Shunt Current Research Articles

Higher performance long wavelength interband cascade photodetector compared with a PBπBN device

In this paper, we reported our design and experimental results of a two-stage long wavelength interband cascade infrared photodetector (ICIP). A 3 × 3 multiple quantum well relaxation region was proposed for long wavelength ICIP. The 50% cutoff wavelength was 11.6 μm at 80 K. The quantum efficiency (QE) of the ICIP was measured to be 24.5% at 8.5 μm. The dark current density at −0.05 V bias of the ICIP was measured to be 3.32 × 10−4 A/cm2 at 55 K, which is approximately 1/3 of a PBπBN superlattice detector. The peak detectivity of ICIP was measured to be 4.6 × 1010 cm·Hz1/2/W at 80 K and further raised to 3.6 × 1011cm·Hz1/2/W when the temperature decreased to 55 K. In comparing with the PBπBN superlattice device, the ICIP shows smaller shunt currents and tunneling currents at low temperatures.

Equisensitive adjustment of planar Hall effect sensor’s operating field range by material and thickness variation of active layers

A novel technique of operating field range adjustment using varying thicknesses of spacer and capping layers is proposed for planar Hall effect (PHE) magnetic sensors. In terms of this technique, the spacer and capping layer thicknesses are varied interdependently, in a way that the variation of the operating magnetic field range is performed without a change of sensitivity. The relationship between the thicknesses of spacer and capping layers required for this ‘equisensitive’ variation of field range are calculated and experimentally approved. The active layer material substitution effect on the performance of PHE sensor is studied. The sensitivity, output voltage, operating field range, and shunt current are compared for PHE sensors, based on NiFe and NiFeMo active ferromagnetic layers. The NiFe/IrMn and NiFeMo/IrMn interface coupling energies are compared and the effect of IrMn crystallinity on their difference is discussed. The range of active layer thicknesses, at which the operating field range can be varied while maintaining the sensitivity at the same value, has been determined.

Analysis of Flow Field Scale-up, Design Tradeoffs, and Shunt Current in Redox Flow Battery Stacks

Recently it has been demonstrated that operating conditions and applications have a significant impact on the effectiveness of different flow field designs commonly used in redox flow batteries (RFBs)1. Depending on the power and energy storage requirements, as well as the system operational capabilities, the optimal flow field design may vary between designs2. These results have only been presented concerning small laboratory scale designs, however. Due to the different transport mechanisms utilized by these various flow field designs, the mass transport performance and efficiency of each design will scale differently when the active area of the cell is increased to a size more representative of a commercial system. Additionally, the most common configuration of these cells in a commercial system is in an RFB stack where several cells are connected in series electronically and in parallel hydraulically. This further complicates the design tradeoffs seen in the smaller single cell design, while also introducing new design concerns in the form of shunt current, a self-discharge phenomenon only present when multiple cells are connected ionically through the liquid electrolyte. Utilizing the energy and efficiency-based analysis previously published by our lab, we have conducted a thorough study of the differences between four flow fields when increasing the active area of the cell. CFD simulations using COMSOL Multiphysics provide quantitative data for electrolyte velocity and pressure drop, while experimental data provides depth of discharge and efficiency results. This analysis has also been extended to a small RFB stack to examine how these design tradeoffs are impacted by placing multiple cells electronically in series and sharing an electrolyte manifold. To quantify the shunt current in this stack, a novel in-situ shunt measurement technique was developed, allowing for real-time measurement of the shunt current present during all phases of stack operation. The results of this study provide insights and guidelines for the future development of commercial RFB systems, specifically ways in which the fluid pathway can be optimized to improve system efficiency.

Investigation of electronic transport mechanisms in Sb2Se3 thin-film solar cells

Electronic transport mechanisms in Sb2Se3 thin-film solar cells were investigated using temperature-dependent current-voltage (J-V) measurements. Sb2Se3 thin films were deposited via the vapor transporting deposition method using a double-temperature-zone tubular furnace system, and comparative studies were performed for Sb2Se3 films formed on substrates located at three different positions away from the furnace center. The device efficiency varied from 3.83 to 6.24%. First, structural properties obtained by X-ray diffraction, Raman and scanning electron microscopy measurements verified the optimal Sb2Se3 film quality for the cell with the highest efficiency. Then, temperature-dependent saturation current and open-circuit voltage (Voc) measurements revealed that the dominant carrier recombination occurred in the CdS/Sb2Se3 interface region, which possibly influenced the Voc for all cells: the highest Voc for the optimal Sb2Se3 cell was at least partly due to it having the lowest CdS/Sb2Se3 interface recombination rate. Finally, the reverse bias current relationship revealed that non-ohmic shunt current (space-charge-limited current, SCLC) plays an important role in affecting the performance of solar cells, as lower-efficiency cells had higher non-ohmic shunt current.

