Electrostatic Shielding Effect Research Articles

Potassium Hexafluorophosphate Additive Enables Stable Lithium-Sulfur Batteries.

Uncontrollable dendrite growth and low Coulombic efficiency are the two main obstacles that hinder the application of rechargeable Li metal batteries. Here, an optimized amount of potassium hexafluorophosphate (KPF6, 0.01 M) has been added into the 2 M LiTFSI/ether-based electrolyte to improve the cycling stability of lithium-sulfur (Li-S) batteries. Due to the synergistic effect of self-healing electrostatic shield effect from K+ cations and the LiF-rich solid electrolyte interphases derived from PF6- anions, the KPF6 additive enables a high Li Coulombic efficiency of 98.8% (1 mA cm-2 of 1 mAh cm-2). The symmetrical Li cell can achieve a stable cycling performance for over 200 cycles under a high Li utilization up to 33.3%. Meanwhile, the polysulfide shuttle has been restrained due to the higher concentration of the LiTFSI in the electrolyte. As a result, the assembled Li-S full cell displays excellent capacity retention with only 0.25% decay per cycle in the final electrolyte. Our work offers a smart approach to improve both the anode and cathode performance by the electrolyte modification of rechargeable Li-S batteries.

A trifunctional electrolyte for high-performance zinc-iodine flow batteries

Zinc-iodine flow battery (ZIFB) holds great potential for grid-scale energy storage because of its high energy density, good safety and inexpensiveness. However, the performance of ZIFB is hindered by conventional electrolyte that offers low ionic conductivity, suffers from iodine precipitation and triggers severe Zn dendrite growth. Here, we report an NH4Br improved electrolyte to address the issues simultaneously. The addition of NH4Br enhances the ionic conductivity of electrolyte from 120 to 180 mS cm−1. Meanwhile, Br− ions complex with I2 forming soluble I2Br−, which frees up I− ions and thus unlocks the battery capacity, while NH4+ ions complex with Zn2+ ions to mitigate Zn dendrite formation with the electrostatic shielding effect. Experimental results reveal that the improved electrolyte promotes the kinetics and reversibility of both positive and negative redox couples. A ZIFB with the improved electrolyte delivers a high energy efficiency (85%), a high charge capacity (35 A h L−1) and a long cycle life (100 cycles without degradation) at 40 mA cm−2, while conventional ZIFB shows an energy efficiency of 80%, a charge capacity of 25 A h L−1, and a short cycle life of only around 15 cycles. These encouraging results indicate that NH4Br, a cost-effective salt, offers great prospects for high-performance ZIFB applications.

A Non-Enzymatic Electrochemical Sensor Using a Wrinkled Gold Film on Shrink Polymer

A non-enzymatic electrochemical uric acid (UA) sensor based on heat-shrinkable polymer was fabricated via a simple and low-cost method without any complex electrode modification for the first time. We sputtered a gold electrode on the heat-shrinkable polymer with shadow masks, taking advantage of the heat shrinkage properties of the polymer to obtain a novel wrinkled gold electrode surface, then detected the UA concentration in aqueous conditions by square wave voltammetry. The performance of the shrink sensor, which was specific to the sensitivity and linearity, improved greatly compared with those non-shrinking ones. The accuracy and long-term stability of tests were also carried out, indicating a more accurate and stable sensor was achieved. Notably, a selectivity enhancement towards glucose interferent was experimentally observed. The selectivity coefficient decreased considerably after the heat shrink process, from −1.28 to −2.6. A new theoretical proposal related to reaction rate suppression was discussed, employing electrostatic shield effect between the wrinkled gold surface and biomolecules with different electrochemical reaction nature. It is a very simple but effective way to monitor UA concentration and the possible reaction control functions of the wrinkled surface can be rationally projected to tailor the electrode properties.

Toward Understanding CB[7]-Based Supramolecular Diels-Alder Catalysis.

