Open-circuit Conditions Research Articles

Influence of voids on the thermal and light stability of perovskite solar cells.

The formation of voids in perovskite films close to the buried interface has been reported during film deposition. These voids are thought to limits the efficiency and stability of perovskite solar cells (PSCs). Here, we studied the voids formed during operation in perovskite films that were optimized during the solution deposition process to avoid voids. New voids formed during operation are found to assemble along grain boundaries at the bottom interface, caused by the loss of residual solvent and conversion of amorphous phase to crystalline phase. Unexpectedly, the formation of these voids did not negatively affect the stability of PSCs. Decreasing the amorphous region in perovskites by thermal annealing decreased the positive iodide interstitial density, and improved the light stability of PSCs. The annealed devices maintained 90% of their initial efficiency and light soaking for 1900 hours at open circuit condition under 1-sun illumination at 50°C.

Vibration characteristics of sandwich plates with GPLRC core and piezoelectric face sheets with various electrical and mechanical boundary conditions

An analysis is performed in the current investigation to study the vibrations of composite laminated plates integrated with piezoelectric layers. Composite laminated plate is reinforced with graphene platelets (GPLs). Also the amount of GPLs in the layers may be different which results in a piecewise functionally graded (FG) media. Elasticity modulus of the GPLRC media is obtained by means of the Halpin-Tsai rule which contains efficiency parameters to capture the size of reinforcements. First order shear deformation theory of plates and parabolic distribution of electric field through the piezoelectric layers are assumed as the basic assumption. For the piezoelectric layers, both the open circuit and closed circuit conditions are applied. The total strain and kinetic energies of the plate are obtained. After that by means of the general idea of the Ritz method and also Chebyshev polynomials as the basic shape functions, the matrix representation of the equations of motion dealing with free vibration of sandwich plate with piezoelectric face sheets are obtained. Results of this study are first compared with the available data in the open literature. After that novel results are given to explore the effects of different parameters such as the electrical and mechanical boundary conditions, plate geometry, GPL weight fraction and GPL distribution profile. It is shown that with introduction of GPLs, frequencies of the plate may be enhanced for both closed circuit and open circuit conditions.

Influence of depolarization field on temperature-misfit strain phase diagram of PbZr0.4Ti0.6O3 ultrathin films

Phase-field simulations are performed to study domain structures in (001)-oriented PbZr0.4Ti0.6O3 epitaxial thin films. Temperature-misfit strain phase diagrams of the domain structures are constructed under various depolarization fields by adjusting surface screening conditions and film thickness. We find that the vortex-array state area in the phase diagram enlarges with the decrement of the depolarization field, which is contrary to the general view of depolarization field conductive to vortex formation. Moreover, a strain-mediated ferroelectric failure mechanism is found, wherein the ferroelectric characteristics of an ultrathin film with a thickness of 4 nm completely disappear (Curie temperature drops to 0 K) under the open-circuit condition when the compressive misfit strain drops to −2.69%. The results guide further understanding and manipulation of domain structures in ferroelectric nanomaterials.

Mathematical Model for SEI Growth under Open-Circuit Conditions

A solid electrolyte interphase (SEI) growth model is developed in a mixed mode that contains solvent diffusion through the SEI layer and corresponding solvent reduction kinetics at the SEI/electrode interface. The governing equations are solved by the Landau transformation, which makes the moving layer fixed to predict the open circuit potential, SEI layer thickness, and capacity loss. The estimated parameters fitted with experimental data from the literature are computed using COMSOL and MATLAB. Results show that the mixed mode model predicts lower capacity loss and thinner SEI layer due to its growth under open circuit conditions than previously reported by others.

A Fault-Tolerant Power Converter With Multi-Switch Fault Diagnosis and Repair Capability for 4-Phase 8/6 SRM Drives

In this article, a modular fault-tolerant power converter for 8/6 four-phase switched reluctance motor (SRM) drives is presented. The proposed converter can work for both open-circuit (OC) and short-circuit (SC) fault conditions in the power semiconductor switches. A semiconductor switch module and a relay circuit are used for achieving the fault tolerance feature. The proposed converter is modular and provides independent fault-tolerant control for all phases. It also uses a minimum number of switches when compared with other fault-tolerant converter topologies. The proposed converter is tested for a fault in single as well as multiple phases using MATLAB/Simulink software and is validated experimentally on a 0.6 hp 8/6 SRM using an FPGA-based hardware setup developed in the laboratory. Detailed results are presented and compared with existing fault-tolerant converter topologies. A fault repair time of 2 ms has been achieved for both open and SC faults.

