Accumulation Of Excess Charge Research Articles

Unveiling frequency-dependent dielectric behavior of cellulose-based polymer electrolyte at various temperature and salt concentration

Dielectric behavior of cellulose-based polymer electrolyte was studied at various temperature and salt concentration. A polymer electrolyte membrane based on cellulose acetate (CA) as the polymer host and LiClO4 as the dopant salt was fabricated using the solution casting technique. The dopant salt concentration was varied as 0.3, 0.5, 0.67, and 1M. Dielectric relaxation spectroscopy characterization were performed using potentiostat at frequency ranging from 0.1 Hz to 1 MHz. Measurements were performed by sandwiching the membrane between stainless steel plates. The ionic conductivity was then calculated based on the Cole–Cole plot obtained from the impedance measurement. It was found that sample 1 M had the highest ionic conductivity at high frequencies. However, the frequency-dependent conductance plot showed that the ionic conductivity of the 1 M sample significantly decreased at low frequencies, i.e. from 3.41×10-5 S/cm at 1 MHz to 1.9×10-8 S/cm at 0.1 Hz. Other samples did not experience this phenomenon, including those with a Celgard© commercial membrane to represent commercial Li-ion batteries. This is caused by excess charge accumulation, leading to a high concentration of immobile charge carriers, which reduces the available free volume surrounding the polymer chain. This resulted in a significant decrease in ionic conductivity at low frequencies. Temperature variation was also performed on the conductivity measurement at 30-70 °C. Temperature variation showed more predictable behavior, where increasing the temperature activated charge carriers and enhanced ionic conductivity, from 1.81×10-5 S/cm at room temperature to 9.04×10-5 at 70°C. Sweeping across the frequency range results in a consistent sequence of ionic conductivities among the samples at various temperatures. This work is beneficial for evaluating a biomass-based polymer electrolyte complex in a Li-ion battery environment. Feasibility studies can be performed at various concentrations and temperatures to determine the optimal level of dopant salt input across a broad frequency range.

The role of conformational change and key glutamic acid residues in the ClC-ec1 antiporter

The triple glutamine (Q) mutant (QQQ) structure of a Cl−/H+ antiporter from Escherichia coli (ClC-ec1) displaying a novel backbone arrangement has been used to challenge the long-held notion that Cl−/H+ antiporters do not operate through large conformational motions. The QQQ mutant substitutes the glutamine residue for an external glutamate E148, an internal glutamate E203, and a third glutamate E113 that hydrogen-bonds with E203. However, it is unknown if QQQ represents a physiologically relevant state, as well as how the protonation of the wild-type glutamates relates to the global dynamics. We herein apply continuous constant-pH molecular dynamics to investigate the H+-coupled dynamics of ClC-ec1. Although any large-scale conformational rearrangement upon acidification would be due to the accumulation of excess charge within the protein, protonation of the glutamates significantly impacts mainly the local structure and dynamics. Despite the fact that the extracellular pore enlarges at acidic pHs, an occluded ClC-ec1 within the active pH range of 3.5–7.5 requires a protonated E148 to facilitate extracellular Cl− release. E203 is also involved in the intracellular H+ transfer as an H+ acceptor. The water wire connection of E148 with the intracellular solution is regulated by the charge states of the E113/E203 dyad with coupled proton titration. However, the dynamics extracted from our simulations are not QQQ-like, indicating that the QQQ mutant does not represent the behavior of the wild-type ClC-ec1. These findings reinforce the necessity of having a protonatable residue at the E203 position in ClC-ec1 and suggest that a higher level of complexity exists for the intracellular H+ transfer in Cl−/H+ antiporters.

