Electrically conductive thermoplastic blends for injection and compression molding of bipolar plates in the fuel cell application

This study aimed at developing highly conductive, lightweight, and low‐cost bipolar plates for use in proton exchange membrane fuel cells. Injection and compression molding of carbon‐filled polypropylene, PP, and polyphenylene sulfide, PPS, were used to fabricate the bipolar plates. Loadings up to 60 wt% in the form of graphite, conductive carbon black, and carbon fibers were investigated. The developed compositions have a combination of properties and processability suitable for fuel cell bipolar plate manufacturing, such as good chemical resistance, sufficient fluidity, and good electrical and thermal conductivity. Two bipolar plate designs were successfully fabricated by molding the gas flow channels over aluminum plates to form a metallic/polymer composite plate or simply by direct injection molding of the conductive polymer composite. For the first design, overall plate volume resistivities of 0.2 and 0.1 Ohm‐cm were respectively attained using PP and PPS based blends as the conductive overmolded layer. A lower volume resistivity of around 0.06 Ohm‐cm was attained for the second design with injection molded plates made of the PPS‐based blend. Polym. Eng. Sci. 44:1755–1765, 2004. © 2004 Society of Plastics Engineers.     

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.     

Electrical,mechanical, and thermal properties of exfoliated graphite/phenolic resin composite bipolar plate for polymer electrolyte membrane fuel cell

Exfoliated graphite (EG) was synthesized from natural flake graphite by acid treatment followed by microwave irradiation. A maximum expanded volume of 560 mL/g was achieved for this exfoliation of graphite. EG/phenolic resin composite bipolar plates for polymer electrolyte membrane fuel cell were fabricated with a high loading of EG by compression molding. The composites possess low density, high electrical conductivity, high thermal stability, and high compressive strength. The composite bipolar plates were also characterized by X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and so on. The composite prepared with 50 wt% of EG has shown the desired properties for bipolar plate as per the US Department of Energy (DOE‐2015) targets. As a result, the EG–resin composites can be used as bipolar plates for polymer electrolyte membrane fuel cell applications. POLYM. ENG. SCI., 55:917–923, 2015. © 2014 Society of Plastics Engineers     

A Promising Alternative to PEMFC Graphite Bipolar Plates: Surface Modified Type 304 Stainless Steel with TiN Nanoparticles and Elastic Styrene Butadiene Rubber Particles

In order to utilise inexpensive bipolar plates for proton exchange membrane fuel cells (PEMFC), a surface modification with TiN nanoparticles and elastic styrene butadiene rubber (SBR) particles has been applied to the most widely commercialised stainless steel of type 304 which did not satisfy the required properties in the bare form. The electro‐conducting agglomerates were electrophoretically deposited on the stainless steel bipolar plates. The surface modification greatly improved the corrosion resistance of the stainless steel as well as the interfacial contact resistance (ICR). As a result, the cell performance was significantly enhanced and become comparable to that with graphite bipolar plate during operation for 1,000 h. Ac‐impedance results indicated that the TiN–SBR coating was effective not only in reducing the ICR but also in retaining the resistance low throughout the operation. The hydrophobic character of the TiN–SBR coating on the stainless steel bipolar plates, which facilitated the removal of the formed water in the cathode side during the single cell operation, is also responsible for the enhanced cell performance. Therefore, the type 304 stainless steel bipolar plate modified with the electro‐conducting nanosized TiN – elastic SBR particles is suggested to be a promising substituent for the PEMFC graphite bipolar plate.     

Synergistic Effects of Carbon Fillers of Phenolic Resin Based Composite Bipolar Plates on the Performance of PEM Fuel Cell

The most essential and costly component of polymer electrolyte membrane fuel cells is the bipolar plate. The production of suitable composite bipolar plates for polymer electrolyte membrane fuel cell with good mechanical properties and high electrical conductivity is scientifically and technically very challenging. This paper reports the development of composite bipolar plates using exfoliated graphite, carbon black, and graphite powder in resole‐typed phenol formaldehyde. The exfoliated graphite with maximum exfoliated volume of 570 ± 10 mL g⁻¹ used in this study was prepared by microwave irradiation of chemically intercalated natural flake graphite in a few minutes. The composite plates were prepared by varying exfoliated graphite content from 10 to 35 wt.% in phenolic resin along with fixed weight percentage of carbon black (5 wt.%) and graphite powder (3 wt.%) by compression molding. The composite plates with filler weight percentage of 35/5/3/exfoliated graphite/carbon black/graphite powder offer in‐plane and trough‐plane electrical conductivities of 374.42 and 97.32 S cm⁻¹, bulk density 1.58 g cm⁻³, compressive strength 70.43 MPa, flexural strength 61.82 MPa, storage modulus 10.25 GPa, microhardness 73.23 HV and water absorption 0.22%. Further, I–V characteristics notify that exfoliated graphite/carbon black/graphite powder/resin composite bipolar plates in unit fuel cell shows better cell performance compared exfoliated graphite/resin composite bipolar plates. The composite plates own desired mechanical properties with low bulk density, high electrical conductivity, and good thermal stability as per the U.S. department of energy targets at low filler concentration and can be used as bipolar plates for proton exchange membrane fuel cells.     