HF-Based Sensorless Control of a FTPMM in Ship Shaftless Rim-Driven Thruster System

Take a dual-winding permanent magnet fault tolerant motor (FTPMM) in the ship shaftless rim-driven thruster (RDT) as the research object, the position sensorless control algorithm based on high frequency (HF) current injection is presented to estimate the rotor position and the rotor position signal is extracted from the voltage. In order to reduce influences of proportional-integral (PI) controller, current regulators and voltage calculation errors, the generalized second-order integrator (SOGI) is discussed along with how to combine with the low-speed sensorless control. And the current vector fault-tolerant control strategy is applied to compensate for the faulty phase current with other healthy phase currents. The rotor position at low speed is estimated under healthy as well as open-circuit faulty conditions by using the HF current injection algorithm based on SOGI (HF-SOGI). After simulation in Matlab/Simulink, the experimental results further demonstrate the feasibility of the HF-SOGI strategy by the FTPMM experimental setup. It can be calculated that the rotor speed ripple is decreased obviously after fault-tolerant control strategy is applied. It can be concluded that the HF-SOGI strategy can estimate the position accurately, which can further improve the reliability and application scope of FTPMM and the RDT system.

An Enhanced Battery Aging Model Based on a Detailed Diffusing Mechanism in the SEI Layer

The impetus for this study is the lack of a detailed knowledge on the formation mechanism of the solid electrolyte interface (SEI) layer and the diffusion mechanisms within this layer that impacts the predictive abilities of the current mathematical models. Specifically, most models continue to employ a constant value of diffusion coefficient along with several lumped fitting parameters, instead of a variable formulation that is dependent on the temperature and concentration of Li-ions, to characterize Li-ion batteries (LIBs). As a result, the current models fail in predicting the capacity fading accurately. In overcoming this gap, we have employed a previously proposed temperature and concentration-dependent diffusion equation to present a modified mathematical model that is capable of accurately predicting the capacity fading and SEI growth rate as a function of temperature, concentration, and time, with just two significantly simplified temperature dependent fitting parameters. Further, these parameters need to be adjusted only for new temperatures. Our enhanced model is validated with respect to the experimental data for different operational conditions, including open circuit condition with different initial state of charges (SOCs) as well as cycling with a constant current.

Multicycle flash sintering of cubic Y2O3-stabilized ZrO2: An in situ energy dispersive synchrotron x-ray diffraction study with high temporal resolution

The current induced unit cell volume changes, (111) Bragg peak full width at half maximum (FWHM) and its integrated intensity in 8 % Y2O3 stabilized ZrO2 (8 %YSZ) solid state electrolyte was monitored during a triple-flash sintering experiment by in situ energy dispersive x-ray diffraction using a polychromatic synchrotron probe (max, photon energy 200 keV) with 2 second temporal resolution. The first spontaneous singularity in the unit cell volume (+0.54 %) was observed at 899 °C under 15 V/mm applied field intensity, which was associated with 13 mA/mm2 current draw and an increase in density to 97 %. Following anelastic relaxation of the unit cell volume under open circuit conditions, the same applied field was applied twice in a row which resulted in additional induced singularities at 925 °C (+0.48 %) and 944 °C (+0.42 %). A floating baseline, which was above the thermal expansion baseline, was observed from 833 to 969 °C and was attributed to Joule heating. The singularity at 899 °C is associated with a sharp change in (111) FWHM and a 34 % decrease in integrated peak area that was attributed to changes in the distribution of oxygen vacancies and the changes in their concentration as induced by the applied field in the spontaneous transient stage of flash sintering.

Electricity generation and enhanced thiacloprid biodegradation in microbial fuel cells using microalgae biocathode

Thiacloprid (THI), as a commonly used neonicotinoid, is frequently detected in environmental media, posing a potential threat to the environment and organisms. In this study, microalgae fuel cells (MFCs) with Chlorella sp. as cathode and wastewater (with sludge) as anode were constructed to remove THI (10, 20 and 50 mg/L) while generating bioelectricity. The results showed that, comparing with the open-circuit condition, the generation of bioelectricity (closed-circuit) significant enhanced the removal of THI by 13.14–32.47%. The presence of low concentration of THI (10–20 mg/L) did not significantly affect the accumulation of Chlorella sp. biomass, while high concentration THI (50 mg/L) strongly depressed its biomass. It was also found that high concentration THI caused obvious oxidative damages (MDA) to Chlorella sp., although SOD activity was upregulated. Both the highest THI removal efficiency (%) and stable bioelectricity voltage (202 mV) occurred at the low THI concentration (10 mg/L). Seven degradation products of THI were identified and the oxidation of the thiazole ring was the main detoxification way of THI. Additionally, toxicity evaluation also showed that the toxicity of degradation products were lower than THI. This study implies that MFCs could be a promising application, coupling pollutants removal, bioenergy generation and biomass production.

