Cell Voltage Difference Research Articles

Modeling Electrode Shape Changes in Electrodeposition and Electrochemical Dissolution

In the fields of metal production, surface finishing, and electronic device manufacturing, achieving precise control over electrochemical processes is crucial for product quality, efficiency, and cost-effectiveness. This paper introduces an open-source modeling tool based on a dynamic mesh technique built on the finite volume method using the C ++ toolbox OpenFOAM. This tool has been validated against both newly proposed analytical solutions and existing numerical and experimental results in various conditions and kinetic controls. The analytical solution predicts the electrode surface position, current, or cell voltage difference for confined electrodes. It considers primary and secondary current distributions with linear kinetics under different electric control modes. Notably, the validation highlights the congruence of the new method with prior studies and underscores its potential to offer enhanced predictive capabilities. Furthermore, this work extends beyond traditional modeling approaches by incorporating pulse reverse plating, which has been successfully modeled using the dynamic mesh method. Additionally, a modified Wagner number (WaPR) is proposed to predict in advance the optimal conditions for achieving a more uniform deposit. This innovative approach contributes to the advancement of theoretical understanding and will improve practical applications in electrochemical deposition and dissolution processes.

Active equalization for lithium-ion battery pack via data-driven residual charging capacity estimation

Considering the limitations in existing voltage-based and state-of-charge (SOC)-based active equalization strategies, including the difficulty in threshold value determination for equalization system on/off controlling, repeated estimation for equalization variable and the corresponding tremendous complexity, this paper designs a novel residual capacity-based active equalization strategy via data-driven residual charging capacity (RCC) estimation to fully charge all in-pack cells during constant current (CC) charging stage. Firstly, taking charge accumulation corresponding to specific voltage window as input, we build a data-driven RCC estimation model to online monitor each cell's RCC at specific voltage. Afterwards, considering the initial cell inconsistences, each cell's current RCC before equalization is further computed based on the estimated RCC and the subsequently measured charge accumulation. Finally, a parallel global search algorithm named particle swarm optimization is adopted to search the optimal combination of in-pack cells' equalization current considering equalization time and energy loss simultaneously. The verification results based on the Oxford battery degradation dataset demonstrate that the established data-driven model can realize accurate RCC estimation and all in-pack cells' totally charged capacity can roughly approach their maximum capacity at the end of CC charging stage using the proposed equalization strategy. Meanwhile, the maximum cell voltage difference and maximum cell SOC difference can be limited below 0.01V and 0.02, respectively. Moreover, by extending the charging time by only about 4min, the developed equalization strategy can further increase battery pack capacity by about 10%.

Online diagnosis of soft internal short circuits in series-connected battery packs using modified kernel principal component analysis

Safe operation of large battery storage systems requires advanced fault diagnosis that is able to detect faults and provide an early warning in the event of a fault. Since Internal Short Circuits (ISC) are the most common abuse condition leading to thermal runaway, this study addresses the early detection of incipient soft ISCs at the stage when the fault is still uncritical and does not lead to significant heat generation. The differences in cell voltages as measured by conventional battery management systems prove to be indicative features for ISC diagnosis. However, due to poor balancing and parameter variations, the cell voltage differences exhibit nonlinear variations. This work addresses this challenge with a nonlinear data model based on Kernel Principal Component Analysis (KPCA). To enable an online application in a vehicle, the present work reduces the computational complexity of the method by an optimal choice of training data. An analysis of the contribution of each cell to the fault statistics enables identification of the faulty cell. Since early-stage ISCs can exhibit a wide range of short-circuit resistances, experimental validation is performed with resistances from 10Ω to 10kΩ, which are correctly detected and isolated by the optimized cross-cell monitoring in all cases.