Electronic control of constant potential capacitive readout of ion-selective electrodes for high precision sensing

Constant potential capacitive readout of ion-selective membranes offers better sensitivity than traditional potentiometry by giving an easily identifiable transient current spike, which can be integrated to give a charge proportional to logarithmic of ion activity. Some concerns of this technique include complex fluidic handling, longer measurement times, baseline drifts and memory effects arising from excess charge accumulation on the capacitor. This work describes an electronic circuit strategy to automate the switching procedure, resulting in rapid and reproducible measurements. In contrast to earlier work, alternating to a reference solution is no longer required for establishing a new current baseline. The open-circuit potential is measured before performing chronoamperometry and its value is applied directly to the sample solution. The intermittent discharging of the capacitor by electronic circuit assures that the potential difference across the capacitor returns again to zero. This electronic capacitive readout system was applied to measure sodium concentration using a 10 μF capacitor to amplify the signal. The precision was found to be improved over direct potentiometry, corresponding to 0.11 mmol L−1 NaCl and 0.13 mmol L−1 NaCl for standard solutions and pooled serum sample, respectively. Using the automated electronic system for ion measurement makes the system more robust while resulting in fast and reliable quantitative measurements.

Ultrafast intraband Auger process in self-doped colloidal quantum dots

Summary Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

Characterization of Electrode-Electrolyte Interfaces in Deep Eutectic Solvents

Deep eutectic solvents (DESs), compromised of hydrogen bond donors and acceptors, are concentrated electrolytes with extremely low volatility and tunable physical properties, and therefore they are promising for large scale energy storage. The electrode-electrolyte interfaces of concentrated and complex electrolytes such as DESs have not been rigorously studied. Owing to the similarity of DESs to ionic liquids (ILs) where a camel shape potential-dependent capacitances have been reported with significant deviations from dilute electrolytes, it will be critical to understanding the DES behavior near polarized surfaces to inform electrochemical kinetics. In this work, the excess charge accumulation of mixtures of choline chloride and ethylene glycol with 1:2 (Ethaline DES composition), 1:4 and 1:6 molar ratios are probed on silver and glassy carbon electrodes via electrochemical impedance spectroscopy. To study the surface species and changes with applied potential, in-situ surface-enhanced Raman spectroscopy was employed on an electrochemically roughened silver substrate as the electrode. Results from these studies suggest Ethaline DES is different than most ILs and present u-shaped differential capacitance and more in line with regular electrolytes. We will present the results from our ongoing studies of the electrode-DES interfaces outlining the impact of composition and electrode material.

Enhancement of reaction rate in small-sized droplets: A combined analytical and simulation study.

Several recent mass spectrometry experiments reveal a marked enhancement of the reaction rate of organic reactions in microdroplets. This enhancement has been tentatively attributed to the accumulation of excess charge on a surface, which in turn can give rise to a lowering of activation energy of the reaction. Here we model the reactions in droplets as a three-step process: (i) diffusion of a reactant from the core of the droplet to the surface, (ii) search by diffusion of the reactant on the surface to find a reactive partner, and finally (iii) the intrinsic reaction leading to bond breaking and product formation. We obtain analytic expressions for the mean search time (MST) to find a target located on the surface by a reactant in both two- and three-dimensional droplets. Analytical results show quantitative agreement with Brownian dynamics simulations. We find, as also reported earlier, that the MST varies as R2/D, where R is the radius of the droplet and D is the diffusion constant of the molecules in the droplet medium. We also find that a hydronium ion in the vicinity can substantially weaken the bond and hence lowers the activation barrier. We observe a similar facilitation of bond breaking in the presence of a static dipolar electric field along any of the three Cartesian axes. If the intrinsic reaction is faster compared to the mean search time involved, it becomes primarily a diffusion-controlled process; otherwise the reaction cannot be accelerated in the droplet medium. The air-droplet interface provides a different environment compared to the interior of the droplet. Hence, we might also expect a completely different mechanism and products in the case of droplet reactions.

Melt Electrospinning Writing of Highly Ordered Large Volume Scaffold Architectures.

