Current Interruption Technique Research Articles

Current Interrupt Technique to Fully Characterize PEMWE Cells

It is common practice to characterize cells in polymer electrolyte membrane water electrolysis (PEMWE) using electrochemical impedance spectroscopy (EIS) and Tafel analysis, which require special equipment and operation procedures. Additionally, these techniques are not suitable for large industrial size cells with very low impedances. We present a simpler approach based on a novel evaluation of the current interrupt (CI) technique. The CI technique utilizes the voltage response after an instantaneous drop of electric current to identify the ohmic resistance R Ω, charge transfer resistance R ct and double-layer capacity C dl in a simplified equivalent circuit (EC) of the cell. A direct link to results of typical EIS and Tafel analysis can be defined by using the improved CI method which considers a non-linear activation resistance instead of a constant charge transfer resistance. Thereby, access to equivalent information as the established standard method is granted, while being applicable to all cell and stack sizes without requiring special equipment (e.g. impedance spectrometer). The agreement with experimental data is significantly improved over the assumption of a constant charge transfer coefficient. Consistency of the proposed interpretation with explicit EIS and Tafel analysis is demonstrated and options for industrial application of the evaluation scheme are discussed.

Understanding the Electrochemical and Interfacial Behavior of Sulfolane based Electrolyte in LiNi0.5Mn1.5O4‐Graphite Full‐Cells

AbstractAn ethylene carbonate‐free electrolyte composed of 1 M lithium bis(fluorosulfonyl) imide (LiFSI) in sulfolane (SL) is studied here for LiNi0.5Mn1.5O4‐graphite full‐cells. An important focus on the evaluation of the anodic stability of the SL electrolyte and the passivation layers formed on LiNi0.5Mn1.5O4 (LNMO) and graphite is being analysed along with intermittent current interruption (ICI) technique to observe the resistance while cycling. The results show that the sulfolane electrolyte shows more degradation at higher potentials unlike previous reports which suggested higher oxidative stability. However, the passivation layers formed due to this electrolyte degradation prevents further degradation. The resistance measurements show that major resistance arises from the cathode. The pressure evolution during the formation cycles suggests that there is lower gas evolution with sulfolane electrolyte than in the conventional electrolyte. The study opens a new outlook on the sulfolane based electrolyte especially on its oxidative/anodic stability.

Understanding the Capacity Fade in Polyacrylonitrile Binder‐based LiNi0.5Mn1.5O4 Cells**

AbstractBinders are electrochemically inactive components that have a crucial impact in battery ageing although being present in only small amounts, typically 1–3 % w/w in commercial products. The electrochemical performance of a battery can be tailored via these inactive materials by optimizing the electrode integrity and surface chemistry. Polyacrylonitrile (PAN) for LiNi0.5Mn1.5O4 (LNMO) half‐cells is here investigated as a binder material to enable a stable electrode‐electrolyte interface. Despite being previously described in literature as an oxidatively stable polymer, it is shown that PAN degrades and develops resistive layers within the LNMO cathode. We demonstrate continuous internal resistance increase in LNMO‐based cells during battery operation using intermittent current interruption (ICI) technique. Through a combination of on‐line electrochemical mass spectrometry (OEMS) and X‐ray photoelectron spectroscopy (XPS) characterization techniques, the degradation products can be identified as solid on the LNMO electrode surface, and no excessive gas formation seen. The increased resistance and parasitic processes are correlated to side‐reactions of the PAN, possibly intramolecular cyclization, which can be identified as the main cause of the comparatively fast capacity fade.

