Redox flow batteries (RFBs) are an emerging technology suitable for grid electricity storage. The vanadium redox flow battery (VRFB) has been one of the most widely researched and commercialized RFB ...systems because of its ability to recover lost capacity via electrolyte rebalancing, a result of both the device configuration as well as the symmetry of the redox chemistry. Despite broad acknowledgement of the benefits of this differentiating feature to system resilience and longevity, assessments of its economic value to the VRFB system have thus far been limited. Here we develop a techno-economic framework that incorporates a physical model of capacity fade and recovery from rebalancing and other servicing methods into a levelized cost of storage (LCOS) metric. We then evaluate the impacts of different contributing factors to the LCOS of a VRFB and identify opportunities for cost reduction through operating strategies (e.g., rebalancing schedule), performance improvements (e.g., reducing fade rates), design decisions (e.g., battery sizing), and investment approaches (e.g., electrolyte leasing). We anticipate this analysis will provide new insights into the cost-drivers for VRFBs and motivate further research efforts in understudied yet important areas.
•Develops a levelized cost of storage (LCOS) model for vanadium redox flow batteries.•LCOS model incorporates capacity loss and recovery via rebalancing.•Explores tradeoffs between changes in upfront versus long-term operational costs.•Investment considerations (i.e., battery sizing, electrolyte leasing) are evaluated.•Demonstrates the need for both capital and levelized costs as comparative metrics.
•Real-time crossover of vanadium species was investigated with a novel system.•Concentration and electrostatic potential gradient-induced crossover was separated.•Interaction coefficients were ...introduced to account for state of charge dependence.•Electric-field-induced crossover is asymmetric for charge and discharge processes.•Net vanadium crossover is from negative to positive half-cell at open-circuit.
One of the major sources of capacity loss in all-vanadium redox flow batteries (VRFBs) is the undesired transport of active vanadium species across the ion-exchange membrane, generically termed crossover. In this work, a novel system has been designed and built to investigate the concentration- and electrostatic potential gradient-driven crossover for all vanadium species through the membrane in real-time. For this study, a perfluorosulphonic acid membrane separator (Nafion® 117) was used. The test system utilizes ultraviolet/visible (UV/Vis) spectroscopy to differentiate vanadium ion species and separates contributions to crossover stemming from concentration and electrostatic potential gradients. It is shown that the rate of species transport through the ion-exchange membrane is state of charge dependent and, as a result, interaction coefficients have been deduced which can be used to better estimate expected crossover over a range of operating conditions. The electric field was shown to increase the negative-to-positive transport of V(II)/V(III) and suppress the positive-to-negative transport of V(IV)/V(V) during discharge, with an inverse trend during charging conditions. Electric-field-induced transport coefficients were deduced directly from experimental data.
This paper reports an efficient fabrication of N-doped graphene quantum dots (GQDs) showing controllable chemical and fluorescence (FL) properties through infrared carbonization (IRC) of citric acid ...and urea. The GQDs prefer to form an equilibrium shapes of circle with an average particle size ranged from 5 to 10 nm. The N/C atomic ratio in GQDs can be precisely tailored in a range from 21.6 to 49.6 at.% by simply controlling the weight ratio of citric acid to urea. With increasing the urea content, the GQDs not only contain N-doped graphene but also incorporate with crystalline cyanuric acid, forming a binary crystallinity. The quantum yield of 22.2% is achieved by N-doped GQDs, prepared from the IRC synthesis of chemical precursor at the citric acid/urea at 3:1. Excessive N and cyanuric acid can lead to FL quenching, red shift and wide spectral distribution. The design of GQDs possesses a multiple chromophoric band-gap structure, originated from the presence of cyanuric acid, defect-related emissive traps, and functional group distributions. This work offers an effective and inspiring approach to engineering both chemical compositions and unique crystalline structures of GQDs, and will therefore facilitate their fundamental research and applications to optical, sensing, energy and biological fields.
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•We report an infrared carbonization to synthesize graphene quantum dots (GQDs).•The N/C atomic ratio in GQDs was tailored in a range from 21.6 to 49.6 at.%.•The quantum yield of 22.2% is achieved, prepared from the citric acid/urea at 3:1.•The design of GQDs possesses a multiple chromophoric band-gap structure.•We offer an inspiring approach to engineering unique crystalline structure of GQDs.
