Current Interruption Method Research Articles

APPLICATION AND COMPARISON OF CURRENT INTERRUPTION AND ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY METHODS TO STUDY A MICROBIAL FUEL CELL

In this research, current interruption and electrochemical impedance spectroscopy (EIS) methods are employed to determine the internal resistance of a dual-chambered mixed-culture microbial fuel cell with glucose feed, graphite anode, platinum sheet cathode, and Nafion 117 proton exchange membrane. Potential recovery curves and EIS spectra are obtained under various time intervals and analyzed using proper electrical circuit models. Polarization results show that the maximum output power of the cell is about 380 mW.m−2 normalized to the cathode surface area. The open circuit potential (OCP) of the cell is about 550 mV, and the value of the short circuit current is 0.35 mA.cm−2 of the cathode geometric surface area. The results show that the current interruption method can monitor in a rather satisfactory way the electrochemical changes such as variations in internal resistance and interfacial pseudo-capacitance inside the microbial fuel cell during the operation and thus can be employed as an easy-to-set-up electrochemical method to gain valuable data and facilitate the study of low power density devices such as microbial fuel cells.

Carbon nanotube powders as electrode modifier to enhance the activity of anodic biofilm in microbial fuel cells

Carbon nanotube (CNT) is a promising electrode material and has been used as an anode modifier in microbial fuel cells (MFCs). In this study, a new method of simultaneously adding CNT powders and Geobacter sulfurreducens into the anode chamber of a MFC was used, aiming to form a composite biofilm on the anode. The performance of MFCs such as startup time and steady-state power generation was investigated under conditions of different CNT powders dosages. Results showed that both the startup time and the anodic resistance were reduced. The optimal dosage of CNT powders pre-treated by acid was 4mg/mL for the anode chamber with an effective volume of 25mL. The anodic resistance and output voltage of the MFC with CNT powders addition were maintained around 180Ω and 650mV during 40 days operation, while those of the MFC without CNT powders addition increased from 250Ω to 540Ω and decreased from 630mV to 540mV, respectively, demonstrating that adding CNT powders helped stabilize the anodic resistance, thus the internal resistance and power generation during long-term operation. Based on cyclic voltammogram, the electrochemical activity of anodic biofilm was enhanced by adding CNT powders, though no significant increase of the biomass in anodic biofilm was detected by phospholipids analysis. There was no remarkable change of ohmic resistance with an addition of CNT powders revealed by current interrupt method, which indicated that the rate of mass transfer might be promoted by the presence of CNT powders.

Preparation and characterization of membrane electrode assembly (MEA) for PEMFC

Fuel cell is a system that converts chemical energy to electrical energy from an oxidation–reduction reaction of hydrogen and oxygen. In this study, Pt/C catalyst, solvent, and a binder agent were mixed to prepare catalyst ink. First, we applied carbon black ink to the carbon paper to supply hydrophobic and hydrophilic structure on its surface, which is called as microporous layer (MPL). Then catalyst ink was deposited on the treated carbon paper to form gas diffusion layers (GDLs) for anode and cathode side of the fuel cell. At this position, catalyst layer surfaces and carbon paper were analyzed by using scanning electron microscopy (SEM) and it was seen by energy dispersive spectroscopy (EDS) analysis that the catalysts were spread uniformly on a carbon paper. A membrane is fixed between GDLs and hot-pressed at 120°C, 75 kg cm− 2 to compose membrane electrode assembly (MEA). In a fuel cell test unit, MEA has internal resistance, which was evaluated by applying current interrupt method and current–voltage curve was drawn by load application. As a result of the test, I-V curves were formed and compared with characteristic curve of commercial MEA. It was seen that the shapes of the curves are similar. Maximum power values are 100, 275, and 390 mW for homemade MEA without MPL, with MPL, and commercial MEA, respectively. MEA without MPL was susceptible to flooding, especially at high-currrent values. MPL is helpful to increase the porosity of the diffusion layer and this effect can improve the oxygen transfer rate and lead to a higher performance. Compared with commercial MEA, homemade MEA did not reach high-current and -power values due to lots of parameters which affects the fuel cell performance as catalyst activity, conditions of MEA preparation, and disorder of measurement conditions, etc. Copyright © 2010 John Wiley & Sons, Ltd.