Standby thermal model of a vanadium redox flow battery stack with crossover and shunt-current effects

This paper presents an original model capable of simulating the thermal behavior of a vanadium redox flow battery stack in standby condition, i.e. without power and reactant flow, where the temperature distribution in the cells evolves because of ions crossover through the membrane, Joule losses due to shunt currents and inherent self-discharge effects. For the first time, a model is presented that is capable of simulating the cell temperature distribution in the stack and its time evolution considering all above effects. The model is applied to a 9 kW/40-cell stack and validated against measurements from a thermal imager. Numerical results show that shunt currents affect the temperature in the stack and can be responsible for local increases of cell temperatures up to 10 °C if the solutions are initially at high state of charge. This effect can be critical if standby occurs after a period of operation, with the electrolyte stack temperature markedly higher than air temperature. In addition, results show that shunt currents can play a major role in the thermal behavior of compact stacks, based on new materials capable of high power density and low ion crossover. The model presented here can constitute the basis for advanced cooling strategies.

A One-Dimensional Stack Model for Redox Flow Battery Analysis and Operation

Current redox flow battery (RFB) stack models are not particularly conducive to accurate yet high-throughput studies of stack operation and design. To facilitate system-level analysis, we have developed a one-dimensional RFB stack model through the combination of a one-dimensional Newman-type cell model and a resistor-network to evaluate contributions from shunt currents within the stack. Inclusion of hydraulic losses and membrane crossover enables constrained optimization of system performance and allows users to make recommendations for operating flow rate, current densities, and cell design given a subset of electrolyte and electrode properties. Over the range of experimental conditions explored, shunt current losses remain small, but mass-transfer losses quickly become prohibitive at high current densities. Attempting to offset mass-transfer losses with high flow rates reduces system efficiency due to the increase in pressure drop through the porous electrode. The development of this stack model application, along with the availability of the source MATLAB code, allows for facile approximation of the upper limits of performance with limited empiricism. This work primarily presents a readily adaptable tool to enable researchers to perform either front-end performance estimates based on fundamental material properties or to benchmark their experimental results.

Operation Protocols To Improve Durability of Protonic Ceramic Fuel Cells.

To develop reliable and durable protonic ceramic fuel cells (PCFCs), the impacts of the operation protocols of PCFCs on the cell durability are investigated through analyses of the main degradation mechanisms. We herein propose three appropriately designed control protocols, including cathode air depletion, shunt current, and fuel cell/electrolysis cycling, to fully circumvent the operating-induced degradation of PCFCs. For this purpose, anode-supported cells, comprised of a NiO-BaCe0.7Zr0.1Y0.1Yb0.1O3-δ anode, BaCe0.7Zr0.1Y0.1Yb0.1O3-δ electrolyte, and NdBa0.5Sr0.5Co1.5Fe0.5O5+δ-Nd0.1Ce0.9O2-δ composite cathode, are prepared, and their long-term performances are evaluated under a galvanostatic condition of 0.5 A·cm-2 at 650 °C. The cell voltages of the protected cells using the operation protocols to prevent performance degradation are stably maintained under the applied current density for more than 1200 h without any noticeable degradation, whereas the performance of the unprotected cell gradually decreased with time, and the decay ratio was 14.9% over 850 h. The significant performance decay of the unprotected cell is strongly associated with the cathode degradation phenomenon, which was caused by the water vapor continuously produced during the electrochemical reactions. Hence, the performance recovery of the PCFCs with the operation protocols is achieved by incrementally decreasing the cathode potential (close to a value of zero) to minimize the effect of high PH2O and PO2 during the PCFC operations.

