Flow‐Field Designs of Bipolar Plates in PEM Fuel Cells: Theory and Applications

A generalized model developed by Wang was modified for flow field designs of the most common layout configurations with U‐type arrangement, including single serpentine, multiple serpentine, straight parallel, and interdigitated configurations. A direct and quantitative relationship was established among flow distribution, pressure drop, configurations, structures, and flow conditions. The model was used for a direct, systematic, and quantitative comparison of flow distributions and pressure drops among the most common layout configurations of interest. The straight parallel configuration had the lowest pressure drops but suffered the most possibility of the uneven flow distribution across the channels. The single serpentine had the best flow distribution but had the highest pressure drops. The flow distribution and the pressure drop in the multiple serpentine was between the straight parallel and the single serpentine. Finally, we suggested basic criteria of the flow field designs of bipolar plates for the industrial applications. This provides a practical guideline to evaluate how far a fuel cell is from design operating conditions, and measures how to improve flow distribution and pressure drop.     

Metallic Bipolar Plates for High Temperature Polymer Electrolyte Membrane Fuel Cells

High temperature polymer membrane fuel cells (HTPEMFCs) are promising devices for future mobile applications. To minimize phosphoric acid migration from the membranes and to reduce the total stack weight and size metallic bipolar plates are a promising alternative. So far only very few published results are available on the use of metallic bipolar plates in HTPEMFCs. During this work a single test cell was equipped with metallic endplates to investigate the possibility of using metallic bipolar plates in HTPEMFC stacks. Furthermore we tried to simulate the environments present in an HTPEMFC by furnace exposures in an attempt to develop a simplified test method for accelerated corrosion of bipolar plate materials. It was found that the performance of the HTPEM test cell decreased by about 15 µV h⁻¹. More corrosion products were seen on the cathode side samples, whereas on the anode side sample the corrosion attack of the steel was more severe. These results were successfully replicated in simulated furnace experiments.     

Polymer Electrolyte Membrane Fuel Cell (PEMFC) Flow Field Plate: Design,Materials and Characterisation

This review describes some recent developments in the area of flow field plates (FFPs) for proton exchange membrane fuel cells (PEMFCs). The function, parameters and design of FFPs in PEM fuel cells are outlined and considered in light of their performance. FFP materials and manufacturing methods are discussed and current in situ and ex situ characterisation techniques are described.     

Effects of Potential on Corrosion Behavior of Uncoated SS316L Bipolar Plate in Simulated PEM Fuel Cell Cathode Environment

The effect of potential on the corrosion behavior of uncoated stainless steel SS316L as bipolar plate material in proton exchange membrane (PEM) fuel cell cathode environment is studied. Electrochemical methods, X‐ray photoelectron spectroscopy, scanning electron microscope are employed to characterize the corrosion behavior of SS316L at different polarization potentials in PEM fuel cell cathode environment. The results show that the corrosion current density of SS316L increases with the increase of polarization potential significantly. When the potential is higher than 0.7 V versus SCE, severe corrosion occurs on SS316L. The work also shed light on the corrosion mechanisms of SS316L at different potential in the PEM fuel cell cathode environment.     

Expanded Graphite–Epoxy–Flexible Silica Composite Bipolar Plates for PEM Fuel Cells

Silica impregnated expanded graphite–epoxy composites are developed as bipolar plates for proton exchange membrane (PEM) fuel cells. These composite plates were prepared by solution impregnation, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance, and contact angles were determined as a function of impregnated content. The plates show high flexural strength with 5% methyltrimethoxysilane (MTMS) addition (20 MPa) and in‐plane conductivity of 131 S cm⁻¹ that meet the DOE target (>100 S cm⁻¹). Corrosion current values as low as 1.09 μA cm⁻² were obtained. The contact angle was found to be 80°. Power density of 1 W cm⁻² was achieved with custom made expanded graphite–polymer composite plates. High efficiency values were obtained at low current regions.     