On-line Measurement for Ohmic Resistance in Direct Methanol Fuel Cell by Current Interruption Method

Electrochemical impedance spectroscopy (EIS) is widely used in fuel cell impedance analysis. However, for ohmic resistance ( R O), EIS has some disadvantages such as long test period and complex data analysis with equivalent circuits. Therefore, the current interruption method is explored to measure the value of R O in direct methanol fuel cells (DMFC) at different temperatures and current densities. It is found that R O decreases as temperature increase, and decreases initially and then increases as current density increases. These results are consistent with those measured by the EIS technique. In most cases, the ohmic resistances with current interruption ( R iR) are larger than those with EIS ( R EIS), but the difference is small, in the range from −0.848% to 5.337%. The errors of R iR at high current densities are less than those of R EIS. Our results show that the R iR data are reliable and easy to obtain in the measurement of ohmic resistance in DMFC.

ChemInform Abstract: Hydrogen Absorption and Li Inclusion in a Pd Cathode in LiOH Solution.

Abstract The amount of electrochemically absorbed hydrogen and lithium in a Pd cathode during electrolysis was measured quantitatively in LiOH solution. The electrode potential was also measured by the current interruption method. Inclusion of Li in Pd was found even at the potential of −0.22 V vs. RHE. This potential is far more positive than the reported UPD potential. Since Li was detected up to a depth of 200 nm, this phenomenon is not a simple UPD. The deposition of Li onto Pd and the formation of PdLi alloy are likely to occur at a much more positive potential than expected. The [ H ] [ Pd ] ratio decreased gradually after 50 h electrolysis at a current density greater than 5 mA cm−2.

Measurement of dissolved hydrogen supersaturation during water electrolysis in a magnetic field

The cathode potential on the gas-evolving electrode in 0.5 M H 2SO 4 solution was measured under a uniform magnetic field. The current interrupter method allowed us to study the IR-drop and the supersolubility of dissolved hydrogen gas. MHD convection by Lorenz force slightly reduced the ohmic resistance between the working and reference electrode, considerably restricted the increase of supersolubility and simultaneously promoted the mass transfer coefficient of the dissolved gas above 50 mA cm −2. Moreover, the supersolubility peak position displayed a strong dependence on the current density in the intermediate current density region from 5 to 30 mA cm −2. The peak location shifted toward lower current density with increasing in magnetic flux density. Our data show that applying a magnetic field has a much greater effect on the supersolubility at intermediate current density region than the mass transfer coefficient.

Effects of Pressurization on Cell Performance of a Microtubular SOFC with Sc-Doped Zirconia Electrolyte

In this study, we fabricated an anode-supported microtubular solid oxide fuel cell (SOFC) with the cell configuration (LSCF)– (CGO) cathode/CGO buffer layer/ (ScSZ) electrolyte/Ni–ScSZ anode. A power generation test of the SOFC was carried out at 0.1–0.7 MPa at . By using a wet gas mixture and air, the maximum power density of the microtubular cell was found to be (at , ) at atmospheric pressure (0.1 MPa). With increasing the operating pressure, the performance of the cell was improved, and the power density reached (at , ). It was confirmed by the current interruption method that both polarization and ohmic resistances decrease under a pressurized condition.

ナフィオン膜を用いる電解セルにおける水電解特性に及ぼす圧力効果

Pressure effects on the water electrolysis performance of the cell using Nafion 117 for electrolyte were investigated. It was found that the internal resistance of the cell decreased with increasing the pressure, while it is expected that the chemical equilibrium shifts to the reactant side. Detail analysis of the internal resistance by a current interruption method suggests that decrease in the internal resistance results from the decreased IR loss, which is assigned to the increased conductivity of Nafion 117 film. On the other hand, the overpotential of cathode and anode slightly increases as the pressure increases. In particular, the concentration overpotential on both electrodes increased under an elevated pressure. Since the internal resistance decreased by elevating water pressure, water electrolysis efficiency was improved to a value of 65% at 20 MPa, 100 mA/cm2. Consequently, this study reveals that pressure shows the prospective effects on the water electrolysis performance of the cell using Nafion 117 electrolyte in an initial short period.

