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CeO2-coated LiMn2O4 spinel cathode was synthesized using two-step synthesis method. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The results of the electrochemical performances on CeO2-coated electrode are compared to those of electrodes based on LiMn2O4 spinel without CeO2 coating. CeO2-coated LiMn2O4 cathode improved the cycling stability of the electrode. The capacity retention of 2wt% CeO2-coated LiMn2O4 was more than 82% after 150 cycles between 3.0 and 4.4V at room temperature and 82% after 40 cycles at elevated temperature of 60°C. The amounts of dissolved manganese-ions in CeO2-coated LiMn2O4 significantly are smaller than pristine LiMn2O4 systems especially at elevated temperatures. Surface-modified LiMn2O4 can suppress the dissolution reaction of manganese-ions at elevated temperature and clearly improve the cyclability of the spinel LiMn2O4 cathode materials.
Recently, the increasing energy demand has caused dramatic consumption of fossil fuels and unavoidable raising energy prices. Moreover, environmental effect of fossil fuel led to the need of using renewable energy (RE) to meet the rising energy demand. Unpredictability and the high cost of the renewable energy technologies are the main challenges of renewable energy usage. In this context, the integration of renewable energy sources to meet the energy demand of a given area is a promising scenario to overcome the RE challenges. In this study, a novel approach is proposed for optimal design of hybrid renewable energy systems (HRES) including various generators and storage devices. The ε-constraint method has been applied to minimize simultaneously the total cost of the system, unmet load, and fuel emission. A particle swarm optimization (PSO)-simulation based approach has been used to tackle the multi-objective optimization problem. The proposed approach has been tested on a case study of an HRES system that includes wind turbine, photovoltaic (PV) panels, diesel generator, batteries, fuel cell (FC), electrolyzer and hydrogen tank. Finally, a sensitivity analysis study is performed to study the sensibility of different parameters to the developed model.
Publisher Summary Rare-earth-containing mixed oxides are widely used in many engineering, electromagnetic, and electronic applications. Among these materials, perovskite-type oxides with the general formula ABO3 are the most widely studied. The ideal perovskite structure is cubic, with the B (smaller cation) in six-fold coordination and the A (larger cation) in twelve-fold coordination with the oxygens. Although there are some limits regarding the size of the cations that can fit the structure, they are wide enough as to allow the incorporation of a large variety of elements. Typical A elements are rare earths, alkalines, and alkaline earths, while the B sites are usually occupied by transition metals. Both anion and cation vacancies occur in perovskite structures. The former are more common than the latter. Vacancies are assimilated into the structure resulting in supercells of the basic network. Anion excess has been reported in several systems. Cation vacancies occur more often than B vacancies. One important driving force is the ability of these oxides to accommodate a large variety of A and B cations with basically the same crystalline structure. This series of isomorphic solids exhibits a wide range of electric, magnetic, optic, and catalytic properties that are readily applied in various commercial devices.
It is generally believed that fast Li-ion transport in batteries can only be achieved when the host material does not change much with the Li movement. Here the authors show that controlled and reversible changes in host structures upon cycling can actually be used to improve the battery kinetics.
In lithium ion batteries anode material is very crucial. Exploring the high-performance anode materials remains a great challenge. Here, Ti2Nb10O29/Ag composite was obtained. Electrochemical measurements demonstrate that Ti2Nb10O29/Ag composite shows good electrochemical performance than pure Ti2Nb10O29, mostly due to enhanced electronic conductivity after Ag-coating. The specific capacities of Ti2Nb10O29/Ag composite can be as high as 253 and 173mAhg−1 at 1 and 10C, respectively, and the specific capacity is 132mAhg−1 at 20C. Moreover, the Ti2Nb10O29/Ag composite exhibited excellent cyclic stability, even after 500 cycles, its specific capacity at 10C still stabilized at a large value of 142mAhg−1, which was in sharp contrast to the corresponding values of pure Ti2Nb10O29 (68mAhg−1). The high electrochemical performance demonstrated that Ti2Nb10O29/Ag composite is highly promising anode materials for Li-ion batteries.
