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Nanostructured carbon materials, including carbon nanotubes, graphene and nanoporous carbon, show promise for expanding renewable energy. In particular, the configuration and electronic properties of graphene edges in relation with their electrochemical activity have become a major issue in carbon-based energy storage devices. Here, we review recent results concerning the important roles of graphene edges as the gateway for lithium ion intercalation in the anode of lithium-ion batteries, as promoters of high capacitance in carbon-based supercapacitors, and as anchoring sites for Pt nanoparticles in fuel cells. We envisage that the controlled synthesis of a specific, clean, and stable edge configuration could be achieved to maximize the electrochemical performance of nanostructured carbon-based energy storage devices.
Bismuth–vanadium oxyfluoride (Bi2VO5F) has been synthesized using a simple, solid-state reaction process at different sintering temperatures. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge experiments. The results show that bismuth–vanadium oxyfluoride belongs to a tetragonal crystal system with space group I4mm. The sample that was synthesized at 550°C (P550) exhibits relatively good electrochemical properties. Sample P550 shows a high, initial discharge capacity of 222mAhg−1 at a rate of 100mAg−1 between 1.4 and 3.5V. Sample P550 also shows acceptable electrochemical cycling properties. After the first cycle, the discharge specific capacity remains between 106 and 155mAhg−1, which plateaus between 2.1 and 1.9V during the first 15 cycles.
Currently, there is a good deal of interest in the possibility that fuel cells will make an important contribution to world energy supplies for both mobile and stationary applications. This paper provides an up-to-date review of fuel cell technology.
A facile, rapid, and scalable method is developed for the fabrication of hierarchical CoFe2O4@graphene (CFO@GN) hybrid films on conductive substrates as a promising binder-free lithium-ion batteries anode. The obtained films show network morphologies, and almost all of the CFO nanoparticles are also homogeneously embedded into the layered graphene network. The resulting binder-free CFO@GN electrode with 35.85wt.% graphene exhibits excellent lithium storage performance with a high specific reversible capacity of 866.67 mAh g-1 at a high current densities of 1000mA g-1, and high rate capability. In addition, the reversible capacity can retain as high as 860 mAh g-1 and has no obvious decay after 200 cycles. This work supplies a versatile strategy for fabrication of other metal oxide@graphene hybrid films as an efficient way to improve the lithium storage performance.
Electrochemical properties of three perovskite oxides with different B-site elements, LaMnO3, La0.6Sr0.4FeO3 and LaNiO3, are examined with and without carbon using gas-diffusion electrodes, in comparison with our previous results on La0.5Sr0.5CoO3. Cyclic voltammetry studies reveal very low oxygen reduction current density of carbon-free perovskite oxides, indicating their poor catalytic activity on oxygen reduction reactions. By mixing carbon with perovskite oxides, the oxygen reduction current density is increased by about two orders. The results are consistent with the peroxide pathway mechanism in which the perovskite oxide is highly active on either electrochemical reduction or chemical decomposition. Electrochemical properties of a three-layered gas diffusion electrode demonstrate the peroxide pathway mechanism works even the perovskite oxide and the carbon exist in separate layers. Oxygen evolution reactions are prominently dependent on the oxide species and also on an addition of carbon. The electrode based on carbon-free LaNiO3 or La0.5Sr0.5CoO3 show moderate oxygen evolution activity, and the activity is further enhanced by an addition of carbon, while LaMnO3 and La0.6Sr0.4FeO3 show poor activity even with an addition of carbon.
A novel hybrid nanocomposite based on de-layered molybdenum disulfide (MoS2) by ionic-liquid (IL, [BMIM]BF4)-assisted exfoliation and graphene oxide (GO) was synthesized via a green, efficient, and high-quality method, which combined liquid-phase stripping method and ion-insertion method. In addition, an electrochemical sensor was developed using the MoS2-IL/GO nanocomposites for the determination of chloramphenicol (CAP). The morphology and structure of these synthetic materials were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction and the electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy. Based on this method, the insertion of IL can effectively exfoliate de-layered MoS2, and the MoS2-IL/GO nanocomposite exhibit 3D structure with higher surface area, excellent electrical conductivity, and synergistic catalytic capabilities. Under optimized conditions, the sensor responded linearly to CAP ranging from 0.1 to 400 µmol L−1 and the detection limit of 0.047 µmol L−1. In addition, the sensor showed excellent stability, repeatability, reproducibility, and selectivity, and has been applied to detect CAP in eyedrops, milk, and urine samples.