The additive manufacturing of highly ordered, micrometer-scale scaffolds is at the forefront of tissue engineering and regenerative medicine research. The fabrication of scaffolds for the regeneration of larger tissue volumes, in particular, remains a major challenge. A technology at the convergence of additive manufacturing and electrospinning-melt electrospinning writing (MEW)-is also limited in thickness/volume due to the accumulation of excess charge from the deposited material repelling and hence, distorting scaffold architectures. The underlying physical principles are studied that constrain MEW of thick, large volume scaffolds. Through computational modeling, numerical values variable working distances are established respectively, which maintain the electrostatic force at a constant level during the printing process. Based on the computational simulations, three voltage profiles are applied to determine the maximum height (exceeding 7 mm) of a highly ordered large volume scaffold. These thick MEW scaffolds have fully interconnected pores and allow cells to migrate and proliferate. To the best of the authors knowledge, this is the first study to report that z-axis adjustment and increasing the voltage during the MEW process allows for the fabrication of high-volume scaffolds with uniform morphologies and fiber diameters.

Generation of surface electron states with a silicon–ultrathin-oxide interface under the field-induced damage of metal–oxide–semiconductor structures

The high-frequency capacitance–voltage characteristics of metal–oxide–semiconductor structures on n-Si substrates with an oxide thickness of 39 A are studied upon being subjected to damage by field stress. It is shown that the action of a high, but pre-breakdown electric field on an ultrathin insulating layer brings about the formation of a large number of additional localized interface electron states with an energy level arranged at 0.14 eV below the conduction band of silicon. It is found that, as the field stress is increased, the recharging of newly formed centers provides the accumulation of excess charge up to 8 × 1012 cm–2 at the silicon–oxide interface. The lifetime of localized centers created under field stress is two days, after which the dependences of the charge localized at the semiconductor–insulator interface on the voltage at the gate after and before field stress are practically the same.

Ozone and dinitrogen monoxide production in atmospheric pressure air dielectric barrier discharge plasma effluent generated by nanosecond pulse superimposed alternating current voltage

The effects of nanosecond pulse superposition to alternating current voltage (NS + AC) on the generation of an air dielectric barrier discharge (DBD) plasma and reactive species are experimentally studied, along with measurements of ozone (O3) and dinitrogen monoxide (N2O) in the exhausted gas through the air DBD plasma (air plasma effluent). The charge-voltage cycle measurement indicates that the role of nanosecond pulse superposition is to induce electrical charge transport and excess charge accumulation on the dielectric surface following the nanosecond pulses. The densities of O3 and N2O in NS + AC DBD are found to be significantly increased in the plasma effluent, compared to the sum of those densities generated in NS DBD and AC DBD operated individually. The production of O3 and N2O is modulated significantly by the phase in which the nanosecond pulse is superimposed. The density increase and modulation effects by the nanosecond pulse are found to correspond with the electrical charge transport and the excess electrical charge accumulation induced by the nanosecond pulse. It is suggested that the electrical charge transport by the nanosecond pulse might result in the enhancement of the nanosecond pulse current, which may lead to more efficient molecular dissociation, and the excess electrical charge accumulation induced by the nanosecond pulse increases the discharge coupling power which would enhance molecular dissociation.

The distribution of excess charges in the diffusion flame of hydrocarbons

The paper discusses the experimental investigation results of the potentials distribution (probing) and the excess charges in diffusion flames of propane and polymers - PMMA (polymethyl methacrylate) and divinyl rubber. The study of the excess charges distribution was made by analysis of flame deformation in the presence of an external lateral electrostatic field. The existence and the accumulation of excess charges in the flame are generally explained on the basis of consideration of the interaction processes of condensed phase particles and charges (electrons) generated during combustion in the presence of a dusty plasma. However, this mechanism does not give the opportunity to consider the sign and magnitude of the excess charges distribution in the flame, depending on the products composition and the value of the oxidant excess. It is unclear how oppositely charged immiscible streams of flame are formed and coexist.