In this paper we exploit the use of a Li2S8-containing electrolyte based on a non-flammable TEGDME in a semi-liquid lithium cell, characterized by a configuration usually employed in conventional lithium ion batteries. The cell, using a sulfur-free, Super P carbon electrode shows a capacity varying from 430 mAh g−1 s to 700 mAh g−1 S. The cycling tests show that the stability of the cell is strongly affected by the voltage cutoff directly controlling the electrochemical process, in particular the polysulfide shuttle reaction. In this respect, XPS measurement shows the deposition of Li2S2 salt at the lithium electrode surface as the cell voltage cutoff is enlarged, thus suggesting that the use of the reduced voltage and capacity regimes may lead to higher stability. Under the best control regime, the 2 V cell delivers a capacity of 530 mAh g−1 S, with extremely low polarization and cycling stability extended up to 100 charge–discharge cycles. Furthermore, we demonstrate that enhanced performances may be effectively reached by adding LiNO3 salt to the electrolyte solution to form a stable, protective SEI film on the lithium surface, thus avoiding the shuttle process and increasing the cell efficiency, even under a full voltage cutoff range, i.e. extending from 1 V to 3 V.
One-dimensional (1D) reduced graphene oxides possess unique structure properties in comparison with conventional graphene sheet material and show great potential in application of high-efficiency energy storage and conversion system. Lithium sulfur batteries have been considered as the promising candidates of high-energy rechargeable batteries due to the high theoretical energy density and cost-efficiency. However, their practical application has been hampered by rapid capacity fading during cycling. In this work, one-dimensional reduced graphene oxide/sulfur nanoscrolls show promise for uniformly confining elemental sulfur in their internal cavities and absorbing polysulfide intermediates. The remarkable electrochemical performance of the reduced graphene oxide/sulfur nanoscroll materials is mainly attributed to the desirable structural features, where sulfur is encapsulated into the RGO nanoscrolls and kept close contact with RGO. The RGO nanoscrolls not only provide the electron transport pathway, but effectively alleviate the dissolution and shuttling of the polysulfides during cycling for lithium sulfur batteries.
A nickel foam-supported Ni(OH)2/NiOOH electrode, synthesized in-situ at a specific electrode overpotential, was used to study the oxidation of ammonia in aqueous solution. Results of voltammetric analysis showed the formal potential of Ni(OH)2/NiOOH transition at +0.6 V (vs. Hg/HgO, pH 11) at which the current profile was improved by electron transfers of NH3 in the electrolyte. Selectivity of NH3 conversion to NO3 − and N2 was evaluated by batch constant current experiments. Electrochemical parameters, including solution pH (6–12), temperature (20–40 °C), current density (0.2–3 mA cm−2), and initial NH3-N concentration (20–450 mg-L−1), that may affect ammonia oxidation toward nitrogen selectivity were studied. At constant current density of 1.5 mA cm−2A, ammonia removal reached 98.5% and NO3 − was the major product at initial NH3-N concentration of 50 mg-L−1 in 7 h. By contrast, N2 evolution dominated at low current density (<1 mA cm−2) and high initial NH3-N concentration (i.e., >100 mg-L−1). A surface steady-state approach, with NH3 deprotonation as the rate-limiting step, provided the reaction pathways of NH3 conversion to molecular nitrogen byproduct.
Objective Hepatic encephalopathy (HE) is characterized by neuropsychological and motor deficits. The present study tested the hypothesis that worsening of motor and sensory symptoms of HE results from a common basic deficit in the cerebral oscillatory processing within the human motor and visual system. Methods We investigated in 32 patients with liver cirrhosis and HE grades 0–2 critical flicker frequency (CFF) and cortico-muscular (M1–EMG) coherence as a measure of coupling between the surface EMGs of hand muscles and primary motor cortex (M1) activity recorded non-invasively with magnetoencephalography (MEG) during forearm elevation. Results Patients with HE-grade 2 developed excessive M1–EMG coherence at low frequencies. In contrast, maximum M1–EMG coherence in patients with no HE showed frequency and amplitude in the physiological range. CFF was continuously reduced with worsening grades of HE. Correlation analysis revealed significant correlation between the frequency of M1–EMG coherence and CFF. Conclusions Taken together, we demonstrate that increased grades of HE lead to a pathological M1–EMG drive which is reduced in frequency. These effects are correlated with an impaired perception of oscillatory visual stimuli. Significance The results suggest that pathological oscillatory neural processing in different human cerebral systems may represent a basic mechanism for the clinical manifestation of HE.