Cobalt ions, extracted from waste LiCoO2 by using a nitric acid leaching solution, are potentiostatically transformed into cobalt hydroxide on a titanium electrode and cobalt oxide is then obtained via a dehydration procedure. In linear sweep voltammetry, distinct cathodic current peak is observed and indicates that hydroxide ions are formed near the electrode via the electroreduction of dissolved oxygen and nitrate ions give rise to an increase in the local surface pH of the titanium. Under appropriate pH conditions, island-shaped cobalt hydroxide is precipitated on the titanium substrate and heat treatment of the cobalt hydroxide results in the formation of cobalt oxide.
Cadmium has been a significant threat to environment and human health due to its high toxicity and wide application in fossil-fuel burning and battery industry. Cyanobacteria are one of the most dominant prokaryotes, and the previous studies suggested that they could be valuable in removing Cd2+ from waste water. However, currently, the tolerance to cadmium is very low in cyanobacteria. To further engineer cyanobacteria for the environmental application, it is thus necessary to determine the mechanism that they respond to high concentration of cadmium.
The preparation of catalyst-coated membranes (CCMs) with two anodic catalyst layers (60% PtRu/C as catalyst) using a decal technique and their characterization by pseudo-half-cell measurements using both sides of the CCMs by simply turning the test cell around, allows the characterization of quasi-identical CCMs with a much smaller experimental uncertainty than observed for the classical direct methanol fuel cell (DMFC) testing of membrane electrode assemblies under similar working conditions (5 mV vs. 12 mV at a current density of 140 mA cm−2). With this new sensitive tool, we study the influence of the dispersing technology and the Nafion content on the performance of DMFC anodes. While the ionomer content shows a broad optimum between 20 and 40%, the dispersing technology does not have a strong impact on the fuel cell performance under the experimental conditions of this study, but influences strongly the stability of the catalyst slurries and the homogeneity of the electrode coatings.
Effective integration of electrochemical devices consisting of enzyme-based biobatteries together with high power double-layer type capacitors is discussed here. An ultimate goal is to overcome a typical drawback of enzymatic power sources (biofuel cells and biobatteries): although their energy is potentially high enough to fulfill the needs of small electronic devices, their power is often too low. It is demonstrated that properly selected capacitor can support operation of such a low power device simply by supplying appropriate power pulses with fast dynamic response that is required for many applications involving fluctuating loads. Our model integrated system is obtained by coupling a series of double-layer capacitors with well-behaved zinc/oxygen biobattery. The biobattery utilizes a stable cathodic material composed of covalently phenylated single-walled carbon nanotubes and the oxygen reduction enzyme, laccase, together with the hopeite-covered zinc rod acting as the anode. The enzymatic power source was characterized by the maximum power density of 1.8 mW cm−2, the open circuit voltage of 1.6 V. Nevertheless, under the 50 Ω loading, the voltage of biobattery (electrode surface areas of ca. 0.3 cm2) drops to 0 V after 2 s. The practical performance (power stability) of a biobattery has significantly improved by its parallel connection to electrochemical capacitor. The importance of such capacitor’s parameters as low resistance (not more than a few hundred of milliohms), proper capacitance, and leakage current (not higher than a few microamperes) is emphasized here. The potential utility of the optimized biobattery/supercapacitor system is discussed in terms of use as a source of power to operate a digital watch.
This work reports the preparation of a V-doped Li4Ti5O12/C (donated as V-doped LTO/C) composite material, applying a solid-state method. Both metal doping and carbon coating are applied on the Li4Ti5O12 material, enhancing its rate capability and cycle stability. Furan polymer is used as a carbon source, and vanadium (V) is selected as a dopant. The properties of the materials are examined by X-ray diffraction (XRD), micro-Raman, scanning electron microscopy (SEM), high-resolution transmission microscopy (HR-TEM), the AC impedance method, and the galvanostatic charge/discharge method. For comparison, Li4Ti5O12/C composite materials with and without V doping are also examined. The Li4Ti4.90V0.10O12/C composite material achieves discharge capacities of 165.59 and 76.76 mAh g−1 at a 0.2/1C and 0.2/20C rate, respectively. A Li4Ti5O12/LiFePO4 full cell (LTO capacity-limited) is constructed and investigated. The full cell exhibits discharge capacities of 181, 178, 167, 142, 110, and 78 mAh g−1 at 0.2, 0.5, 1, 3, 5, and 10C, respectively. We determine that the Li4Ti4.95V0.05O12/C composite anode is an outstanding candidate for application in high-power Li-ion batteries.
