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In order to improve the wettability and electrochemical activity of electrospun carbon nanofibers, the partially reduced graphene oxide doped electrospun carbon nanofibers have been successfully prepared by introducing graphene oxide into the electrospinning solution with a simple electrospinning and subsequent carbonization process. It is found that some of the partially reduced graphene oxide nanosheets with plenty of wrinkles are embedded between the nanofibers, which directly enhances the physical surface area. Despite the introduced graphene oxide is partially reduced during the carbonization process, the corresponding oxygen content is greatly increased, which results in the improved wettability and further a significant enhancement in the electrochemical surface area. It is worth noting that the electrocatalytic activity is almost unchanged, indicating the improved electrochemical response is attributed to the enhanced electrochemical surface area. Moreover, vanadium flow battery with such composites presents a remarkable improvement in the electrochemical performances such as energy efficiency and discharge capacity, further suggesting that such composites are promising high-efficient electrode materials for vanadium flow battery. Therefore, it is believed that the construction of carbon-based electrode with high electrochemical surface area through the anchoring effect of hydrophilic materials is an effective approach to obtain high-efficient electrode materials for vanadium flow battery.
Lithium–sulfur (Li–S) batteries have been recognized as promising substitutes for current energy-storage technologies owing to their exceptional advantages in very high-energy density and excellent material sustainability. The cathode with high sulfur areal loading is vital for the practical applications of Li–S batteries with very high energy density. However, the high sulfur loading in an electrode results in poor rate and cycling performances of batteries in most cases. Herein, we used diameters of 5.0 (D5) and 13.0 (D13) mm to probe the effect of electrodes with different sizes on the rate and cycling performances under a high sulfur loading (4.5 mg cm−2). The cell with D5 sulfur cathode exhibits better rate and cycling performances comparing with a large (D13) cathode. Both the high concentration of lithium polysulfides and corrosion of lithium metal anode impede rapid kinetics of sulfur redox reactions, which results in inferior battery performance of the Li–S cell with large diameter cathode. This work highlights the importance of rational matching of the large sulfur cathode with a high areal sulfur loading, carbon modified separators, organic electrolyte, and Li metal anode in a pouch cell, wherein the sulfur redox kinetics and lithium metal protection should be carefully considered under the flooded lithium polysulfide conditions in a working Li–S battery.
Mark-recapture approaches are among the most powerful fisheries methods for estimating demographic parameters relating to survival, components of mortality (i.e. fishing, catch and release, or predation), and abundance. Yet conventional fisheries mark-recapture studies are logistically challenging and can suffer low recapture probabilities and poor precision that may bias parameter estimates. Current methods to infer mortality indirectly from life-history parameters often fail to describe spatiotemporal or age-class specific variation in mortality rates. Despite the ability of acoustic telemetry-based mark-recapture methods to address many of these issues, they are not commonly used within fisheries management. This systematic review identifies the types of mark-recapture study designs that have used acoustic telemetry to date, including the species and habitats studied. The key benefits of acoustic telemetry mark-recapture studies are highlighted, and considerations for planning acoustic telemetry mark-recapture studies are presented to encourage their wider application. Bayesian multistate models that include auxiliary data should provide the most appropriate framework to expand the use of acoustic telemetry mark-recapture in geographically large open populations, further supporting the use of acoustic telemetry mark-recapture within fisheries management.
Recently, the use of polymer-supported bimetallic catalysts to reduce the cost of direct methanol fuel cells (DMFCs) and increase the efficiency of catalysts has been considered. In this work, the preparation of platinum–palladium supported on polyaniline-doped camphorsulfonic acid/graphene (Pt–Pd@ PANI-CSA/graphene) nanocomposites as an anode material in DMFCs is reported. PANI-CSA/graphene nanocomposite was prepared from aniline-doped CSA and graphene by in situ polymerization in ice water. In order to characterize the structure and the surface properties of prepared materials, Fourier transform infrared spectrum (FTIR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) techniques were employed. The electrochemical properties of the nanocatalysts were evaluated through cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The results suggested that PANI-CSA/graphene nanocomposite as a support material had an especially positive effect on the electrocatalytic activity of Pt–Pd for methanol oxidation reaction (MOR) in alkaline media. Also the results of chronoamperometric studies showed that Pt–Pd@ PANI-CSA/graphene was more stable than unsupported Pt–Pd for methanol electrooxidation.
