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Over the last decades, iodine-free redox couples have been widely investigated as alternatives for the ubiquitous triiodide/iodide redox shuttle in dye-sensitized solar cells (DSCs). This is mainly motivated by desires to overcome the disadvantages associated with the latter, such as large energy loss in the dye regeneration process, visible light absorption and corrosiveness towards current-collecting metal grids. However, conventional Pt cathodes show poor catalytic activity towards those iodine-free redox couples, resulting in poor fill factors and relatively moderate power conversion efficiencies. The ultimate solution to address this challenge is to develop alternative economical Pt-free catalysts. This review selectively discusses and summarizes the recent advances in novel cathode materials for electrolytes free of iodine-based redox couples, mainly including inorganic transition metal compounds, organic conductive polymers and carbonaceous materials (particularly carbon nanotubes and graphene). Most of these advances have been realized by judiciously controlling the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, this review highlights the importance of matchup between catalysts and the redox couples, and points to crucial issues that should be addressed in the pursuit of developing low-cost and high-catalytic cathodes for DSCs.
Surface modification is an effective strategy to address the critical issues of Ni-rich LiNi1-x-yCoxMnyO2 (NCM) cathode material, including fast energy loss and stability in lithium ion battery. However, both single/double layers coating strategies suffer many fatal drawbacks, such as functional unitary or poor components contacting. Herein, we present a dual-component in one coating layer strategy, which composed of LixTiO2 nano-particles embedding in amorphous silica (LTSO) through a facile method. The coating material could not only be used as a physical protective layer to enhance the stability of NCM cathode, but also improve the ion diffusion kinetics with the contribution from the coating components. Thus, the battery performance was significantly enhanced. This dual-component coating strategy is novel, effective, simple and scalable, which could be extended and applied to other practical Ni-rich material modification designs.
A series of LiM1xM2yMn2−x−yO3.8F0.2 (M1 = Cr, M2 = V; x = y = 0.2) cathodes, viz., LiMn2O3.8F0.2, LiCr0.2Mn1.8O3.8F0.2 and LiCr0.2V0.2Mn1.6O3.8F0.2 along with native LiMn2O4 have been synthesized by Citric Acid assisted Modified (CAM) sol–gel method, with a view to understand the effect of synthesis methodology and the effect of dual category dopants, viz., anion and/or cation upon spinel cathodes individually. An acceptable capacity retention (94%) observed up to 50 cycles for native LiMn2O4 cathodes is attributed to the significance of CAM sol–gel method. Similarly, the encouraging charge–discharge results of LiMn2O3.8F0.2 (130 mAh g−1) and LiCr0.2Mn1.8O3.8F0.2 (142 mAh g−1) cathodes revealed a possible augmentation in the reversible capacity behavior of the spinels upon F− substitution at 32e site and the simultaneous substitution of Cr3+ and F− at 16d and 32e sites respectively.
Determination of the cell or battery impedance is critical to predicting and managing the battery performance, especially in a remote application such as in a spacecraft. While electrochemical impedance spectroscopy provides more quantitative and diverse information on the electrochemical processes, it is less informative in the absence of a reference electrode and/or more cumbersome in multi-cell batteries. DC impedance values, on the other hand, are relatively easy to implement and with subtle variations in the pulse conditions, i.e., pulse magnitude and pulse width, may provide useful trends in the ohmic, charge transfer and mass transfer components. In order to assess the impedance values of the Li-ion cells and batteries and their impact on the current-limiting series resistors in the Mars Exploration Rovers (MER), we, therefore, adopted DC methods under a variety of test conditions, i.e., magnitude and duration of the sampling current pulses, states of charge of the cells and batteries, as well as at different (low) temperatures. Understandably, higher current pluses tend to lower the contribution from the charge transfer, while longer pulses result in a higher share of the diffusional component in the overall impedance. Based on relatively simple analyses, we derived useful trends for the ohmic, charge transfer and mass transfer components of the cell impedance, as a function of temperature and obtained activation energies for these processes. Finally, these measurements assisted us in the assessment of risk associated with the series resistors during the launching of the Mars Rover missions.