The titration of the interfacial capacitance of a C-cloth electrochemical capacitor electrode was undertaken for the purpose of evaluating the cyclic voltammetry (CV) responses as a function of the pH of an aqueous electrolyte over the range of 0–14. As the pH was increased from 0 (aqueous H2SO4) to a progressively more alkaline (NaOH) solution of pH 11, a 30% loss in capacitance is seen, partly attributable to the disappearance of the pseudocapacitive peaks based on the oxidation/reduction of the surface quinone groups. As the pH is increased above 11, the capacitance increases ca. 20%, as other surface functionalities (a pyrone derivative and another unknown species) become activated in alkaline solution. When the C-cloth is titrated from pHs of 14 to 2, the CV current profile shrinks (with a concomitant decrease in charge-storage capacity). However, at electrolyte pHs below ca. 2, the quinone functionalities are activated and the charge-storage capacity increases ca. 30% above the initial value. It was found that the CV current responses in pH 14 electrolytes are smaller when the titration is base-initiated, rather than acid-initiated, due to an activation step required to make the pyrone functionalities active in alkaline solution.
Knowledge of groundwater contamination sources is critical for effectively protecting groundwater resources, estimating risks, mitigating disaster, and designing remediation strategies. Many methods for groundwater contamination source identification (GCSI) have been developed in recent years, including the simulation–optimization technique. This study proposes utilizing a support vector regression (SVR) model and a kernel extreme learning machine (KELM) model to enrich the content of the surrogate model. The surrogate model was itself key in replacing the simulation model, reducing the huge computational burden of iterations in the simulation–optimization technique to solve GCSI problems, especially in GCSI problems of aquifers contaminated by dense nonaqueous phase liquids (DNAPLs). A comparative study between the Kriging, SVR, and KELM models is reported. Additionally, there is analysis of the influence of parameter optimization and the structure of the training sample dataset on the approximation accuracy of the surrogate model. It was found that the KELM model was the most accurate surrogate model, and its performance was significantly improved after parameter optimization. The approximation accuracy of the surrogate model to the simulation model did not always improve with increasing numbers of training samples. Using the appropriate number of training samples was critical for improving the performance of the surrogate model and avoiding unnecessary computational workload. It was concluded that the KELM model developed in this work could reasonably predict system responses in given operation conditions. Replacing the simulation model with a KELM model considerably reduced the computational burden of the simulation–optimization process and also maintained high computation accuracy.
A simulation model for modeling photovoltaic (PV) system power generation and performance prediction is described in this paper. First, a comprehensive literature review of simulation models for PV devices and determination methods was conducted. The well-known five-parameter model was selected for the present study, and solved using a novel combination technique which integrated an algebraic simultaneous calculation of the parameters at standard test conditions (STC) with an analytical determination of the parameters under real operating conditions. In addition, the simulation performance of the model was compared with other models, and further validated by outdoor tests, which indicate that the proposed model fits well the entire set of experimental field test I–V curves of the PV module, especially at the characteristic points. After validation, this model was employed to predict the PV system power output under real conditions. The results show that the predictions agree very well with the PV plant field collected data. Thus, the operating performance of a standalone PV system located on a remote island in Hong Kong has been further evaluated with the aid of this model. It is found that the PV array power output is restricted by the status of the battery bank. This research demonstrates that the PV simulation model developed during the study is simple, but very helpful to PV system engineers in understanding the I–V curves and for accurately predicting PV system power production under outdoor conditions.
The degradation and failure of Li-ion batteries is strongly associated with electrode microstructure change upon (de)lithiation. Now, an operando X-ray tomography approach is shown to correlate changes in the microstructure of electrodes to cell performance, and thereby predict degradation pathways.
Gallium electrodeposition onto vitreous carbon was studied in chloride solution using potentiostatic and potentiodynamic techniques. The morphology and composition of the deposits were analysed by SEM/EDX. The effects of solution pH, applied potential and the hydrodynamic conditions on the electroreduction process were investigated. Results indicate that the reduction to Ga+1 species takes place at the lower overpotentials, while at high overpotentials gallium deposition occurs through progressive nucleation and growth under diffusion control. The influence of the simultaneous hydrogen evolution reaction on the electrodeposition process is discussed.
An asymmetric supercapacitor (ASC) uses very thin petal-shaped MnO2 nanosheets as the positive electrode and a network of carbon nanotube-embedded polyacrylonitrile-based carbon nanofibers (CNT-CNF electrodes) as the negative electrode. It has a high specific capacitance and a high specific energy density in 0.5 M Na2SO4. An assembled MnO2//CNT-CNF ASC is operated reversibly at a high cell voltage of 2.0 V and exhibits a high specific capacitance of 93.99 F g−1 and an excellent energy density of 52.22 Wh kg−1, which is better than those of ASCs that are based on MnO2//carbon, which can be found in the literature. The MnO2//CNT-CNF ASC has superior cycling stability with 92% retention of initial specific capacitance after 2000 cycles.
Coulombic efficiency (CE) has been frequently used to assess the cyclability of newly developed materials for lithium metal batteries. The authors argue that caution must be exercised during the assessment of CE, and propose a CE testing protocol for the development of lithium metal batteries.