Cucurbiturils (CBs) are robust and versatile macrocyclic compounds, often used as molecular hosts in complex supramolecular systems. In previous work, remarkable catalytic activity has been observed for asymmetric cycloadditions under very mild conditions. Herein, we investigate the nature of supramolecular catalysis using DFT calculations and QM/MM techniques. We discuss induced conformational changes, electrostatic shielding effects from the highly polar aqueous environment and cooperativity in hydrogen bonding of the substrates in explicit water using QM/MM simulation techniques. Our results show little specificity for the chosen molecules, suggesting an excellent opportunity to expand the scope for catalytic use of these supramolecular macrocyclic containers.

Hybrid approach to modeling large area field emitters

Large area field electron emitters, typically consisting of several thousands of nanotips, pose a major challenge since numerical modeling requires enormous computational resources. We propose a hybrid approach where the local electrostatic field enhancement parameters of an individual emitter are determined numerically while electrostatic shielding and anode-proximity effects are incorporated using recent analytical advances. The hybrid model is tested numerically on an ordered arrangement of emitters and then applied to recent experimental results on randomly distributed gold nanocones. Using the current-voltage data of two samples with vastly different emitter densities but having similar nanocone sizes, we show that an appropriate modeling of the emitter apex together with the analytical results on shielding and anode-proximity effects leads to consistent results for the apex radius of curvature. In both cases, the I−V data are approximately reproduced for Ra≃9 nm. Importantly, it is found that anode-proximity plays a significant role in counter-balancing electrostatic shielding, and ignoring this effect results in the requirement of a much smaller value of Ra.

Solution pH affects single, sequential and binary systems of sulfamethoxazole and cadmium adsorption by self-assembled cellulose: Promotion or inhibition?

A new self-assembled cellulose (SACS) containing multi-functional amine, carboxyl and hydroxyl groups was successfully obtained through etherification, cross-linking and grafting processes. Then, the adsorption of sulfamethoxazole (SMZ) and Cd(II) onto SACS at pH values of 3, 5.7 and 7.5 was systematically investigated by batch experiments of single, sequential and binary systems, characterization and density functional theory (DFT) calculations. The presence of Cd(II) decreased the adsorption of SMZ because of hydrophilic site competition, while SMZ inversely increased the adsorption of Cd(II), which was attributed to bridging and especially to electrostatic shielding effects; moreover, both the inhibitory and synergistic effects were more obvious in the binary system and at a pH of 7.5. There was a dynamic balance between the inhibitory and synergistic effects that depended on the system, pH value and concentration ratio. DFT results further indicated that SMZ– more easily coordinated with Cd(II) at sulfonyl oxygen and nitrogen sites, and the cationic bridge of Cd(II) with SMZ– mainly occurred in the sequential system. Moreover, a complexation–decomplexation–complexation balance of SMZ– and Cd(II) probably occurred in the binary system.

Interactions between tapioca starch and Mesona chinensis polysaccharide: Effects of urea and NaCl

Non-starch polysaccharide and starch interactions have been extensively studied. However, few researches focus on their interactions mechanism. In this study, the effects of hydrogen bond and electrostatic interactions on the tapioca starch-Mesona chinensis polysaccharide (TM) gels were investigated. The results of pasting and thermal experiments (heating phase) showed that the peak viscosity (PV) of TM gels increased with the addition of urea. The addition of urea caused the hydrogen bonds to be destroyed and the rearrangement of starch during cooling was inhibited, which led to the final viscosity of TM gels decreased. The interactions between 0.5% NaCl and starch hydroxyl groups resulted in a significant increase in PV, while excessive addition of NaCl produced an electrostatic shielding effect, resulting in a decrease in PV, but still higher than TM gels. The results of rheological, texture, and particle size experiments (gel cooling stage) showed that hydrogen bond played a decisive role in the final texture of TM gels. Scanning electronic microscopy results showed that the addition of urea loosened the starch structure, and the high concentration of urea caused the structure appear fragmented.