Revealing the impact of the voltage-induced interfacial effect on conduction properties of CeO2-based electrolyte: A modeling investigation

As widely used electrolyte materials in intermediate-temperature solid oxide fuel cells, the acceptor-doped CeO2 possesses not only high oxygen-ionic conductivity but also nonnegligible electronic conductivity. It has been experimentally confirmed that the voltage-induced interfacial effect can significantly affect the properties of the CeO2-based electrolyte. However, the voltage-induced interfacial effect is not yet properly treated in modeling studies concerning the charged defect distribution in the CeO2-based electrolyte. In this study, a new mathematical model of mixed oxygen-ionic and electronic conducting electrolyte, considering the voltage-induced interfacial effect upon the charged defect distributions within the electrolyte layer, is built. The mathematical treatment of the model based on the finite element method is clearly presented. The good agreements between the experimental data and model-predicted results at both open-circuit and operation conditions well validate the developed model. The modeling results elucidate that output voltages can significantly affect the distribution of charged defects, particularly for the localized electron, then further influencing its mixed conduction properties and behaviors. The results of this work can provide fundamental insight into the mixed ionic and electronic conducting properties and behaviors of the CeO2-based electrolyte.

Duffing-type digitally programmable nonlinear synthetic inductance for piezoelectric structures

Piezoelectric shunt damping techniques using linear circuits (e.g. resistive-inductive) and switching circuits (e.g. synchronized switch on inductor) have been extremely well studied for suppressing resonant vibrations in flexible structures. Both analog circuits and synthetic impedance circuits with digital control have been explored for linear concepts. In a parallel body of work, from the domain of mechanical methods of vibration attenuation, it is also known that leveraging nonlinearities (e.g. stiffness nonlinearity) can enhance the frequency bandwidth and offer amplitude-dependent suppression over a range of frequencies. However, the existing piezoelectric shunt damping techniques have been mostly limited to linear or switching nonlinear circuits, with the exception of a few nonlinear capacitance efforts. This work aims to introduce cubic inductance to emulate Duffing-type hardening nonlinearity in the shunt circuit with precise digital programming and tuning capability. Experiments are performed on a piezoelectric bimorph cantilever under base excitation for concept demonstration and model validation. First, linear frequency response functions of the cantilever are obtained for the short- and open-circuit conditions, and for linear resistive-inductive synthetic shunt damping, to confirm the standard linear behavior and electromechanical model parameters. Then, cubic inductance is introduced to the circuit and nonlinear experiments (up- and down-frequency sweep) are conducted. Cantilever tip to base motion transmissibility frequency response is measured along with piezoelectric voltage to base motion counterpart for a range of base excitation amplitudes. The distortion of the frequency response curves with increased base acceleration levels is observed. The nonlinear cubic coefficient is then varied to alter the manifestation of nonlinear frequency response at a given base excitation level, demonstrating the ease of tuning and triggering the nonlinear behavior on demand by means of the digitally-controlled synthetic impedance shunt. Nonlinear electromechanical model simulations are also validated against the experiments, yielding a very good agreement.

Dynamics of pendulum-based systems under human arm rotational movements

Wearable devices have applications in health monitoring and patient assistance devices. Harvesting energy from human motion kinetic energy by the pendulum-based electromagnetic generator is a promising way of extending the battery life of these devices. In this paper, the oscillatory and rotary dynamical response of pendulum-based systems under an open-circuit condition is investigated for two different models considering the lower arm’s rotation. The arm pitching model (in-plane excitation) represents the swing of the lower arm during walking. The arm rolling rotation model (out-of-plane excitation) represents the twisting type of motion of the lower arm movement associated with a specific kind of disorder, for example, tremors experienced by Parkinson’s patients. The governing equations of motion around stable equilibria are derived using Lagrange formulation, and their nondimensional forms are introduced for the two models. A special case of these models is developed for experimental validation and system identification, where the system parameters are identified by fitting frequency response functions on the experimental data. The system’s nonlinear dynamical response shows various bifurcations, including limit point bifurcation (i.e., saddle-node bifurcation), pitchfork bifurcation, a cascade of period-doubling bifurcations under amplitude or frequency sweeps. When the system shows a bi-stable response, the rotary response usually has a higher angular velocity amplitude than the oscillatory response. Basins of attraction plots for different operating conditions are presented to show the effect of initial conditions on the system’s type of steady-state response: oscillatory or rotary.

