Charge Stability Research Articles

Polylactic Acid/Calcium Stearate Hydrocharging Melt-Blown Nonwoven Fabrics for Respirator Applications.

Non-biodegradable polypropylene, which poses a serious threat to the environment, is the most utilized material in air filtration systems. Moreover, under conditions of high temperature and high humidity, the electrostatic charge in melt-blown nonwoven fabrics treated with traditional corona electrets will quickly dissipate. Here, biodegradable polylactic acid, calcium stearate, and an innovative hydrocharging technique are reported to develop environmentally friendly polylactic acid/calcium stearate hydrocharging melt-blown nonwoven fabrics with high charge stability. Compared with polylactic acid melt-blown nonwoven fabrics, the crystallization structure and charge storage of polylactic acid/calcium stearate melt-blown nonwoven fabrics have been greatly improved due to the presence of calcium stearate. In PM0.3, it exhibited a high filtration efficiency (96.78%), a low pressure drop (65.20 Pa), and a good quality factor (0.053 Pa-1), which can meet the N95 respirator standard. Furthermore, it is worth mentioning that the filtration performance remained at a high level (>95.00%) after 2 months. Importantly, based on the test and analysis of surface electrostatic potential, crystallization, and charge storage and distribution, we proposed plausible charge generation and stable storage mechanisms. It demonstrated more potential for electret air filtration and smart respirators as the further possible step of research in the field.

Bismuth Metal–Organic Framework/Carbon Nanosphere Composites for Ultrasensitive Simultaneous Electrochemical Detection of Lead and Cadmium

An amino-functionalized bismuth metal–organic framework (Bi-BDC-NH2) composited with nitrogen-doped mesoporous carbon nanosphere (NMCS) was prepared to fabricate a Bi-BDC-NH2@NMCS electrochemical sensor for simultaneous determination of Pb(II) and Cd(II). The synthesized Bi-BDC-NH2 was granular, amorphous, and loosely aggregated to form a porous structural composition where NMCS was embedded. The large specific area and exposed sites of Bi-BDC-NH2@NMCS copromote the adsorption and electron transfer of metal ions on the electrode surface. Compared with the traditional bismuth film electrode, the Bi-BDC-NH2@NMCS electrode can improve the charge transfer, stability, and conductivity. The developed method exhibited superior stripping performance with a detection limit of 0.36 ng mL–1 for Pb(II) and 0.44 ng mL–1 for Cd(II), respectively, and a linear range of 1.0–1500 ng mL–1. It was applied to detect Pb(II) and Cd(II) in liver, fish, and shrimp samples with recoveries of 93.6–99.7% and 94.4–103.2%, respectively.

Effects of Fabrication Conditions on the Partial Discharge Mitigation Performance of Electrets for Power Electronic Driven Systems

In our previous studies, we have shown that electrets can be designed to mitigate partial discharge (PD) in power electronic converter (PEC)-driven systems by neutralizing locally-enhanced harmful electric fields. Surface charge density is one of the main factors that determines the PD mitigation performance of electrets. In this study, we fabricate electrets from polyvinylidene fluoride (PVDF) films under various charging conditions including voltage magnitude, charging duration, voltage polarity, and temperature using triode-corona discharge method. The surface charge density and PD mitigation performance of the fabricated electret films are assessed by surface potential measurements and PD experiments. <styled-content style="color:black">The effects of fabrication temperature on electret surface charge stability, and the impacts of atmospheric conditions on electret surface charge density and PD magnitude are discussed.</styled-content> This study provides knowledge that is essential for establishing the fabrication conditions of electrets that can effectively mitigate PD in PEC-driven systems.

Monosodium glutamate as an effective electrolyte additive in lead acid battery

High-rate partial state of charge (HRPSoC) life and stability of lead-acid batteries are largely limited by the surface morphology of lead sulfate and the reactivity of anode plates. In this study, sodium glutamate (MSG) was introduced as an electrolyte additive for lead-acid battery to improve lead sulfate deposition process and lead sulfate crystal morphology at the interface between lead anode and sulfuric acid electrolyte, and the influence of MSG on battery performance were explored. By electrochemical tests and material characterization, it was proved that glutamic acid anion can promote the formation of uniform deposition of lead sulfate with a structure similar to stacked flakes, which make it easy to form active lead and restrain irreversible sulfate during the fast charging and discharging process.