Determination of Surface Recombination Velocity From Current–Voltage Characteristics in SiC p-n Diodes

Surface recombination velocity on mesa sidewalls of SiC p-n diodes with various surface passivation conditions was evaluated from the device-size-dependent preexponential factor of recombination current ( ${J}_{\text {0rec}}$ ). The diodes passivated by SiO2 with postoxidation nitridation were dipped into HF to eliminate a shunt current, which is evoked by the nitrided SiO2 layer and disturbs the analysis of the recombination current. For accurate determination of the surface recombination velocity, an effective recombination zone width was precisely derived taking account of the distribution of carrier density in the depletion layer. The surface recombination velocity of the diodes without any passivation and with the postoxidation nitridation (NO annealing at 1250 °C for 70 min) was determined as $\text {1.2}\times \text {10}^{\text {7}}$ and $\text {6.0}\times \text {10}^{\text {5}}$ cm/s, respectively, which indicates that the postoxidation nitridation can reduce the surface recombination by a factor of about 20. We confirmed that TCAD simulation could reproduce the current–voltage characteristics by utilizing the extracted parameters. In addition, an evaluation method was proposed to determine the surface recombination velocity from the high-current region, where diffusion current is dominant.

Mechanisms and modification of nonlinear shunt leakage in Sb2Se3 thin film solar cells

Antimony selenide (Sb2Se3) based thin film solar cells have recently drawn a growing research interest due to their increasing power conversion efficiency, proper bandgap, high absorption coefficient, and earth abundant nature. Herein, the Sb2Se3 thin films were prepared by close spaced sublimation (CSS) for efficient Sb2Se3 solar cells. The origin and the mechanisms of shunt current were analyzed. Non-ohmic space-charge limited current (SCLC) was identified to be an important contribution to the nonlinear shunt current in Sb2Se3 thin film solar cells. To tackle this issue, a high-resistance SnO2 buffer was introduced at the front contact. With the insertion of a SnO2 buffer, the micro-shunt paths were modified and a significant efficiency improvement to 5.18% was obtained.

Influencing factors on nugget formation during multipoint welding by single-side resistance spot welding

ABSTRACTRecently, weight reduction and improvement of crashworthiness of auto bodies have become important issues. At the same time, stiffness of auto bodies is also needed to ensure a smooth ride. Using hollow parts, such as bended pipes and hydroformed parts, is one of the solutions to the demand for both rigidity and light weight.To weld hollow parts and sheet panels together, welding methods which allow us to access from one side are required. Single-side resistance spot welding (single-side RSW) process is one of those, and has recently been attracting attention.However, because of the long current path and small electrode force, it is difficult to concentrate the electric current in the welding spot compared with conventional direct resistance spot welding (direct RSW). Furthermore, in multipoint welding, shunt current will occur easily, and the nugget formation will be inhibited.To obtain a guideline for making sound nuggets, influencing factors for shunt current were investigated. In addition, a numerical study was carried out to discuss the difference between direct RSW and single-side RSW.According to the CAE analysis, the shunt current of single-side RSW will be higher rate than direct RSW. The rate of shunt current was influenced by the electrical resistance of its current path. For this reason, with shorter distance between welding points, or with lower electrical resistance of material, it is difficult to get large nuggets. By enhancing the electrical resistance of shunt current path, shunt current could be reduced and a larger nugget would be obtained.

Modeling the effect of shunt current on the charge transfer efficiency of an all-vanadium redox flow battery

In an all-vanadium redox flow battery (VRFB), a shunt current is inevitable owing to the electrically conductive electrolyte that fills the flow channels and manifolds connecting cells. The shunt current decreases the performance of a VRFB stack as well as the energy conversion efficiency of a VRFB system. To understand the shunt-current loss in a VRFB stack with various designs and operating conditions, a mathematical model is developed to investigate the effects of the shunt current on battery performance. The model is calibrated with experimental data under the same operating conditions. The effects of the battery design, including the number of cells, state of charge (SOC), operating current, and equivalent resistance of the electrolytes in the flow channels and manifolds, on the shunt current are analyzed and discussed. The charge-transfer efficiency is calculated to investigate the effects of the battery design parameters on the shunt current. When the cell number is increased from 5 to 40, the charge transfer efficiency is decreased from 0.99 to a range between 0.76 and 0.88, depending on operating current density. The charge transfer efficiency can be maintained at higher than 0.9 by limiting the cell number to less than 20.

Reduction of shunt current in buffer-free IrMn based spin-valve structures

The presence of thick buffer layers in magnetic sensor devices decreases sensor sensitivity due to shunt currents. With this motivation, we produced IrMn-based spin-valve multilayers without using buffer layer. We also studied the effects of post-annealing and IrMn thickness on exchange bias field (HEB) and blocking temperature (TB) of the system. Magnetization measurements indicate that both HEB and TB values are significantly enhanced with post-annealing of IrMn layer. In addition, we report that IrMn thickness of the system strongly influences the magnetization and transport characteristics of the spin-valve structures. We found that the minimum thickness of IrMn layer is 6 nm in order to achieve the lowest shunt current and high blocking temperature (>300 K). We also investigated the training of exchange bias to check the long-term durability of IrMn-based spin-valve structures for device applications.