Steric and electric field driven distortions in aromatic molecules: spontaneous and non-spontaneous symmetry breaking.

The structures of molecules form the cornerstone of our chemical knowledge. Lowering of symmetry in closed-shell molecules is often attributed to the Pseudo Jahn-Teller (PJT) distortions wherein non-adiabatic coupling (NAC) between the ground state and excited states creates vibrational instability along specific normal modes. Nevertheless, other factors like steric interactions are also well known in the literature to induce structural distortions. In this article, we consider two specific cases of molecular distortions - the first one being spontaneous for contorted polyaromatic hydrocarbons (c-PAH) where non-bonded repulsions between the two pairs of syn H-atoms in tribenzopyrene, TBP (1), can enforce either a C2v → C2 or C2v → Cs distortion. PJT-effects account for the correct preference of the Cs structure over C2 (by 4.6 kcal mol-1). The second case (non-spontaneous symmetry breaking) is that of benzene (2) and coronene (3) which upon application of sufficiently strong static external electric field develop vibrational instability along q(a2u) to cause D6h → C6v and D6h → C2 distortions for 2 and 3 respectively. An external electric field (FZ) was applied parallel to the aromatic ring of 2-3 for investigation of non-spontaneous symmetry breaking. Such electric field induced structural distortion is understood on the basis of excess charge accumulation of the planar rings which is circumvented by symmetry lowering. PJT effects seem to have significant consequences for identification of global minima amongst several local minimal molecular structures.

Influence of an embedded low-temperature AlN strain relaxation layer on the strain states and the buffer characteristics of GaN films grown on (110) Si substrates by using ammonia molecular beam epitaxy

The effect of a low-temperature AlN strain relaxation layer on the strain state and the leakage characteristics of GaN buffer layers grown on (110) Si substrates by using ammonia molecular beam epitaxy has been investigated. Excess charge accumulation at the position of LT-AlN strain relaxation layer is found to result in a leakage current through the GaN buffer layer that is a few orders of magnitude higher than through the GaN buffer layer without the LT-AlN strain relaxation layer. An approach to grade the Al composition of the LT-AlN layer reduces the detrimental leakage current induced by the use of the LT-AlN layer while keeping the compressive strain state of the GaN buffer layer on a (110) Si substrate. A complete understanding of charge formation in the strain relaxation layer in the GaN buffer layers on (110) Si substrates is required to accomplish a crack-free and dopant-free GaN buffer layers for use in high-power/high-frequency electronic devices.

Experimental Investigation of Electrostatic Reduction in a Gas–Solid Fluidized Bed by an in Situ Corona Charge Eliminator

Accumulation of excess charges on insulated particles due to triboelectric charging can cause various powder industrial hazards. This work developed a novel in situ corona charge eliminator (ICCE) to neutralize the electrostatic charge in a gas–solid fluidized bed. In order to verify the feasibility of this method, variation of the electrostatic voltage, charge-to-mass ratio, and electric field before and after the application of ICCE was systemically investigated. The results showed that, under gas velocities of less than 2 U/Umf, particles were less charged, and the negative corona discharge caused a polarity reversal. As the gas velocity was increased, particles were more charged, and the charges on the particles were only partially neutralized by an identical corona discharge. Further analyses indicate that the charge neutralization efficiency was significantly influenced by both the triboelectric- and corona-charging processes. The superficial gas velocity was found to have a strong influence on the above two charging processes, and the charge neutralization efficiency favored a larger gas velocity. Besides, the equilibrium charge of the particles after the application of ICCE strongly depended on the initial charge accumulation in the fluidized bed.