Theory of multidimensional quantum capacitance and its application to spin and charge discrimination in quantum dot arrays

Quantum states of a few-particle system capacitively coupled to a metal gate can be discriminated by measuring the quantum capacitance, which can be identified with the second derivative of the system energy with respect to the gate voltage. This approach is here generalized to the multivoltage case, through the introduction of the quantum capacitance matrix. The matrix formalism allows us to determine the dependence of the quantum capacitance on the direction of the voltage oscillations in the parameter space and to identify the optimal combination of gate voltages. As a representative example, this approach is applied to the case of a quantum dot array, described in terms of a Hubbard model. Here, we first identify the potentially relevant regions in the multidimensional voltage space with the boundaries between charge stability regions, determined within a semiclassical approach. Then, we quantitatively characterize such boundaries by means of the quantum capacitance matrix. Altogether, this provides a procedure for optimizing the discrimination between states with different particle numbers and/or total spins.

Efficient Synthesis, Spectroscopic Characterization, and Nonlinear Optical Properties of Novel Salicylaldehyde-Based Thiosemicarbazones: Experimental and Theoretical Studies.

Currently, we reported the synthesis of six novel salicylaldehyde-based thiosemicarbazones (BHCT1-HBCT6) via condensation of salicylaldehyde with respective thiosemicarbazide. Through various spectroscopic methods, UV-visible and NMR, the chemical structures of BHCT1-HBCT6 compounds were determined. Along with synthesis, a computational study was also performed at the M06/6-31G(d,p) functional. Various analyses such as natural bond orbital (NBO) analysis, natural population analysis, frontier molecular orbital (FMO) analysis, and molecular electrostatic potential surfaces were carried out to understand the nonlinear optical (NLO) characteristics of the synthesized compounds. Additionally, a comparative study was carried out between DFT and experimental results (UV-vis study), and a good agreement was observed in the results. The energy gap calculated through FMOs was found to be in decreasing order as 4.505 (FHCT2) > 4.499 (HBCT6) > 4.497 (BHCT1) = 4.497(HMCT5) > 4.386 (CHCT3) > 4.241(AHCT4) in eV. The global reactivity parameters (GRPs) were attained through E HOMO and E LUMO, which described the stability and hardness of novel compounds. The NBO approach confirmed the charge delocalization and stability of the molecules. Among all the investigated compounds, a larger value (557.085 a.u.) of first hyperpolarizability (βtot) was possessed by CHCT3. The NLO response (βtot) of BHCT1-HBCT6 was found to be 9.145, 9.33, 13.33, 5.43, 5.68, and 10.13 a.u. times larger than that of the standard para-nitroaniline molecule. These findings ascertained the potential of entitled ligands as best NLO materials for a variety of applications in modern technology.

Reduced basis emulation of pairing in finite systems

In recent years, reduced basis methods (RBMs) have been adapted to the many-body eigenvalue problem and they have been used, largely in nuclear physics, as fast emulators able to bypass expensive direct computations while still providing highly accurate results. This work is meant to show that the RBM is an efficient and accurate emulator for the strong correlations induced by the pairing interaction in a variety of finite systems like ultrasmall superconducting grains, interacting topological superfluids and mesoscopic hybrid superconductor-semiconductor devices, all of which require an expensive, beyond-mean-field, particle-number conserving description. These systems are modelled by the number-conserving Richardson pairing Hamiltonian and its appropriate generalizations. Their ground state is solved for exactly using the Density Matrix Renormalization Group. The reduced basis is assembled iteratively from a small number of exact ground state vectors, well-chosen from across the relevant parameter space using a fast estimate of the emulation error and a greedy local optimization algorithm. The reduced basis emulation is found to accurately describe the weak-to-strong pairing cross-over in small grains, the third-order topological phase transition of the interacting Richardson-Kitaev chain, and the complex charge stability diagram of a hybrid quantum dot - superconductor device. RBMs are thus confirmed to be cheap and accurate emulators for the widely encountered superconducting phenomena. Capable of providing orders of magnitude computational speed-up with respect to approaches based only on traditional many-body solvers, they open new possibilities in building and solving models of interacting many-body systems and in better interfacing them with experimental design and data analysis.