Degradation behaviors of three typical La-Mg-Ni alloys, La2MgNi9, La1.5Mg0.5Ni7 and La4MgNi19, were studied. La1.5Mg0.5Ni7 with (La,Mg)2Ni7 as main phase presents better discharge capacity and cycling stability. The three alloys suffer severe pulverization and corrosion after electrochemical cycles, which are considered to be the significant factor attributing to the capacity deterioration. However, the overall corrosion extent of the three cycled alloys aggravates successively, which is inconsistent with the result that La2MgNi9 presented poor cycling stability and also the assumption that alloy with high Mg content is easy to be corroded. The intrinsic anti-corrosion and anti-pulverization characteristics of the three alloys are mainly focused in this work. Immersion corrosion experiments demonstrate that the Mg-rich phases are more easily to be corroded. The corrosion resistance of the three alloys presents an improved trend which is inversely proportional to abundance of the Mg-rich phases. However, the anti-pulverization abilities present an inverse trend, which is closely related to the mechanical property of various phase structures. LaNi5 with the highest hardness is easy to crack, but the soft (La,Mg)Ni2 is more resistant to crack formation and spreading. Thus, the weaker corrosion of La2MgNi9 after electrochemical cycling is attributed to the better intrinsic anti-pulverization capability though the anti-corrosion is poor. As La4MgNi19 possesses excellent corrosion resistance, enhancement of the anti-pulverization ability is urgent for improvement in the cycling stability.
The dominant paradigm in drug discovery is the concept of designing maximally selective ligands to act on individual drug targets. However, many effective drugs act via modulation of multiple proteins rather than single targets. Advances in systems biology are revealing a phenotypic robustness and a network structure that strongly suggests that exquisitely selective compounds, compared with multitarget drugs, may exhibit lower than desired clinical efficacy. This new appreciation of the role of polypharmacology has significant implications for tackling the two major sources of attrition in drug development—efficacy and toxicity. Integrating network biology and polypharmacology holds the promise of expanding the current opportunity space for druggable targets. However, the rational design of polypharmacology faces considerable challenges in the need for new methods to validate target combinations and optimize multiple structure-activity relationships while maintaining drug-like properties. Advances in these areas are creating the foundation of the next paradigm in drug discovery: network pharmacology.
We report the structural and electrochemical characteristics of Li4/3Me5/3O4 (MeTi, Mn) spinel materials exhibiting nanostructured morphology. We have applied Raman and FTIR spectroscopy to study the local structure. Vibrational features are in good concordance with the factor group analysis (Oh 7 symmetry). The zero-strain insertion material Li4/3Ti5/3O4 delivers 150mAh/g while Li4/3Mn5/3O4 inserts 2.8 Li/mole of oxide leading to a specific capacity of 158mAh/g.
Pakistan has a very limited fossil fuel resource base. The poor economy does not allow the import of fossil fuels, particularly oil, on a large scale. Moreover, too much reliance on imported oil is critical from energy security point of view. A large fraction of the population lives in remote areas and is still waiting to be connected to the national electricity grid. To help these remote communities in particular, and to overcome energy shortages in general, Pakistan needs to develop its indigenous energy resources like hydropower, solar and wind. More than 1000km long coastline in south and some places in northern mountainous areas provide an excellent resource of wind energy. This vast potential can be exploited to produce electricity on both community and wind farm scales. Applications other than electricity production, such as water pumping, also have vast applications. This article discusses the past, the present and the future of wind energy use in Pakistan. The efforts for the utilization of wind energy in the country are presented as well, along with barriers to its development. It is concluded that the potential exists, but significant efforts are needed to effectively make use of this cheap renewable energy source.