Herein, we have constructed a flexible asymmetric supercapacitor (FASC) with outstanding energy density (ED) using MoS2-rGO and CuO@MnO2-rGO hybrid electrodes as the negative and positive electrodes respectively. The CuO@MnO2-rGO electrode represents significant electrochemical properties, such as significant specific capacitance (Csc) of 421.30 F g−1, superior rate capability, and outstanding durability. Furthermore, the MoS2-rGO electrode displays superior electrochemical behavior containing a good specific capacitance (Csc) of 329 F g−1 with a satisfactory rate capability of 56% and significant durability. Due to the excellent specific capacitance (Csc) and remarkable rate performance of CuO@MnO2-rGO and MoS2-rGO electrodes, the FASC illustrates outstanding electrochemical performance consisting of supreme cycle life (only 8.1% loss after 10,000 cycles), an outstanding energy density (ED) of 165.66 Wh kg−1 and a power density (PD) of 1992 W kg−1.
Scientists in the USA at Georgia Tech Research Institute's (GTRI) Center for Innovative Fuel Cell and Battery Technologies believe that understanding how and why fuel cells fail is the key to both reducing costs and improving durability.
A novel titanium-supported nickel electrode (Ni/Ti) is fabricated by a simple hydrothermal process using hydrazine hydrate as a reduction agent. Its electrocatalytic activity towards cyclohexanol oxidation has been investigated by cyclic voltammetry (CV), chronoamperometry (CA), quasi-steady state polarization and electrochemical impedance spectroscopy (EIS). Effects of various parameters such as potential scan rate and cyclohexanol concentration on the electro-oxidation of cyclohexanol are investigated. Results show that the Ni/Ti electrode behaves as an efficient catalyst for the electro-oxidation of cyclohexanol in basic media and its electrocatalytic activity towards cyclohexanol oxidation is higher than a nickel oxyhydroxide modified nickel electrode (NOMN). It is confirmed that during the anodic potential sweep the electro-oxidation of cyclohexanol follows the formation of NiOOH on the electrode surface and is then catalysed by NiOOH. The rate-determining step for cyclohexanol oxidation is the reaction between the high oxidation state nickel (Ni3+) and the adsorbed cyclohexanol on the surface of the Ni/Ti.
The stability of electrochemical double layer capacitors (EDLC) utilizing an ionic liquid and tetraethylammoninium tetrafluoroborate (TEABF4) in acetonitrile electrolyte was tested by cycling and by constant voltage hold tests. It turned out that possible degradation of the EDLC is visible in the voltage hold test after a time period which is typically much shorter if compared to the cycle tests. A constant capacitance during several thousands of cycles does not necessarily indicate stability. For capacitor cells using a carbon black as active material and an ionic liquid as electrolyte constant capacitance could be demonstrated over 12,000 cycles between 0 V and 3.75 V. Clear ageing was observed, however, during the voltage hold test at 3.75 V after 300 h. For a maximum voltage of 3.5 V both the cycle and the voltage hold test indicated stable performance over 12,000 cycles or 500 h, respectively. For capacitors using an activated carbon as active material and standard electrolyte TEABF4 in acetonitrile both tests clearly demonstrated degradation for a maximum cell voltage of 3.5 V. The evolution of capacitance loss observed for the voltage hold test at 3.25 V is in good agreement with the degradation observed at 3.5 V for the voltage hold test.
Earth-abundant Na0.67[Mn1−xMgx]O2 (0 ≤ x ≤ 0.2) cathode materials with the P2 structure have been synthesized as positive electrodes for sodium-ion batteries. Na0.67MnO2 exhibits a capacity of 175 mA h g−1 with good capacity retention. A Mg content of 5% is sufficient to smooth the charge/discharge profiles without affecting the capacity, whilst further increasing the Mg content improves the cycling stability, but at the expense of a lower discharge capacity (∼150 mA h g−1 for Na0.67Mn0.8Mg0.2O2). It was observed that the cooling process during synthesis, as well as Mg content, have an influence on the structure.