An optimization model based on temperature field and series–parallel structure for battery‐package of a stratospheric airship

AbstractStratospheric airships are long‐endurance flight platforms that utilize renewable energy systems. The solar array in these systems cannot generate electricity at night; only an energy storage battery pack can be used to power the entire system. Therefore, accurate modeling and estimation of the output characteristics and operating conditions of battery packs have become the focus of current research. During the actual flight of an airship, uneven temperature distribution causes changes in the output characteristics and differences in the cell voltage of the battery packs. To address this problem, this study establishes an output characteristic model, series–parallel structure coupled with a temperature field model (SPTM), for a battery pack based on the series–parallel structure of a single cell. In addition, the influence of temperature distribution was considered in the model. Then, a flight verification test was conducted, and the test data and simulation data were compared. The average absolute error of the SPTM was maintained at approximately 0.61 V, which accurately reflected the output characteristics of the battery pack. The simulation model was then used to study the cell voltage difference under changes in the temperature distribution and demonstrate the relationship between the cell voltage difference and temperature difference.

Early detection of Internal Short Circuits in series-connected battery packs based on nonlinear process monitoring

While the development of new materials in recent years has enabled an increase in energy density, power density and cycle life of batteries, safety remains a challenge. For electric vehicle applications, thermal runaway of a battery cell can lead to serious consequences. Thermal runaways are often caused by an Internal Short Circuit (ISC). This study aims to detect ISCs in the early latent phase, before extensive heat generation on the battery cell surface is measurable. To obtain high sensitivity, we apply a novel data-driven approach based on the cell voltage differences within the battery pack. Using the Kernel Principal Component Analysis (KPCA), a nonlinear data model is trained and applied for online detection of ISCs. By combining multiple kernel functions, fast detection and robust behavior is achieved for progressed ISCs while maintaining high sensitivity to soft ISCs. To demonstrate the applicability of the method in the presence of cell inconsistencies, the approach is experimentally validated on a calendar and cyclic aged module. A comparison with existing methods shows significant reduction in the detection time using the presented approach.

Simulation analysis on optimization of tungsten carbide recovery efficiency by molten salt electrolysis

The molten salt electrochemical method is an efficient one-step process to extract tungsten from tungsten carbide (WC). Owing to the limitation of molten salt electrochemical experiments and the number of data points, determining the optimal process conditions is challenging. In addition, the mechanism that affects the current efficiency is difficult to obtain intuitively. In this study, simulations of tungsten carbide anode electrolysis were obtained using the COMSOL Multiphysics 5.3, and the results were compared to the dissolution experiment of tungsten carbide with varying content of sodium tungstate (Fig. 1). The experimental data fitted well with the theoretical current efficiency of 75%. At concentrations below 0.5 wt% of sodium tungstate, the anode dissolution showed a linear relationship against the concentration of sodium tungstate. At a constant concentration of sodium tungstate, the anodic dissolution decreased with increasing immersion depth, consistent with the variation of cell voltage difference before and after electrolysis. The optimal immersion depth and effective area of the anode estimated by simulations were 2.5 mm and 0.465 mm2, respectively (Fig. 2). Under the optimum electrolysis conditions simulated by COMSOL, the nano tungsten powder was obtained.

Improvement strategy of overcharging characteristics of a new type lithium iron phosphate battery in substation

In order to solve the hidden trouble for the long-term overcharging condition of lithium iron phosphate batteries, it is urgent to develop overcharging protective lithium iron phosphate batteries. A strategy combining autonomous equalization technology and passive equalization technology is proposed in this paper to improve the overcharging characteristics of lithium iron phosphate batteries. A certain proportion of oxidizing reductant is added to the electrolyte of ordinary lithium iron phosphate battery. And a comparative test is conducted between conventional lithium iron phosphate battery module and self-equalization lithium iron phosphate battery module in continuous overcharging state. The test results show that the proposed comprehensive strategy has reduced the voltage difference between the cells significantly, and the single cell voltage difference is small in the long-term overcharging process, so as to maintain the safe voltage level.