Insights into the effect of the shape of collecting plates on particle precipitation processes in an electrostatic precipitator

ABSTRACT Collecting plate is the core component of the electrostatic precipitator. In order to explore the influences of the plates shape and electrode configuration on the particle precipitation process, numerical models of an ESP with seven different types of collecting plates were established and calculated. The simulation results showed that the shape of the collecting plate did have a great impact on the electric field, airflow particles movement. From the perspective of electric field characteristics, the space current density and electrostatic shielding effect in multielectrode ESPs varied with the shape of the plates under the same supply voltage. When using C-type plate, the shielding effect was minimal and the current density distribution of the plate was more uniform. When it comes to airflow distribution, small vortex structures were easily generated near the plates when the CW type, the rod-curtain and Z-type plates were used, leading to particle re-entrainments. In terms of collection efficiency, the C-type plate enjoyed the highest efficiency, while the ZT-type and corrugated plate were less efficient. Implications: The main source of air pollution is the flue gas released by fuel combustion. electrostatic precipitator plays an important role in pollutant discharge control and environmental protection. As the core component of the electrostatic precipitator, the form of the collecting plate exerts a serious impact on its dust removal performance. The study focuses on the analysis of the collecting plate shape on the electric field characteristics of electrostatic precipitators, flow distribution characteristics and the influence of the collecting efficiency. It is expected that through the research, some guidance will be provided with the electrode configuration selection and optimization of ESP.

Ion-Solvent Chemistry-Inspired Cation-Additive Strategy to Stabilize Electrolytes for Sodium-Metal Batteries

Summary Building stable electrolytes is one of the key technologies for sodium (Na)-metal batteries as the reactive nature and the dendritic growth of Na-metal anodes. Herein, a paradigmatic and rational strategy of cation additive was proposed to stabilize electrolytes for Na metal batteries. Three principles, including the electrode potential of introduced cations, the lowest unoccupied molecular orbital energy level decrease of solvents after coordinating with cations, and the interaction strength between cations and solvents, were proved through first-principles calculations and molecular dynamics simulations. Li+ was predicted to be a good cation additive candidate for Na metal batteries. Finite element method simulations, in situ optical microscopic observations, and electrochemical tests further validated the resisted Na dendritic growth due to the electrostatic shield effect and enhanced electrolyte stability after introducing Li+ additives. The proven cation additive strategy affords emerging chances for rational electrolyte design for stable and safe Na metal batteries.

Combined effect of weak electric field and ions on critical water cluster: Insight from molecular dynamics simulation

The effects of ion and electric field on the vapor–liquid transition of water, are studied by using the optimal point charge (OPC) water model in this paper. A canonical Molecular Dynamics (MD) simulation approach, which calculates equilibrium time and the number of water molecules in the clusters, is employed to study the factors affecting the nucleation of water molecules. In addition, Quantum Mechanics (QM) method is adopted to calculate the hydration free energy of ions as a supplement. The results demonstrate that the ion has a significant promoting effect on vapor–liquid nucleation below the critical nucleus size (1–3 nm). However, as the cluster grows, the ion will no longer promote cluster growth, due to electrostatic shielding effect from the aggregated water molecules. When a weak uniform electric field (less than 0.1 V/nm) is applied, the promotion of the ion reappears. According to the trajectory analysis of ion in the water droplet, we believe that the electric field changes the relative position of ions in the droplets, thus weakening the shielding of water molecules. It is further demonstrated by a proposed novel statistical method, which provides an alternative, visualized and effective approach to evaluate the promotion effect in similar analyses, compared to radial distribution function.