Pulse-opencircuit voltammetry: A novel method characterizes bioanode performance from microbe-electrode interfacial processes

Bioanode is a key component of bioelectrochemical systems, but the methods characterizing its resistance distribution are lacked. We propose a novel pulse-opencircuit voltammetry (POV) based on the analytical principle clarified from the electron flow pathways of microbe-electrode interfacial processes (MEIPs). A dual-cathode cell is designed to provide an experimental platform for ensuring precise data acquisition of bioanodes. This POV method enables to measure steady state polarization curves and ohmic potential loss curves by integrating potentiostatic discharge and current interruption techniques. They determines reaction resistance (RB,act) and ohmic resistance (RB,ohm) of biofilm with the assistance of impedance spectroscopy measuring material resistance. The results of various bioanodes demonstrate that RB,act is the principal limiting factor and its value relies on catabolism state. Whilst RB,ohm is relevant to extracellular electron transfer behaviors. They are two useful indicators of the dynamic evaluation of biofilm. We anticipate that this method together with the cell platform is accessible to users and has wide applications in bioanode construction and electroactive bacteria investigation.

Implementing intermittent current interruption into Li-ion cell modelling for improved battery diagnostics

A novel electroanalytical method, the intermittent current interruption (ICI) technique, has recently been promoted as a versatile tool for battery analysis and diagnostics. The technique enables frequent and continuous measurement of battery resistance, which then undergoes statistical analysis. Here, this method is implemented for commercial Li-ion cylindrical cells, and combined with a physics-based finite element model (FEM) of the battery to better interpret the measured resistances. Ageing phenomena such as solid electrolyte interphase (SEI) formation and metallic Li plating on the surface of the negative graphite particles are considered in the model. After validation, a long-term cycling simulation is conducted to mimic the ageing scenario of commercial cylindrical 21700 cells. The large number of internal resistance measurements obtained are subsequently visualized by creating a ‘resistance map’ as a function of both capacity and cycle numbers, providing a straight-forward image of their continuous evolution. By correlating the observed ageing scenarios with specific physical processes, the origins of ageing are investigated. The result shows that a decrease of the electrolyte volume fraction contributes significantly to the increase of internal resistance and affect the electrolyte diffusivity properties. Additionally, effects of porosity and particle radius of the different electrodes are investigated, providing valuable suggestions for battery design.

Study on PCFC Total Voltage Loss Analysis by Current Interruption Technique to Separate IR Drop and Overvoltage

Study on PCFC Total Voltage Loss Analysis by Current Interruption Technique to Separate IR Drop and Overvoltage

An Attempt to Formulate Non‐Carbonate Electrolytes for Sodium‐Ion Batteries

AbstractNon‐aqueous carbonate solvents have been the main choice for the development of lithium‐ion batteries, and similarly most research on sodium‐ion batteries have been performed using carbonate‐based solvents. However, the differences between sodium and lithium batteries – in term chemistry/electrochemistry properties as well as electrode materials used – open up opportunities to have a new look at solvents that have attracted little attention as electrolyte solvent. This work investigates properties of a wide range of different solvent classes in the context of sodium‐ion battery electrolytes and compares them to the performance of propylene carbonate. The thirteen solvents studied here include one or several members of glymes, carbonates, lactones, esters, pyrrolidones, sulfones, and alkyl phosphates. Out of those, five outperforming solvents of γ‐butyrolactone (GBL), γ‐valerolactone (GVL), N‐methyl‐2‐pyrrolidone (NMP), propylene carbonate (PC), and trimethyl phosphate (TMP) were further investigated using additives of ethylene sulfite (ES), vinylene carbonate (VC), fluoroethylene carbonate (FEC), prop‐1‐ene‐1,3‐sultone (PES), sulfolane (TMS), tris(trimethylsilyl) phosphite (TTSPI), and sodium bis(oxalato)borate (NaBOB). The solvents TMS and tetraethylene glycol dimethyl ether (TEGDME) were tested in 1 : 1 mixtures by volume with the co‐solvents; NMP, dimethoxyethane (DME), and TMP. All electrolytes used NaPF6 as the salt. Primary evaluation relied on electrochemical cycling of full‐cell sodium‐ion batteries consisting of Prussian white cathodes and hard‐carbon anodes. Galvanostatic cycling was performed using both two‐ and three‐electrode cells, in addition, cyclic and linear sweep voltammetry was used to further evaluate the electrolyte formulations. Moreover, the resistance was measured on the anode and cathode, using Intermittent current interruption (ICI) technique.

