Single Cell Stack Research Articles

Porous transport layers with low Pt loading having Nb–Ta alloy as interlayer for proton exchange membrane water electrolyzers

Titanium (Ti), commercially used as substrate for porous transport layers (PTLs) in proton exchange membrane water electrolyzers (PEMWEs), tends to form passivating oxide layer, increasing interfacial contact resistance (ICR) and reducing performance and durability; practice of using precious metal coatings for mitigation significantly increases costs. This study investigates niobium-tantalum (Nb–Ta) alloys as cost-effective interlayer coatings on Ti-felt to reduce precious metal loading. Nb–Ta coated samples significantly increase corrosion potential, lower current densities by 3–4 orders of magnitude, reduce ICR by 3.5 times, and improve durability. The best performance sample with an ultra-low amount of platinum, shows 8 times greater durability, 12.5% reduction in ohmic resistance and 28% increase in current density at +2.0 V than the commercial PTL in a single cell stack. Improved contact angle, electrical, and thermal conductivity highlight Nb–Ta interlayer coatings for PTLs, offering a cost-effective strategy to enhance PEMWE performance and durability for green hydrogen production.

Ultralow degradation cold start of proton exchange membrane fuel cell with alternating hydrogen pump method

Cold start impedes widespread diffusion of fuel cell vehicles (FCVs) in regions with temperatures below zero. Alternating hydrogen pump (AHP) method, distinguished by its unlimited ohmic heating capability without generating water, has been shown to be a quick and efficient method of cold starts in both single cell and short stacks. In this paper, we continue to examine possible degradation with this novel method. For this purpose, we carefully designed three experiments with different levels of stress, aimed to separate the contribution to any degradation from major factors. It was found there was no significant difference among the three cases. AHP method incurred minimal degradation after 3600 times of equivalent −30 °C cold starts. This study concludes that AHP method is not only quick and efficient, but also highly durable, hence AHP is a promising alternative cold start strategy with great potential to facilitate the diffusion of FCVs.

(Invited) Shunt-currents in Alkaline Water-Electrolyzers and Renewable Energy

Shunt-currents in bipolar cell stack design with a common electrolyte-feed and -outlet is an inevitable physical phenomenon governed by Ohms law that causes some extra challenges when alkaline water-electrolysers shall operate on renewable energy that is both dynamic and intermittent. Shunt-currents are also referred to as bypass-current or creep-current. The shunt-currents are to much degree governed by the electrolyte inside the cell stack manifold system that transports lye in and out of the cells. The electrolyte inside the manifold system also electrically connects the individual cells together and enables transport of ions/electricity in parallel to the cell stack. Thus, a small portion of the rectifier current is being shunted outside the cells and does not contribute to any production. Previous work on shunt-current modelling brought new insight on how to design the manifolds and raised the awareness on shunt-current and the use of metallic manifolds which both reduced the ohmic resistivity of the manifold system and was a source of secondary electrolysis.Classic alkaline water-electrolysers are typically using an internal manifold system where the inlet ports are located at the bottom of the cell stack and the outlet ports are located at the top, and where the ports connecting the cell-interior and the common manifold channel are short and straight. Such design has in the past worked satisfactory for alkaline water-electrolysers that have been working on a high nominal load and only being shut-down for maintenance a few times over the stack-lifetime, mainly causing a modest reduction in the current efficiency. Membrane-chlorine electrolysers on the other hand, are designed for very small shunt-currents by using an external manifold system, which enables a current protection system that protects electrodes from corrosion under shutdown conditions.Shunt-currents bypassing the cell stack does not contribute to any product and therefore constitutes a loss in current efficiency and, hence, an accordingly loss in the energy efficiency (the shunt-currents still adds to the electricity bill). The atmospheric alkaline electrolyser has a modest loss in current efficiency at nominal load where the high gas volume blocks much of the current path in the rather open outlet ports. The high-pressure alkaline electrolysers on the other hand, where the gas volumes are much smaller, the current efficiency can be as low as 89% at nominal load due to shunt-currents when using simple internal manifold system. For an electrolyser with already low current efficiency at the nominal load, the current efficiency will drop dramatically as the electrolyser is taken to lower load, severely compromising the energy efficiency. The impact on shunt-currents also dramatically increases for increased number of cells in a cell stack, and eventually limits the number of cells that can be assembled in one single cell stack operating on the same common lye system.Shutdown and discharge of the electrodes may further lead to corrosion and degradation of the electrodes, strongly influenced by the shunt-currents and the manifold system. Large cell stacks will discharge faster and deeper, eventually causing corrosion of the electrodes. As the cell stack is discharged the current in the cell stack is reversed where the hydrogen electrode is being polarized to anodic potentials, and the oxygen electrode is polarized to low cathodic potentials which eventually may challenging the material stability. Thus, evaluation of electrode potentials must be an integral part of development of industrial electrodes [LeRoy] and especially in intermittent operation where frequent shutdown will occur. A good integration of the manifold system into the cell stack can potentially mitigate both the loss of current efficiency under dynamic operation and the electrode corrosion under intermittent operation.