Some basic properties and compatibility toward lithium electrode for electrolytes based on substituted imidazolium ionic liquid have been investigated. The ionic liquids having imidazolium cation substituted by methylcarboxyl or cyano group suffers from low conductivity. However, reversible lithium deposition–dissolution process was observed in electrolytes based on these electrolytes. In particular, lithium salt solution in cyanomethyl-substituted imidazolium ionic liquid provided similar cycle efficiency to conventional organic solvent electrolyte at constant-current condition. The mixed ionic liquid electrolyte containing the cyanomethyl-substituted ionic liquid also provided good cycle performance despite of containing large amount of 1-ethyl-3-methyl imidazolium (EMI)-based ionic liquid. Such mixed electrolyte system serves both the stability of lithium electrode process and valid conductivity for practical use.
This work investigates the heat generation characteristics of a cylindrical lithium-ion battery. The battery consists of the graphite, LiPF6 of the propylene carbonate/ethylene carbonate/dimethyl carbonate (PC/EC/DMC) solution, and spinal as anode, electrolyte and cathode, respectively. The coupled electrochemical–thermal model is developed with full consideration of electrolyte transport properties as functions of temperature and Li ion concentration. A truly conservative finite volume numerical method is employed for the spatial discretization of the model equations. Three types of heat generation sources including the ohmic heat, the active polarization heat and the reaction heat are quantitatively analyzed for the battery discharge process. The ohmic heat is found to be the largest contribution with around 54% in the total heat generation. About 30% of the total heat generation in average is ascribed to the electrochemical reaction. The active polarization contributes the least comparing to the ohmic heat and reactions heat. The results also show that the Li ion concentration and its gradient in electrolyte are the main factors giving the effect on the heat generations of active polarization and electrolyte electric resistance. The raised temperature in the battery discharge is positive related with the thickness of both separator and electrodes.
A novel composite anode material consisted of electrodeposited Sn dispersing in a conductive micro-porous carbon membrane, which was directly coated on Cu current collector, was investigated. The composite material was prepared by: (1) casting a polyacrylonitrile (PAN)/dimethylformamide (DMF) solution that contained silica particles on a copper foil, (2) removing the solvent by evaporation, (3) dissolving the silica particles by immersing the copper foil into an alkaline solution, (4) drying the copper foil coated by micro-porous membrane, (5) electrodepositing Sn onto the copper foil through the micro-pores in the micro-porous membrane, and (6) annealing as-obtained composite material. This method provided the composite material with high decentralization of Sn and supporting medium purpose of conductive carbon membrane deriving from pyrolysis of PAN. SEM, XRD and EDS analysis confirmed this structure. The characteristic structure was beneficial to inhibit the aggregation between Sn micro-particles, to relax the volume expansion during cycling, and to improve the cycleability of electrode. Galvanostatic tests indicated the discharge capacity of the composite material remained over 550mAhg−1 and 71.4% of charge retention after 30 cycles, while that of the electrode prepared by electrodepositing Sn on a bare Cu foil decreased seriously to 82.5mAhg−1 and 13%. These results show that the composite material is a promising anode material with larger specific capacity and long cycle life for lithium ion batteries.
Single crystalline ammonium vanadium oxide bronze NH4V4O10 nanobelts were synthesized by the hydrothermal treatment of H2C2O4·2H2O and NH4VO3 at 140°C for 48h. The NH4V4O10 nanobelts were characterized using a combination of techniques including X-ray diffraction, transmission electron microscopy, selected area electronic diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy techniques. The as-obtained nanobelts are several microns long, typically 30–40nm wide, and 10–20nm thick. The electrochemical properties of the nanobelts were tested in cells with metallic lithium as the negative electrode, the first discharge capacity of 171.8mAhg−1 was achieved.