Na+-induced gelation of a low-methoxyl pectin extracted from Premna microphylla Turcz

In this paper, Na+-induced gelation of a low-methoxyl pectin extracted from Premna microphylla Turcz were studied by rheological analysis, texture test, microstructure observation, thermodynamics study and gelling forces analysis. The results showed that Na+ could induce the gelation of ammonium oxalate extraction pectin from Premna microphylla Turcz (AOP) at room temperature. Besides, The Na+ concentration had a significant effect on the generation of AOP gel. There was an optimal Na+ concentration (0.6 M) for AOP to form a gel with the highest solid-like properties, water holding capacity (WHC) and crystallinity. With the further increase of Na+ concentration from 0.6 M to 0.7 M, the gel properties of the pectin gel would be weakened. Gelling forces analysis revealed that Na+-induced gelation of AOP was mainly caused by electrostatic shielding and hydrogen bonds. When sufficient content of Na+ was added to AOP, the electrostatic shielding effect of Na+ would reduce the expansion degree of AOP chains and make the pectin molecules get close to each other. Subsequently, hydrogen bonds in and between the pectin chains would be formed, thus building up the gel. The results of this study can provide references and methods for the mechanism study of monovalent cation-induced gelation of pectin.

Alcohol solvent treatment of PEDOT:PSS hole transport layer for optimized inverted perovskite solar cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely used as a hole transport materials in perovskite solar cells, due to a variety of suitable properties. However, the existence of the insulated PSS chain leads to the low electrical conductivity, which should be improved for the further development of inverted perovskite solar cells. In this study, three alcohol solvents were proposed for post-treatment of PEDOT:PSS thin films, which utilized the electrostatic shielding effect of alcohol molecules to promote phase separation of the PEDOT chain and the PSS chain. At the same time, The insulated PSS chain was removed by dissolving in highly hydrophilic alcohols. In the end, we successfully improved the conductivity of PEDOT:PSS thin films. By ethanol solvent treatment, the short-circuit current density of the perovskite solar cell based on glass/ITO/PEDOT:PSS was increased from 15.64 to 17.45 mA/cm2, the power conversion efficiency (PCE) reached 11.36%, which was 25% higher than the traditional structure. For flexible devices, a preliminary PCE of 9.20% was achieved.

Opposite impacts of K+ and Ca2+ on membrane fouling by humic acid and cleaning process: Evaluation and mechanism investigation

Understanding the influences of cations on membrane fouling was important to improve the performance of membrane filtration system, however, opposite conclusions were made in different studies. Meanwhile, although the influences of cation concentration have been studied extensively, few attentions have been paid to the cation valence. To clarify it, the effects of typical cations on membrane fouling and cleaning, as well as the related mechanisms were investigated systemically in this study. K+ and Ca2+ were chosen as the representative cations, and humic acid (HA) was chosen as the membrane foulants. The results demonstrated Ca2+ promoted the formation of reversible fouling, meanwhile higher removal efficiency of HA could also be achieved with the assistance of filtration cake containing HA + Ca2+. However, K+ led to the formation of more recalcitrant irreversible fouling. By comparing the concentration of cations in feed and permeate, analyzing the influence of cations on size of HA flocs, and the detailed SEM, AFM and TEM observation, it could be found that different mechanisms dominated the interaction between cations and HA. The bridging effect induced by Ca2+ attributed to the extension of HA molecules, while the electrostatic shielding effect induced by K+ led to the compression of them. Moreover, the different characteristics of hydrated Ca2+ and K+ also contributed to the different structures of foulant layers formed by HA + Ca2+ and HA + K+. Given the abundance of K+ and Ca2+ in natural water, results of this study can provide valuable advice for practical membrane filtration process.

A long-lasting dual-function electrolyte additive for stable lithium metal batteries