Double Conductive Ni-pads for a kW-class micro-tubular solid oxide fuel cell stack

Double Conductive Ni-pads (DCNPs) are prepared for the anode collector of micro-tubular solid oxide fuel cells (MTSOFCs) to fabricate a kW-class MTSOFC stack. The dimensions of the pad, in terms of width and length, are approximately 3.1 mm and 11.3 mm respectively. COMSOL Multiphysics software is utilized to simulate the multi-physical field of a single cell and SOFC stack to study anodic DCNPs current distribution and mass transfer operated at various voltages. A 160-cell stack consists of eight 20-cell sub-stacks exhibits a maximum power output exceeding 1 kW at an operating temperature of 700 °C. Furthermore, long-term operation tests under constant current or constant voltage conditions are conducted on both the 20-cell sub-stack and the 80-cell stack, demonstrating excellent performance and stability when utilizing DCNPs as anode collectors. The application potential for DCNPs as anode collectors in micro-tubular solid oxide fuel cells extends to various fields including auxiliary power units or high-power stacks, thereby introducing new possibilities for MTSOFC technology.

Transient modelling of a multi-cell alkaline electrolyzer for gas crossover and safe system operation

Due to the intermittency of renewable energy sources, alkaline water electrolyzers are typically operated at partial load compared to the nominal design value. It is well-known that gas crossover is dominant at low current densities leading to higher anodic hydrogen content and higher cathodic oxygen content in the separator tanks. High anodic hydrogen content is tantamount to loss of product hydrogen which results in an explosive atmosphere in the gas phase if the volumetric hydrogen content in oxygen exceeds 4%. We have developed a transient model of a multi-cell stack which can describe the operation of the electrolyzer with mixed electrolyte flows (anolyte and catholyte), separated flows, or a combination thereof (dynamic switching). This is a major extension of the steady-state model developed by Haug et al. (International Journal of Hydrogen Energy, 2017, 42, 15,689–15707). In sharp contrast to the steady-state model by Haug et al., the transient model can calculate the gas crossover as the operating conditions (e.g. electrolyte flow cycles) dynamically change in time. Depending on the size of the stack and the separator tanks, the model estimates different rates for impurities to build up. The transient model is validated using independent experimental results by Haug et al. and Brauns et al. (Electrochimica Acta, 2022, 404, 139,715) The results show that the dynamic model can follow experimental results for fluctuating current densities for a period of several days. We found that the dynamic response and transition time to steady state depend significantly on the geometrical volume of the gas separators with respect to the single-cell stack. For a multi-cell stack, we find that the impurities build-up faster when increasing the number of cells in the stack. This model serves as a tool for sizing and process management of the electrolyzer system and the separator tanks especially with respect to explosion safety.