A Novel Active Cell Balancing Circuit and Charging Strategy in Lithium Battery Pack

A novel, active cell balancing circuit and charging strategy in lithium battery pack is proposed in this paper. The active cell balancing circuit mainly consists of a battery voltage measurement circuit and switch control circuit. First, all individual cell voltages are measured by an MSP430 microcontroller equipped with an isolation circuit and a filter circuit. Then, the maximum cell voltage difference is calculated by subtracting the minimum cell voltage from the maximum cell voltage. When the maximum cell voltage difference exceeds 0.05 V, the balancing action starts to carry on. The MSP430 microcontroller output controls signals to close the switches corresponding to the battery cell with the maximum voltage. At this time, the balancing charge power performs a balancing charge for other batteries, except for the one that is switched on. In addition, a three-stage balancing charge strategy is also proposed in this paper to achieve the goal of speedy charging with balancing action. In the first stage, a 0.5 C balancing current is used to perform pre-balanced charging on all battery cells until the maximum cell voltage difference is less than 0.05 V, which is required for entry to the second stage of charging. In the second stage, constant current charging of 1 C, coupled with 0.2 C balancing current charging is carried out, until the maximum battery cell voltage reaches 4.2 V, which is required for entry into the third stage of charging. In the third stage, a constant voltage charging is coupled with 0.2 C balancing current charging, until the maximum battery cell voltage reaches 4.25 V, which is required to complete the balancing charge. The imbalance of power between the battery cells during battery pack charging, which reduces battery charging efficiency and battery life, is thus effectively improved. In this paper, a six-cells-in-series and two-in parallel lithium battery pack is used to perform a balancing charge test. Test results show that the battery cells in the battery pack are capable of quickly completing a balancing charge under different initial voltages, the maximum voltage difference is reduced to within the range of 0.05 V, and the total time required for each balancing charge is approximately 3600 s.

Intact Transition Epitope Mapping - Thermodynamic Weak-force Order (ITEM - TWO)

We have developed an electrospray mass spectrometry method which is capable to determine antibody affinity in a gas phase experiment. A solution with the immune complex is electrosprayed and multiply charged ions are translated into the gas phase. Then, the intact immune-complex ions are separated from unbound peptide ions. Increasing the voltage difference in a collision cell results in collision induced dissociation of the immune-complex by which bound peptide ions are released. When analyzing a peptide mixture, measuring the mass of the complex-released peptide ions identifies which of the peptides contains the epitope. A step-wise increase in the collision cell voltage difference changes the intensity ratios of the surviving immune complex ions, the released peptide ions, and the antibody ions. From all the ions´ normalized intensity ratios are deduced the thermodynamic quasi equilibrium dissociation constants (KDm0g#) from which are calculated the apparent gas phase Gibbs energies of activation over temperature (ΔGm0g#T). The order of the apparent gas phase dissociation constants of four antibody – epitope peptide pairs matched well with those obtained from in-solution measurements. The determined gas phase values for antibody affinities are independent from the source of the investigated peptides and from the applied instrument. Data are available via ProteomeXchange with identifier PXD016024. SignificanceITEM - TWO enables rapid epitope mapping and determination of apparent dissociation energies of immune complexes with minimal in-solution handling. Mixing of antibody and antigen peptide solutions initiates immune complex formation in solution. Epitope binding strengths are determined in the gas phase after electrospraying the antibody / antigen peptide mixtures and mass spectrometric analysis of immune complexes under different collision induced dissociation conditions. Since the order of binding strengths in the gas phase is the same as that in solution, ITEM – TWO characterizes two most important antibody properties, specificity and affinity.