Non-Isothermal Modeling of Dark Current-Voltage Measurements of a CIGS Solar Cell

Dark current density-voltage measurements were performed in a temperature range 110–290 K in both forward and reverse bias on a 0.5 cm2 solar cell sample to determine current and voltage losses in a CIGS solar cell. For the first time a JD − V model applicable in a wide temperature range was constructed by adding non-ideality terms to the Shockley diode equation and comparing the experimentally acquired data to the model simulation results. The shunt current was modeled assuming space charge limited current by a uniform distribution of trap levels. A total of only 9 adjustable parameters in the final JD − V model sufficed to simulate all experimental data simultaneously, i.e., no re-estimation had to be performed at different temperature levels. The estimates for the diode ideality factor n = 1.8 and the diode activation energy ΔE = 1.20 eV coincide with values typically obtained for CIGS solar cell dominated by recombination in the absorber. The quality of the CIGS solar cell used in this study was also confirmed by the low back contact activation barrier of 52 meV and the high shunt resistance. We demonstrate that this flexible model can be used to make an initial prediction of the resistive losses and non-idealities in thin film solar cells.

Electrochemical energy storage for renewable energy integration: zinc-air flow batteries

A 1 kW–4 kWh zinc-air flow battery has been built at Tecnicas Reunidas facilities. The battery is divided in three different stacks connected in parallel, each of them comprising 20 cells connected in series and 0.25 m3 of electrolyte. The main challenges found on scaling up include the necessity of using three electrodes per cell, electrolyte leakage, ohmic resistance and gas diffusion electrode flooding. The three electrode solution is not optimal because it adds mechanical complexity and cost but it is a robust solution to evaluate the performance of the system as a baseline. During pilot plant operation, a phenomenon called shunt currents has revealed to reduce coulombic efficiency by 18%. In order to better understand this phenomenon, a mathematical model has been developed and it has been validated using real measurements taken on one of the 20-cell stacks. The major part of the challenges were solved and technical viability has been evaluated. However, efficiency, durability and the bifunctional air electrode are the challenges to overcome before this technology becomes ready for commercialization.

Acetaminophen Metabolite N-Acylphenolamine Induces Analgesia via Transient Receptor Potential Vanilloid 1 Receptors Expressed on the Primary Afferent Terminals of C-fibers in the Spinal Dorsal Horn.

The widely used analgesic acetaminophen is metabolized to N-acylphenolamine, which induces analgesia by acting directly on transient receptor potential vanilloid 1 or cannabinoid 1 receptors in the brain. Although these receptors are also abundant in the spinal cord, no previous studies have reported analgesic effects of acetaminophen or N-acylphenolamine mediated by the spinal cord dorsal horn. We hypothesized that clinical doses of acetaminophen induce analgesia via these spinal mechanisms. We assessed our hypothesis in a rat model using behavioral measures. We also used in vivo and in vitro whole cell patch-clamp recordings of dorsal horn neurons to assess excitatory synaptic transmission. Intravenous acetaminophen decreased peripheral pinch-induced excitatory responses in the dorsal horn (53.1 ± 20.7% of control; n = 10; P < 0.01), while direct application of acetaminophen to the dorsal horn did not reduce these responses. Direct application of N-acylphenolamine decreased the amplitudes of monosynaptic excitatory postsynaptic currents evoked by C-fiber stimulation (control, 462.5 ± 197.5 pA; N-acylphenolamine, 272.5 ± 134.5 pA; n = 10; P = 0.022) but not those evoked by stimulation of Aδ-fibers. These phenomena were mediated by transient receptor potential vanilloid 1 receptors, but not cannabinoid 1 receptors. The analgesic effects of acetaminophen and N-acylphenolamine were stronger in rats experiencing an inflammatory pain model compared to naïve rats. Our results suggest that the acetaminophen metabolite N-acylphenolamine induces analgesia directly via transient receptor potential vanilloid 1 receptors expressed on central terminals of C-fibers in the spinal dorsal horn and leads to conduction block, shunt currents, and desensitization of these fibers.