Startup optimization of an automotive polymer electrolyte membrane fuel cell system with dynamic hydrogen reference electrodes

Efficient polymer electrolyte membrane fuel cell (PEM-FC) systems with minimal degradation are indispensable for automotive applications. A decisive measure to achieve this goal is the optimization of the startup procedure as part of the system operating strategy. This applies in particular to startups where the anode is partly or completely filled with ambient air after long downtimes. When displacing the air in the anode with hydrogen, damage to the cathode is inevitable and should be minimized. Basic approaches for this optimization are known from literature but are mainly derived from single cell and short stack experiments. In this paper, we optimize a full PEM-FC system by utilizing Dynamic Hydrogen Electrodes and show how gas replacement speed and half cell voltage evolution can be improved to mitigate degradation. The experimental results show that a homogeneous flow of the hydrogen/air front across the stack is to prioritize over its speed as only this enables additional upper voltage control in large stacks. The system optimum is achieved by maximizing startup pressure and purge valve flow, adapting the anode recirculation rate and precise voltage clipping. This study thus forms a procedural template for the optimization of the SUSD procedure in automotive fuel cell systems.

Assessing the Impact of Electrode Structure on the Fast Charge Performance of Lithium-ion Batteries

Increasing electrode thickness can increase the energy density of lithium-ion batteries. However, increasing electrode thickness increases transport limitations and the risk of lithium plating. This work analyzes prospective improvements to the conventional lithium-ion cell that may facilitate high energy density and fast charging capabilities. A 2D lithium-ion battery model is applied to understand the impact of thick electrode at different C-rates in a single cell stack. Five different cell geometries were analyzed for this work: one conventional cell and four test cases in which the conventional electrode geometries were modified by adding electrolyte channels to increase the rate transfer capability of lithium ions at high C-rates and reduce the risk of lithium plating. All five configurations were simulated in discharge at C/10, C/2, and 1 C followed by simulated charging at 1 C, 3 C, and 5 C with no rest period prior to charge. The addition of electrolyte channels in the anode only results in improved performance with respect to reduced plating risk. Dimensionless parameter analysis was performed to compare the battery performance with different electrode modifications at different C-rates. Scaling behavior based on these parameters clarifies the benefits and limitations of the varied electrode modification approaches.

Multiscale Study of PEMFC in Marine Environment: Impact of a NaCl Spray on Durability

In the wake of the growing environmental challenges, hydrogen produced from renewable energy is a good candidate as a substitute for conventional fuels. Indeed, fuel cells can produce electricity thanks to air and hydrogen, and only reject water. The use of this technology is currently emerging in various sectors, such as the maritime industry. However, sea salt aerosols, mostly composed of sodium chloride (NaCl), can damage fuel cells. So far, only a few studies have been dedicated to the impact of NaCl on Proton Exchange Membrane Fuel Cells (PEMFCs) though showing that salty air can induce a significant loss of performance without clearly identifying the underlying physicochemical mechanisms [1][2][3].Thus, the present experimental work investigates the effects of a salt spray injected into the airflow of single PEMFC cells and stacks at various time scales and contamination levels, with the final aim of identifying the appropriate PEMFC stack protection needed for maritime applications. A dedicated experimental setup generating salt spray in the cathode airflow of a single cell and 5-cells stack has been designed, realized and characterized. The NaCl concentration range used is from 10 mg/m3 to 5 g/m3, to reproduce different types of salty environments. Cells and stacks are operated in constant current density mode.The study is conducted under the conditions of accelerated stress tests. When polluted at high concentrations, single cells degradation becomes significant after only a few minutes of operation (Figure 1) and after a few hours for stacks. Even under low concentrated environments, the single cell voltage decreases faster than the baseline (ie reference voltage with pure water in air stream), leading to PEMFC lifetime shortening. It has been observed that cathode rinsing with nitrogen flow or operation under pure water results in partial cell performance recovery. Moreover, starts-up and shuts-down operated during tests can have a positive or negative influence on cell performance, depending on the break duration.Even when the tests revealed only weak decrease in power, Membrane Electrode Assemblies (MEA) and bipolar plates (BP) post-mortem characterizations highlight degradations. Scanning Electron Microscopy (SEM) studies coupled with Energy Dispersive X-ray Spectroscopy (EDS) have contributed to the identification of components in MEA and BP. As expected, chlorine reaches not only the cathode gas diffusion layer (GDL) and catalyst layer (CL) but also the anode CL by crossing the membrane [4]. According to the literature, chloride adsorption on Pt surface or Pt dissolution reduces the active area [3] whereas sodium ion contaminates the membrane [1]. Moreover, corrosion products from metallic components have been found. Corrosion marks identified as stainless steel from BP are present in the stack effluents and MEAs. As for single cell, compounds from current collectors (gold, nickel and copper) are present in the GDL and CL. In the near future, for single cell tests, non-metallic current collectors will be used in order to discriminate the effects of the direct degradation of salt spray on MEA and indirect degradation coming from corrosion products of metallic cell components.Overall, the present study reports that NaCl effects on PEMFCs not only depend on the concentration of the NaCl mist but also on the MEA type, current collectors/BP material, and startup/shutdown procedure. In the full paper and oral presentation, tests conducted with less concentrated NaCl droplets will also be presented, with the aim of determining adegradation threshold for single cells.