Evaluation of Ni‐Mo and Ni‐Mo‐P Electroplated Coatings on Stainless Steel for PEM Fuel Cells Bipolar Plates

Stainless steel bipolar plates (BPPs) are the preferred choice for proton exchange membrane fuel cells (PEMFCs); however, a surface coating is needed to minimize contact resistance and corrosion. In this paper, Ni–Mo and Ni–Mo–P coatings were electroplated on stainless steel BPPs and investigated by XRD, SEM/EDX, AFM and contact angle measurements. The performance of the BPPs was studied by corrosion and conduction tests and by measuring their interfacial contact resistances (ICRs) ex situ in a PEMFC set‐up at varying clamping pressure, applied current and temperature. The results revealed that the applied coatings significantly reduce the ICR and corrosion rate of stainless steel BPP. All the coatings presented stable performance and the coatings electroplated at 100 mA cm⁻² showed even lower ICR than graphite. The excellent properties of the coatings compared to native oxide film of the bare stainless steel are due to their higher contact angle, crystallinity and roughness, improving hydrophobicity and electrical conductivity. Hence, the electroplated coatings investigated in this study have promising properties for stainless steel BPPs and are potentially good alternatives for the graphite BPP in PEMFC.     

Analysis of Optimal Heat Transfer in a PEM Fuel Cell Cooling Plate

An analysis of three‐dimensional computational fluid dynamics (CFD) is conducted to investigate the coupled cooling process involved in fluid flow and heat transfer between the solid plate and the coolant flow for optimization of the cooling design of a fuel cell stack. A conception of IUT (Index of Uniform Temperature) across the entire area is presented to evaluate the degree of uniform temperature profile across the cooling plates. Six cooling modes, including three serpentine‐type modes and another three parallel‐type modes, are presented and analyzed for optimization of the cooling mode of fuel cells. The prediction finds that the cooling effect of serpentine‐type cooling modes could be better than that of parallel‐type cooling modes.     

Characterising PEM Fuel Cell Performance Using a Current Distribution Measurement in Comparison with a CFD Model

The characterisation of a proton exchange membrane (PEM) fuel cell with a straight channel flow field design is performed. Spatially resolved current distribution measurements, at different air flow rates, are compared to numerical simulation results. The numerical model is validated by agreement of the measured and simulated current distribution. The test cell is segmented. It is operated at steady state conditions and the gas flow rates and cell temperature are controlled. The numerical simulation is realised with a PEM fuel cell model based on FLUENT™ computational fluid dynamics (CFD) software. It accounts for mass transport in the gaseous phase, heat transfer, electrical potential field and the electrochemical reaction. It provides three‐dimensional distributions of, e.g., current densities, reactant concentrations and temperature.     

Low Cost and Rapidly Processed Randomly Oriented Carbon/Carbon Composite Bipolar Plate for PEM Fuel Cell

The objective of the present work is to develop carbon/carbon (C/C) composite bipolar plate at low cost with rapid processing time by a novel process. Carbon/carbon composite was developed using exfoliated carbon fiber reinforcement, isroaniso as primary matrix precursor, and resole type phenolic resin as secondary matrix precursor. Randomly oriented hybrid carbon fiber (T‐800 and P‐75) reinforced hybrid carbon matrix composite was fabricated. The slicing and channel forming were carried out using simple and conventional machines. The competency of the material was investigated by characterizing and analyzing density, scanning electron miscroscopy (SEM), compressive strength, compressive modulus, flexural strength, tensile strength, impact strength, hardness, electrical conductivity, thermal conductivity, coefficient of thermal expansion, permeability, and corrosion current. The C/C composite bipolar plate with exfoliated carbon fibers offered bulk density 1.75 g cm⁻³, tensile strength 45 MPa, flexural strength 98 MPa, compressive strength 205 MPa, electrical conductivity 190 (through‐plane) and 595 S cm⁻¹ (in‐plane), and thermal conductivity 24 (through‐plane) and 51 W m⁻¹ K⁻¹ (in‐plane). Further, single cell test was performed to evaluate the effectiveness of the C/C composite bipolar plate in the PEM fuel cell and the performance was compared with the commercial graphite bipolar plate at different operating temperatures.     