Solid electrolyte interphases (SEI) plays a vital role in stabilizing lithium (Li) metal anodes for rechargeable batteries. However, forming robust SEI layers is challenging in the state-of-the-art electrolytes. Herein, we report a long-lasting and dual-function additive (potassium nonafluoro-1-butanesulfonate or KPBS) for dual-salt LiFSI-LiTFSI ether electrolyte. Our work suggests that the electrostatic shield effect from potassium ion (K + ) and the F-rich PBS − anions with a middle lowest unoccupied molecular orbital (LUMO) level together promote the formation of a LiF-rich SEI during the Li plating/striping process, which effectively restricts Li dendrite growth and suppresses electrolyte consumption. As a consequence, the designed electrolyte endows small nucleation overpotential, highly reversible Li plating/stripping, and excellent cycling stability. Specifically, with such an electrolyte, Li–Cu cells can maintain stable cycling during 400 cycles at 1 mA cm −2 for 1 mA h cm −2 with a high coulombic efficiency (CE) of 99.1%. Li–LiFePO 4 full cells displayed dramatically improved cycling stability after 100 cycles with high CE of 99.6% under relatively lean electrolyte condition (7.5 μL mA h −1 ), limited Li supply (N/P = 1.2) and high areal capacity (4.1 mA h cm −2 ). • A long-lasting electrolyte additive, KPBS, promoting the formation of robust LiF-rich SEI layer on the anode side was discovered. • The K + cations can offer effective electrostatic shielding that prevents the formation of Li-metal “hot-spots”. • The F-rich PBS − anions with a unique lowest unoccupied molecular orbital (LUMO) level is responsible for the formation of LiF-rich SEI layer. • Li–LiFePO 4 full cells with KPBS showed improved cycling stability with relatively lean electrolyte, limited Li supply and high areal capacity. • The electrolyte additive shows promise for practical Li-metal cell applications.

Electrostatic shielding versus anode-proximity effect in large area field emitters

Field emission of electrons crucially depends on the enhancement of the local electric field around nanotips. The enhancement is maximum when individual emitter-tips are well separated. As the distance between two or more nanotips decreases, the field enhancement at individual tips reduces due to the shielding effect. The anode-proximity effect acts in quite the opposite way, increasing the local field as the anode is brought closer to the emitter. For isolated emitters, this effect is pronounced when the anode is at a distance less than three times the height of the emitter. It is shown here that for a large area field emitter (LAFE), the anode-proximity effect increases dramatically and can counterbalance shielding effects to a large extent. Also, it is significant even when the anode is far away. The apex field enhancement factor for an LAFE in the presence of an anode is derived using the line charge model. It is found to explain the observations well and can accurately predict the apex enhancement factors. The results are supported by numerical studies using comsol multiphysics.

Experimental and numerical studies on electric field distribution of a premixed stagnation flame under DC power supply

In this work, we achieve a sub-breakdown electric field measurement in a premixed stagnation flame by electric-field-induced second-harmonic generation (ESHG) using a nanosecond laser. Under the application of a DC voltage, the premixed flame can transit from a flat substrate-stabilized mode to a conical nozzle-stabilized mode due to the two-way interaction between the electric and hydrodynamic responses of the flame. The average electric fields along the laser pathway for these two flame modes are measured at different heights above the burner. Combining the measurement and the numerical simulation of a charge transport model, we further elucidate that the flame affects the electric field distribution in two different ways. For the flat flame mode, the electric field strength is shielded at the flame front and then quickly increases both upstream and downstream, reaching the maximum at the electrodes. The charge transport model reveals that the electrostatic shielding effect of the flame front can be attributed to the charge redistribution in the chemi-ionized conductive layer. For the conical flame mode, the electric field strength has a large gradient near the conical tip and remains almost zero downstream. The conical flame front then serves as a conductive layer to guide the charge transport under the application of the electric field. The positive and negative charges are separated at different radial positions because of the inclined asymmetric flame front. Thus, the largest electric field gradient is generated upstream of the flame conical tip, where the net charge and the electric body force maximize and create a virtual flame stabilization mode.

Study on Optimization Application of Iron Ion Stabilizer in the Polymer Injection Process of Offshore Oilfield

A large amount of Fe2+/Fe3+ ions are produced by corrosion and fouling in the high-pressure polymer injection process of offshore platforms, which will affect the viscosity of the polymer solution, and is difficult to effectively control by the addition of stabilizers in the curing tank. In order to solve this problem, this paper has carried out related research and the results show that: 1) Fe2+ mainly generates free radicals (·OH) by oxidation catalysis, to destroy long chains of polymer molecules, causing irreversible fragment breakage, resulting in a significant decrease in polymer viscosity; 2) Fe3+ mainly binds to hydroxyl groups, resulting in flocculation and viscosity reduction of polymers; 3) Stabilizers with complexation can effectively control Fe3+ to form water-soluble complexes, while excess stabilizers increase salt content and reduce polymer viscosity by electrostatic shielding effect. In order to effectively control the influence of Fe2+/Fe3+ and the stabilizer on the polymer solution in the production process, an appropriate amount of complex stabilizer should be added to the diluent inlet of the mixture of the polymer mother liquor and the diluent.