A copper sulfide (CuS) nanowire (NW) array with a hierarchical nanoarchitecture is directly fabricated on copper foil using a simple and cost-effective liquid-solid reaction. The morphology and microstructure of CuS NW arrays are systematically investigated by scanning electron microscopy, X-ray diffraction spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical results obtained at various polarization cut-offs and scan rates reveal that the CuS NW array shows highly reversible features and favorable rate abilities. Most importantly, the excellent specific capacitance that is achieved in CuS NW nanoelectrodes is as high as 305 F g−1, which is one of the high value reported CuS-based pseudocapacitors. An energy density of 70.8 Wh kg−1 is obtained at a current density of 2mAcm−2. The CuS NW nanoelectrode has superior cycling stability with 87% retention of initial specific capacitance after 5000 cycles.
Due to the ex-situ assembly technology of solid-state electrolyte, solid-state lithium batteries commonly show a poor electrolyte/electrode interfacial contact. Herein, we report an in-situ polymerized poly (tetrahydrofuran) (PTHF)-based solid polymer electrolyte (PTSPE) to resolve the poor interfacial contact problem in solid state lithium batteries. The in-situ formed PTSPE exhibits a high ionic conductivity (2.3 × 10−4 S cm−1) and a wide electrochemical window (4.5 V) at 60 °C. More importantly, the in-situ formed PTSPE improves interfacial compatibility remarkably, suppressing the growth of lithium dendrites. It is revealed that boron trifluoride initiator works as functional additive to form LiF and B-O species at interface layer of lithium metal anode, alleviating lithium dendrites growth and undesired parasitic reactions. An as-assembled LiFePO4/Li cell employing this in-situ formed PTSPE delivers a high discharge capacity of 142.3 mA h g−1 even after 100 cycles. The aforementioned results suggest that the in-situ polymerization technology of solid-state electrolyte is very promising for high-performance solid-state lithium batteries.
In a sensor network the sensors, or nodes, obtain data and have to communicate these data to a central node. Because sensors are battery powered they are highly energy constrained. Data aggregation can be used to combine data of several sensors into a single message, thus reducing sensor communication costs at the expense of message delays. Thus, the main problem of data aggregation is to balance the communication and delay costs. In this paper we study the data aggregation problem as a bicriteria optimization problem; the objectives we consider are to minimize maximum energy consumption of a sensor and a function of the maximum latency costs of a message. We consider distributed algorithms under a synchronous time model, under an asynchronous time model, and under an almost synchronous time model, where sensor clocks are synchronized up to a small drift. We use competitive analysis to assess the quality of the algorithms.
Tungsten oxide is a versatile material with different applications. It has many polymorphs with varying performance in energy storage application. We report simple and facile way to synthesize four phases of tungsten oxide from same precursor materials only by changing the pH and temperature values. Monoclinic, hexagonal, orthorhombic and tetragonal phase obtained, were analyzed and tested for supercapacitor application. The electrochemical analysis of four phases indicates that the hexagonal phase is best-suited electrode material for supercapacitor. The hexagonal phase exhibits higher specific capacitance (377.5 Fg−1 at 2 mV s−1), higher surface capacitive contribution (75%), better stability and rate capability of all four phases.