Functional complexed zincate ions enable dendrite-free long cycle alkaline zinc-based flow batteries

Highly reliable alkaline zinc-based flow batteries are promising options for stationary energy storage and require uniform zinc plating determined by anolyte chemistry. However, the anolyte properties, particularly molecular structure of zincate ion are intricate and yet to be clearly identified. Herein, we report a N, N, N′ N′-Tetra(2-hydroxyethyl) ethylenediamine (THEED) additive to enable uniform zinc plating by altering molecular structure of zincate couple. The THEED can complex with Zn(OH)42- and form Zn(OH)xx−2-THEED-H2O with slow-down deposition kinetics on anode and realizing uniform plating of zinc, and form new hydrogen bond networks with water, favoring trapping water molecules. These in turn enable alkaline zinc-iron flow battery single cell and cell stack with dramatically improved reliability. Additionally, the THEED could suppress the migration of water during charge/discharge process. This work illustrates new ways for realizing uniform zinc plating based on scientific understanding of electrolyte chemistry to promote the development of alkaline zinc-based flow batteries.

Testing of solid oxide cells at high current densities

Abstract Solid Oxide Cells (SOCs) have gained an increasing interest as electrochemical energy converters due to their high efficiency, fuel flexibility and ability of reversible fuel cell/electrolysis operation. During the development process as well as in quality assurance tests, the performance of single cells and cell stacks is commonly evaluated by means of current/voltage- (CV-) characteristics. Despite of the fact that the measurement of a CV-characteristic seems to be simple compared to more complex, dynamic methods as electrochemical impedance spectroscopy or current interrupt techniques, the resulting performance strongly depends on the test setup and the chosen operating conditions. In this paper, the impact of different single cell testing environments and operating conditions on the CV-characteristic of high performance cells is discussed. The influence of cell size, contacting and current collection, contact pressure, fuel flow rate and composition on the achievable cell performance is presented and limitations arising from the test bed and testing conditions will be pointed out. As today’s high performance cells are capable of delivering current densities of several ampere per cm2 a special emphasis will be laid on single cell testing in this current range.