Theoretical modelling of electrode overvoltage for an all-solid-state electrochemical device

Understanding the mechanism of electrode overvoltage generation is important for development of functional new all-solid-state electrochemical devices. The theory of electrode overvoltage developed for liquid-state electrochemical systems led to ambiguous causality when applied to solid-state systems. In this paper, the solid-state overvoltage is formulated from ionic transport theory in solids. The solid-state device was treated as an inhomogeneous thermodynamic system. Overvoltage was derived as a function of entropy production rate and found to be attributable to diffusion of neutral compounds in the electrodes. We discussed (1) measurement of the electrode overvoltage by the current interruption technique; (2) composite electrodes consisting of the electrolyte, electronic conductor, and active material; and (3) the problem on separation of charge transfer reaction process. Physical role of the electrode overvoltage was discussed on the basis of classical irreversible thermodynamics.

Anodic Polarization Behavior of X80 Steel in Na₂SO₄ Solution under High Potential and Current Density Conditions.

X80 steel has great risk of corrosion in high voltage direct current (HVDC) interference cases. In this study, the anodic polarization behavior of X80 steel under high potential and current density in Na2SO4 solution was investigated. The I × R drop was eliminated using current interrupt technique during the potentiodynamic measurement. Therefore, the real polarization curve was obtained. The corrosion behavior was investigated by galvanostatic polarization, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results show a new form of passivation route. The steel dissolved actively below −0.388 VSCE, then became partly passivated from −0.388 to 1.448 VSCE, and fully passivated above 1.448 VSCE. The passive film was formed containing Fe2O3 and FeOOH, and resistant to SO42− ions. It not only blocked the direct dissolution of steel, but also facilitated oxygen evolution. The corrosion rates of steel samples decreased after the passivation.

Understanding the Capacity Loss in LiNi0.5Mn1.5O4–Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive positive electrode because of its operating voltage around 4.7 V (vs Li/Li+) and high power capability. However, problems including electrolyte decomposition at high voltage and transition metal dissolution, especially at elevated temperatures, have limited its potential use in practical full cells. In this paper, a fundamental study for LNMO∥Li4Ti5O12 (LTO) full cells has been performed to understand the effect of different capacity fading mechanisms contributing to overall cell failure. Electrochemical characterization of cells in different configurations (regular full cells, back-to-back pseudo-full cells, and 3-electrode full cells) combined with an intermittent current interruption technique have been performed. Capacity fade in the full cell configuration was mainly due to progressively limited lithiation of electrodes caused by a more severe degree of parasitic reactions at the LTO electrode, while the contributions from active mass los...

Effect of TiO2 Addition on Grain Growth, Anodic Bubble Evolution and Anodic Overvoltage of NiFe2O4-Based Composite Inert Anodes

A two-step powder compaction and sintering process was employed to fabricate TiO2-doped NiFe2O4 ceramic-based inert anodes. Grain growth during isothermal sintering was analyzed using Brook grain growth model. The bubble behavior of NiFe2O4 ceramic-based inert anodes was investigated in a two-compartment see-through quartz cell for aluminum electrolysis process. Anodic overvoltage and potential decay curves of the inert anodes were measured by using the steady state and current interruption technique. The results showed that the kinetic index of grain growth decreased with an increase in temperature. The average activation energy of grain growth for 1.0 wt.% TiO2-doped NiFe2O4 ceramic samples with a sintering temperature range from 1373 to 1673 K dropped from 675.30 to 183.47 kJ/mol. The diameter size of bubbles before releasing from the bottom surface of the anodes was reduced with increasing the current density, and the larger average releasing bubble size for carbon anode at the same current density could be obtained, which was compared to the NiFe2O4 inert anodes. Besides, the cell voltage of carbon anodes fluctuated much more violently under the same experimental conditions. After adding small amount of TiO2, a minor reduction in anodic overvoltage of NiFe2O4-based anodes can be observed.