Cathode electrocatalyst in aprotic lithium oxygen (Li-O2) battery: A literature survey

Lithium oxygen battery (LOB) is a highly promising energy storage device for the next generation electric vehicles due to its high theoretical energy density. However, many challenges hinder its practical application. The electrochemical performances, such as discharge capacity, discharge and charge overpotentials, power density and stability are all far from satisfactory. In recent years, a great progress has been made and numerous works on cathode materials have been published. This article focuses on the state-of-the-art of LOB cathode materials and the reaction mechanism happens on the cathode. The principles of cathode reactions are summarized and the requirements for cathode materials are discussed. The performance of LOBs with carbon-based and carbon free cathode materials are described. The approaches on improving the cathode performance via temperature increase, material surface engineering, texture optimization and oxygen vacancy regulation are elaborated. A perspective on the research trend on the cathode catalyst is finally proposed.

Charge stabilization of shallow nitrogen-vacancy centers using graphene/diamond junctions

We studied the charge-state stabilization of shallow nitrogen-vacancy (NV) centers in (111) diamond using graphene/diamond junctions. Measurement of the fluorescence stability and evaluation of the charge-state stability were conducted on the NV centers at the graphene and the graphene-free region. The results revealed that about half of the total NV centers (NV0 + NV−) at the graphene-free region were unstable, while over 90% of the measured NV centers at the graphene region were stabilized as NV− centers. Graphene/diamond junctions contribute significantly to charge-state stabilization of shallow NV− centers in (111) diamond.

5.7% Efficiency Si Photoanodes for Solar Water Splitting Catalyzed by Vertically Grown and Oxygen‐Vacancy‐Rich NiFe Hydroxides

AbstractThe sluggish oxygen evolution reaction (OER) kinetics and adverse charge transfer and stability at the multi‐interfaces from Si to electrolyte severely impede the application of Si photoanodes. Herein, oxygen vacancy (OV)‐rich NiFe‐layered hydroxides (NiFe‐OH) nanosheet arrays are vertically orientated on Ni‐protected Si photoanodes by a facile solvothermal method followed by a hot Fe ion‐exchange treatment. By virtue of the formation of OVs on NiFe‐OH nanosheets and the vertical contact between the NiFe‐OH and Si substrate, the as‐prepared Si photoanode not only enables abundant active sites for OER but also boosts charge and mass transfer when compared to traditional electro‐deposit samples. Moreover, the vertical contact of NiFe‐OH on Ni/Si benefits to release the interfacial stress and thereby promotes the electrode stability. Consequently, the optimal Si photoanode shows an ultrahigh applied bias photon‐to‐current efficiency of 5.7% and a good stability of over 200 h, outdoing almost all of the recently reported Si photoanodes.

Triboelectric Nanogenerators for Efficient Low-Frequency Ocean Wave Energy Harvesting with Swinging Boat Configuration

To reach ocean resources, sea activities and marine equipment variety are increasing, requiring offshore energy supply. Marine wave energy, the marine renewable energy with the most potential, offers massive energy storage and great energy density. This research proposes a swinging boat-type triboelectric nanogenerator concept for low-frequency wave energy collection. Triboelectric electronanogenerators with electrodes and a nylon roller make up the swinging boat-type triboelectric nanogenerator (ST-TENG). COMSOL electrostatic simulations and power generation concepts of independent layer and vertical contact separation modes of operation explain the device functionality. By rolling the drum at the bottom of the integrated boat-like device, it is possible to capture wave energy and convert it into electrical energy. Based on it, the ST load, TENG charging, and device stability are evaluated. According to the findings, the maximum instantaneous power of the TENG in the contact separation and independent layer modes reaches 246 W and 112.5 μW at matched loads of 40 MΩ and 200 MΩ, respectively. Additionally, the ST-TENG can retain the usual functioning of the electronic watch for 45 s while charging a 33 µF capacitor to 3 V in 320 s. Long-term low-frequency wave energy collection is possible with the device. The ST-TENG develops novel methods for large-scale blue energy collection and maritime equipment power.

