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Triallyl phosphite (TAPi) was used as an electrolyte additive to improve performance of LiNi0.6Co0.2Mn0.2O2/graphite pouch cells at elevated temperature. The high temperature storage and cycling performances of pouch cells were investigated by various electrochemical methods and microscopy techniques. The results show that TAPi can effectively enhance the discharge capacity retention ratio after high temperature storage test. In the storage experiment, compared with the cells without TAPi, the cells containing 0.5wt% and 1wt% TAPi exhibit excellent initial discharge capacity retention of 91.7% and 89.5%, respectively. Besides, for the high temperature cycling at 45°C, the cells containing 0.5wt% exhibit optimal cycling performance. The results of X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) suggest that the interfacial film derived from TAPi is helpful for protecting the electrode surface at elevated temperature, thus promoting the capacity performance and retention during the high temperature cycling test. Overall, these results suggest that TAPi can be regarded as a candidate electrolyte addition for lithium-ion batteries with high-nick-content NCM cathode to accommodate elevated temperature condition.
Ternary NiCo2O4 synthesized via annealing NiCo-precursor has been extensively studied as an advanced electrode material for high-performance supercapacitors. In this work, we demonstrate a facile hydrothermal synthesis of NiCo2S4 nanotube arrays (NTAs) by simply treating the NiCo-precursor with Na2S solution based on the Kirkendall effect. The NiCo2S4 NTAs grown on nickel foam substrate are directly evaluated as binder-free electrode for supercapacitors. Impressively, the NiCo2S4 NTA electrode delivers an ultrahigh capacitance of 15.58F cm−2 at a current density of 10mAcm−2, which is much higher than 3.63F cm−2 of the mesoporous NiCo2O4 nanowire array (NWA) electrode. In addition, the NiCo2S4 NTA electrode also exhibits good cycling stability with 79.3% capacitance retention at high current density of 60mAcm−2 after 2000 cycles. In view of the excellent electrochemical performance and the facile and cost-effective synthesis, such NiCo2S4 NTA electrode would hold great promise for high-performance supercapacitor applications in future.
A cyclic voltammetric study of the electrochemistry and chemical stability of the poly(vinylferrocene) (PVFc) redox couple, coated on a gold substrate, in aqueous solutions of H2SO4, HClO4 and HCl was carried out. It was found that the anodic peak potential (E pa) did not depend on the acid concentration in the range (1.0×10−2 to 1.0×10−7 molL−1). However, the E pa values shifted linearly to less positive potentials when investigated in more concentrated acid solutions in the range 1–5molL−1. The slope of the E pa versus acid concentration graph was found to be in the order H2SO4 >HCl>HClO4. In this regard PVFc behaved very similar to 1,1′-bis(11-mercaptoundecyl)ferrocene (Fc(C11SH)2) except for its chemical stability. In H2SO4 media the PVFc was found to be much less stable than 1,1′-Fc(C11SH)2. The dependence of E pa on acid concentration could be used to monitor state of charge of lead-acid batteries. However, for this application Fc(C11SH)2 would be a better choice because of its superior chemical stability.
Battery chemistry based on earth-abundant elements has great potential for the development of cost-effective, large-scale energy storage systems. Herein, we report, for the first time, that maricite NaFePO4 can function as an excellent cathode material for Na ion batteries, an unexpected result since it has been regarded as an electrochemically inactive electrode for rechargeable batteries. Our investigation of the Na re-(de)intercalation mechanism reveals that all Na ions can be deintercalated from the nano-sized maricite NaFePO4 with simultaneous transformation into amorphous FePO4. Our quantum mechanics calculations show that the underlying reason for the remarkable electrochemical activity of NaFePO4 is the significantly enhanced Na mobility in the transformed phase, which is ∼one fourth of the hopping activation barrier. Maricite NaFePO4, fully sodiated amorphous FePO4, delivered a capacity of 142 mA h g−1 (92% of the theoretical value) at the first cycle, and showed outstanding cyclability with a negligible capacity fade after 200 cycles (95% retention of the initial cycle).