An Equalization Time Reduction Method Using a Pseudo‐Random Number Sequence for a Cell Voltage Equalization Circuit with an LC Series Circuit

SUMMARYWhen the cells of energy storage devices such as electric double‐layer capacitors are connected in series, it results in voltage imbalance in each cell because of the nonuniform properties of the individual cells. In a previous research, the authors proposed a novel cell voltage equalization circuit using an LC series circuit, and they examined the effectiveness of this circuit. However, the characteristics of the cell voltage equalization operation depend on each cell voltage difference. Therefore, the proposed circuit has a disadvantage that the equalization time tends to be longer than other cell voltage equalization circuits with a boosting circuit. This paper proposes an equalization time reduction method that uses a pseudo‐random number sequence generated by the linear congruential generators. The proposed method can reduce the average equalization time without adding any other active or passive elements. The effectiveness of the proposed method is verified through the experimental results. According to the experimental results, the proposed equalization time reduction method reduces the equalization time to 86.5% of the conventional method.

Analysis of MPL Impact in PEFC with in-Situ Temperature Measurement in through-Plane Direction

Water management is a key issue to the practical operation of PEFC. Drying up in polymer electrolyte membrane (PEM) increase the ionic resistance and rises IR overvoltage. On the other hand, supplying excessive water causes flooding and increases the concentration overvoltage, and hence cell performance deteriorates. Therefore, appropriate water management is required. Micro porous layer (MPL) has been developed to control the water and gas flow in cell. MPL is a hydrophobic component which consists of carbon black and PTFE on the surface of gas diffusion layer (GDL) by the CL side. MPL can control liquid water and gases transport, and keep high performance even when severe flooding or drying-up condition. Recently, MPLs are improved with adding hydrophilic layer for further robustness in PEFC operation. However, the impact of MPL on cell performance is not sufficiently understood, and this situation becomes an obstacle in the development and improvement of MPL. Impacts of the structure and hydrophobicity in MPL are usually evaluated with IV characteristics. It is difficult to elucidate the change of water and gases transport only from IV characteristics. Local water behavior, temperature and current should be clarified in advance to efficiently optimize MPL. Some methods have been reported to measure the internal state inside cell in-plane and through-plane direction. For example, neutron imaging discloses in-situ liquid water distribution in the cell, contributing to the understanding the relationship between operation parameters and local water behavior. Not only water behavior but also temperature may change with MPL, because thermal conductivity in MPL is different from cell components, such as GDL and CL. Temperature distribution especially in through-plane direction may change as MPL is employed and water behavior changes. These backgrounds motivate us to challenge to measure the temperature distribution by fabricating ultrafine in-line thermocouples and placing them in a cell. The tailor-made thermocouples are accurately positioned under rib or channel and also placed in through-plane direction, so that temperature distribution measurement in the cell with and without MPL is conducted. Though the temperature difference between under the rib and channel did not vary from presence of MPL, the distribution in the through-plane direction changed considerably, suggesting that MPL impacts on water behavior significantly. This study discusses the impact of MPL on water behavior with the in-situ measured temperature distribution. Ultrafine in-line thermocouples are fabricated in the following manner. Butt-welded K-type thermocouple wires in diameter 50 μm formed an in-line thermocouple. Electrical insulation is required to insert the thermocouple into the cell. For this purpose, the thermocouple was coated with polyimide. The fabricated thermocouple is precisely placed into cell with the fixing tool which has a squire frame shape. In-line thermocouples were stretched across the tools, with an adjustment so that the thermocouple junctions are positioned under rib or channel. Four sets of the fixing frames are arrayed in piles, and temperature is measured along through-plane direction on the four points: anode GDL, anode CL, cathode GDL and cathode CL. Air and hydrogen were supplied into the cathode and anode respectively with relative humidity of 20 % and the utilization ratio of 0.1 at 1A/cm2. The cell voltage difference between the cases with and without MPL was about 0.1 V. The temperature around CL with MPL was slightly higher than that without MPL. The distribution without MPL was homogeneous, however, the MPL case tended to have the maximum temperature at cathode CL; it might be caused by the low thermal conductivity of MPL. Cell voltage in the case with MPL was 0.42 V higher than that without MPL, while cell was operated under relative humidity of 95 % and gas utilization ratio of 0.4. Although it is expected that flooding occurs at cathode CL and cell performance decreases in this condition, MPL promotes to drain the bulk liquid water. This is the reason that the performance with MPL became higher. Temperature with MPL was also higher than that in the case without MPL. The cell without MPL tends to accumulate water at CL, and water evaporates there. Thus, the latent heat with the evaporation decreases the temperature in the cell without MPL. From the above, water behavior differences between with and without MPL is explained through the measured temperatures. It is suggested that the developed temperature measurement method can contribute to cell performance improvement with water management by MPL.