Love waves propagation in layered waveguide structures including flexomagneticity/flexoelectricity and micro-inertia effects

A gradient-type theory with flexomagnetic/flexoelectric and micro-inertia effects is used to study Love wave propagation in the layered magneto-electro-elastic structures. Two waveguide structures are considered: flexo-piezoelectric layer deposited on the piezomagnetic half-space and flexo-piezomagnetic layer resting on the piezoelectric half-space. The dispersion equations are numerically investigated for the magneto-electrically open and short circuit conditions. It is concluded that the profile of dispersion curves depends on the material composition of the waveguide structure, the guiding layer thickness, and the relative values of flexomagnetic/flexoelectric coefficients and the micro-inertia length-scale parameter. The obtained results are helpful for mathematical modeling of new small-sized acoustic devices.

Highly Stable and Selective Sensing of Hydrogen Sulfide in Living Mouse Brain with NiN4 Single-Atom Catalyst-Based Galvanic Redox Potentiometry

Hydrogen sulfide (H2S) is recognized as a gasotransmitter and multifunctional signaling molecule in the central nervous system. Despite its essential neurofunctions, the chemical dynamics of H2S during physiological and pathological processes remains poorly understood, emphasizing the significance of H2S sensor development. However, the broadly utilized electrochemical H2S sensors suffer from low stability and sensitivity loss in vivo due to sulfur poisoning-caused electrode passivation. Herein, we report a high-performance H2S sensor that combines single-atom catalyst strategy and galvanic redox potentiometry to overcome the issue. Atomically dispersed NiN4 active sites on the sensing interface promote electrochemical H2S oxidation at an extremely low potential to drive spontaneous bipolarization of a single carbon fiber. Bias-free potentiometric sensing at open-circuit condition minimizes sulfur accumulation on the electrode surface, thus significantly enhancing the stability and sensitivity. The resulting sensor displays high selectivity to H2S against physiological interferents and enables real-time accurate quantification of H2S-releasing behavior in the living mouse brain.

Fault tolerant nine-level inverter topology for solar water pumping applications

<span>Diminished voltage pressure and occasional-general harmonic distortion are the essential causes for such a ways and extensive usage of multi-level inverters (MLIs) in numerous industrial applications. Nonetheless, unwavering quality is one of the significant worries of MLIs as it utilizes countless switches as contrasted to 2-level inverters. Here, a fault tolerant 9-level inverter setup for the use of photovoltaic (PV) system-water pumping applications is suggested. This fault tolerant 9-level inverter is accomplished by combining a 2-level inverter, a 3-level fault tolerant inverter alongside switches with bidirectional ability. The setup is taken care of with four PV fed sources. The arrangement suggested shows the behavior towards switch fault in at least one inverter legs under open circuit conditions. On account of source failure, it could use the better hotspot for introducing continuous power to the water pumping motor. Meanwhile, the suggested fault-tolerant inverter works as seven-level inverter. The activity related to proposed inverter in the course of various failure modes is mentioned and simulated the usage of MATLAB/Simulink.</span>

Circulating-Current-Excited Switched Reluctance Generator System With Diode Rectifier

In this article, a circulating-current-excited switched reluctance generator system using a standard diode rectifier is proposed and examined. It features a dc power source connected in series with the ring-connected windings, which provides the dc-bias current as the excitation current in the windings. Using a series-connected dc power source, a dc-bias current is easily realized in the ac winding. Compared with the existing machine having dc-bias in the ac winding, the proposed generator can provide dc power with a standard diode rectifier. Less active legs and no rotor position sensor are needed for the control of the circulating current of the proposed generator, which increases the reliability of the generation system. The system configuration and the operation principle are introduced in detail. Then, the electromagnetic performance of the proposed generation system is analyzed at both open-circuit and load conditions. The asymmetric current distributions are deduced and verified by the simulations. At last, the prototype is tested under varied operation conditions and the experiments agree well with the analysis.