Effect of Postoxidation Nitridation on Forward Current–Voltage Characteristics in 4H–SiC Mesa p-n Diodes Passivated With SiO2

An origin of shunt current, a ledge in forward current–voltage ( ${I}$ – ${V}$ ) characteristics, in 4H-SiC mesa p-n diodes was investigated by adopting various surface passivation processes. Experimental results indicated that the shunt current path is located along the mesa sidewall and the shunt current is enlarged with increasing NO-annealing period and temperature. Based on these results, we qualitatively explain that nitrogen-related positive charges near the SiC/SiO2 interface, which are formed by postoxidation nitridation, induce band bending and lowering of the diffusion potential along the mesa sidewall, resulting in occurrence of the shunt current.

Variation of UPFC controllable parameters during power swing and their impacts on distance relay

Unified power flow controller (UPFC) has impact on the performance of distance relay during power swing. Generally, power system's parameters oscillate during power swing and since UPFC operation depends on some of these parameters (bus voltage, active and reactive power), the UPFC injects oscillated series voltage and draws oscillated shunt current. These oscillating series voltage and shunt current influence distance relays, as the impedance seen by a distance relay during power swing changes in UPFC-compensated lines. This study shows how and why series voltage and shunt current change during power swing. Moreover, the admittance swing characteristic is proposed in this study and effects of series and shunt branches of UPFC on the admittance seen by a distance relay during power swing have been examined.

A framework to reconcile frequency scaling measurements, from intracellular recordings, local-field potentials, up to EEG and MEGsignals.

In this viewpoint article, we discuss the electric properties of the medium around neurons, which are important to correctly interpret extracellular potentials or electric field effects in neural tissue. We focus on how these electric properties shape the frequency scaling of brain signals at different scales, such as intracellular recordings, the local field potential (LFP), the electroencephalogram (EEG) or the magnetoencephalogram (MEG). These signals display frequency-scaling properties which are not consistent with resistive media. The medium appears to exert a frequency filtering scaling as 1/f, which is the typical frequency scaling of ionic diffusion. Such a scaling was also found recently by impedance measurements in physiological conditions. Ionic diffusion appears to be the only possible explanation to reconcile these measurements and the frequency-scaling properties found in different brain signals. However, other measurements suggest that the extracellular medium is essentially resistive. To resolve this discrepancy, we show new evidence that metal-electrode measurements can be perturbed by shunt currents going through the surface of the brain. Such a shunt may explain the contradictory measurements, and together with ionic diffusion, provides a framework where all observations can be reconciled. Finally, we propose a method to perform measurements avoiding shunting effects, thus enabling to test the predictions of this framework.

The Relationship between Shunt Currents and Edge Corrosion in Flow Batteries

Shunt currents occur in electrochemical reactors like flow batteries, electrolyzers, and fuel cells where many bipolar cells that are connected in series electrically contact a mobile electrolyte through one or more common fluid distribution manifolds. Shunt currents reduce energy efficiency, and can cause unwanted side reactions including corrosion and gas generation. Equivalent-circuit models have been widely used to examine shunt currents in multi-cell electrochemical reactors. However, a detailed investigation of the interesting electrochemical processes occurring at the edges of the active areas has not been presented. In this work, the generation of shunt currents and their tendency to drive corrosion at the edges of positive electrodes in the most positive cells in a reactor stack are investigated with a comprehensive numerical model. An analytical model based on the penetration of current into a semi-infinite electrode, that can be used in conjunction with traditional equivalent-circuit models to assess the tendency for shunt currents to drive corrosion, is developed and compared to the numerical model. The models provided here can be used to set requirements on maximum allowable port currents in order to achieve a particular durability goal.

Compact and General Strategy for Solving Current and Potential Distribution in Electrochemical Cells Composed of Massive Monopolar and Bipolar Electrodes

A compact, fast and general algorithm based on Dirichlet boundary conditions for the potential field is derived to enable the calculation of local current distribution, shunt currents and the local potential distribution on massive electrodes in electrochemical cells of any type of geometry in three dimensions, composed of bipolar electrodes at an unknown floating potential and/or terminal monopolar electrodes. The algorithm allows performing the calculation of current-potential distributions and bypass currents for a fixed cell potential (potentiostatic) or a fixed cell current (galvanostatic) enforced to the cell. The proposed approach can be extended to take into account concentration variations of one or several species inside the cell or electrical conductivity variations due to the presence of separators or liquid-gas-solid phases. In order to validate the algorithm, a detailed comparison, between the suggested strategy with experimental results is made in the case of secondary current distribution for i) a segmented one bipolar electrode ii) a cell stack composed of 14 bipolar electrodes in the industrial process of alkaline water electrolysis. The proposed tool can help designers to develop more efficient electrochemical reactors by comparing results using different electrode materials, electrolytes and cell designs.