Measurement Of Current Distribution Research Articles

Suppressed Formation of Conductive Phases in One-Pot Electrodeposited CuInSe2 by Tuning Se Concentration in Aqueous Electrolyte.

The single-bath electrochemical deposition of CuInSe2 often leads to short-circuit behavior of the resulting solar cells due to the high shunt conductance. In this study, in an attempt to resolve this problem, the influence of the Se precursor concentration (CSe) on electrodeposited CuInSe2 films and solar cell devices is examined in the CSe range of 4.8 to 12.0 mM in selenite-based aqueous solutions containing Cu and In chlorides along with sulfamic acid (H3NSO3) and potassium hydrogen phthalate (C8H5KO4) additives. As CSe increases, the CuInSe2 layers become porous, and the grain growth of the CuInSe2 phase is restricted, while the parasitic shunting problem was markedly alleviated, as unambiguously demonstrated by measurements of the local current distribution. Due to these ambivalent influences, an optimal value of CSe that achieves the best quality of the films for high-efficiency solar cells is identified. Thus, the device prepared with 5.2 mM Se exhibits a power-conversion efficiency exceeding 10% with greatly improved device parameters, such as the shunt conductance and the reverse saturation current. The rationale of the present approach along with the physicochemical origin of its conspicuous impact on the resulting devices is discussed in conjunction with the electro-crystallization mechanism of the CuInSe2 compound.

In-Situ Analysis of the in-Plane Current Distributions in an Electrolyte-Supported Planar Solid Oxide Fuel Cell By Segmented Electrodes

Solid oxide fuel cells have been of practical concern as a high efficiency power generation device. Problems of the SOFCs include current distribution that decays the total cell performance and efficiency, and causes electrode degradation chemically and thermo-­mechanically. In the planar SOFCs, the fuel and oxidant distributions cause current and temperature distributions over the electrodes under the separator ribs and flow channels. Optimized design of the separator is hence required to improve the power generation characteristics and durability of practical fuel cell stacks. Although there have been a number of numerical analyses, very few experimental investigations confirming in-­situ current distributions to reveal the influence of the separator structure have been reported. We have therefore addressed measurements of in­-plane spatial current variations of an electrolyte-­supported planar SOFC having segmented cathodes under the rib and the flow channels so far1. In the present study, we investigate the effect of the rib width on the current distribution. We used the planar cell having three segmented cathodes assembled with segmented cathode separators for electrical insulation. The segmented cathodes were employed opposing to a rib and a set of parallel flow channels of the anode separator. The cell was composed of NiO­-10Sc1CeSZ anode, 10Sc1CeSZ electrolyte, GDC interlayer, and LSCF-­GDC cathode. The electrode area for the channel was 1.3 cm2 (2.5 x 0.5 cm) each while those for the ribs were 0.63 cm2 (2.5 x 0.25 cm), 1.3 cm2 (2.5 x 0.5 cm), 1.9 cm2 (2.5 x 0.75 cm). The anode and cathode separator made of SUS430 had the flow channels with a width of 3 mm, a depth of 1 mm, and a length of 2.5 cm. Silver mesh was employed for the current collection of both sides. Current voltage (I­V) measurements were carried out under voltage control using three electric loads to reproduce the electrode potential of a single cell2. The anode and cathode were electrically connected with the four-­terminal method. The anode NiO was reduced to Ni by feeding H2/N2 mixture gas for 2 hours prior to measurements. During measurements, anode and cathode were fed upward with mixtures of H2/N2 and dried air at constant flow rates, respectively. The cell was maintained at 800 °C by a tubular electric furnace at open circuit voltage (OCV). We prepared cathode separators with flow channels facing those of the anode. Several flow channels were added opposing to the anode rib to minimize the cathode overpotential by poor oxygen transport under the cathode rib indicated in our previous report1 since we focus on the current distributions ascribed to the anode overpotential. Larger rib width results in larger anodic overpotentials under the anode rib compared with the anode flow channel according to a decrease in the inlet hydrogen flow rate. We also model the current and hydrogen partial pressure distributions by finite element simulation (COMSOL Multiphysics) so that the model agrees with the in­-situ current distributions derived by the segmented cathodes from setting the exchange current densities, electrode porosities, electrolyte ion conductivities, and electrode ion/electron conductivities. This modeling is useful to design separators to improve the performance and durability of practical stacks. 1. Takahiro Koshiyama, Hironori Nakajima, Takahiro Karimata, Tatsumi Kitahara, Kohei Ito, Soichiro Masuda, Yusuke Ogura, Jun Shimano, Direct Current Distribution Measurement of an Electrolyte-Supported Planar Solid Oxide Fuel Cell under the Rib and Channel by Segmented Electrodes, ECS Trans., Vol. 68, 1, 2217-2226 (2015). 2. Özgür Aydin, Takahiro Koshiyama, Hironori Nakajima, Tatsumi Kitahara, In-­situ Diagnosis and Assessment of Longitudinal Current Variation by Electrode­-Segmentation Method in Anode­-Supported Microtubular Solid Oxide Fuel Cells, J. Power Sources, Vol. 279, 218–223 (2015).