Damage Modeling of Solid Oxide Fuel Cells Accounting for Redox Effects

This paper applies a multiscale mechanistic damage model developed for porous brittle ceramics and implemented in finite element analysis (FEA) packages [1] to study progressive damage in solid oxide fuel cells (SOFC) subjected to thermomechanical loading under operating and shutdown states. The damage model captures the micromechanics of stiffness reduction due to material porosity change and microcracking and integrates the as-obtained stiffness reduction law into a continuum damage mechanics (CDM) formulation for the evolution of microcracks up to fracture. An Eshelby-Mori-Tanaka approach (EMTA) [2-3] is first used to model the ceramic containing pores and aligned microcracks regarded as inclusions with negligible stiffness. The stiffness of the actual porous ceramic is obtained from the EMTA solution averaged over all possible microcrack orientations using an orientation averaging method. The evolution of microcracking damage is described by a CDM formulation derived from our previous model [4]. Apart from the operating and shutdown states, additional damage that may occur due to reduction and re-oxidation (redox cycling) of Ni/YSZ anodes is also studied. The reduction of NiO into Ni leads to changes in volume and porosity of the anode layer that consequently change its physical and thermomechanical properties. The volume change or volumetric “swelling” during redox cycling may affect the structural integrity of the anode and may cause fracture of the electrolyte under high tensile stresses leading to operational failure for SOFCs. In the constitutive relations, volumetric swelling is treated in a similar way to thermal expansion using the models developed in Refs [5-6] for fusion energy ceramic materials. However, while thermal expansion vanishes if temperature change tends to zero, swelling is irreversible and significantly contributes to degrade SOFC stacks during redox cycling.This damage model was implemented in the commercial FEA software ABAQUS© and ANSYS© via user subroutines. First, it has been validated through predictions of strength and stress-strain response for the typical SOFC ceramic materials. Figs 1(a) and 1(b) show the predicted stress-strain responses as a function of temperature for dense NiO/YSZ and Ni/YSZ, respectively. These figures also illustrate the predicted responses at 750°C with prescribed initial values of porosity. The damage model predicts significant reductions in strength and elastic modulus with higher initial porosity and higher temperatures, and the predicted trends are in good agreement with the experimental findings [7-8].Next, the damage model was applied to predict the potential for degradation in a generic planar SOFC stack with large active area cells modeled in ANSYS. Stack models with single and multi-cells were simulated in both co-flow and counter-flow configurations. The thermomechanical loads representing the operating and shutdown conditions were simulated. The realistic thermal gradients that occur in an operating stack were imposed in the models by solving the electrochemistry under various operating conditions using the in-house SOFC multiphysics code (SOFC MP-3D) [9-10]. In addition to the operating and shutdown conditions, a constant temperature redox cycle was also simulated to capture overall cell electrode damage due to volumetric swelling of the Ni/YSZ anode in the anode supported cells. The results from single cell stack models showed little damage at operating and shutdown conditions which could be attributed to enough out-of-plane support for the PEN assembly. The results from the multicell stacks (Fig. 2) showed higher damage in counter-flow configuration. Within the stack, the top cells experienced the highest damage and the middle cells experienced the lowest. Overall, no significant damage that may lead to total failure of the cells was observed in the multicell stack models with the operating conditions considered in this study.

The Influence of Structure on the Electrochemical and Thermal Response of Li-Ion Battery Electrodes

Abstract Advancement of lithium-ion batteries for transportation applications requires addressing two key challenges: increasing energy density and providing fast charging capabilities. The first of these challenges can be met using thicker electrodes. However, the implementation of thick electrodes inherently presents a trade-off with respect to fast charging. As the thickness is increased, transport limitations reduce the ability of the battery to meet aggressive charge conditions. At the particle scale, interactions between solid diffusion and reaction kinetics influence the effective storage of lithium. At the electrode scale, diffusion limitations can lead to local variations in salt concentrations and electric potential. These short-range and long-range effects can combine to influence local current and heat generation. In the present work, a pseudo-2D lithium-ion battery model is applied to understand how active material particle size, porosity, and electrode thickness impact local field variables, current, heat generation, and cell capacity within a single-cell stack. The model was built assuming that the active particles are representative spherical particles. The governing equations and boundary conditions were set following the common Newman model. Cell response under varied combinations of charge and discharge cycling is assessed for rates of 1 C and 5 C. Aggressive charge and discharge conditions lead to locally elevated C-rates and attendant increases in local heat generation. These variations can be impacted in part by tailoring electrode structures. To this end, results for parametric studies of active material particle size, porosity, and electrode thickness are presented and discussed.