Semi-empirical evaluation of PEMFC electro-catalytic activity

The investigation of the performance of small single PEMFC was carried out by employing a purposely designed test bench with complete control of the operational parameters. A MEA preparation method was also developed constituting the base for testing new electrocatalytic materials or improved electrode assembling techniques. Beyond determining the polarization curves, other tests have been carried out like electrical resistance measurement by the current interruption method and voltammetric characterization. A semi-empirical approach based on a simplified mathematical model has been used to fit the experimental polarization data, providing useful parameters for evaluating the electrocatalytic activity together with other significant data of the MEA performance. The analysis of polarization curves includes the determination of the OCV by considering the mixed potential at the oxygen electrode by fitting the initial data with an arbitrary oxidation reaction. This can provide an estimate of hydrogen crossover. Possible change of ohmic resistance with current intensity is discussed. The preliminary results, demonstrating the feasibility of the method are reported.

Water Electrolysis under a Magnetic Field

The energy efficiency of water electrolysis was considerably improved under a high magnetic field. This was proved by measuring the cell voltage, the IR-drop, and the electrode potentials for the electrolysis which was galvanostatically operated in alkaline (4.46 and KOH) and acidic ( ) solutions. A large reduction in the cell voltage was achieved in a magnetic field, especially at a high current density. The decrease of the IR-drop, which was measured by the current interrupter method, depended on the concentration of electrolyte solutions. In a magnetic field, the oxygen overpotential was reduced more than the hydrogen overpotential.

Morphology Control of Ni-GDC Cermet Anode for Lower Temperature SOFC

A Ni-GDC cermet is expected as one of the materials for lower temperature SOFC anode, which is obtained from reducing NiO-GDC powder. In this work, we report the effects of NiO-GDC powders produced by mechano-chemical technique on the fabricating processes of anode and the electrical performance of the anode. The properties of sintering and dispersion of NiO-GDC powders were studied and the morphology of Ni-GDC anode was characterized. The performance of the cell which consisted of Ni-GDC anode, GDC electrolyte and LSCF cathode was evaluated by current interruption method. The experimental results indicated that the maximum power densities were 0.93 and 0.31 W/cm2 when the cell was operated at 600{degree sign}C and 500{degree sign}C respectively.

Cell Performance of Microtubular SOFCs with Sc-Doped Zirconia Electrolyte under Pressurized Conditions

n this study, we fabricated anode-supported solid oxide fuel cell (SOFC) tubes of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) - Ce0.8Gd0.2O1.9 (CGO) cathode / CGO buffer layer / (ZrO2)0.89 (Sc2O3)0.1(CeO2)0.01 (ScSZ) electrolyte / Ni-ScSZ anode. The power generation test of the SOFC was carried out at 0.1 - 0.7 MPa at 650{degree sign}C. Using wet H2-N2 mixture gas and air, the maximum power density at 0.1 MPa was 0.68 W cm-2 (@2.6 A cm-2, Uf = 78%). With increase operating pressure, the performance has been improved, and the power density finally became over 1.48 W cm-2 (@2.8 A cm-2, Uf = 86%). It was conformed by current interruption method that both of the polarization resistance and ohmic resistance reduced under the pressurized condition.

