the stronger number size effect for children with arithmetical disabilities was seen as a delay in the development of quick and direct transcoding. The relation between transcoding problems and arithmetical disabilities is discussed. A defect in the linking of numerical symbols to analog numerical representations is proposed as an explanation for the transcoding problems found in some children.
We synthesize carbon nanocapsules (CNCs) by a flame combustion method and evaluate their potential as the electrode material for electrochemical double layer capacitor using a titanium cavity electrode (TCE). Identical process is conducted on commercially available carbonaceous materials such as Vulcan XC72R, Black Pearl 2000 (BP2000), multi-walled carbon nanotubes (MWCNTs), and active carbon (AC1100) for comparison purposes. Images from Scanning electron microscope and Transmission electron microscope on the CNCs demonstrate irregular-shaped particles in average size of 10–20nm with graphene layers on perimeter compassing a hollow core. Electrochemical characterizations including cyclic voltammetry (CV), current reversal chronopotentiometry (CRC), and impedance spectroscopy are carried out in 1N H2SO4 to determine the specific capacitance and cycle life time. Among these samples, the BP2000 still delivers the highest specific capacitance in Fg−1 but the CNCs demonstrate the largest value in μFcm2. In addition, the CNCs exhibit impressive life time for 5000 cycles without notable degradation. Consistent results are obtained by CV, CRC, and impedance measurements, validating the TCE as a facile tool to perform reliable electrochemical evaluations.
This study investigated the effects of a number sense intervention in 5-year-old Italian children (n = 96) from different socioeconomic status (SES) backgrounds. We investigated whether a short-term intervention could enable low SES children to reach the same level of their middle-upper SES peers in number sense; in addition, we compared the efficacy of the intervention for low SES children at two levels of intensity. Four groups of children were compared as follows: 2 low SES groups that received 8 or 20 intervention sessions, 1 middle-upper SES group that received eight intervention sessions, and 1 middle-upper SES control group. The results show that at the baseline, the middle-upper SES children obtained higher scores than the low SES children in three of the four scales of the Battery of Numerical Intelligence (BIN). Regarding the effectiveness of the intervention, all intervention groups showed a higher change in the counting subscale score than the control group. The low SES group that received the high-intensity intervention showed a greater change in the BIN total score than all other groups.
The kinetics of Li-ion intercalation/alloying into Cu6Sn5 electrode was determined by potentiostatic intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) method. Although the Li-ion diffusion coefficient (D Li) values are relatively high (from 10−11 to 10−10 cm2/s) in the most voltage range, two minima (below 10−11 cm2/s) in the D Li vs. voltage curve were observed at ∼0.4 and 0.1V, coinciding with the voltage plateau in the charge/discharge curves, indicating reversible structural phase transition or order/disorder transition in the compound. The D Li derived from PITT and EIS were confirmed well both in the magnitudes and in the variation within Li composition (voltage) range.
The direct formic acid fuel cell (DFAFC) has two major shortcomings that limit its lifespan and performance: (i) the poor electrocatalytic stability of the carbon supported Pd (Pd/C) catalyst for the oxidation of formic acid and (ii) rapid decomposition of formic acid over the Pd/C catalyst. To solve the problems, the Pd/C catalyst is modified with ethylenediamine-tetramethylene phosphonic acid (EDTMP). The resulting catalyst is designated as Pd/C-E catalyst. It is found that the Pd/C-E catalyst can inhibit the decomposition of formic acid and promote the oxidation of formic acid through the direct pathway. Consistently, the Pd/C-E catalyst is significantly protected from CO poisoning. As compared to the Pd/C catalyst, the electrocatalytic performance of the Pd/C-E catalyst is significantly superior. These results provide the first proof of the concept that DFAFC can be significantly improved by Pd/C-E catalyst.