Low temperature properties of spin filter NbN/GdN/NbN Josephson junctions

A ferromagnetic Josephson junction (JJ) represents a special class of hybrid system where different ordered phases meet and generate novel physics. In this work we report on the transport measurements of underdamped ferromagnetic NbN/GdN/NbN JJs at low temperatures. In these junctions the ferromagnetic insulator gadolinium nitride barrier generates spin-filtering properties and a dominant second harmonic component in the current-phase relation. These features make spin filter junctions quite interesting also in terms of fundamental studies on phase dynamics and dissipation. We discuss the fingerprints of spin filter JJs, through complementary transport measurements, and their implications on the phase dynamics, through standard measurements of switching current distributions. NbN/GdN/NbN JJs, where spin filter properties can be controllably tuned along with the critical current density (Jc), turn to be a very relevant term of reference to understand phase dynamics and dissipation in an enlarged class of JJs, not necessarily falling in the standard tunnel limit characterized by low Jc values.

分割電極による平板型固体酸化物形燃料電池の直接電流分布測定

分割電極による平板型固体酸化物形燃料電池の直接電流分布測定

In Situ Localized Current Distribution Measurements in All-Vanadium Redox Flow Batteries

A printed circuit board (PCB) was implemented for in-plane, two-dimensional distributed current measurements in an all-vanadium redox flow battery (VRFB). A PCB with built-in shunt resistors is a passive method of measuring localized currents in-situ, in real time. It is demonstrated that lateral current spread through non- or partially-segmented flow field plates will produce a distribution that does not properly reflect the distribution within the electrode; this issue is resolved in this work via fully-segmented flow plates. Large current gradients develop when a cell reaches a mass-transport limitation. Based upon the resultant distributions, it is shown that they reflect a combination of electrolyte velocity and local concentration within the electrode. The impact of flow rate and electrode material properties such as wettability, surface area, porosity, and thickness on current distribution are presented.

A 128-channel picoammeter system and its application on charged particle beam current distribution measurements.

A 128-channel picoammeter system is constructed based on instrumentation amplifiers. Taking advantage of a high electric potential and narrow bandwidth in DC energetic charged beam measurements, a current resolution better than 5 fA can be achieved. Two sets of 128-channel strip electrodes are implemented on printed circuit boards and are employed for ion and electron beam current distribution measurements. Tests with 60 keV O(3+) ions and 2 keV electrons show that it can provide exact boundaries when a positive charged particle beam current distribution is measured.