Degradation Studies of Single Cell and Short Stack for High Temperature Proton Exchange Membrane Fuel Cells Based on PBI/H3PO4 Membrane

AbstractDurability is a premise of extensive application for high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) based on H3PO4 doped polybenzimidazole membrane, but is far unsatisfactory. In this work, using our home‐made electrodes, a single cell with a start‐stop operation for 1900 h and a short stack with a continuous operation for 1344 h are separately conducted at 0.2 A cm−2 with hydrogen‐air feed. After 1900 h operation, an average degradation rate of 59.5 μV h−1 is obtained. Combined scanning electron microscope with energy dispersive spectrometer, transmission electron microscope, and electrochemical methods, the start‐stop operation cause more serious H3PO4 loss, cobalt element leaching, and platinum particles agglomeration, which produces a decreased ion conductivity and a big active polarization loss. In short stack test, we find electrode consistency is more important. An inferior cell enables a rapid failure due to almost complete acid loss in the membrane. The bigger polarization loss and more joule heat at the inferior electrode from a lower ionic and electrical conductivity further make acid loss aggravated, and it is a vicious circle. Despite a big gaps with life requirement, we believe our work will give a guidance for the design of high stable HT‐PEMFCs.

Development and Evaluation of Thin Flexible Metal-Supported Solid Oxide Fuel Cells

The porous nickel-molybdenum alloy sheets with 25 and 100 cm2 in size and 0.2 mm in thickness are used as supporting substrates in producing metal-supported solid oxide fuel cells. The atmospheric plasma spraying (APS) is applied for coating all functional layers in sequence. These cells have YSZ-Ni and GDC-Ni as anode layers, LDC as diffusion barrier layer, LSGM as electrolyte layer, and 50%SDC-50%SSC and 25%SDC-75%SSC as cathode layers. The 25 cm2 cell delivers maximum power densities of 313, 581, 890 and 1098 mW cm-2 at 600, 650, 700 and 750°C respectively. The assembled single cell stack of 100 cm2 cell shows power of 33 W (407 mW cm-2) and 39.4 W (486 mW cm-2) at 700 and 750°C. The long-term stability test of this single cell stack shows a degradation rate of about 0.93% k-1 h-1 over 800 h at 300 mA cm-2 and 700°C.

Fabrication and Characterization of Metal-Supported Solid Oxide Fuel Cell Fabricated by Atmospheric Plasma Spraying

Institute of Nuclear Energy Research (INER) has been developing fabrication method for metal-supported solid oxide fuel cells (MS-SOFCs) operating in the range of 600-750oC. The planar MS-SOFC cell with 10×10 cm2 in size were fabricated by atmospheric plasma spraying. The measured powers of the MS-SOFC in cell test achieve 55, 44.6 and 28 W at 0.8 V and 750, 700 and 650oC, respectively. The power outputs of MS-SOFC single-cell stack are 54.7 and 44.3 W at 0.7 V and 750 and 700oC, respectively. The durability tests of the MS-SOFC cell had performed for 3,500 hours at the test condition of 400 mA/cm2 and 700oC. The measured degradation rate is less than 1 %/1000hr, which indicates that the plasma-sprayed MS-SOFC cell made by INER reveals an inspired performance.

Experimental study on performance evaluation of PEM fuel cell by coating bipolar plate with materials having different contact angle

Bipolar plates that have generally been made of graphite or composite materials are a fuel cell component that must be mechanically durable, easy to process, corrosion resistant, electrically and thermal conductive in contact with a gas diffusion layer, which is a porous material. In this study, instead of developing new materials with above features, water management has been improved by coating the bipolar plates and performance review has been carried out experimentally. The flow channels of the bipolar plates were coated with PTFE and SiO2. Physical vapor deposition (PVD) was used as the coating method. After the coating process, 120.2° contact angle with PTFE and 35° contact angle with SiO2 was approximately obtained in the flow channels. Single cell and 3-cell stack tests were performed with bipolar plates coated with these materials and uncoated polymer composite bipolar plates for given variable O2 and H2 flow rate and cell temperature at constant humidification conditions. 3-cell stack were tested after assembly. In PEM fuel cell stack tests, the highest current and power density values were also obtained in the hydrophobic PTFE coated plates. But in hydrophilic fuel cell stack, no voltage and current values could be measured due to the sudden decreases due to excessive flooding of the flow channels. A decrease in power density by 12.53% was observed when the single cell having hydrophobic flow channels with coated PTFE compared to 3-cell stack at the same operating conditions.