Recent Progress on Synthesis, Intrinsic Properties and Optoelectronic Applications of Perovskite Single Crystals

AbstractMetal halide perovskite have shown great potential for applications in photovoltaics, light‐emitting diodes and photon detectors, mainly owing to their superb optoelectronic properties, low‐cost raw materials and facile fabrication process. Although, polycrystalline perovskite thin‐films have been actively investigated for preparing various optoelectronic devices, the presence of detrimental defects at grain boundaries, serious ion migration and limited stability unfortunately hinder their device performance and practical application. As a contrast, perovskite single crystals (SCs) exhibit no grain boundaries, much lower trap density and much improved stability, hence providing a more attractive choice for not only optoelectronic device applications but also fundamental research. In this review, recent progress in the growth methods of perovskite SCs is summarized, followed by giving a detailed introduction of the intrinsic properties of perovskite SCs including optical properties, defects, charge carrier dynamics, ion migration and stability. On these base, the applications of perovskite SCs in various optoelectronic devices like solar cells, photodetectors, and radiation detectors are discussed, where the relationship between the composition, device architecture and device performance is highlighted. Finally, a tentative discussion on the current challenges and future opportunities in the development of perovskite SCs and optoelectronic devices is presented.

On the stability of charge and spin order in the spin-one-half Falicov–Kimball model with the Ising-type Hund coupling

Density matrix renormalization group (DMRG) method is used to study effects of various factors on the stability of charge and spin order in the spin-one-half Falicov–Kimball model with the Ising-type Hund coupling Jz. In particular we examine effects of (i) the exchange interaction (J) between d and f electrons, which is responsible for spin-flip processes, (ii) the f-electron hopping (tf) and (iii) the interband d–f hybridization V. It is shown that for all mentioned generalizations there exists some critical value of the exchange interaction (Jc), the f-electron hopping (tfc) and the interband d–f hybridization Vc at which the magnetic order detected within the spin-one-half Falicov–Kimball model with the Ising interaction is broken. Above these critical points new types of spin orderings are generated, and namely, spin density waves commensurate with charge density waves detected at J=0 in the case of exchange interaction and spin separated phases in the case of f-electron hopping (hybridization), which are at sufficiently large tf (V) replaced by homogeneous phases.

Thermal, Electrical, and Environmental Safeties of Sulfide Electrolyte-Based All-Solid-State Li-Ion Batteries.

The next generation of all-solid-state lithium-ion batteries (ASLIBs) based on solid-state sulfide electrolytes (SSEs) is closest to commercialization. Understanding the overall safety behavior of SSE-ASLIBs is necessary for their product design and commercialization. However, their safety behavior in real-life situations, such as battery exposure to high temperature, overcharge, mechanical rupture, and air exposure, remains largely unknown. Herein, we report preliminary but needed evidence of (i) significantly improved resistance to electrical shorting at high temperatures, (ii) reduced heat generation when subjected to excessive heat, (iii) tolerable harmful gas generation when subjected to air exposure followed by high-temperature heating, and (iv) high-voltage charge stability when a battery is overcharged (5.5 V charge) in SSE-based ASLIBs compared to commercial liquid electrolyte-based LIBs (LE-LIBs). Furthermore, the result shows that SSEs can self-induce a fast and effective battery shut-down capability in ASLIBs and avoid thermal runaway upon mechanical damage and exposure to air.