The lithium/sulfur battery is a very promising technology for high energy applications. Among other advantages, this electrochemical system has a high theoretical specific capacity of 1675mAhg−1, but suffers from several drawbacks: poor elemental sulfur conductivity, active material dissolution and use of the highly reactive lithium metal electrode. More particularly, the discharge capacity is known to be dictated by the short lithium polysulfide precipitation. These poorly soluble and highly insulating species are produced at the end of discharge, and are responsible for the positive electrode passivation and the early end of discharge. Nevertheless, the discharge capacity can be improved by working on the positive electrode specific surface area and morphology, as well as on the electrolyte composition. In this paper, we focused on the positive electrode issue. To this purpose, various current collector structures have been tested in order to achieve a high positive electrode surface area and a stable morphology during cycling. We demonstrated that the discharge capacity could be increased up to 1400mAhg−1 thanks to the use of carbon foam. As well, the capacity fading could be dramatically decreased in comparison with the one obtained for conventional sulfur composite electrodes.
Zinc electrodeposition and electrodissolution in methanesulfonic acid (MSA) electrolytes mixed with chloride or sulfate are investigated in a 3-electrode cell for eventual use in divided and undivided zinc-cerium redox flow batteries (RFB). Cyclic voltammetry and polarization experiments show that the addition of chloride to methanesulfonate-based electrolytes shifts the nucleation potential in the positive direction, lowers the nucleation overpotential and enhances the kinetics of Zn deposition and subsequent dissolution relative to that achieved when sulfate is added or MSA is the only anion present. In addition, the diffusion coefficient of Zn(II) and the resulting limiting current density for Zn deposition have been found to be moderately higher in mixed methanesulfonate/chloride media than when chloride is absent. The effects of temperature, MSA concentration, Zn(II) concentration and current density on the Zn/Zn(II) system have also been investigated under potentiostatic and galvanostatic conditions. Although an increase in temperature and/or MSA concentration tends to lower the charge efficiency for Zn deposition in both mixed and MSA-only electrolytes due to the higher rate of hydrogen evolution, the amount of zinc deposited, charge and voltage efficiency always remain significantly higher in the mixed methanesulfonate/chloride media than the pure MSA media. Thus, the use of a mixed methanesulfonate/chloride media should enable both divided and undivided zinc-cerium RFBs to operate over a wider range of temperatures and MSA concentrations compared to the case with pure MSA electrolyte. The addition of sulfate to MSA-based electrolytes, however, does not improve the performance of the Zn/Zn(II) system relative to that possible in the MSA-only electrolytes.
Lithium sulfur (Li-S) batteries are an important next generation high energy density battery technology. However, the phenomenon known as the polysulfide shuttle causes accelerated degradation, reduced Coulombic efficiency and increased heat generation, particularly towards the end of charge. The real-time detection of the onset of shuttle during charge would improve the safety and increase cycle life of Li-S batteries in real applications. In this study, we demonstrate that the Differential Thermal Voltammetry (DTV) technique can be used for tracking shuttle during Li-S charging. By combining voltage and temperature measurements, DTV is shown to be sensitive to the magnitude of shuttle. We demonstrate significant differences in the DTV curves for Li-S cells charged at different currents and temperatures. Quantitative interpretations of the experimental DTV curves are performed through a thermally-coupled zero-dimensional Li-S model. The DTV technique, together with the model, is a promising tool for real-time detection of shuttle in applications, to inform control algorithms for deciding the end of charging, thus preventing excessive degradation and charge inefficiency.
α-MoO3@MnO2 core-shell nanorods are synthesized via a facile two-step method. The electrochemical measurement of lithium-ion batteries (LIBs) shows that prepared α-MoO3@MnO2 core-shell nanorods as the anode exhibit high discharge capacity, high rate capability, and excellent cycling stability. The reversible capacity of α-MoO3@MnO2 core-shell nanorods is 1475mAh/g at 0.1C rate (10hours per charging cycle) and retains at 1127mAh/g after 50 cycles, much higher than that of pure α-MoO3 and MnO2. Even at high current rate of 6C, the reversible capacity of α-MoO3@MnO2 core-shell nanorods is 394mAh/g and retains at 286mAh/g after 50 cycles. Our results indicate that α-MoO3@MnO2 core-shell nanocomposites have enormous potential for application in lithium-ion batteries.