AMn2O4 spinels (A - Li, Mg, Mn, Cd) as ORR catalysts: The role of Mn coordination and oxidation state in the catalytic activity and their propensity to degradation

Using the rotating disk electrode (RDE) and cyclic voltammetry (CV) techniques, we studied electrochemical behavior, including activity in the oxygen reduction reaction (ORR) in an alkaline solution, of different AMn2O4 (A=Mn(II), Mg(II), Li(I) and Cd(II)) oxides with the spinel structure. With the help of postmortem XPS characterization we demonstrate that the surface of the studied spinels (except for MgMn2O4) undergoes essential modification not only under potential cycling but also after contacting alkaline solution under open circuit conditions, and even during the electrode preparation. The widely studied Mn3O4 spinel demonstrates the strongest surface modifications due to the presence of easily oxidizable and unstable Mn(II). The results of this work are of importance for the field of electrocatalysis and emphasize significant influence of degradation processes occurring at the surface and in the near-surface layers of materials on their electrochemical characteristics.

Synergistic Restriction to Polysulfides by a Carbon Nanotube/Manganese Sulfide-Decorated Separator for Advanced Lithium–Sulfur Batteries

Polysulfide dissolution and shuttling limit the capacity output and cycle life of lithium–sulfur batteries to a great extent. Separator modification using polar materials exploiting the ability to entrap polysulfides has been demonstrated as an effective approach to deal with the conundrum of polysulfide shuttling. Herein, a carbon nanotube/manganese sulfide nanocomposite is designed as a separator modifier in lithium–sulfur batteries for the first time. Furthermore, the carbon nanotube network provides a continuous network for rapid electronic conduction, imparts structural stability, and acts as a secondary barrier for polysulfides. Consequently, the cell displays an initial discharge capacity of 876 mAh g–1 at 0.5 C and sustains excellent stability with a retained capacity of 76% after 500 cycles. The self-discharge of the cell is also conspicuously reduced, maintaining a constant voltage for 100 h under open-circuit conditions. The electrochemical results represent an effective strategy to realize better performing Li–S batteries.

Imaging Current Paths in Silicon Photovoltaic Devices with a Quantum Diamond Microscope

Magnetic imaging with nitrogen-vacancy centers in diamond, also known as quantum diamond microscopy, has emerged as a useful technique for the spatial mapping of charge currents in solid-state devices. In this work, we investigate an application to photovoltaic (PV) devices, where the currents are induced by light. We develop a widefield nitrogen-vacancy microscope that allows independent stimulus and measurement of the PV device, and test our system on a range of prototype crystalline silicon PV devices. We first demonstrate micrometer-scale vector magnetic field imaging of custom PV devices illuminated by a focused laser spot, revealing the internal current paths in both short-circuit and open-circuit conditions. We then demonstrate time-resolved imaging of photocurrents in an interdigitated back-contact solar cell, detecting current build-up and subsequent decay near the illumination point with microsecond resolution. This work presents a versatile and accessible analysis platform that may find distinct application in research on emerging PV technologies.

Unified polarizable electrode models for open and closed circuits: Revisiting the effects of electrode polarization and different circuit conditions on electrode-electrolyte interfaces.

A precise understanding of the interfacial structure and dynamics is essential for the optimal design of various electrochemical devices. Herein, we propose a method for classical molecular dynamics simulations to deal with electrochemical interfaces with polarizable electrodes under the open circuit condition. Less attention has been given to electrochemical circuit conditions in computation despite being often essential for a proper assessment, especially comparison between different models. The present method is based on the chemical potential equalization principle, as is a method developed previously to deal with systems under the closed circuit condition. These two methods can be interconverted through the Legendre transformation so that the difference in the circuit conditions can be compared on the same footing. Furthermore, the electrode polarization effect can be correctly studied by comparing the present method with conventional simulations with the electrodes represented by fixed charges, since both of the methods describe systems under the open circuit condition. The method is applied to a parallel-plate capacitor composed of platinum electrodes and an aqueous electrolyte solution. The electrode polarization effects have an impact on the interfacial structure of the electrolyte solution. We found that the difference in circuit conditions significantly affects the dynamics of the electrolyte solution. The electric field at the charged electrode surface is poorly screened by the nonequilibrium solution structure in the open circuit condition, which accelerates the motion of the electrolyte solution.