The Field Shielding Effect of Mountain on the Lightning Electromagnetic Field

In this paper we have studied the effect of strike to a cone-shaped mountain surrounded by two chains of hills on the lightning vertical electric field and azimuthal magnetic field at different distances, by using two-dimensional finite-difference time-domain (2-D FDTD) method in cylindrical coordinate systems. In order to analyze the electrostatic shielding effect of strike to a cone-shaped mountain surrounded by two chains of hills on the lightning, we chose three mountains, and the left one is stroke by lightning, and the right one is near the obervation site, and the middle one with the top heights increasing from 0 to 2 km is between them. For the observed point, the electrostatic shielding effect of the right one on the lightning vertical electric field is the most serious, and the electric field is much less than that for strike to flat ground level; compared with the electric field, the shielding effect of the right one on the lightning azimuthal magnetic field becomes less, for most cases, the lightning magnetic field at the observed site is larger than that for flat ground cases mainly due to that of the increment caused by strike to the right mountain. With the increase of distance (e.g., 20 km from the lightning strike point), the shielding effect of the right mountain on the lightning field becomes less, because the reflected wave from the right mountain bottom plays a more important role over intermediate ranges, and the far radiation electromagnetic field peak value becomes larger due to such a reflecting wave. Therefore, in the lightning detecting technique, we should pay more attention to the effect caused by chains of hills on the lightning location and the estimation of lightning current peak.

Association behavior and fluorescence quenching between cationic zinc porphyrin pendant groups on water-soluble polymers and anionic iron porphyrin guests

An amphiphilic cationic tripyridiniumylporphyrin monomer, i.e., ZnTrMPyP, was synthesized and copolymerized with acrylamide in water and dimethyl sulfoxide, respectively, to prepare the water-soluble random copolymer P-D and microblock copolymer P-W. The association behavior and fluorescence quenching between the copolymers and tetra(p-sulfonato phenyl)porphyrin (Fe(III)TSPP(Cl)) were studied via absorption and emission spectra. The results showed that relatively discrete pendant groups of ZnTrMPyP within P-D could form a ground state complex with FeTSPP by electrostatic interactions, and both static and dynamic mechanisms were active in this quenching process. In contrast, the microblock porphyrin pendant groups within P-W interacted with FeTSPP as an entity, and static quenching was dominant in this process. Salt effects on the formation of the copolymers and FeTSPP complex were also investigated through the addition of KNO3, and the results showed that this association can be weakened by the electrostatic shielding effect, and the fluorescence quenching constant could be reduced.

Dynamic dispersion stability of graphene oxide with metal ions

Graphene oxide (GO), an important chemical precursor of graphene, can stably disperse in aqueous surrounding and undergo aggregation as metal cations introduced. The usual instability of GO with ions is caused by the shielding effect of ions and crosslinking between GO and ions. However, the dynamic stability of GO under ions exchange still remains unclear. Here, we investigated the dynamic dispersion stability of GO with metal ions and observed a redispersion behavior in concentrated Fe3+ solution, other than permanent aggregation. The exchange with Fe3+ ions drives the reversion of Zeta (ζ) potential and enables the redispersion to individual GO-Fe3+ complex sheets, following a dynamic electric double layer (EDL) mechanism. It is found that the specifically strong electrostatic shielding effect and coordination attraction between Fe3+ and functional oxygen groups allows the selective redispersion of GO in concentrated Fe3+ solution. The revealed dynamic dispersion stability complements our understanding on the dispersive stability of GO and can be utilized to fabricate graphene-metal hybrids for rich applications.