Thermal rectification in defect-engineered graphene with asymmetric hole arrangements is assessed via molecular dynamics simulations. Asymmetry in two different configurations (triangular and ...rectangular hole arrangements) is controlled by manipulating geometrical parameters, such as hole size; effects of geometry on the resultant rectification are investigated. Filtering of phonon propagation directions by geometrical confinement, and asymmetric relaxation distance induce a difference in heat transfer depending on transport direction, or thermal rectification. Increase in porosity, which results in additional confinement and larger difference in relaxation, produces more significant thermal rectification. While a rectangular arrangement of holes results in 70% of the maximum thermal rectification, up to 78% of rectification was achieved using a triangular arrangement within 47.5 nm of graphene, which can be attributed to more effective phonon-hole boundary scattering with a triangular arrangement. This study suggests a feasible approach to create thermal rectification and enables its fine control, contributing to the development of phononic devices and enhancement of thermal system design for electronics.
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In this work, we have studied how the vertical illuminance of the human eye position, illuminance of the horizontal work surface, and the brightness of the computer screen in the office space ...lighting are correlated under an energy-saving environment. This investigation was conducted in a full-scale laboratory that simulates an office space with 20 adults. It was found that when the indoor ambient lighting illuminance changes, the vertical illuminance of the subject’s eye position is affected accordingly, and the two factors are strongly correlated. On the other hand, when the surrounding environment is brighter and the vertical illuminance increases, the illuminance of the horizontal working surface adjusted by the subject during the visual display terminal (VDT) operation is significantly reduced. The horizontal illuminance value can even be lower than the value frequently employed in various countries around the world, since the computer screen brightness will be adjusted accordingly. Therefore, in an energy-saving environment, the illuminance of the horizontal working surface and the brightness of the computer screen adjusted by the users will vary with the ambient lighting. Especially in the current mainstream VDT operating environment and within a certain range of conditions, the interior setting can be lower than the current horizontal illuminance benchmark for additional energy conservation.
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The ongoing COVID-19 (i.e., coronavirus) pandemic continues to adversely affect the human life, economy, and the world’s ecosystem. Although significant progress has been made in ...developing antiviral materials for the coronavirus, much more work is still needed. In this work, N-functionalized graphene quantum dots (GQDs) were designed and synthesized as the antiviral nanomaterial for Feline Coronavirus NTU156 (FCoV NTU156) and Enterovirus 71 (EV71)) with ultra-high inhibition (>99.9%). To prepare the GQD samples, a unique solid-phase microwave-assisted technique was developed and the cell toxicity was established on the H171 and H184 cell lines after 72 h incubation, indicating superior biocompatibility. The surface functionality of GQDs (i.e., the phenolic and amino groups) plays a vital role in interacting with the receptor-binding-domain of the spike protein. It was also found that the addition of polyethylene glycol is advantageous for the dispersion and the adsorption of functionalized GQDs onto the virus surface, leading to an enhanced virus inhibition. The functionality of as-prepared GQD nanomaterials was further confirmed where a functionalized GQD-coated glass was shown to be extremely effective in hindering the virus spread for a relatively long period (>20 h).
Magnesium-ion batteries are fabricated with MgCo
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/graphite composites as the cathode material. MgCo
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nanoparticles are prepared using a co-precipitation method. A three-dimensional mixing ...process is utilized to mechanically decorate MgCo
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nanoparticles on graphite particles. The MgCo
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spinel crystals of size ranging from 20 to 70 nm on micrometer-sized graphite chunks are analyzed by using X-ray diffraction and scanning electron microscopy. The electrochemical properties of the as-prepared composites are well characterized by cyclic voltammetry, charge and discharge cycling, and electrochemical impedance spectroscopy (EIS). Surprisingly, the MgCo
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/graphite composite with a relatively low proportion of MgCo
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, compared with the other as-prepared composites, achieves the highest specific capacity of 180 mAh g
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at a
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rate of 0.05 C. EIS results suggest that the electrical conductivity of the composite material is an increasing function of the graphite proportion. The superior performance of the MgCo
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/graphite composite could be ascribed to the decoration of nanosized MgCo
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particles as well as to the increased conductivity provided by graphite.
Cascaded multilevel inverters (MLIs) have been proposed that utilise transformers in the basic unit. The proposed inverters primarily serve to step up the input voltages in addition to using lower ...number of components in comparison to traditional MLIs. In order to generate all voltage levels (even and odd) at the output, three different algorithms are proposed to determine the magnitude of DC voltage sources and transformer turn ratios. Also, the basic inverter unit was further developed and two new flexible MLI structures have been obtained. The developed structures increase the input voltage with no need for an additional boost converter. A reduction in the number of power switches, the peak inverse voltage, and the number of DC voltage sources are other advantages of the proposed topologies. Also, a simple cost model was developed and the dimensionless cost coefficient was determined. The overall cost of the proposed MLIs was compared to the similar MLIs from the literature. It was shown that the proposed MLI decrease the overall cost of the system if the cost coefficient is selected appropriately. To verify the performance of the proposed topologies simulated by the mathematical model; several lab-scale inverters were built and tested and good agreement was achieved.
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