Advancements on scaling-up simulation of Proton Exchange Membrane Fuel Cells impedance through Buckingham Pi theorem

This article addresses a generalized scaling-up technique applied to proton exchange membrane fuel cells. Such a methodology allows simulating the impedance related to a full stack from that of a single cell or short stack, combining experimental data with physical reasoning and phenomenological modelling. The use of such technique can reduce electrochemical impedance spectroscopy testing costs, with a significant impact on fuel cell manufacturing and performance assessment processes. The procedure described in this paper relies on a former approach, already presented by the authors, which has been improved with respect to two main aspects. Firstly, non-dimensional parameters are computed, by referring to the Buckingham Pi theorem, through a generalized physical model. Secondly, single cell or short stack internal states (i.e., water content and limiting current) are evaluated through significant information gained from impedance measurements and inverse modelling. Stack impedance simulation is performed through proper internal states distribution assumptions. To prove the consistency and robustness of the proposed technique, experimental data taken from the literature and the European funded project HEALTH-CODE are used, with stack impedance accurately reproduced by means of only a single cell spectrum.

Development and performance evaluation of a direct ammonia fuel cell stack

In the present study, the experimental investigation and performance evaluation of a newly developed direct type ammonia fuel cell stack are performed. A solid anion exchange membrane electrolyte is also utilized. The performances of a single-cell and a 5-cell stack are investigated through thermodynamic efficiencies. The open circuit voltages for a single cell and 5-cell stack are obtained as 280 ± 8 mV and 1249 ± 37.5 mV respectively. Furthermore, the peak power densities are found as 6.4 ± 0.2 W m−2 and 13.4 ± 0.4 W m−2 for a single-cell and a 5-cell stack respectively. Moreover, the effects of varying humidifier temperatures on their efficiencies are studied, and hence increasing humidifier temperatures are found to provide higher efficiencies. Both energetic and exergetic efficiencies at the peak power density are determined to be 52.4 ± 1.6% and 49.3 ± 1.6% respectively under the ambient conditions considered.

Hysteresis of output voltage and liquid water transport in gas diffusion layer of polymer electrolyte fuel cells

The hysteresis of PEM fuel cell output voltage of the single cell and multi-cell stack is presented by experiments, during which the in-situ liquid water visualization at certain point of gas channel, quantitative measurement of the RH (relative humidity) and HFR (high frequency resistance) by EIS (electrochemical impedance spectroscopy) were carried out. It is found that HFR makes little contribution to the hysteresis of voltage. Instead, the hysteresis of liquid water saturation s in GDL is believed to dominant this process. Although the hysteresis of capillary pressure of liquid water in GDL has already been the presented in previous works, it is for the first time that a simplified one-dimensional model on liquid water saturation is updated considering this effect to understand the possible relation between them. Two different liquid water saturation s distributions during imbibition and drainage are obtained by simulation and related hypothesis of different water morphology in GDL is proposed. Furthermore, according to the simulation results, the GDL consisting of material with high resistance to water penetrating is found to have the better performance in the flooding condition, but weak capability to maintain residual water during drainage of PEM fuel cell.

Series-parallel grouping modeling simulation and experimental analysis of zinc-nickel single flow batteries

This study investigates a battery system with a zinc-nickel single flow battery (ZNB) stack by a series-parallel-connected system based on a two-order Thévenin equivalent circuit model for single-cell stack and parameter identification of the experimental model. Two single-cell stacks are simulated with three kinds of series-parallel battery pack equivalent circuit models, and compared with the experimental data. The results show that the simplified equivalent circuit model can accurately characterize the voltage of discharge for the series-parallel battery pack. The relative errors of the series/parallel battery pack are 0.8% and 0.71%. Furthermore, the simulation and experimental test data of the large-scale series-parallel system are compared, thereby indicating that the simplified equivalent circuit model of the series/parallel battery based on the two-order Thévenin model can provide a high-precision prediction for the external characteristics of a large-scale ZNB energy storage system.