As potential anode materials for lithium-ion batteries, mesoporous metal oxides show high reversible capacities but relatively poor cycle stability due to the structural collapse during cycles. Graphene-encapsulated mesoporous metal oxides may increase the electronic conductivity of the composite as well as stabilize the mesostructure of metal oxides, thereby enhancing the electrochemical performance of mesoporous metal oxides. Herein we describe a novel strategy for the preparation of graphene-encapsulated mesoporous metal oxides (SnO2, Mn3O4), which exhibit superior electrochemical performance compared to pure mesoporous metal oxides. Moreover, some mesoporous metal oxides may be further reduced to low-valence metal oxides when calcined in presence of graphene. Mesoporous metal oxides with high isoelectric points are not essential for this synthesis method since metal oxides are connected with graphene through mesoporous silica template, thus expanding the types of graphene-encapsulated mesoporous metal oxides.
Single particle technique was employed to investigate the intrinsic electrochemical properties of LiFePO4. A micro-size LiFePO4 single particle composed of a plurality of primary particles was contacted with a micro Pt electrode in an electrolyte solution using a micromanipulator under optical microscope observation, and then galvanostatic charge/discharge tests were performed. The specific capacity of the particle with a diameter of 24μm was estimated to be 1.5nAh in the potential rage of 2.0–4.2V vs. Li/Li+. The particle had a good reversibility for charge/discharge processes, and also showed excellent rate performance, for example, that more than 50% of the full capacity was maintained even when the discharge current was as high as 750nA corresponding to 4s discharge (900C rate). From the dependency of over-potential in the single particle electrode on discharge current density, it was expected that the discharge reaction was controlled at the discharge current densities higher than 2.56mAcm−2 by Li+ diffusion step in the particle accompanied with the phase conversion from FePO4 to LiFePO4. According to this assumption, Li+ diffusion coefficient in the particle was estimated as 2.7×10−9 cm2 s−1.
It is important to identify Developmental Coordination Disorder (DCD) early in a child's life to allow for proper and timely intervention and support, and to reduce the negative secondary consequences associated with this condition. In this study we assessed the psychometric properties (construct validity, concurrent validity, reliability and test accuracy) of the Developmental Coordination Disorder Questionnaire (DCD-Q-07) in preschool children. A community-based sample of children ages 4–6 (n =181) were screened for motor difficulties using the Movement Assessment Battery for Children (M-ABC-2). Use of the M-ABC-2 resulted in the identification of 29 children below the 15th percentile, which we classified as probable DCD. Parents of these children concurrently completed the DCD-Q-07 to report their child's motor performance. The DCD-Q-07 demonstrated high internal consistency for both the full scale (alpha=0.881) and each subscale: control during movement (alpha=0.813), fine motor and handwriting (alpha=0.869) and general coordination (alpha=0.728). Moderate correlations (r =0.47–0.63) were also seen between the subscales on the DCD-Q-07, the strongest correlation being between control during movement and general coordination (r =0.63). Based on published age and sex cut points, the DCD-Q-07 showed poor sensitivity (20.7%) but high specificity (92.1%) against the M-ABC-2. Overall agreement with the M-ABC-2 was low using ROC analysis (area under the curve=0.654). Although it is important to screen for DCD in young children, the DCD-Q-07 may not be the best choice as a screening tool for DCD in preschool children ages 4–6 due to its low test accuracy.
Nanostructured MnO2 was synthesized using a facile hydrothermal technique with potassium permanganate as a precursor. Rare earth elements, lanthanum and cerium, were used to control the porosity of the MnO2 nanostructures. Nanorod-, nanoflower-, nanoneedle-, and nanoneedles/nanopetal-shaped MnO2 nanostructures were synthesized by changing the concentration of the rare earth elements. The as-synthesized MnO2 nanorods, La – MnO2 nanoneedles, Ce – MnO2 nanoflowers, and La/Ce – MnO2 nanoneedles/nanopetals were examined using a range of physico chemical characterization techniques. Scanning electron microscopy and transmission electron microscopy – energy dispersive X-ray spectroscopy confirmed the morphology of the MnO2 nanostructures and the elemental distribution. The porous natures of the synthesized MnO2 nanostructures were analyzed by nitrogen adsorption technique. The electrochemical behavior of the MnO2 nanostructures was examined by cyclic voltammetry, charge – discharge and electrochemical impedance spectroscopy tests. The La/Ce – MnO2 nanoneedles/nanopetals electrode exhibited a high specific capacitance of 825 F g−1 at an applied current density of 10 A g−1. The La/Ce – MnO2 nanoneedles/nanopetals were also mixed with 5, 10, 15 and 20 wt% of rGO nanosheets to enhance the electrochemical behavior. The 20 rGO@La/Ce – MnO2 sample showed extraordinary electrochemical behavior; the calculated specific capacitance was 1165 F g−1 at an applied current density of 10 A g−1. A 20 rGO@La/Ce – MnO2 and activated carbon asymmetric supercapacitor coin cell device exhibited ∼93% capacitance retention after 1000 cycles. These results highlight the potential of 20 rGO@La/Ce – MnO2 as an electrode material for supercapacitor applications.