Distributed relaxation times technique for the determination of fuel cell losses with an equivalent circuit model to identify physicochemical processes

This paper shows the developments of an equivalent circuit model adopted to interpret the deconvoluted electrochemical impedance spectra of an Ni-YSZ/YSZ/GDC/LSCF solid oxide fuel cell obtained by varying the operating temperature and the oxygen partial pressure under a fixed load. This allowed to unfold the physicochemical processes occurring within the anode supported cell and to identify which elements are responsible for major polarization losses. Furthermore, this model has proved to be effective even in the high frequency region, which is often beset by the onset of troublesome artifacts, as underlined by the comparison with the galvanic current interruption technique.

Estimation of kinetic and electric parameters of liquid feed passive DMFCs

The study of polarization curves is an important part for evaluating the performance of passive direct methanol fuel cells (DMFCs). This study must be essentially followed by other experiments to gain knowledge of important kinetic and electrical parameters such as exchange current density, charge transfer coefficients, ohmic resistance, etc. This experimentation include in-situ characterization techniques such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and current interrupt (CI) technique which are expensive to carry out. Hence, this study develops a semi-analytical model for estimating exchange current density, charge transfer coefficients and ohmic resistance directly from the polarization curves. In addition, a simple “3/4-Point method” is introduced, utilizes the polarization curves for the estimation of kinetic and electric parameters. The triad (proposed model, 3/4-Point method and polarization/EIS experiment) are compared and exhibited similar trends, thereby validating it as a tool for estimation of a large class of parameters. The model is comprehensive as it is valid throughout the polarization curves, thereby avoiding the need for multiple strategies in different regions of the polarization curves to calculate various parameters. The model can serve to know the values of these parameters by-hand before other experimentations which involves high cost and sophisticated experimental conditions.

Solution Resistivity, Ohmic Drop and Oxygen Reduction Rate at High Temperature Pressurized Water

The solution resistivity (Rsol) and ohmic drop (ΔEΩ) of a three electrode high temperature electrochemical autoclave system containing a water+11550ppb NH4OH (pH(25°C) 10) solution were analyzed in the temperature range of 25°C to 285°C using electrochemical impedance spectroscopy (EIS) and galvanostatic potentiometry combined with automatic current interrupt iR compensation technique. The determined values were compared with the conductivity values calculated by a pH & Conductivity Calculator software. The results showed that when the temperature of the solution is increased the magnitude of the Rsol and therefore ohmic drop of the system decrease and after a defined temperature (150°C for EIS and 180°C for current interrupt) increase. The variations in the conductivity of the solution versus temperature calculated by the pH & Conductivity Calculator software were in more agreement with the impedance based Rsol values determined in this study. While investigation of the oxygen reduction reaction on platinum versus temperature showed that exactly at 180°C (the temperature corresponding to minimum Rsol and ohmic drop values determined using the current interrupt technique) the oxygen reduction reaction reached its maximum rate and by further increasing the temperature the oxygen reduction rate decreased and the reaction mechanism switched from a mixed mass–charge transfer controlled process to a charge transfer controlled process. The experiment results revealed that the Rsol values determined by the current interrupt technique are more accurate than the values obtained by EIS.

Suppression of Oxide Growth on Ti Substrate of Ir1-XSnxO2/Ti Anodes in Electrolytic Oxygen Evolution