In this paper, I argue that the ultimate argument for Scientific Realism, also known as the No-Miracles Argument (NMA), ultimately fails as an abductive defence of Epistemic Scientific Realism (ESR), where (ESR) is the thesis that successful theories of mature sciences are approximately true. The NMA is supposed to be an Inference to the Best Explanation (IBE) that purports to explain the success of science. However, the explanation offered as the best explanation for success, namely (ESR), fails to yield independently testable predictions that alternative explanations for success do not yield. If this is correct, then there seems to be no good reason to prefer (ESR) over alternative explanations for success.
High voltage cathode materials Li-excess layered oxide compounds Li[NixLi1/3−2x/3Mn2/3−x/3]O2 (0 < x < 1/2) are investigated in a joint study combining both computational and experimental methods. The bulk and surface structures of pristine and cycled samples of Li[Ni1/5Li1/5Mn3/5]O2 are characterized by synchrotron X-Ray diffraction together with aberration corrected Scanning Transmission Electron Microscopy (a-S/TEM). Electron Energy Loss Spectroscopy (EELS) is carried out to investigate the surface changes of the samples before/after electrochemical cycling. Combining first principles computational investigation with our experimental observations, a detailed lithium de-intercalation mechanism is proposed for this family of Li-excess layered oxides. The most striking characteristics in these high voltage high energy density cathode materials are 1) formation of tetrahedral lithium ions at voltage less than 4.45 V and 2) the transition metal (TM) ions migration leading to phase transformation on the surface of the materials. We show clear evidence of a new spinel-like solid phase formed on the surface of the electrode materials after high-voltage cycling. It is proposed that such surface phase transformation is one of the factors contributing to the first cycle irreversible capacity and the main reason for the intrinsic poor rate capability of these materials.
Thermal electrochemical models for porous electrode batteries (such as lithium ion batteries) are widely used. Due to the multiple scales involved, solving the model accounting for the porous microstructure is computationally expensive; therefore, effective models at the macroscale are preferable. However, these effective models are usually postulated ad hoc rather than systematically upscaled from the microscale equations. We present an effective thermal electrochemical model obtained using asymptotic homogenisation, which includes the electrochemical model at the cell level coupled with a thermal model that can be defined at either the cell or the battery level. The main aspects of the model are the consideration of thermal effects, the diffusion effects in the electrode particles, and the anisotropy of the material based on the microstructure, all of them incorporated in a systematic manner. We also compare the homogenised model with the standard electrochemical Doyle, Fuller & Newman model.
To understand the summertime variation pattern of CH4 oxidation in the rhizosphere, CH4 oxidation was evaluated in a freshwater marsh vegetated with Carex lasiocarpa and Carex meyeriana in the Sanjiang plain of northeast China at the three growing stages. Two methods through covering plants with a black cloth and applying acetylene to inhibit CH4 oxidation were used to quantify CH4 oxidation rates in the field. CH4 fluxes and CH4, dissolved organic carbon (DOC) and CO2 concentrations in porewater in the freshwater marsh were determined before and after the plants were covered or acetylene was applied. Temperature and redox potential in the vertical profile as well as aboveground and underground plant biomass were measured as well. Due to CH4 oxidation, CH4 concentrations in porewater in the C. lasiocarpa and C. meyeriana marsh were reduced by 2.1–18.2% and 0.7–25.8%, and the fluxes of potential CH4 emissions were lowered by 3.2–35.9% and 4.3–38.5%, respectively. The highest CH4 oxidation rate occurred in June, up to 30.1–38.5% of the potential CH4 fluxes, whereas the correspondent value was only 3.2–15.8% in July and August. CH4 oxidation rates in the Carex marsh decreased with increasing temperature in the vertical profile over the growing season. This is due likely to more O2 released from the roots in porewater to be consumed by other aerobic microbes in the rhizosphere at high temperature, resulting in the decrease of the CH4 oxidation rate.