Impact of Cathode Current Collector on High Temperature PEM Water Electrolysis

1. Introduction Polymer Electrolyte Membrane Water Electrolysis (PEMWE) is a hydrogen production method, which has advantages on conversion efficiency, compactness and gas purity. Also, PEMWE is expected to be applied to load leveling of electricity between consumer demands and supply from renewable energies [1]. Higher conversion efficiency has been realized in two strategies: higher temperature operation with new composite electrolyte membranes and development of current collector. The new membrane can endure high temperature up to 120°C, and a high temperature operation can reduce overpotentials, leading to further performance[2]. Developing the current collector is concentrated on anode side, major source of overpotentials exist. Optimizations of current collector on its hydrophobicity and stricture play a key role on water/gas management and improve performance[3]. This study evaluates the current collector in cathode if it changes the performance of PEMWE especially under high temperature condition. As well know, high temperature tends to dehydrate PEM and results in low performance, although temperature dependence of non-leaner overvoltages predicts their reduction. This study aims to suppress the dehydration with possible candidates of current collector in cathode. Impact of hydrophobicity in cathode current collector on the dehydration is experimentally evaluated through IV characteristic and high frequency resistance. 2. Experimental apparatus and method The PEMWE cell consists of a CCM, porous current collectors, and separators with flow channels. The CCM was fabricated by spraying catalyst ink on Nafion® 117 membrane and hot-pressing. Iridium oxide (IrO2powder, type IV, Tokuriki Co., Japan) was used for anode catalyst, and a commercial 46% Pt/C (Tanaka Kikinzoku Japan) was for cathode catalyst. As for cathode current collector, carbon paper (SGL Co., Germany, 20BA, thickness 0.2mm) or SUS316L sheet (Nikko Techno, fiber diameter 35μm, thickness 0.3mm) was selected. The two collectors have different hydrophobicity. The carbon paper indicates rather hydrophobic characteristic. On the other hand, The SUS sheet shows opposite characteristic. In the case of carbon paper, two layers of it was built in the cell considering the thickness of seal material and contact resistances. Ti mesh (Nikko Techno Co., Japan, fiber diameter 20μm) was used for anode current collector. 3. Results and discussion Fig.1 and Fig.2 show the measured I-HFR and I-V characteristics during PEM electrolysis with different cathode current collectors at 80°C and 100°C. The HFR in the case of carbon paper had lower value, suggesting lower ohmic resistance. Corresponding to I-HFR characteristic, the I-V characteristic in the carbon paper case indicated lower cell voltage. The cell voltage in the case of carbon paper is smaller than that in the case of SUS sheet. As expected, the carbon paper, which has rather hydrophobic property, hydrates the PEM and make its ionic resistance low. The hydrophobic carbon paper placed in cathode may work to block the water transport driven by electro-osmosis from anode to cathode. It also enhances the back diffusion of water, resulting in the hydration of PEM and lower resistance. However, this mechanism, in which PEM is hydrated with hydrophobic carbon paper, is not enough to explain the cell voltage difference by 110 mV at 2 A/cm2appeared in Fig. 2. The ohmic resistance difference of 10 Ω*cm2 at 2 A/cm2 appeared in Fig.1 predicts a cell voltage difference 20 mV, which is 90 mV smaller than that in I-V characteristic. A possible explanation to the gap of 90 mV is the overvoltage reduction in anode. Generally, the overvoltage in anode is larger than that in cathode. Also, the water content in anode catalyst layer impacts the overvoltage in anode. These concern and the water back diffusion with carbon paper in cathode, above mentioned, can suggests that the water back diffusion from cathode may reach to the anode catalyst layer and hydrate the ionomer in the anode catalyst layer even though cell is operated at high temperature. This mechanism may explain the gap of 90 mV, where the water back diffusion reduces the overvoltage in anode.