INTRODUCTION In order to prevent global warming and to supply renewable energy in the form of methane, Hashimoto et al. have been proposing global CO2 recycling and have tailored the necessary key materials, that is, the anodes and cathodes for seawater electrolysis and catalysts for CO2 methanation by the reaction with hydrogen. The most difficult was the anode for seawater electrolysis, because the anode should evolve only oxygen without forming chlorine even in seawater electrolysis. Titanium is generally used as the electroconductive substrate. We usually covered the titanium substrate with IrO2 for prevention of oxidation of titanium. In chloride containing electrolytes, chlorine evolution occurs preferentially on the IrO2-covered titanium. Thus, we needed to prepare g-MnO2-type electrocatalysts covering the IrO2 layer for exclusive oxygen evolution in seawater electrolysis. We revealed that the Ir1-xSnxO2 double oxides have better protectiveness against oxidation of titanium than IrO2. The Mn1-x-yMoxSnyO2+x/Ir1-xSnxO2/Ti anode showed more than 99.9% oxygen evolution efficiency for 4200 h in the electrolysis of 0.5 M NaCl solution of pH 1 at 1000 Am-2. Although the oxygen evolution efficiency was close to 100%, the oxide growth on the titanium substrate was unavoidable due to the inward diffusion of oxygen through electrocatalyst and intermediate layers during oxygen evolution. The present work aimed to improve the protectiveness of Ir1-xSnxO2 double oxide. Since the Ir1-xSnxO2/Ti anodes themselves are oxygen evolution anodes in chloride free aqueous solutions, the protectiveness of Ir1-xSnxO2 double oxide during oxygen evolution at high current densities was examined using the Ir1-xSnxO2/Ti anodes in H2SO4 solutions. EXPERIMENTAL After surface roughening by immersion in 11.5 M H2SO4 the titanium substrate was coated with butanol solutions of H2IrCl6 and SnCl4, in which the sum of metallic cations was 0.1, 0.26 or 0.52 M. The specimens were dried at 80oC for 10 min and calcined at 250-450oC for 10 min. This procedure was repeated three times and the final calcination was continued for 0.5-24 h. The anodes were previously used for the electrolysis at 13,333 Am-2 in 3 M H2SO4 solution at room temperature for various periods of time, and then characterization of the used anodes was carried out by electrochemical measurements in 1 M H2SO4 solution at 25°C. Galvanostatic polarization curves were measured by the current density rise every 1 min. The potential rise due to the solution resistance at high current densities was corrected by the ordinary current interruption technique. Two more different current interruption techniques were applied at higher current densities using a digital oscilloscope for the measurement of the potential decays at every 0.0625 ms and 0.4 ms, respectively. RESULTS AND DISCUSSION The oxide growth on the titanium substrate occurred during electrolysis at high current densities for long periods. The oxide growth rate was estimated with anodic polarization curves and current interruption technique by the assumption of equivalent circuit of oxide covered metal electrode. When the sum of Ir4+ and Sn4+ was 0.52 M, the solely IrO2-coated anode showed the lowest rate of resistance growth. However, when the sum of Ir4+ and Sn4+ was 0.26 M, an increase in Ir4+ higher than 0.13 M was not effective to decrease the oxide growth. When the sum of Ir4+ and Sn4+ was 0.1 M, the minimum oxide growth rate appeared at 0.04 M Ir4+, where the oxide growth rate was similar to that of the anode prepared in 0.13 M Ir4+ - 0.13 M Sn4+ solution. Consequently, in order to save iridium, lower concentrations of Ir4+ and Sn4+ will be useful. On the other hand, an increase in calcination temperature led to incorporation of oxidized titanium in Ir1-xSnxO2. This also led to a resistance increase. Furthermore, the increase in calcination temperature resulted in potential increase at low current densities. This implied a decrease in the oxygen evolution activity due to inclusion of Ti2+ in Ir1-xSnxO2. However, the formation of triple oxide of Ir1-x-ySnxTiyO2 was not always detrimental for the elongation of the life of the anode. The growth rate of titanium oxide during anodic polarization at 13,333 Am-2 in 3 M H2SO4 solution was lowest when the anode was formed by calcination at 450°C. Consequently, the protectiveness of Ir1-x-ySnxTiyO2 formed by calcination at 450°C was highest even if oxidized titanium was included in the active anode for oxygen evolution. Consequently, the optimum preparation condition of Ir1-xSnxO2/Ti anodes was coating of Ti substrate with butanol solution of 0.13 M Ir4+ and 0.13 M Sn4+ and calcination at 450°C for 1 hour.