Feedback control of electrode offset voltage during functional electrical stimulation

Control of the electrode offset voltage is an important issue related to the processes of functional electrical stimulation because excess charge accumulation over time damages both the tissue and the electrodes. This paper proposes a new feedback control scheme to regulate the electrode offset voltage to a predetermined reference value. The electrode offset voltage was continuously monitored using a sample-and-hold (S/H) circuit during stimulation and non-stimulation periods. The stimulation current was subsequently adjusted using a proportional–integral (PI) controller to minimise the error between the reference value and the electrode offset voltage. During the stimulation period, the electrode offset voltage was maintained through the S/H circuit, and the PI controller did not affect the amplitude of the stimulation current. In contrast, during the non-stimulation period, the electrode offset voltage was sampled through the S/H circuit and rapidly regulated through the PI controller. The experimental results obtained using a nerve cuff electrode showed that the electrode offset voltage was successfully controlled in terms of the performance specifications, such as the steady- and transient-state responses and the constraint of the controller output. Therefore, the proposed control scheme can potentially be used in various nerve stimulation devices and applications requiring control of the electrode offset voltage.

Oxidation of Magnesia-Supported Pd30 Nanoclusters and Catalyzed CO Combustion: Size-Selected Experiments and First-Principles Theory

Experimental and theoretical investigations of the oxidation reaction of CO to form carbon dioxide, catalyzed by size-selected Pd30 clusters soft-landed on MgO(100), are described. The consequences of pretreatment of the deposited clusters with molecular oxygen, 16O2, at a temperature of ∼370 K followed by annealing at around 450 K are explored. Subsequent to the above pretreatment stage, the system was cooled to 120 K, and after exposure to 18O2 and 13C16O the temperature was ramped and a temperature-programmed reaction (TPR) spectrum recorded. The onset of catalyzed combustion of CO starts at a temperature of 180 K, and the TPR spectrum shows oxidation to occur over a broad temperature range, up to 550 K. Using first-principles density-functional theory, the optimal adsorption geometry of the Pd30 cluster on the MgO(100) surface is found to be a square-base pyramidal structure, with an excess electronic charge of 1.25e, originating from the underlying magnesia support, found to be localized near the interfacial region of the cluster with the supporting surface. Structural and energetic properties of a variety of oxygen adsorption sites on the supported palladium cluster and effects due to multiple adsorbed O2 molecules were explored. It is found that the barriers for dissociation of the adsorbed molecules depend strongly on the locations of the adsorption sites, with very small (<0.1 eV) dissociation energy barriers found for adsorption sites on the Pd30 cluster that are closer to its interface with the Mg(100) surface. This correlates with our finding that adsorption at these interfacial sites is accompanied by excess charge accumulation on the adsorbed molecule through excess partial (0.25e) occupation of the molecular antibonding 2π* orbital, resulting in activation of the molecule to a peroxo-like state. This activation mechanism depletes the excess charge on the cluster, resulting in a self-limiting partial oxidation of the cluster. The information obtained through isotope labeling in the TPR experiments is explored through first-principles quantum simulations of various reaction pathways, with a focus on the multiple coadsorption system Pd30O10(CO)13/MgO. These theoretical calculations allow us to correlate the measured isotope and temperature-dependent TPR features, with operative Langmuire–Hinshelwood, LH, and Mars–van Krevelen-type (MvK) reaction mechanisms, catalyzed by the partially oxidized cluster. The LH mechanism was found to contribute to the reaction at lower temperatures, while the MvK dominates for higher temperatures.

Analyzing photovoltaic effect of double-layer organic solar cells as a Maxwell-Wagner effect system by optical electric-field-induced second-harmonic generation measurement

By using time-resolved optical electric-field-induced second-harmonic generation measurement, we directly probed photo-voltage generation process in organic double-layer (pentacene/C60) solar cells. Results showed that photoillumination induced negative excess charge Qs = −3.6 × 10−9 C/cm2 at the pentacene/C60 interface, and the induced charge caused generation of the open-circuit voltage 0.26 V. Using an equivalent circuit based on a Maxwell-Wagner (MW) effect model well accounted for the excess charge accumulation process. The MW model analysis also well accounted for the open-circuit voltage, the short-circuit current, and the fill-factor of organic solar cells (OSCs). We concluded that the excess charges due to the MW effect give a significant effect on the photovoltaic effect of OSCs.