Two tin–graphite composites (“core-shell” structures) with different metal content (80wt% and 20wt%) as well as their structural and electrochemical characteristics are presented. Mitsubishi's synthetic carbon was used as starting material for the modification experiments. Chemical reduction was applied for the coating process, which was carried out under inert argon atmosphere. Although a homogeneous film of the nanoscale tin particles (∼60nm) have been achieved, the electrochemical performance improvement strongly depends on the thickness of the “shell’ layer and the progressively increased active surface area together with the tin metal contents. The electrode with low metal concentration displayed both improved cycling performance and stable discharge capacity of 435Ahkg−1 compared with untreated graphite electrode. The tin-rich composite shows a higher medial discharge capacity (540mAhg−1) but increased capacity fading, while higher metal contents lead to bulk-coated film with disassociated and agglomerated tin nanoparticles as well as higher surface area and likely presence of oxide impurities. The obtained electrochemical results lead to the assumption, that there is a critical metal ratio up to which good cycling behavior can be achieved. Moreover, the properties of the coating film are closely related with the synthesis conditions and the type of the graphite. In this case, the optimal amount for tin–graphite composite with improved electrochemical performance is about 20wt%.
In an agroforestry system, short wave radiation distribution under the canopy of the trees is important to the activity of the annual crops growing beneath. A three-dimensional model is proposed to describe the short wave radiation distribution under the tree canopy in an agroforestry system. In the model, the agroforestry system is assumed to be planted in regular arrays and have spherical crowns. The short wave radiation that reaches a prescribed point on the ground is computed as the integration of radiation from all the differential directions of the whole hemisphere. The canopy depth in each differential direction is computed, and the extinction coefficient of the tree canopy is estimated by computer analysis of photograph images of the tree crowns taken by a conventional camera. A major advantage of this method is that the laborious leaf area index (LAI) and leaf inclination measurement can be eliminated. The model is able to predict both the short wave radiation distributions below the canopy of an agroforestry system at a prescribed time and the diurnal variation of the total hemispherical short wave radiation at a prescribed point below the canopy. Comparison of the modeled results with the measured values showed that the proposed model describes the daily patterns of the short wave radiation under the tree canopy quite well for both discontinuous canopy and overlapping canopy and for different shading conditions. The difference between the modeled daily total values of the short wave radiation under the canopy and the measured daily total values is usually less than 5% of the global radiation. Results from sensitivity analyses of the model to crown radius and canopy gap fraction are reported.
Poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene nanosheets (GNSs) were employed for direct methanol fuel cell applications. PDDA-functionalized GNSs (PDDA-GNSs) distributed positive charges on the surfaces of GNSs, favoring electrostatic self-assembly of negatively charged PtCl6 2− ions on the PDDA-GNSs. Subsequent reduction process was conducted using ethylene glycol, resulting in uniformly deposited Pt nanoparticles on PDDA-GNSs. Carbon black was functionalized by PDDA as well using a similar process, and the composite was denoted as PDDA-C. Experiments on Pt nanoparticles deposited on PDDA-C and GNSs were performed in the same manner as well. Pt electrocatalysts supported on the PDDA-GNSs exhibited higher electro-catalytic activity for the electro-oxidation of methanol compared with both Pt supported on the GNSs and PDDA-C. Therefore, PDDA-GNS can be an ideal support for Pt in direct methanol fuel cells.
Objective To compare the efficacy of gait training using a single-leg version of the Hybrid Assistive Limb (HAL) on the paretic side with conventional gait training in individuals with subacute stroke. Design Randomized open controlled pilot trial. Setting Hospitalized care. Participants Convenience sample of 44 patients who met the criteria; 12 patients refused. After randomization (N=32), 10 patients withdrew and a total of 22 poststroke participants (HAL group: n=11; conventional group: n=11) completed the randomized controlled trial. Interventions All participants received twelve 20-minute sessions in 4 weeks of either HAL (wearing the single-leg version of the HAL on their paretic side) or conventional (performed by skilled and experienced physical therapists) gait training. Main Outcome Measures Outcome measures were evaluated prior to training and after 12 sessions. Functional Ambulation Category (FAC) was the primary outcome measure, whereas secondary outcome measures included maximum walking speed, timed Up and Go test, 6-minute walk distance, Short Physical Performance Battery, Fugl-Meyer Assessment of Lower Extremity, and isometric muscle strength (hip flexion and extension, knee flexion and extension). Results No participants withdrew because of adverse effects. Participants who received gait training with the HAL showed significantly more improvement in the FAC than those who received conventional gait training (95% confidence interval, .02–.88; P=.04). Secondary measures did not differ between the 2 groups. Conclusions The results obtained in this randomized controlled trial suggest that a gait training program with the HAL could improve independent walking more efficiently than conventional gait training.