Durability of Electrodeposited Ni-Fe-Co-C Anodes for Alkaline Water Electrolysis

IntroductionWe have been studying more than a quarter of century for supply of renewable energy in the form of methane via electrolytic hydrogen generation using carbon dioxide as the feedstock. Although we created cathodes and anodes for direct seawater electrolysis, the energy efficiency was not sufficient. For immediate industrialization, we are concentrating our current effort on alkaline water electrolysis, creating efficient cathodes and anodes. The present work aimed to determine the composition of active Ni-Fe-Co-C alloy anodes prepared by electrodeposition and to examine the durability for continuous electrolysis at a high current density of 6000 Am-2 in 4.5 M KOH at 90°C. Experimental Procedures The substrate for electrodeposition was a chemically etched Ni plate. Electrodeposition was carried out at a current density of 300 Am-2 for 10 min in 1.14 M NiSO4-0.189 M NiCl2-0.49 M H3BO3-0.104 mM CH3(CH2)11OSO3Na solutions containing various concentrations of FeSO4, CoSO4 and lysine, the pH of which was adjusted at 1.5 by the addition of 18 M H2SO4. Lysine was added as the carbon source. The composition of metallic elements in the electrodes was analyzed by electron probe microanalysis, and carbon was chemically analyzed by combustion infrared absorption method. The solution used for oxygen evolution was 4.5 M KOH at 90oC. The activity of the anodes was evaluated from galvanostatic polarization curves measured by the current density rise every 1 min. The potential rise due to the solution resistance at high current densities was corrected by the current interruption technique. Potentiodynamic polarization curves were also measured at a potential sweep rate of 0.52mV-1 for comparison. Results and Discussion As-deposited alloys were used for examination of oxygen evolution activity. Ni was a stable anode but less active for industrial electrolysis. The addition of Co ion and lysine to the deposition electrolyte containing Ni ion enhanced the oxygen evolution activity, but the activity of Ni-Co-C alloys was not yet sufficiently high. Ni-Fe-Co-C alloys deposited showed significantly high activity for oxygen evolution. An increase in Fe content in the alloy was more effective than the increase in Co content for enhancement of oxygen evolution activity. Thus, an increase in Co concentration in deposition electrolytes did not largely change the activity because the increase in Co content in the alloy resulted in the decrease in the content of Fe. The addition of lysine to the deposition electrolytes containing Ni, Fe and Co ions enhanced the oxygen evolution activity. The highest activity was attained at 0.2 M lysine in the deposition solution, but further increase in lysine concentration was not effective. An increase in lysine concentration led to asymptotic increase in the C content in the Ni-Fe-Co-C alloys up to about 6 at%. The deposition electrolyte to form the most active Ni-Fe-Co-C alloy for oxygen evolution was 1.33M Ni-0.072M Fe-0.018M Co-0.2M lysine solution. When the Ni-Fe-Co-C alloy prepared from this electrolyte was used for oxygen evolution at a current density of 6000 Am-2 for 800 h, the mass loss was about 5 % of the original mass. The galvanostatic polarization potential of as-deposited Ni-Fe-Co-C alloy measured by the current density rise every 1 min was in the active region at lower current densities, but the potential shifed to the oxygen evolution region at higher current densities. Once the specimen was polarized in the oxygen evolution region, the potential was stayed in the oxygen evolution region even when the current density was lowered. After oxygen evolution at 6000 Am-2 for long period of time, the potential stayed in the oxygen evolution region regardless of current densities. In fact, the dissolution current density estimated from the mass loss by polarization at 6000 Am-2 for 800 h even on the assumption of Fe dissolution in the form of Fe6+ as FeO4 2- was only 4.5 x 10-3 Am-2 that is less than one-millionth of oxygen evolution current. Consequently, the active Ni-Fe-Co-C alloy anode thus prepared is sufficiently stable maintaining the passive state in the severe environment for oxygen evolution at 6000 Am-2 in a concentrated KOH solution at 90°C for long period of time. Conclusion The active oxygen evolution anode in alkaline water electrolysis for hydrogen production was created. The addition of Fe, Co and C to Ni enhanced the oxygen evolution efficiency in 4.5 M KOH solution at 90°C. The Ni-Fe-Co-C alloy thus prepared kept the passive state during electrolytic oxygen evolution at 6000 Am-2 for a long period of time.