Measurements of current density distribution in shaped e-beam writers

In this paper, we present four measurement methods for the two-dimensional mapping of the current density distribution in variable-shaped e-beam writers. All the methods use only the native equipment of the e-beam writer which provides the advantage of relatively easy implementation. The first and second measurement methods are based on the knife-edge technique in which the e-beam is scanned in two directions across a Faraday cup opening and across shaping shutters of the forming system, respectively. In the third method, a phosphor screen is irradiated by a magnified e-beam spot and the current density distribution is represented by the luminescence image on the screen. The fourth method uses electron sensitive resist which is exposed by the e-beam. The developed resist is observed under a microscope and the current density distribution is judged from the resist profile. All the methods are demonstrated in an example, compared, and their spatial resolution and accuracy evaluated.

Feasibility of in-plane GDL structuration: Impact on current density distribution in large-area Proton Exchange Membrane Fuel Cells

In the present work, the in-plane structuration of the electrode Gas Diffusion Layer (GDL) is proposed as an interesting approach to reduce the operating heterogeneities occurring within the cell along the gas flow fields, especially in dry operating conditions. This is especially important for transportation applications where the fuel cell is often operated in these conditions. Structured and homogeneous large-area (220 cm2) membrane electrode assemblies (MEAs) are tested in single-cell and 6-cell stack configurations.An S++® electronic card inserted in the stack is used to measure the current distribution within the cell, which is an indicator of the local electrochemical reaction conditions. The results of the current distribution measurements together with the cell performances obtained for the structured and the homogenous MEAs indicate that the electrode in-plane structuration is effective in reducing the functioning heterogeneities within the cell under specific operating conditions.

Anode Current Density Distribution Measurements for Different Vacuum Arc Modes Subjected to Axial Magnetic Field

We report our measurements of anode current density distributions for different modes in vacuum arc discharge using a split-anode and a cup-shaped axial magnetic field cathode configuration system. The modes investigated included the diffuse arc and anode spot. The anode surface was divided into four regions: one central region and three symmetrical-disposed peripheral annular-arc regions. Three different-sized central regions were selected with diameters of 12, 18, and 20 mm. The contact material was CuCr25 (25% Cr). The arc current in the tests ranged from 6 to 14 kA (rms) at 50 Hz. The opening velocities were 1.8 and 2.4 m/s, respectively. The currents of the four areas on the anode contact were measured by four Rogowski coils situated outside the vacuum chamber. The experimental results show the current density distribution in different arc modes. For the diffuse arc mode with arc currents of 6 and 8 kA (rms), the average current density in the central region at current peak ranged from 8.5 to 15.9 A/mm $^{2}$ . The anode spot current density ranged from 31.9 to 37.7 A/mm $^{2}$ , estimated from the current density in the eroded region caused by the anode spots covering the entire central region of diameters 12 and 18 mm, at currents of 12 and 14 kA, respectively, regarded as the lower limit current density of the anode spot. Moreover, the dependence of the current density distribution on opening velocity in diffuse arcs was slight. For the anode spots, the current density distribution with higher opening velocity was more concentrated.

16-Channel micro magnetic flux sensor array for IGBT current distribution measurement

Current crowding of IGBT and power diode in a chip or among chips is a barrier to the realization of highly-reliable power module and power electronics system. Current crowding occurs because of the parasitic inductance, difference of chip characteristics or temperature imbalance among chips. Although current crowding among IGBT or power diode chips has been analysed on numerical simulations, no sensor with sufficiently high special resolution and fast measurement time has yet been demonstrated. Therefore, the author developed and demonstrated 16-channel flat sensitivity sensor array for IGBT current distribution measurement. The sensor array consists of tiny-scale film sensors with analog amps and shield case against noise. The array and digital calibration method will be applied for reliability analysis, designing and screening of IGBT modules.