Lead (Pb) has adverse effects on our nervous system and renal systems. Young children are more vulnerable to Pb exposure. However, the role of low-level Pb exposure in the immune system and allergic diseases in children is not well established. The aims of this study are to investigate the associations between Pb exposure and allergic diseases; between Pb and immunoglobulin E (IgE) as an intervening variable; and gender-based differences. We used multistage stratified random sampling to recruit kindergarten children nationwide in Taiwan. Information about allergic diseases and environmental exposures was collected by questionnaire. We compared children with and without allergic diseases for blood Pb levels measured by inductively coupled plasma mass spectrometry. The association between blood Pb and allergic diseases was assessed by logistic regression and those between Pb and IgE by generalized linear models. We also conducted mediation analysis to evaluate how much risk of allergic diseases related to Pb exposure is explained by IgE. A total of 930 children completed specimen collections. There was a positive association between Pb and asthma. Blood Pb were also positively linked with serum IgE (β=0.26 kU/l per ln-unit increase Pb concentration; 95% CI 0.009–0.50 kU/l), after adjusting for potential confounders. Analyses stratified by gender revealed that blood Pb correlated with IgE only in boys (β=0.40 kU/l; 95% CI 0.03–0.76 kU/l). We estimated that 38% of the total effect of Pb exposure on asthma is mediated by IgE levels. In conclusion, Pb exposure is associated with both blood IgE and asthma in boys. Moreover, the effect of Pb exposure on asthma may be mediated by IgE levels.
Studies on the voltammetric responses, capacitance, and charge storage capability of single-wall carbon nanotube sheets or papers are described. Broad redox responses have been observed probably due to the presence of oxygen-containing functional groups attached to the surface of the nanotubes or to the impurities produced during nanotube purification in nitric acid. Annealing the material at 900°C eliminates these responses. The voltammetry and capacitance of the nanotube paper varies little with either anion or cation molar mass, ion charge, or ion hydrophobicity. Acids as a group tend to produce higher capacitance but similarity between the electrochemical responses in various acids is also observed. The small variation of the capacitance within a wide range of scan rates suggests that in the time scale investigated the double layer charging process is controlled by the RC time constant and not by electrolyte ion diffusion into the pores of the nanotube paper.
Battery management systems (BMS) require computationally simple but highly accurate models of the battery cells they are monitoring and controlling. Historically, empirical equivalent-circuit models have been used, but increasingly researchers are focusing their attention on physics-based models due to their greater predictive capabilities. These models are of high intrinsic computational complexity and so must undergo some kind of order-reduction process to make their use by a BMS feasible: we favor methods based on a transfer-function approximation to battery-cell dynamics. In prior works, transfer functions have been found from full-order PDE models via two assumptions: (1) a linearization assumption—which is a fundamental necessity in order to make transfer functions—and (2) an assumption made out of expedience that decouples the electrolyte-potential and electrolyte-concentration PDEs in order to render an approach to solve for the transfer functions from the PDEs. This paper shows how to eliminate the need for the second assumption, thus retaining the coupling between these two PDEs and improving overall model accuracy. Time-domain models created from these transfer functions are especially improved when simulating constant-current profiles since the electrolyte concentration gradient increases the coupling between the electrolyte-potential and electrolyte-concentration PDEs.
The electrostatic assembly of calf thymus DNA on multi-walled carbon nanotubes (MWNTs)-modified gold electrode via poly(diallyldimethylammonium chloride) (PDDA), a cationic polyelectrolyte, has been studied. Piezoelectric quartz crystal impedance (PQCI) technique was employed to monitor the assembly of DNA in real time. Electrochemical impedance spectroscopy was also used to characterize the modification process. It has been found that modification of the electrode with MWNTs has significantly enhanced the effective electrode surface area in addition to providing negatively charged groups for the electrostatic assembly of cationic polyelectrolyte. PDDA plays a key role in the attachment of DNA to MWNTs and acts as a bridge to connect DNA with MWNTs, though the direct adsorption of DNA on MWNTs has been observed. Moreover, the interaction between DNA and chlorpromazine hydrochloride was observed with PQCI technique. This shows that DNA assembled on MWNTs still has the ability to interact with drug molecules, which has great importance in the construction of new types of miniature DNA biosensors.