An Experimental Study of Scale-up, Oxidant, and Response Characteristics in PEM Fuel Cells

It is important for fuel cell to become flexible in order to accommodate the situations of application areas for reducing costs and expanding coverage. Scale ups in series and parallel to 1-kW class proton exchange membrane (PEM) fuel cell stack are characterized experimentally with oxidant as air and oxygen. Through a serial scaled-up 4-cell stack with an active area of 25 cm 2 and a parallel scaled-up single cell with an active area of 100 cm 2 , respectively, the 1-kW class 20-cell stack with an active area of 150 cm 2 per cell is scaled up from the basic unit cell with maintaining their performances. The polarization and power curves of the 1-kW class PEM fuel cell stack with the reactants H 2 /air and H 2 /O 2 are evaluated. Sufficient power of the PEM fuel cell can operate at flexible nominal current of 40-80 A and nominal voltage of 12-15 V for providing durability and balance between cells. The 1-kW class PEM fuel cell stack is characterized through the comparison of cell voltage differences utilizing H 2 /air and H 2 /O 2 . Both cell voltages with H 2 /air and H 2 /O 2 follow well the one-twentieth of the responding stack voltages with the small difference.

Cell state-of-charge inconsistency estimation for LiFePO4 battery pack in hybrid electric vehicles using mean-difference model

Identification of cell SOC (state-of-charge) inconsistency for LiFePO4 battery packs is challenging due to the demanding conditions in hybrid electric vehicles (HEVs) and the relatively flat SOC–OCV (open circuit voltage) curve of LiFePO4 cells compared to others. We experimentally investigate cell voltages in a small battery pack and propose a Mean-plus-Difference Model (M+D Model). The M+D Model uses a cell mean model (CMM) representing the overall performance of the pack in high frequency. Meanwhile cell voltage differences (CVDs) between cells and the “mean cell” are studied by a cell difference model (CDM) in low frequency. A CDM considering SOC and internal resistance differences is subsequently presented and OCV differences are estimated. We further propose an SOC strategy to accurately identify cell SOC inconsistency by intermittently lowering pack SOC to 30% during HEV operation. Finally we discover that SOC differences can be determined with estimated OCV differences using SOC-difference/OCV-difference curve. The proposed method is verified by simulation and experiment. With the proposed method, LiFePO4 cell SOC inconsistency can be precisely estimated with existing measuring technology during HEV operating and cell equalization can be ultimately implemented.

A convective transport theory for high rate discharge in lithium ion cells

A solution phase transport theory considering solvent effects is developed for lithium ion cells. The solvent convection velocity is derived from a volume conservation argument, leading to a diffusive correction, a transference number gradient correction and a pore-wall flux correction to the material balance equation. The diffusive correction exactly cancels the solvent-related (1−dlnc0/dlnc) factor in the original diffusion term. The transference number gradient and pore-wall flux corrections lead to a larger effective value of the lithium ion transference number.Comparative discharge simulations are carried out for a graphite–LiMn2O4 cell with 1M or 2M LiPF6 solution. The convective transport theory demonstrates little cell voltage difference at low rates (1C and 3C) compared with the original approach that neglects convection. Nevertheless, at a 6C rate, a maximum of 51.32mV excess cell voltage is predicted by the convective theory for the 1M cell. For the 2M cell the convective theory predicts a slightly slower voltage drop at the beginning of discharge, but a faster drop at the end of the 6C discharge. At all rates the convective theory also gives a lower salt concentration profile within the negative electrode, but higher within the positive electrode. This implies that the concentration gradient is diminished by convection. Detailed analysis shows that the transference number gradient correction is always positive during discharge and is highly rate sensitive; the pore-wall flux correction is not only rate sensitive but also proportional to the salt concentration and is thus more prominent in the 2M cell.