This study assesses the synergy effects of governance in mobile phone penetration for inclusive human development in Sub-Saharan Africa with data for the period 2000–2012. It employs a battery of interactive estimation techniques, namely: Fixed effects, Generalised Method of Moments and Tobit regressions. Concepts of political (voice and accountability and political stability/no violence), economic (government effectiveness and regulation quality) and institutional (corruption-control and rule of law) governance are employed. The following findings are established. The previously apparent positive correlation between mobile phones and inclusive development can be extended to a positive effect. Although political governance is overwhelmingly not significant across estimated models, the average effects from economic governance are higher relative to institutional governance. On the interactions between mobile phones and governance variables, while none are apparent in Fixed effects regressions, there are significant synergy effects in Generalised Method of Moments and Tobit estimations, notably, from: regulation quality in the former and political stability, voice and accountability and rule of law in the latter. There is consistent evidence of convergence in inclusive human development. Policy implications are discussed.
This paper presents a closed-loop hierarchical energy management control strategy for a group of connected hybrid electric vehicles (HEVs) considering the feedback of propulsion and recuperation efficiencies. The higher level controller utilizes model predictive control (MPC) incorporating signal phase and timing (SPAT) information for the prediction of the optimal velocity profile over a finite time horizon, with periodically updated efficiencies from the lower level controller. The adaptive equivalent consumption minimization strategy (A-ECMS)-based lower level controller then makes use of the optimal velocity profile for the energy management control of the HEVs. Meanwhile, the lower level controller calculates and feeds back the average propulsion and recuperation efficiencies of the current time window to the higher level controller, which updates the efficiencies with the average values and corrects the fuel consumption model for the calculation of the velocity profile of the next time window. Simulation results validate the control effectiveness of the proposed control strategy.
Transcription factors, including the basic helix–loop–helix (bHLH) family, regulate numerous genes and play vital roles in controlling gene expression. Consequently, transcription factor mutations can lead to phenotypic pleiotropy, and may be a candidate mechanism underlying the complex genetics and heterogeneous phenotype of schizophrenia. Neurogenin1 (NEUROG1; a.k.a. Ngn1 or Neurod3), a bHLH transcription factor encoded on a known schizophrenia linkage region in 5q31.1, induces glutamatergic and suppresses GABAergic neuronal differentiation during embryonic neurodevelopment. The goal of this study is to investigate NEUROG1 effects on schizophrenia risk and on phenotypic features of schizophrenia. We tested 392 patients with schizophrenia or schizoaffective disorder and 226 healthy normal volunteers for association with NEUROG1. Major alleles on two NEUROG1-associated SNPs (rs2344484-C-allele and rs8192558-G-allele) were significantly more prevalent among patients (p ≤.0018). Approximately 80% of the sample also underwent high-resolution, multi-spectral magnetic resonance brain imaging and standardized neuropsychological assessment. There were significant rs2344484 genotype main effects on total cerebral gray matter (GM) and temporal GM volumes (p ≤.05). C-allele-carrier patients and healthy volunteers had smaller total cerebral GM and temporal GM volumes than their respective T-homozygous counterparts. rs2344484-C-allele was further associated with generalized cognitive deficits among schizophrenia patients but not in healthy volunteers. Our findings replicate previous association between NEUROG1 and schizophrenia. More importantly, this is the first study to examine brain morphological and neurocognitive correlates of NEUROG1. rs2344484-C-allele may affect NEUROG1's role in transcription regulation such that brain morphology and cognitive abilities are altered resulting in increased susceptibility to develop schizophrenia.