Thermal behavior and electrochemical heat generation in a commercial 40 Ah lithium ion pouch cell

Quantitative data on the thermal behavior of lithium ion batteries under charging and discharging conditions are essential for designing thermal management systems and improving battery safety. In this work, commercial 40 Ah lithium ion pouch cells with Li(Ni1/3Mn1/3Co1/3)O2 cathodes were tested under isoperibolic and adiabatic conditions in an Accelerating Rate Calorimeter at different charging/discharging currents from 5 A to 40 A. Adiabatic tests simulate the worst-case scenario of a battery pack without cooling. For charging and discharging an overall exothermic behavior was found and a total temperature increase for one half cycle between 3 and 11 K. Isoperibolic tests simulate a single cell under constant environmental temperature. Here an exothermic behavior for discharging and an endothermic behavior for charging were observed. To transfer the measured temperature changes into heat data, the effective specific heat capacity and the heat transfer coefficient were determined. For the first time the heat generation data for a large format pouch cell have been determined using both isoperibolic and adiabatic conditions. These data were compared with the total heat data calculated as the sum of reversible and irreversible heat that were measured by potentiometric and current interruption techniques respectively. A good agreement was found between all three heat generation determination methods.

A fundamental approach to applying an insulated-gate bipolar transistor to current interruption in a low-voltage direct current delivery system

Summary A fundamental approach to apply an insulated gate bipolar transistor to a current interruption technique in a low-voltage direct current (DC) power delivery system is described. By considering the dependence of collector–emitter resistance on the gate–emitter voltage, a circuit configuration of circuit-breaker components was contrived to operate a DC interruption. Based on this design, a model DC circuit breaker composed of an insulated gate bipolar transistor was constructed to verify the interrupting performance of various DCs IDC under different source voltages EDC. The experimental results demonstrate that the model circuit breaker successfully decreased the instantaneous current to zero over an elapsed time and then interrupted the current. In addition, the results show that the current-interrupting time was almost constant against higher IDC and EDC. The results also verify that by adjusting the time constant of the gate–emitter voltage, the current-interrupting time could be controlled. Copyright © 2014 John Wiley & Sons, Ltd.

Poly(ethylene glycol) modified activated carbon for high performance proton exchange membrane fuel cells

A high water retention membrane is developed by co-assembling poly(ethylene glycol) (PEG) grafted activated carbon (AC-PEG) with Nafion. The AC-PEG is prepared via a sol–gel process. The use of PEG as a transporting medium in AC-PEG shows a largely improved water retention ability, a higher proton conductivity and a reduced swelling ratio, making it well suited for proton exchange membrane fuel cells (PEMFCs). Further, the composite membranes show improved mechanical properties at high temperature, thus ensuring the structural stability of membranes during the fuel cell operation. Compositional optimized AC-PEG/Nafion composite membrane (15 wt% compared to Nafion) demonstrates a better performance than the commercially available counterpart, Nafion 212, in fuel cell measurements. To identify the key factor of the improved performance, current interrupt technique is used to quantitatively verify the changes of resistance under different relative humidity environment.

Electrical Properties of La<sub>0.7</sub>Sr<sub>0.3</sub>CuO<sub>3-δ</sub>Cathode Based on SDC-YSZ Composite Electrolyte

The cathode material La0.7Sr0.3CuO3-δ was synthesized by a sol-gel method. X-ray diffraction revealed it to be form a single phase of perovskite. The SDC（Sm0.15Ce0.85O1.925）was synthesized by glycine-nitrate processes. The 90%SDC and 10%YSZ powders are mixed to prepare as SDC-YSZ composite electrolyte. The high temperature electrical conductivity of La0.7Sr0.3CuO3-δ was measured by using the four-point dc technique, and cathodic overpotential with SDC-YSZ composite electrolyte support was measured by using a current-interruption technique. Using La0.7Sr0.3CuO3-δ as cathode and 65%NiO/SDC as anode based on SDC-YSZ composite electrolyte one can obtain high current density and power density at intermediate temperatures.