Direct Current Distribution Measurement of an Electrolyte-Supported Planar Solid Oxide Fuel Cell under the Rib and Channel by Segmented Electrodes

Solid oxide fuel cells have been of practical concern as a high efficiency power generation device. Problems of the SOFCs include current distribution that decays the total cell performance and efficiency, and causes electrode degradation chemically and thermo-mechanically. In the case of the planar SOFCs, the fuel/oxidant distributions and current collecting resistance cause current and temperature distributions over the electrodes under the separator ribs and flow channels. Optimized design of the separator is hence required to improve the power generation characteristics and durability of practical fuel cell stacks. Although there have been a number of numerical analyses, very few experimental investigations confirming in-situ current distributions to reveal the influence of the separator structure have been reported. The aim of the present study is thus to measure in-plane spatial current variations of an electrolyte-supported planar SOFC with segmented cathodes under the rib and the flow channel. We used the planar cell having three segmented cathodes (Fig. 1) assembled with segmented cathode separators for electrical insulation. The segmented cathodes were placed opposing to a rib and a set of parallel flow channels of the anode separator. The cell was composed of NiO-10Sc1CeSZ anode, 10Sc1CeSZ electrolyte, GDC interlayer, and LSCF-GDC cathode. The electrode area was 1.4 cm2(2.8 x 0.5 cm) each. The anode and cathode separator made of SUS430 had the flow channels with a width of 3 mm, a depth of 1 mm, and a length of 2.8 cm. Silver mesh was employed for the current collection of both sides. Current voltage (I-V) measurements were carried out under voltage control using three electric loads to reproduce the electrode potential of a single cell[1]. The anode and cathode were electrically connected with the four-terminal method. The anode NiO was reduced to Ni by feeding H2/N2 mixture gas for 2 hours prior to measurements. During measurements, anode and cathode were fed upward with mixtures of H2/N2and dried air at constant flow rates, respectively. The cell was maintained at 800 °C by an electric furnace at open circuit voltage (OCV) We prepared two types of the cathode separators. One of them had the same flow channel configuration as the anode separator where the rib and flow channels faces each other. The other had additional flow channels opposing to the anode rib. With the former cathode separator, the overpotential at the electrodes under the anode rib was significantly large compared with the flow channel part, whereas the latter case exhibited smaller overpotentials under the rib. This indicates that oxygen transport becomes poor under the wider rib in the cathode side. The latter case also indicated that the electrode under the rib exhibited smaller overpotential than the flow channel part when fuel is sufficient, owing to the smaller contact resistance under the rib by the compression. We also calculated current and hydrogen/oxygen partial pressure distributions by finite element simulation (COMSOL Multiphysics). The current distributions can be calculated so that they agree with the in-situ current distributions derived by the segmented cathodes from setting the exchange current densities, electrode porosities, electrolyte ion conductivities, and electrode ion/electron conductivities. Thereby oxygen starvation under the wider cathode rib and larger electron conduction resistance for the flow channel part were numerically evaluated to explain the in-situ currents for the segmented cathodes. We will present the results for the case of H2 starvation. [1] Ö. Aydin, T. Koshiyama, H. Nakajima, T. Kitahara, In-situ Diagnosis and Assessment of Longitudinal Current Variation by Electrode-Segmentation Method in Anode-Supported Microtubular Solid Oxide Fuel Cells, J. Power Sources, Vol. 279, 218–223 (2015).Fig. 1 Segmented cathodes on the planar SOFC. Figure 1

Current Distribution Mapping for PEMFCs

A developed measurement system for current distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFCs). Currently, there are many issues with the methods to measure current distribution; some of the problems that arise are breaking up the fuel cell component and these measurements are costly. Within this field of work, there is a cost effective method and an easy technique of mapping the current distribution within a fuel cell while not disrupting reactant flow. The physical setup of this method takes a current distribution board and inserts it between an anode flow field plate and a gas diffusion layer. From this layout, the current distribution can be directly measured from the current distribution board. This novel technique can be simply applied to different fuel cell hardware. Further it also can be used in fuel cell stack by inserting multiple current distribution boards into the stack cells. The results from the current distribution measurements and the electrochemical predictions from computational fluid dynamics modeling were used to analyze water transports inside the fuel cell. This developed system can be a basis for a good understanding of optimization for fuel cell design and operation mode.