Fe2(SO4)3 was investigated as an additive to improve the thermal stability of the positive electrolyte for an all-vanadium flow battery (VFB). The effects of the Fe2(SO4)3 addition on the electrochemical activity, capacity, and charge/discharge cycle performance were also studied. The addition of Fe2(SO4)3 significantly enhanced the thermal stability of V(V) in the positive electrolyte. For a positive electrolyte consisting of 2.0 M vanadium ions, the addition of Fe2(SO4)3 within the concentration range of 0.5–0.7 M enabled the electrolyte to remain stable for more than 168 h at 50 °C. Cyclic voltammetry (CV) measurements showed that the peak positions of the Fe2+/Fe3+ and VO2+/VO2 + couples did not cross each other, indicating that the Fe2(SO4)3 addition did not lead to any side reactions. Electrochemical impedance spectroscopy (EIS) analysis revealed that the addition of Fe2(SO4)3 led to a slight increase of the electrolyte ohmic resistance and reduction of the charge-transfer resistance on the carbon electrode. Both the CV and EIS results indicate that Fe2(SO4)3 had no adverse effects on the reversibility or electrochemical activity of VO2+/VO2 +. The capacity for battery charge/discharge cycles hardly changed compared with that of the pristine electrolyte during operation for over 360 h at 50 °C. The improved vanadium positive electrolyte with the Fe2(SO4)3 addition is expected to be used for practical applications. The Fe2(SO4)3 addition can extend the VFB operation temperature to 50 °C, thus reducing the cost of thermal management of the energy storage system and improving the technical and economic performance of VFBs.
Staff turnover is problematic for behavioral health agencies implementing evidence-based practices (EBPs), which are costly and time-consuming. The current study examined the association between EBP training methods and turnover and explored predictors of turnover for different types of staff. Participants (100 clinicians, 50 supervisors, 50 administrators) were randomized to one of three training conditions for an EBP. Results indicated low annual rates of turnover for clinicians, supervisors, and administrators. However, contrary to hypothesis, no statistically significant differences were found in rates of turnover across training conditions. Partially consistent with prior research, organizational climate was a significant predictor of supervisor and administrator turnover at 24 months, but was not a significant predictor of clinician turnover. Implications and future directions for research are discussed.
A series of Li2BaTi6O14 samples are synthesized by a traditional solid-state method by calcining at different temperatures from 800 to 1000 °C. Structural analysis and electrochemical evaluation suggest that the optimum calcining temperature for Li2BaTi6O14 is 950 °C. The Li2BaTi6O14 calcined at 950 °C exhibits a high purity phase with an excellent reversible capacity of 145.7 mAh g−1 for the first cycle at a current density of 50 mA g−1. After 50 cycles, the reversible capacity can be maintained at 137.7 mAh g−1, with the capacity retention of 94.51%. Moreover, this sample also shows outstanding rate property with a high reversible capacity of 118 mAh g−1 at 300 mA g−1. The excellent electrochemical performance is attributed to the stable lithium storage host structure, decreased electrochemical resistance and improved lithium-ion diffusion coefficient. In-situ and ex-situ structure analysis shows that the electrochemical reaction of Li2BaTi6O14 with Li is a highly reversible lithiation–delithiation process. Therefore, Li2BaTi6O14 may be a promising alternative anode material for lithium-ion batteries.