SOFCs with Sc-Doped Zirconia Electrolyte and Co-Containing Perovskite Cathodes

Recently, much attention has been directed toward the study of Sc-doped zirconia electrolyte for intermediate-temperature SOFCs (IT-SOFCs) due to its fairly good ionic conductivity compared with conventional Y-doped zirconia, which can reduce the internal ohmic loss of the cell. For improving unit cell performance, another important point to be considered is the selection of appropriate electrode materials to reduce the polarization loss at the electrode. In this study, we fabricated anode-supported SOFCs with a % codoped % (CeSSZ) electrolyte. Various kinds of cathode materials such as , (LSCo), , and (SSCo) have been applied in order to identify the most suitable cathode material for Sc-doped zirconia. We evaluated the power-generating characteristics of scaled unit cells as well as the cathode polarization effect via a dc current-voltage measurement, a dc current interruption method, and ac impedance spectroscopy. We also thoroughly investigated the interfacial reaction between the electrolyte and the cathode in order to identify appropriate heat-treatment conditions for each candidate cathode material on the CeSSZ electrolyte. According to the investigation, unit cells with a SSCo and LSCo cathode showed superior power density of 1.13 and , respectively, at 700°C and fairly stable cell performance without any serious interfacial reaction.

Performance modeling for low pressure vehicle proton exchange membrane fuel cell stack

According to the status in the vehicle, a low pressure vehicle proton exchange membrane fuel cell (PEMFC) stack model is developed using a semi-empirical modeling technique. First, the oxygen concentration item is derived from the PEMFC output voltage equation, and the concept of oxygen concentration resistance coefficient is presented. Secondary, the ohm losses in many different temperatures are determined via the experiments with the current interrupt method, which is formulized with linear regression method. Then, the oxygen concentration item is studied by the experiments with different air stoichiometric ratios while keeping the other operating parameters unchanged, and the oxygen concentration resistance coefficient is obtained by the genetic arithmetic which is used to process the difference voltages of the PEMFC stack in different air stoichiometric ratios. Then, the activation loss is obtained based on PEMFC output voltage and the loss of ohm and the loss of concentration. Finally, with the correlation of the model to 20 actual experimental data, the good agreement between the computation results and the experimental results is found out. The credibility of the modeling method is verified and the precision of the model is in accord with the systematic optimization and control.

A semi-empirical voltage degradation model for a low-pressure proton exchange membrane fuel cell stack under bus city driving cycles

A voltage degradation model for the low-pressure proton exchange membrane fuel cell (PEMFC) stack used in a fuel cell bus is presented: (1) the oxygen concentration term was derived from the PEMFC output voltage equation, and the concept of oxygen concentration resistance coefficient was introduced; (2) a 5 kW low-pressure PEMFC stack was used in this study. Two similar tests were carried out before and after the stack operating in the driving cycle for 640 h. First, the ohmic losses under different temperatures were measured using the current interrupt method and formulized with linear fitting method. Then, the oxygen concentration term was studied by the experiments with different air stoichiometric ratios while keeping the other operating parameters unchanged. The oxygen concentration resistance coefficient was obtained from the difference of voltages for the PEMFC stack in different air stoichiometric ratios using the genetic optimization algorithm. Then, the activation loss was obtained based on the PEMFC output voltage, the ohmic loss, and the concentration loss. The degradation model of the stack was built finally by comparing the two test results; (3) the correlation of the model to the actual experimental data is good; (4) the overvoltage of the stack with aging was analyzed using this model. The analysis showed that the activation overvoltage dominated the stack loss with about 80% of the total losses, followed by the ohmic loss. The concentration loss almost does not change with aging in the driving cycle condition; (5) the comparison of the simulation with the actual data from the PEMFC bus running for 30,000 km indicated that after 36,000 km the rated power of the PEMFC bus must be reduced.

Ohmic Resistance Measurement of Bubble Froth Layer in Water Electrolysis under Microgravity

Galvanostatic water electrolysis was conducted in and solutions under microgravity. The corresponding terrestrial experiments employed two kinds of electrode configurations: a vertical cathode and downward-facing horizontal cathode-over-anode (C/A) arrangement. The latter configuration was designed to simulate the microgravity condition. The ohmic resistance of the gas bubble dispersion zone near electrodes was measured by the current interrupter method and compared for these three different cases. The transient variation of resistance for C/A configuration behaved similarly to that under in , but the resistance varied more slowly in . When water electrolysis was conducted with a vertical plane cathode under , the resistance reached an essentially constant value within a few in , whereas the resistance increased linearly for a few seconds, followed by a zig-zag variation in . Water electrolysis under resulted in stable froth layer formation, and the accompanying ohmic resistance increased in linear proportion to the froth layer thickness. The contributions of electrode surface coverage by bubbles and electrolyte-phase bubble void fraction to the ohmic drop were also assessed. These parameters were compared with corresponding values in terrestrial experiments analyzed by Balzer and Vogt.