An Active Approach for Charge Balancing in Functional Electrical Stimulation

Charge balancing is a major concern in functional electrical stimulation, since any excess charge accumulation over time leads to electrolysis with electrode dissolution and tissue destruction. This paper presents a new active approach for charge balancing using long-term offset regulation. Therefore, the electrode voltage is briefly monitored after each stimulation cycle and checked if it remains within a predefined voltage range. If not, an offset current is adjusted in order to track the biphasic current mismatch in upcoming stimulations. This technique is compared to a previously introduced active charge balancer as well as commonly used passive balancing techniques. Subsequently, the techniques are verified through experiments on a platinum black electrode in 0.9% saline solution.

Photocatalytic production of hydrogen in systems based on Cd x Zn1–x S/Ni0 nanostructures

A relation was established between the composition of Cd x Zn1–x S nanoparticles and their ability to accumulate excess negative charge during irradiation. The rate of expenditure of the accumulated charge depends on the composition of the nanoparticles and is determined by their electric capacitance. A correlation was found between the photocatalytic activity of the Cd x Zn1–x S nanoparticles in the release of hydrogen from solutions of Na2SO3, their composition, and their capacity for photoinduced accumulation of excess charge. It was shown that Ni0 nanoparticles photodeposited on the surface of Cd x Zn1–x S are effective cocatalysts for the release of hydrogen. It was found that ZnII additions in photocatalytic systems based on Cd x Zn1–x S/Ni0 nanostructures have a promoting action on the release of hydrogen from water–ethanol mixtures.

Complexation of the Carbonate, Nitrate, and Acetate Anions with the Uranyl Dication: Density Functional Studies with Relativistic Effective Core Potentials

The structures and vibrational frequencies of uranyl carbonates, [UO2(CO3)n](2-2n) and [(UO2)3(CO3)6]6-, uranyl nitrates, [UO2(NO3)n](2-n), and uranyl acetates, [UO2(CH3COO)n](2-n) (n = 1,2,3) have been calculated by using local density functional theory (LDFT). Only bidentate ligand coordination modes to the uranyl dication have been modeled. The calculated structures and frequencies are compared to available experimental data, including IR, Raman, X-ray diffraction, and EXAFS solution and crystal structure data. The energetics of ligand binding have been calculated using the B3LYP hybrid functional. In general, the structural and vibrational results at the LDFT level are in good agreement with experimental results and provide realistic pictures of solution phase and solid-state behavior. For the [UO2(CO3)3]6- anion, calculations suggest that complexity in the CO3(2-) stretching signature upon complexation is due to the formation of C=O and C-O domains, the latter of which can split by as much as 300 cm(-1). Assessment of the binding energies indicate that the [UO2(CO3)2]2- anion is more stable than the [UO2(CO3)3]4- anion due to the accumulation of excess charge, whereas the tri-ligand species are the most stable in the nitrate and acetate anions.

Surface charging and current collapse in an AlGaN∕GaN heterostructure field effect transistor

This work investigates the correlation between surface charging and current collapse in an AlGaN∕GaN heterostructure field effect transistor. Surface charging due to applied biases was sensed by mapping the surface potential between the gate and drain using scanning Kelvin probe microscopy. Due to the bias, the surface band bending near the gate edge was observed to increase by as much as 1 eV. This increase of band bending is caused by an accumulation of excess charge near the surface during the applied bias. By varying the duration of the applied bias, we find that this accumulation of excess charge near the gate takes about 20 s to saturate. Continuous monitoring of the surface potential after switching off the bias shows that a complete relaxation of the excess band bending requires about 800 s. Drain current transient measurements show that the collapse and recovery of the drain current also occur on similar time scales. This correlation between time scales indicates that the accumulation of excess charge near the gate edge causes current collapse by depletion of the channel.