Laser physical vapor deposition is used to deposit thin films of lithium phosphorous oxynitride in nitrogen and lithium nickel manganese oxide in oxygen ambient on Si substrate. LIPON film is also deposited on LiNiMnO film that is deposited on Si. Graphene films consisting of graphene platelets are deposited on Si substrate from a suspension in isopropyl alcohol. Li-graphene films are obtained after Li adsorption by immersion in LiCl solution and further drying. Transient thermo reflectance signal is used to determine the cross-plane thermal conductivity of different layers and interface thermal conductance of the interfaces. The results show that LIPON film with lower thermal conductivity is a thermal barrier. The interface thermal conductance between LIPON and Au or Si is found to be very low. Thermal conductivity of LiNiMnO is found to be reasonably high so that it is not a barrier to thermal transport. Film with graphene platelets shows a higher value and Li adsorbed graphene film shows a much higher value of cross-plane thermal conductivity. The value of interface thermal conductance between graphene and Au or Si (100) substrate is also much lower. The implications of the results for the thermal transport in thin film Li batteries are discussed.
A novel data logger incorporating a 3-axis gyroscope, a 3-axis accelerometer, and a 3-axis magnetometer was developed and externally attached to Japanese amberjacks, Seriola quinqueradiata, to investigate the possibility of using this device for monitoring the movement performance of the fast-start behaviour of fish in the field. Triggered escape behaviours were measured simultaneously by the data logger (500Hz) and a high-speed camera (200Hz) in a tank. By using a gyroscope, the data logger accurately reconstructed the gravity-based acceleration, 3-dimensional attitude, dynamic acceleration, and angular velocity of fish during the fast-start movement, which was impossible by previous methods using only an accelerometer and a magnetometer; these variables can therefore be used to assess the distance-related performance and manoeuverability of fish. The escape movements can be categorised into two mechanical types (single- and double-bend) using the obtained locomotor variables, which showed significant differences between movement types. These results indicate the possibility of using this animal-mounted data logger to quantify the movement performance of the fast-start behaviour of fish in nature.
Stack reliability is of great importance in commercialization of vanadium redox flow battery (VFB) since practical VFB stacks are prone to undergo material failure and electrolyte leakage caused by unreliable stack design and improper assembling conditions. A comprehensive evaluation of mechanical behavior and analysis of stack failure is thus highly valued for material fabrication, stack design and assembly. In this study, mechanical behavior and Weibull statistics based failure analysis of the VFB stacks are investigated. The Weibull parameters of two key components are firstly determined from tensile strength tests, which, in combination with finite element analysis of the stack mechanical behavior, are subsequently used to calculate the stack failure probability at specified clamping forces for two different stack designs that both contains 20 individual cells. The results demonstrate that the stack failure probability can be significantly reduced by properly decreasing the clamping forces for both designs, while adding a thick plate to the middle of the stack can effectively lower the probability of failure thus offering a superior stack mechanical performance and a prolonged stack life cycle. Such an approach to analyze stack failure can be readily accessed by flow battery engineers for design and assembly of commercial VFB stacks.
This paper firstly reports a facile hydrothermal method to prepare CuFeS2 spike-like nanorods as a promising anode material for lithium ion batteries. When being evaluated as an anode material in traditional carbonate-based (EC/DEC/DMC) and ether-based (DOL/DME) electrolytes, it's found that the type of the electrolytes plays a key role in contribution to the electrochemical performance. The CuFeS2 binary mental sulfide material has initial discharge capacities of 632.6mAh/g in the carbonate-based electrolyte and 674.9mAh/g in the other at the rate of 0.2C. After 50 circles, the discharge capacity decays severely, down to 64.3mAh/g while the one performed in the ether-based electrolyte still possesses a capacity of 425.3mAh/g, whose capacity retention is far more higher. Besides, an outstanding rate capability (∼190mAh/g) can be obtained at a high rate of 10C in the ether-based electrolyte, which is indicative of becoming promising anode materials for high-rate lithium batteries.
Olivine–LiCoPO4 powders have been processed by mechanical grinding for time periods ranging from 0.5 to 10h with conductive carbon contents of 0, 8 and 20% (w/w). In all cases the grinding process produces an amorphization of the crystalline materials and decreases both the crystallite and particle sizes. Secondary phases are detected by scanning electron microscopy and X-ray diffraction in the materials milled for times greater than 2h without carbon. The addition of conductive carbon during the milling process decelerates the degradation of the material and secondary phases are not detected even after 10h of grinding. The electrochemical performance of olivine–LiCoPO4 is improved in all the materials milled for 0.5h; a lower cell polarization and a larger reversible specific capacity are observed. These characteristics are enhanced in the materials grinded with conductive carbon, which also display a capacity retention with cycling clearly superior to that of the fresh LiCoPO4. Ball milling LiCoPO4 for times greater than 1h is detrimental for the response of the electrode, independently on the amount of conductive carbon in the grinding media.