Excitation Wavelength-Dependent Charge Stabilization in Highly Interacting Phenothiazine Sulfone-Derived Donor–Acceptor Constructs

Prolonging the lifetime of charge-separated states (CSS) is of paramount importance in artificial photosynthetic donor-acceptor (DA) constructs to build the next generation of light-energy-harvesting devices. This becomes especially important when the DA constructs are closely spaced and highly interacting. In the present study, we demonstrate extending the lifetime of the CSS in highly interacting DA constructs by making use of the triplet excited state of the electron donor and with the help of excitation wavelength selectivity. To demonstrate this, π-conjugated phenothiazine sulfone-based push-pull systems, PTS2-PTS6 have been newly designed and synthesized via the Pd-catalyzed Sonogashira cross-coupling followed by [2 + 2] cycloaddition-retroelectrocyclization reactions. Modulation of the spectral and photophysical properties of phenothiazine sulfones (PTZSO2) and terminal phenothiazines (PTZ) was possible by incorporating powerful electron acceptors, 1,1,4,4-tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD (exTCBD). The quadrupolar PTS2 displayed solvatochromism, aggregation-induced emission, and mechanochromic behaviors. From the energy calculations, excitation wavelength-dependent charge stabilization was envisioned in PTS2-PTS6, and the subsequent pump-probe spectroscopic studies revealed charge stabilization when the systems were excited at the locally excited peak positions, while such effect was minimal when the samples were excited at wavelengths corresponding to the CT transitions. This work reveals the impact of wavelength selectivity to induce charge separation from the triplet excited state in ultimately prolonging the lifetime of CCS in highly interacting push-pull systems.

Improving Out-of-Plane Charge Mobility and Phase Stability of Dion-Jacobson Lead-Free Perovskites via Intercalating π-Conjugated Aromatic Spacers.

The layered quasi-2D perovskites are recognized as one of the effective strategies to resolve the big problem of intrinsic phase instability of the perovskites. However, in such configurations, their performance is fundamentally limited due to the correspondingly weakened out-of-plane charge mobility. Herein, the π-conjugated p-phenylenediamine (PPDA) is introduced as organic ligand ions for rationally designing lead-free and tin-based 2D perovskites with the aid of theoretical computation. It is evidenced that both out-of-plane charge transport capacity and stability can be significantly enhanced within as-established quasi-2D Dion-Jacobson (DJ) (PPDA)Csn -1 Snn I3 n +1 perovskites. The obviously increased electrical conductivity and reduced carrier effective masses are attributed to the enhanced interlayer interactions, limited structural distortions of diamine cations, as well as improved orbital coupling between Sn2+ and I- ions of (PPDA)Csn -1 Snn I3 n +1 perovskites. Accordingly, by dimension engineering of the inorganic layer (n), the bandgap (Eg ) of quasi-2D perovskites can be linearly tailored toward the suitable Eg (1.387eV) with optimal photoelectric conversion efficiency (PCE) of 18.52%, representing their great potential toward promising applications in advanced solar cells.

Highly Coupled Heterobicycle-Fused Porphyrin Dimers: Excitonic Coupling and Charge Separation with Coordinated Fullerene, C60.

Porphyrin dimers have been widely explored and studied owing to their importance in photosynthetic systems. A vast variety of dimers linked by different groups and at different angles have been synthesized and studied; however, the means by which to synthesize rigidly fused porphyrins with direct conjugation of the chromophores remains limited. Such a class of porphyrins may possess interesting properties that unconjugated or stacked dimers may not exhibit. In this study, bisbenzimidazole-fused porphyrin dimers and their mono- and bis-zinc derivatives are synthesized and characterized. As a consequence of excitonic coupling, these dimers exhibit a split Soret band irrespective of the metal ion in the porphyrin cavity. Steady-state fluorescence and excitation spectra followed by femtosecond transient absorption spectral studies of the heterometallated dimer, (free-base and zinc porphyrin) reveals the occurrence of efficient singlet-singlet energy transfer (>95 % efficiency and rate constant >1012 s-1 ) within the dyad. Further, donor-acceptor conjugates were formed by metal-ligand axial coordination of phenyl imidazole functionalized C60 and were characterized by a variety of physicochemical techniques. Excited state charge separation from both singlet and triplet excited states of ZnP in the conjugates has been established. The lifetime of the final charge-separated state was in the 30-40 μs range revealing charge stabilization. Interestingly, no charge separation in the conjugate derived from the heterometallated dimer was observed wherein excitation transfer dominated the process. The present study brings out the importance of the rigid π-spacer connecting porphyrin dimers in governing the energy and electron transfer events when coupled with an electron acceptor.