Direct Current Distribution Measurement of an Electrolyte-Supported Planar Solid Oxide Fuel Cell under the Rib and Channel by Segmented Electrodes

In the planar SOFCs, the fuel/oxidant distributions and current collecting resistance cause current and temperature distributions over the electrodes under the separator ribs and flow channels. Optimized design of the separator is hence required to improve the output power and chemical/thermo-mechanical durabilities of practical stacks. To clarify the distributions, we prepare planar cells having three segmented cathodes. Current-voltage characteristics are measured with voltage control using three electric loads to reproduce the electrode potentials of a single cell at around 800°C. We find significantly small in-plane oxygen transport rate under the cathode rib and higher current collecting resistance under the channel. Increased anode rib width gives large overpotential under the rib due to fuel starvation. Finite element modeling supports the above experimental results. We demonstrate an improved separator design of a practical stack, taking advantage of this model. Thereby ca. 17% higher maximum power is given in the finite element simulation.

Three temperature regimes in superconducting photon detectors: quantum, thermal and multiple phase-slips as generators of dark counts.

We perform measurements of the switching current distributions of three w ≈ 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijärvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced.

Experimental and Numerical Characterization of Corona Discharge Generated by a Triode Electrode System

The triode electrode system is frequently employed for accurately controlling the corona charging of insulating materials. The primarily aim of this paper is to characterize this electrode system by current–voltage and current density distribution measurements. The electrostatic aspect of the electric field generated by the triode electrode system is also numerically analyzed using a charge simulation program. The ionizing element of the electrode system is a thin tungsten wire (diameter: 200 $\mu\hbox{m} $ ) attached to a cylinder (diameter: 26 mm) and distanced at 34 mm from its axis. The wire-cylinder assembly is a “dual” electrode, facing a grid electrode, connected to a well-defined potential, and grounded plate electrode (aluminum, 250 mm $\times$ 130 mm) . The interelectrode spacing has a very significant influence on the current–voltage characteristics of the triode system and on the extension of the corona discharge generated by it. The experimental results obtained for different geometries of the electrode system are interpreted in the light of the numerical modeling of the electric field, in order to make some recommendations regarding its design: reduce/increase the wire-grid distance in order to diminish the operating high voltage/expend the surface affected by the corona discharge.

Analysis of the Correlation Between Local Temperature and Observed Degradations during Durability PEMFC Tests for Automotive Application