Effects of Distribution Channel Dimensions on Flow Distribution and Pressure Drop in a Plate‐Fin Heat Exchanger

A numerical investigation on flow distribution and pressure drop characteristics in a plate‐fin heat exchanger is presented. Influences from length and width of the distribution channel were particularly investigated. Flow distribution in the studied model was improved by increasing the length or reducing the width of the distribution channel, but at the cost of an increased pressure drop. The relationship of flow distribution and pressure drop was analyzed by the porous medium approach. A dynamic balance phenomenon was observed and further studied. Based on the results, a novel strategy for the attainment of flow uniformity, which causes negligible pressure drop variation, was proposed. Finally, a performance effectiveness factor was developed for predicting the effect of the proposed strategy on the performance of plate‐fin heat exchangers.     

Detection of Liquid Water in PEM Fuel Cells' Channels: Design and Validation of a Microsensor

Suitable water management is a critical issue to reach the full potential of PEM fuel cells: whereas the membrane must be hydrated enough, liquid droplets formed by water in excess can block the flow in the gas distribution channels and hinder the fuel cell performance. In order to detect the presence of droplets in cathode flow channel, an electrochemical sensor has been developed and tested in a dedicated emulation cell. It is based on the widely used principle of two‐electrode cells for conductivity measurements; the collected signal is converted to impedance values. The sensor, mounted in a gas flow channel grooved in a graphite plate, reacts to the passage of water droplets, either being injected into the continuous air stream or produced by condensation of humidified air at the graphite plate. The time variation of the electrical impedance could be correlated to the observations allowed by the high‐speed digital camera. Water droplets separated from each other by less than a second can be distinguished by the sensor, which is of a sufficient rapidity.     

Optimization of Parallel and Serpentine Configurations for Polymer Electrolyte Membrane Fuel Cells

A network‐based optimization model was developed to optimize the channel dimensions of flow fields in order to achieve a uniform flow distribution and improve the performance of polymer electrolyte membrane (PEM) fuel cells. Different flow field configurations, including parallel, parallel‐in‐series, and serpentine, were investigated using the present optimization model. Two cases, with and without considering reactant consumption, were compared to show the effect of including reactant consumption on the flow field designs. The results demonstrated that the optimized designs significantly improved the flow velocity distribution in all the configurations investigated. The optimized designs with consideration of reactant consumption exhibited more uniform flow velocity distribution when the entire fuel cell unit was considered. Additionally, the performances of PEM fuel cells for the conventional and optimized flow field designs were studied with a three‐dimensional, two‐phase fuel cell simulation model, and the computational results showed that the optimized designs with considering reactant consumption produced the highest maximum power density for each configuration investigated. These results show that the network‐based model is capable of optimizing various flow field configurations with flexibility and indicate the importance of considering reactant consumption in the optimization model.     

Corrosion Investigation of Chromium Nitride and Chromium Carbide Coatings for PEM Fuel Cell Bipolar Plates in Simulated Cathode Condition

Transition metals nitrides and carbides are used as coatings on bipolar plates for proton exchange membrane fuel cells (PEMFCs) due to their suitable electrical conductivity and corrosion resistance. Chromium electroplated AISI 316L stainless steel bipolar plates were treated by plasma nitriding and solid carburizing to form chromium nitride and chromium carbide, respectively. The presence of CrN/Cr₂N and Cr₇C₃/Cr₂₃C₆ was verified by X‐ray diffractometry (XRD) in chromium nitride and chromium carbide coatings, respectively. The corrosion behavior of coatings was investigated by potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy (EIS) in simulated cathode condition. Coated samples showed better corrosion behavior than untreated bare sample. EIS results indicated decrease in corrosion current density after 500 hours, however coatings acted as barrier against solution access to substrate. Corrosion current densities of coatings were close to targets of United Stated department of energy (DOE).     