Un estudio comparativo de diferentes compuestos de poli(3-hexiltiofeno)-carbono como capas transportadoras de huecos sobre la estabilidad de celdas solares de perovskita preparadas bajo condiciones ambientales

Hole transport layers (HTLs) play an important role in efficiency and stability of perovskite solar cells (PSCs).&nbsp; Most of the highly efficient PSCs use spiro-OMeTAD doped with Li-TFSI as HTLs, which has to be prepared under inert atmosphere, because the hygroscopic feature of the lithium salt deteriorates the stability of PSCs under ambient conditions. In this work, we report a comparative study of the electrical and morphological properties of different poly(3-hexylthiophene) (P3HT) thin films: pristine, doped with FeCl3, and composites with carbon nanotubes (CNT) or reduced graphene oxide (rGO). Although the electrical conductivity of P3HT films is found to increase with any of those modification methods, the photovoltaic performance of PSCs is highly dependent on the modification agent. P3HT:FeCl3 reduces the photocurrent density of PSCs, while the addition of rGO in P3HT improves charge extraction and stability of PSCs. Furthermore, the insertion of conductive carbon paint between P3HT and the metal contact maintains the original efficiency of non-encapsulated PSCs after continuous illumination for 30 min. It is concluded that carbon modifications in P3HT based HTL can improve the stability of perovskite solar cells totally fabricated under ambient conditions.

Parylene as an electret for condenser microphones

Electrets in condenser microphones are typically made from varieties of Teflon. This work evaluates different formulations and thicknesses of vapor deposited Parylene electrets as potential alternatives to Teflon. Parylene-coated condenser backplates used in this study were obtained from two different suppliers, as a third variable in addition to formulation and thickness. Long-term charge stability of the electrets was tested with a thermally stimulated discharge (TSD) method. Charge stability was also evaluated by building the charged backplates into condenser microphones and running them through environmental accelerated-life testing. Standard PTFE and FEP Teflon backplates were used as controls in these tests. The experiments showed clear differences in the long-term charge stability of the Parylene electrets due to thickness, formulation, and supplier. Several combinations of thickness, formulation, and supplier were found to perform comparably to traditional Teflon electrets and appear suitable for use in high-end condenser microphones.

Charge diffusion in relativistic resistive second-order dissipative magnetohydrodynamics

We study charge diffusion in relativistic resistive second-order dissipative magnetohydrodynamics. In this theory, charge diffusion is not simply given by the standard Navier-Stokes form of Ohm's law, but by an evolution equation which ensures causality and stability. This, in turn, leads to transient effects in the charge diffusion current, the nature of which depends on the particular values of the electrical conductivity and the charge-diffusion relaxation time. The ensuing equations of motion are of so-called stiff character, which requires special care when solving them numerically. To this end, we specifically develop an implicit-explicit Runge-Kutta method for solving relativistic resistive second-order dissipative magnetohydrodynamics and subject it to various tests. We then study the system's evolution in a simplified 1+1-dimensional scenario for a heavy-ion collision, where matter and electromagnetic fields are assumed to be transversely homogeneous, and investigate the cases of an initially non-expanding fluid and a fluid initially expanding according to a Bjorken scaling flow. In the latter case, the scale invariance is broken by the ensuing self-consistent dynamics of matter and electromagnetic fields. However, the breaking becomes quantitatively important only if the electromagnetic fields are sufficiently strong. The breaking of scale invariance is larger for smaller values of the conductivity. Aspects of entropy production from charge diffusion currents and stability are also discussed.