Hierarchical mesoporous γ-Fe2O3/carbon nanocomposites were prepared from metal organic frameworks (MOFs) MIL-100(Fe). The γ-Fe2O3/carbon nanocomposites and its precursor MIL-100(Fe) was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra (Raman), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry analysis (TGA) and N2 adsorption/desorption measurements. It is found that the as-prepared materials possess a hierarchical mesoporous nanostructure between the carbon and γ-Fe2O3 nanoparticles. When applied as cathode catalysts in rechargeable Li-O2 batteries, it is demonstrated from the galvanostatic discharge-charge process and cyclicvoltammetry (CV) that the electrode with γ-Fe2O3/carbon nanocomposites exhibits a lower charge and discharge over-potential, higher discharge capacity and better cycling stability than the pure Super P electrode, indicating its potential as a promising catalyst for Li-O2 batteries. The electrode with γ-Fe2O3/carbon nanocomposites shows a discharge capacity up to ∼5970 mAh g−1 carbon+catalyst at 0.1mAcm−2 and a high C-rate performance, and exhibits a very stable discharge voltage plateau of 2.7V and a charge voltage plateau of ∼3.75V. With the addition of γ-Fe2O3/carbon nanocomposites, the Li-O2 batteries can obtain good cycle performance over 30 cycles as confining the discharge/charge capacities to 600mA h g−1 carbon+catalyst.
The oxygen reduction reaction (ORR) was investigated using two new cathode materials based on neodymium nickelate with formula Nd2-xSrxNi1-yCoyO4±δ (with x and y=0 or 0.05) prepared by the citrate method. The ORR was measured in 0.5M NaOH with a rotating disk electrode (RDE) at different rotation speeds after purging with pure oxygen. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), whereas the electrochemical analysis was obtained by linear voltammetry and impedance spectroscopy. The results show that before the ORR, the grains of the undoped material are spherical in shape with a size around 400nm, while after the oxygen reduction reaction, the grain size increases. In the doped material, on the contrary, the results are reversed and the grain size becomes smaller. In addition, we show that the ORR mechanism proceeds in a single step in the undoped material while it is carried out in two successive steps in the case of the doped one. XPS analysis confirms that the sites responsible for the ORR are the OH− groups. Doping with Sr or Co does not improve the electrochemical properties: this dopant adversely affects the formation of the sites responsible for the dissociation of molecular oxygen. For larger hydroxide groups content (2.30, Nd2NiO4±δ) the electrochemical currents are much greater relative to that of the other Nd1.95Sr0.05Ni0.95Co0.05O4±δ (0.98) material. This work helps to understand the role of OH− groups, and the reduction mechanisms with 2 and 4 electrons.
The main challenge associated with sodium-ion battery (SIB) anodes is a search for novel candidate materials with high capacity and excellent rate capability. The most commonly used and effective route for graphene-based anode design is the introduction of in-plane “hole” defects via nitrogen-doping; this creates a spacious reservoir for storing more energy. Inspired by mountains in nature, herein, we propose another way – the introduction of blistering in graphene instead of making “holes”; this facilitates adsorbing/inserting more Na+ ions. In order to properly answer the key question: ““protrusions” or “holes” in graphene, which is better for sodium ion storage?”, two types of anode materials with a similar doping level were designed: a phosphorus-doped graphene (GP, with protrusions) and a nitrogen-doped graphene (GN, with holes). As compared with GN, the GP anode perfectly satisfies all the desired criteria: it reveals an ultrahigh capacity (374 mA h g−1 after 120 cycles at 25 mA g−1) comparable to the best graphite anodes in a standard Li-ion battery (∼372 mA h g−1), and exhibits an excellent rate capability (210 mA h g−1 at 500 mA g−1). In situ transmission electron microscopy (TEM) experiments and density functional theory (DFT) calculations were utilized to uncover the origin of the enhanced electrochemical activity of “protrusions” compared to “holes” in SIBs, down to the atomic scale. The introduction of protrusions through P-doping into graphene is envisaged to be a novel effective way to enhance the capacity and rate performance of SIBs.