Modeling and Parametric Study of a Single Solid Oxide Fuel Cell by Finite Element Method

A 2D isothermal axisymmetric model of an anode‐supported solid oxide fuel cell has been developed. The model, which is based on finite element approach, comprises electronic and ionic charge balance, Butler–Volmer charge transfer kinetic, flow distribution and gas phase mass balance in both channels and porous electrodes. The model has been validated using available experimental data coming from a single anode‐supported cell comprising Ni–YSZ/YSZ/LSM–YSZ as anode, electrolyte and cathode, respectively. Hydrogen and steam were used as fuel inlet and air as an oxidant. The validation has been carried out at 1 atm, 1,500 ml min^–1 air flow rate and three different operating conditions of temperature and fuel flow rate: 1,073 K and 400 ml min^–1, 1,073 K and 500 ml min^–1, and 1,003 K and 400 ml min^–1. The polarization and power density versus current density curves show a good agreement with the experimental data. A parametric analysis has been carried out to highlight which parameters have main effect on the overall cell performance as measured by polarization curve, especially focusing on the influence of two geometrical characteristics, temperature and some effective material properties.     

Modelling and Analysis of Electro‐chemical,Thermal, and Reactant Flow Dynamics for a PEM Fuel Cell System

In this paper an approach for the dynamic modelling of polymer electrolyte membrane fuel cells is presented. A mathematical formulation based on empirical equations is discussed and several features, exhibiting dynamic phenomena, are investigated. A generalized steady state fuel cell model is extended for the development of a method for dynamic electrochemical analysis. Energy balance and reactant flow dynamics are also explained through physical and empirical relationships. A well‐researched system (Ballard MK5‐E stack based PGS‐105B system) is considered in order to understand the operation of a practical fuel cell unit. Matlab‐SIMULINK^TM has been used in simulating the models. The proposed method appears to be relatively simple and consequently requires less computation time. Simulation results are compared with available experimental findings and a good match has been observed.     

整体多层包扎式高压容器筒体与球形封头连接区应力状态有限元分析

建立了整体多层包扎式高压容器多层筒体与球形封头连接区有限元接触分析模型,得到了端部阶梯式连接结构的应力分布状况,并与相同尺寸非多层结构的应力分布进行了比较。结果表明,两种结构内外壁应力变化趋势相似,在连接区出现明显的应力集中,连接处轴向应力上升趋势大于周向应力,达到最大应力值后迅速衰减。     

带翼阀旋风分离器料腿内静压分布试验研究

在φ800mm×12000mm流化床试验装置上,用多点压力测量仪测量料腿内的静压分布。试验结果表明,二级料腿内气固两相流的流态一般由入口旋转段、稀相下落段和下部密相段3部分组成,料腿内的料封高度随料腿两端负压差的增大而升高,颗粒质量流率对轴向空隙率影响明显,翼阀浸没在密相床时颗粒流动稳定性和流动失流化的机会都增加。     

Design,testing and field deployment of a composite clamp for pipeline repairs

A novel method of repairing leaking or otherwise damaged metallic pipelines using composites is presented. The method uses a uniquely designed resin-infused composite clamp. This is a significant improvement over commercially available metal clamps, providing lightweight and corrosion-resistant benefits. The design, analyses and testing presented here show that these benefits are in addition to providing uncompromising strength and reliability to the repaired structure. The design includes a combination of calculations and design of experiment optimisation with Finite Element models. The developed design methodology is shown to be robust for designing different clamp sizes. Testing involved short- and long-term survival tests of the clamps as per industrial standards, as well as hot-wet conditioning followed by mechanical testing of the composite material. Finally, a case study field deployment of the clamp on a 4-in propane pipeline with internal corrosion is presented.     

Modeling the two-way coupling of stress,diffusion, and oxidation in heterogeneous CMC microstructures

A multiphysics methodology and a corresponding numerical scheme are proposed for modeling the complex interactions between oxygen diffusion, matrix cracking, oxidation, and the state of stress in carbon silicon carbide (C/SiC) ceramic matrix composites (CMCs) at the microstructural scale. The model is derived from the governing equations for force equilibrium and conservation of mass for oxygen and carbon, which are coupled through reaction terms, oxygen diffusivities and solubilities, and damage in the matrix. The Galerkin method of weighted residuals is used to derive the finite element method (FEM) equations, and the model is demonstrated on a representative stochastic heterogeneous microstructure to investigate the creep-like strain acceleration of stressed oxidation experiments and analyze the fundamental differences between the reaction-limited and diffusion-limited temperature regimes.