Performance of an Intermediate-Temperature Fuel Cell Using a Proton-Conducting Sn0.9In0.1P2O7 Electrolyte

Performance of a fuel cell using as the electrolyte was evaluated in the temperature range of under unhumidified conditions. The IR drop and electrode overpotential of the cell were measured separately by the current interruption method. The dc conductivity values of the electrolyte between 150 and , estimated from the IR drop, were comparable to the ac conductivity values of the electrolyte. The cell performance was improved by forming an intermediate layer consisting of and catalyst powders at the interface between the electrolyte and cathode, which significantly reduced the cathode polarization. As a result, the peak power density reached at using the -thick electrolyte. The present fuel cell also showed high stability at low relative humidities and 10% CO concentration.

B114 小型円筒形状固体酸化物形燃料電池単セルの発電特性(分散エネルギーシステムにおける要素技術とその集積化1)

In this paper, we investigate the power generation performance of a small-scale tubular solid oxide fuel cell (SOFC), in particular the effects of steam content in fuel flow on the terminal voltage are discussed. In the present experiments, hydrogen and nitrogen mixture, of which volume ratio H_2/N_2 was adjusted at 5%/95%, was supplied into the anode side of the single cell. The performance curves, i.e., the relationships between current and voltage, were measured on the different fuel flow rate conditions and the constant furnace temperature of 800℃. At the same current output operation, the voltage of the wet fuel supply was lower than that of the dry fuel case. In order to investigate the influence of steam addition on the voltage drop, we tried to measure the voltage loss, which was caused by the electrical and ionic resistance, through the current-interruption method. As a result, it is found that the ohmic voltage drops in the wet and the dry cases account for 9% and 27% to the total voltage drops, respectively. The absolute value of the ohmic loss is independent on the steam content. Hence, we guess that the larger voltage loss in the case of the wet fuel results from activation and concentration overpotentials.

혼합전도체 LSCF(La0.6Sr0.4Co0.2Fe0.8O3)양극의 기공률에 따른 음극지지형 단전지의 출력특성 평가

We analyzed the unit cell performance against the cathode porosity, which is supposed to be closely related with active sites for the cathode reaction. In order to fabricate the unit cells with different porosity in the cathode layer we changed the mixing ratio of fine and coarse LSCF cathode powders. The final porosity of each cathode layer was 14, 23, 27, respectively. According to the electrochemical analysis of unit cell performance via DC current interruption and AC impedance method, the electrodic polarization resistance was diminished as the cathode porosity increased. The decrease of polarization resistance was attributed due to the increase of active reaction sites and the enhancement of overall unit cell performance could be explained in the same line.

G123 小型固体酸化物形燃料電池単セルの発電特性(一般セッション 燃料電池II)

In this paper, we investigate the effects of fuel supply conditions on the power generation characteristics of a small tubular solid oxide fuel cell (SOFC), In the experiments, the furnace inside temperature is fixed at 800℃, and the hydrogen/nitrogen mixture (10%/90%) is fed into the single cell as the fuel with the different flow rate conditions. The results show that the flow rate affects the current-voltage characteristics, that is, the net voltage becomes higher with increasing the fuel flow rate. The data of the fuel utilization and the power generation efficiency at the operating points, which give the maximum power output individually, are estimated. Under the operation with 10% hydrogen, the power generation efficiency reaches to 9.0% with the fuel flow rate of 20mL/min. But lower fuel flow rate condition, the fuel utilization and efficiency greatly decrease simultaneously. In addition, by using current interruption method, the detail of the voltage drop is estimated. It is found that the fuel flow rate does not quite affect the ohmic loss.