High total homocysteine (tHcy) is associated with cognitive impairment in the elderly. The impact of high tHcy on different cognitive domains deserves further investigation, as does the role of the C677T polymorphism of the 5,10 methylenetetrahydrofolate reductase (MTHFR) gene. A cross-sectional analysis of 903 subjects from the population-based “InveCe.Ab” study was performed. The participants had no psychosis or active neurological disorders. They underwent a neuropsychological assessment. Principal component analysis allowed cognitive performance to be condensed into two components: executive functions and memory. Novel components were evaluated for association with tHcy, controlling for potential confounders. Regression models showed that high serum tHcy was associated with lower executive functions, but not with memory. MTHFR C677T TT was associated with higher tHcy but did not affect cognitive performance per se. However, when combined with the apolipoprotein E (APOE)-ε4 allele, it was a risk factor for lower executive performance, independently of tHcy levels. In summary, high tHcy per se, or MTHFR C677T TT in combination with the APOE-ε4 allele, might be associated primarily with executive dysfunctions rather than memory loss.
This paper analyses the field performance of different off-grid generation technologies applied to the electrification of rural villages. Autonomous diesel generators are the most extended technology. It is a well known application, although it has also some disadvantages: fuel transportation and consumption costs, maintenance needs or environmental problems. In places where accessibility is difficult and costly, the use of local energy resources (basically renewable) constitutes a significant advantage. Due to the intermittent character of those resources, renewable generation systems are sometimes associated to diesel gen-sets in order to increase the reliability of supply of small and medium-size communities. A comparative analysis between diesel, hydro-diesel and photovoltaic-diesel technologies is presented in this article. It is based on data collected from systems installed in the rural area of the province of Jujuy, northwest of Argentina. The study covers from year 2001 to 2008, with a research universe of 16 locations supplied by thermal diesel generation (1 with a large-diesel system and other 15 with smaller ones), 5 locations with hydro-diesel and 7 with photovoltaic-diesel systems. The energy demand evolution of rural villages is also studied because of its influence on the system operation and sustainability.
In this paper, graphene sheets with different reduction levels have been produced through thermal reduction of graphene oxide in the temperature range of 200–900°C. The effects of interlayer spacing, oxygen content, BET specific surface area and disorder degree on their specific capacitance were explored systematically. The variation of oxygen-containing groups was shown to be a main factor influencing the EDL capacitor performances of the pyrolytic graphene. The highest capacitance of 260.5Fg−1 at a charge/discharge current density of 0.4Ag−1 was obtained for the sample thermally reduced at about 200°C.
Future vehicle applications require the development of reliable and long life batteries operating under high-rate partial-state-of-charge (HRPSoC) working conditions. Work presented in this paper deals with the study of different design parameters, manufacturing process and charging conditions of spiral wound valve-regulated lead-acid (VRLA) batteries, in order to improve their reliability and cycle life for hybrid vehicle applications. Test results show that both electrolyte saturation and charge conditions have a strong effect on cycle life at HRPSoC performance, presumably because water loss finally accelerates battery failure, which is linked to irreversible sulphation in the upper part of the negative electrodes. By adding expanded graphite to the negative active mass formulation, increasing the electrolyte saturation degree (>95%) and controlling overcharge during regenerative braking periods (voltage limitation and occasional boosting) it is possible to achieve up to 220,000 cycles at 2.5% DOD, equivalent to 5500 capacity throughput. These results could make lead acid batteries a strong competitor for HEV applications versus other advanced systems such as Ni–MH or Li-ion batteries.