Metal-free doped-graphene materials are emerging as electrocatalysts for energy conversions, but their activity remains low. Here, Jiao et al. explore the origins of catalytic activity for hydrogen evolution, suggesting pathways to metal-free catalysts with activity to rival metal-containing benchmarks.
The influence of the suspension of positive active mass particles in the electrolyte on the performance of the negative electrode in a lead-acid battery is studied. A significant increase in the rate of corrosion of the lead electrode is shown when slime particles get in contact with its surface, which may result in the rise of macro-defects on the lugs of the negative electrodes.
In one-way electric vehicle (EV) carsharing systems, a practical issue that needs to be addressed is the imbalance of EVs with respect to the spatial time-dependent user reservations at different carsharing stations. In practice, appropriate EV rebalancing operations can satisfy user reservations with limited resources and effectively save system investments. This paper proposes an integrated framework that can determine the optimal allocation plan of EVs and staff on the strategic level while considering the operational EV relocation and staff relocation decisions, in order to minimize the total cost, including the EV and staff investment, EV rebalancing and staff relocation costs. In this framework, the dispatching routes of EVs and staff are represented by two sets of space-time paths in the planning time horizon by using a space-time network representation, and the considered problem is then formulated into a mixed-integer linear programming model (MILP). This model explicitly considers (1) the satisfaction of time-dependent user reservations through dynamically rebalancing EVs and relocating staff to keep the service quality of carsharing system, and (2) the EV battery capacity with limited traveling distance and the charging process of EVs at parking stations. A Lagrangian relaxation-based solution approach is developed to decompose the primal problem into several sets of computationally efficient subproblems. In order to generate good-quality solutions, we also propose a three-phase implementing algorithm based on dynamic programming according to the values of Lagrangian multipliers. An illustrative numerical example and a real-world case study (based on the operation data of Seattle, WA) are conducted to verify the applicability of the formulated model and effectiveness of the proposed approach.
We report here for the first time Sn-contained N-rich carbon nanowires, which are prepared via a facile and scalable procedure using poly-pyrrole as the carbon source. As-obtained nanowires with a diameter of about 50nm crosslink with each other with enough void space, beneficial to accommodating lithiation-induced volumetric change and mechanical stress. In particular, this product contains abundant nitrogen (9.8wt.%), favorable for Li+ diffusion and storage. It therefore exhibits excellent cycling stability of 682.6 and 760.1mAhg−1 at 500mAg−1 after 200 and 600 cycles, respectively. It also delivers great high rate performance even at 10Ag−1.
MgFe2O4/reduced graphene oxide composites (MFO/RGO) were prepared via a facile microwave assisted reduction of graphene oxide in MFO precursor solution, and used as anode materials for sodium ion batteries (SIBs). Their morphology, structure and electrochemical performance were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption isotherms, galvanostatic charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. The results show that MFO/RGO composite with 20wt.% RGO exhibits a maximum reversible capacity of about 347.5mAhg−1 at 50mAg−1 after 70 cycles with good cycling stability. The excellent electrochemical performance of MFO/RGO composites should be attributed to the synergistic effect of MFO and RGO to form a porous conductive network structure which offers the increased specific surface area, the facilitated electron transfer ability and the effective buffering of volume expansion.
The synthesis of graphene in both high quality and quantity via economic ways is highly desirable and meaningful for practical applications. Here we report a simple, green and cost- effective multiple electrochemical exfoliation approach to high quality and high yield (nearly 50%) graphene flakes by using graphite rod from spent zinc–carbon as graphene source. The graphite rod (anode) and platinum (cathode) were placed vertically at bottom and top of the electrochemical cell, with protonic acid (i.e, H2SO4, H3PO4 or H2C2O4) aqueous solution as electrolyte. The vertical cell configuration enables multiple exfoliation process to improve both the quality and yield of graphene sheets from electrochemical exfoliation of graphite. After nitrogen doping, the exfoliated graphene flakes processes excellent electrocatalytic activity, stability and toxicity tolerance for oxygen reduction reaction in alkaline solution.