Nanostructured nickel was electrodeposited on a stainless steel plate. The convective-diffusion mass transfer to this nanostructured electrode was compared to that of a planar, mirror polished solid nickel electrode using the limiting current technique, for the reduction of ferricyanide, hexacyanoferrate (III) ion in an undivided cell. The effect of introducing a turbulence promoter into the electrolyte channel was also evaluated for each electrode under steady state conditions. At a Reynolds number of 700, the product of mass transfer coefficient and active electrode area, k L A for the nanostructured nickel electrode increases over 11 times compared to the mirror polished planar nickel electrode. In the presence of a turbulence promoter, the nanostructured nickel electrode shows an approximately 23 times increase in k L A compared to the planar mirror polished nickel electrode. The dimensionless mass transfer correlations S h = a R e b S c d L e e are compared to others in the literature.
This study investigates Iranian students’ attitudes and motivations toward learning English. The sample of the study consists of 123 male and female students from two high schools in the second academic years. The instrument used is a questionnaire which comprises 18 items developed to achieve the aims of the study. Results showed that the Girl students are more integrative motivated and boy students are more instrumental motivated to learning English. In addition, the girls have more positive attitude toward learning English than boys, they also are more inclined to bilingualism. However, there is no significant difference between high school students in motivational orientations, while they have positive attitude to learning English as a second language.
Current challenges in the electric grid progression demand energy storages to cope with any imbalances between supply and demand side. Application possibilities of energy storages are numerous, but the requirements vary from case to case. However, not every storage technology operates equally to be useful in any situation. In fact, the feasibility of energy storages depend on their technical characteristics, i.e., for example efficiency, response times, power rating and capacity for a selected application. Comparing and assessing different storage options is imperative for decision-making, which requires an in-depth understanding of the technology and its dynamics. Hence, a general model approach of energy storages as equivalent circuit models has been proposed to unify and analyze storages of different physical backgrounds. This allows a more direct and intuitive evaluation of energy storages tested in a specific application. This paper focuses on the experimental validation of energy storages (ultra-capacitor, li-ion battery, lead-acid battery and flywheel) to be uniformly described in one general model. A simple and budget friendly experimental setup to test the storages is designed.
Nitrogen-doped graphene sheets (NGS) were obtained using a simple hydrothermal reaction with graphene oxide and hexamethylenetetramine (HMT). HMT plays important roles in both reducing graphene oxide and doping nitrogen into the graphene sheets. The prepared nitrogen-doped graphene sheets reduced by hexamethylenetetramine (NGS-HMT) have a high nitrogen (8.62atom%) content, in which various nitrogen species, such as pyridinic-N, pyrrolic-N, and quaternary-N, are detected. For supercapacitor applications, NGS-HMT shows a value of 161Fg−1 at a current density of 0.5Ag−1, and it also exhibits a high cycle stability.
Composites of positive electrodes for rechargeable lithium batteries have been prepared from LiMn2O4 as electrochemically active material, carbon black (CB) as good electronic conductor, and polyvinylidenefluoride (PVDF) as binder. The composites having different contents in LiMn2O4 and CB, and nearly the same content in PVDF have been processed by a route that is currently used. The microstructure of the composites, as followed by scanning electron microscopy (SEM), is heterogeneous showing extended regions of PVDF–CB, and clusters of LiMn2O4. The electrical conductivity shows a sharp increase at the CB content of 3vol.% (2wt.%) in accordance with a percolation process. The capacity shows also a sharp increase at that content. A maximum in capacity at ca. 10wt.% of CB is observed when the overall weight of the composite is taken into account. Both features, sharp increase in capacity and maximum of capacity, have been found in discharge experiments made at different currents. The composites show an elastic behavior up to a stress of ca. 6MPa. Above this, the composites breaks down through a crack that propagates slowly according to a ductile behavior. The microstructure as well as the electrical, electrochemical, and mechanical properties of the composites are compared with those reported on composites having the same three components but processed by a different route.