In Proton Exchange Membrane Fuel Cells, local temperature is a driving force for many degradation mechanisms such as hydrothermal deformation, creep, platinum dissolution, and bipolar plates corrosion [1, 2]. In order to investigate and quantify those effects, durability testing in automotive-related operating conditions is conducted in this work. In particular, two ageing tests have been conducted: a stationary test over 2000 h under nominal operating conditions and a load/thermal cycling test (1500 cycles) which corresponds to peaks in power demand. During the ageing tests, punctual characterizations like polarization curves, Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), Electrochemical Impedance Spectroscopy (EIS) and Fluoride Release Rate (FRR) are performed in order to investigate respectively the overpotentials (and global performance), the electrochemical surface area, the hydrogen crossover though the membrane, the transfer resistances and the membrane chemical degradation. Continuous in situ measurements of current density distribution and local temperature are made with a printed circuit board (Current Scan Lin S++ device [3]) inserted in the middle of 30 cells stacks. At the end of life, post-mortem analysis of the aged components via optical microscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) are conducted in order to investigate their microstructure and chemical composition. Infrared Imaging (IR) is used to study the local permeation in the aged membrane. In order to study the correlation between the observed degradation and the local conditions inside the PEMFC (temperature, relative humidity, molar fraction of hydrogen and oxygen, water fluxes…), a pseudo-3D physic based model has been developed at the cell scale (220 cm²) and validated against the in situ experimental data of the printed circuit board. Given the aspect ratio of the different cell components, the idea of the pseudo-3D approach is to consider each component as a plane layer, which is coupled to the other components through appropriate exchange conditions. With this approach, it is thus possible to compute the 2D (in-plane) distribution of the different physical parameters (temperature, species concentration…) in each cell component (active layers, gas diffusion layers, membrane, bipolar plates, cooling circuit…) at a reasonable cost. The model takes into account the thermal effects, including the exchanges with the cooling circuit, species transport and the electrochemical behavior of the electrodes. The model is implemented in the software Comsol Multiphysics. The simulation results highlight different zones where temperature and linked parameters, such as humidity, have extreme values causing notably lower local performance and increasing risks of water flooding. The post-mortem analysis mainly point out heterogeneous bipolar plates and membrane degradations that are different in the anode and cathode sides both at the cell and at the channel/rib scale but quite reproducible along the stack (See Figure 1). The correlation of the simulations with the experimental results highlight the effects of local temperature and gases humidity on in-situ performance losses and ex-situ observed degradations from the cell scale to the channel/rib scale. Furthermore, the impact of dynamic thermal cycles on degradation acceleration is quantified. [1] P. Pei et al. Main factors affecting the lifetime of Proton Exchange Membrane fuel cells in vehicle applications: A review, Applied Energy 125 (2014) 60–75 [2] S.F. Burlatsky et al. A mathematical model for predicting the life of polymer electrolyte fuel cell membranes subjected to hydration cycling, Journal of Power Sources 215 (2012) 135 - 144 [3] S++ Simulation Services, Waldstraße 5, 82418 Murnau-Westried, Germany. www.splusplus.com Figure 1

Dynamics of anode–cathode interaction in a polymer electrolyte fuel cell revealed by simultaneous current and potential distribution measurements under local reactant-starvation conditions

Low stoichiometry operation of fuel cells induces nonuniformities in the current generation and electrode potentials across the active electrode area. In this study, current and potential distributions are measured simultaneously in a fuel cell operating under reactant (fuel/air)-starvation conditions. During the galvanostatic operation under local reactant starvation, the localized increase of current density is observed closer to the inlet. Here under air starvation, cathode potentials dropped uniformly across the electrode area. However, during fuel starvation, a nonuniform cathode potential profile is observed. During the potentiostatic mode of operation under air-starvation condition, cathode potentials remained uniform and constant across the electrode area. However, under fuel starvation, the cathode potential profile is influenced by the anode potential profile. Electrode–electrode interaction especially during fuel starvation is captured by simultaneous measurements of current and potential distribution.

911 Verification of Accuracy on Measurement of Current Distribution in Polymer Electrolyte Fuel Cell

911 Verification of Accuracy on Measurement of Current Distribution in Polymer Electrolyte Fuel Cell

Influence of Cathode Shape on Vacuum Arc Thruster Performance and Operation

Vacuum arc thrusters (VATs) are a potentially useful technology for use as microthrusters, given their simplicity, low mass, and low-power requirements. However, further development is still needed to improve and mature their performance and operation. In an effort to improve thruster characteristics, we investigate the use of conically shaped convergent cathode surface profiles in a low-power coaxial VAT design. Experimental measurements of ion current density distribution, thrust, and erosion rate were taken for a range of cathode profiles and materials. Results show that modifying the profile of the cathode face can affect the plasma jet's plume distribution and even improve thrust production in certain cases. One likely cause of the thrust improvement is speculated to be increased charge exchange collisions resulting in a lower average ion charge state of the ejecting plasma.

微型法拉第筒阵列束流均匀性测量

微型法拉第筒阵列束流均匀性测量