Mesures des concentrations en moisissures dans l’air au poste de travail : un exemple dans l’industrie agroalimentaire

The energy efficiency of water electrolysis has been considerably improved in the presence of an ultrasonic field. This was demonstrated by measuring the cell voltage, efficiency and energy consumption of the generated gas from the electrolysis. These measurements were carried out in alkaline solution using linear sweep voltammetry (LSV) and galvanostatic polarization techniques. A large reduction of the cell voltage was achieved under the ultrasonic field, especially at high current density and low electrolyte concentration. With the same current density, the cell voltage difference with and without the ultrasonic field fell as the concentration of the electrolyte was increased. The efficiency of H2 generation was improved at a range of 5–18% at high current density in the ultrasonic field but the efficiency of O2 generation fell a little due to the difference in the behavior of the gas bubbles. The energy saving for H2 production by using the ultrasonic field was about 10–25% for a certain concentration of the electrolyte when a high current density was used. On the other hand, the energy consumption for O2 production with and without the ultrasonic field was almost the same.

Water electrolysis in the presence of an ultrasonic field

The energy efficiency of water electrolysis has been considerably improved in the presence of an ultrasonic field. This was demonstrated by measuring the cell voltage, efficiency and energy consumption of the generated gas from the electrolysis. These measurements were carried out in alkaline solution using linear sweep voltammetry (LSV) and galvanostatic polarization techniques. A large reduction of the cell voltage was achieved under the ultrasonic field, especially at high current density and low electrolyte concentration. With the same current density, the cell voltage difference with and without the ultrasonic field fell as the concentration of the electrolyte was increased. The efficiency of H 2 generation was improved at a range of 5–18% at high current density in the ultrasonic field but the efficiency of O 2 generation fell a little due to the difference in the behavior of the gas bubbles. The energy saving for H 2 production by using the ultrasonic field was about 10–25% for a certain concentration of the electrolyte when a high current density was used. On the other hand, the energy consumption for O 2 production with and without the ultrasonic field was almost the same.

Plate In-Plane Electrical Resistance Impact to Stack Performance

In a cell consisting of composite bipolar plates and a polymer electrolyte membrane a significant cell voltage difference has been measured between the reactant inlet end and the reactant outlet end when the cell is aged or defective. In order to gain further understanding, modeling and experimental studies were conducted simulating the effects of local defects in the MEA. The studies indicate that in the presence of a high local resistance in the MEA or GDL, current bypasses the region creating voltage differences due to high in-plane current. The studies also included incorporating metal plates into the cell with a region of the MEA blocked. In this case, both experimental and modeling results show uniform cell voltage from inlet to outlet. It was concluded that both bipolar plate through-plane electrical resistance and in-plane electrical resistance are important metrics for plate selection and design.

Dynamic Characteristics of a Direct Methanol Fuel Cell

The detailed dynamic characteristics of direct methanol fuel cells need to be known if they are used for transportable power sources. The dynamic response of a direct methanol fuel cell to variable loading conditions, the effect of cell temperature and oxygen flow rate on the cell response, and the cell response to continuously varying cell temperatures were examined experimentally. The results revealed that the cell responds rapidly to variable current cycles and to continuously varying cell temperatures. The increasing rate of gradual loading significantly influences the dynamic behavior. The effects of cell temperature and oxygen flow rate on the cell dynamic responses are considerable, but the cell voltage differences over the range of cell temperatures and oxygen flow rates are small for gradual loading. The cell response value to cell temperature during decreasing temperature is lower than that during increasing temperature.