On a new degradation mode for high-temperature polymer electrolyte fuel cells: How bipolar plate degradation affects cell performance

The contribution of the bipolar plate material to the overall degradation of a high temperature membrane electrode assembly (HT MEA) for polymer electrolyte fuel cells (PEFCs) is studied in terms of performance decrease, phosphoric acid uptake in the bipolar plates and change of surface morphology of the bipolar plates. Two different high temperature graphite composites, a surface treated graphite and a gold coated stainless steel flowfield and the respective MEAs are compared after operation at 180 °C. Both graphite surface treatment and gold coating lead to negligible uptake of the electrolyte and ensure low degradation rates, whereas the composite plates exhibit high uptake of acid from the MEA into the surface near bulk. Apparent MEA degradation caused by acid redistribution from the MEA to the increasingly porous plates is observed in terms of increased ohmic cell resistances and reduction of catalyst utilization as consequence of acid loss from the catalyst layers.     

Development of Low‐Cost Advanced Composite Bipolar Plate for Proton Exchange Membrane Fuel Cell�

The bipolar plate is one of the most imperative components of proton exchange membrane fuel cells (PEMFC) which consumes up to 80% of weight and near about 50% of the total cost of the cell. Development of cost‐effective composite bipolar plate with high electrical conductivity and high mechanical strength is both technically and economically demanding. In this paper, a low‐cost advanced composite bipolar plate is developed by bulk moulding compression (BMC) technique. It is clear from the experiments that by increasing the matrix volume fraction, bulk density and electrical conductivity of a composite bipolar plate decrease but shore hardness increases. Test results clearly show that best overall properties are achieved when a constant volume fraction of polymer matrix and natural graphite is reinforced with synthetic graphite, carbon black and carbon fibre. This bipolar plate was found to have high conductivity, less porosity and high mechanical strength. The I–V characteristics in single cell test exhibited more uniform power density at both higher and lower current densities     

Corrosion-resistant lightweight metallic bipolar plates for PEM fuel cells

Corrosion resistant treated metal bipolar plates with higher rigidity and electrical conductivity than graphite were developed and tested for PEM fuel cell applications. Six replicas of single cells were used three of which were made of graphite composites bipolar plates and the other three of the treated metallic plates. A Membrane Electrode Assembly (MEA) with 5.55 cm² active electrode areas, 0.3 mg cm^–2 Pt loading and Nafion membrane 115 was fitted to each cell and operated under identical conditions. The experimental testing was conducted at room temperature (20 °C). The average value of the data obtained for the three graphite cells was plotted. Similarly, the average value of the data obtained for the three treated metal cells was plotted on the same graph for comparison. Generally, the treated metal bipolar plate provided at least 12% saving in hydrogen consumption in comparison to graphite. This is attributed to the lower bulk and surface contact resistance of the metal used in this study in relation to graphite. The results of lifetime testing, conducted at room temperature under variable loading showed no indication of power degradation due to metal corrosion for at least 1500 hours.     

Carbon‐Polymer Composite Bipolar Plate for HT‐PEMFC

Graphene reinforced carbon‐polymer composite bipolar plate is developed using resole phenol formaldehyde resin, and conductive reinforcements (natural graphite, carbon black, and carbon fiber) using compression molding technique. Graphene is reinforced into the composite to alter various properties of the composite bipolar plate. The developed composite bipolar plate is characterized and the effect of temperature on mechanical and electrical properties is investigated with an overall aim to achieve benchmark given by US‐DOE and Plug Power Inc. The flexural strength and electrical conductivity of the composites was almost stable with the increase in temperature upto 175 °C. The composite bipolar plate maintained high in‐plane and through‐plane electrical conductivities, which is about 409.23 and 98 S cm^–1, respectively, at 175 °C. The flexural strength and shore hardness of the developed composite was around 56.42 MPa and 60, respectively, at 175 °C, and on further increase in the temperature the mechanical strengths deceases sharply. The electrical and mechanical properties of the composite bipolar plates are within the US‐DoE target. However, the various properties of the composite bipolar plate could not be sustained above 175 °C.     

A Novel Design of Wave‐Like PEMFC Stack with Undulate MEAs and Perforated Bipolar Plates

Commercialisation of proton exchange membrane fuel cell (PEMFC) technology depends on high volumetric power density and specific power for a given cost. In the present study, a novel wave‐like architecture for PEMFC stack based on undulate membrane electrode assembles (MEAs) and perforated bipolar plates (PBPs) was presented. Different from conventional plate‐and‐frame architecture, this design increased active area and achieved higher volumetric power density due to undulate MEAs. Moreover, perforated sheet metal was used as bipolar plates so that it could improve specific power. A single cell was designed and fabricated in house to evaluate the performance of the novel architecture stack. Stamped PBPs with open rate of 28.26% and hot pressed 5‐layer undulate MEAs with Nafion® 112 were adopted. The results indicated that the peak volumetric power density and specific power are 2,715.94 W L^–1 and 2,157.86 W kg^–1, respectively, while they are 2,151.28 W L^–1 and 1,709.22 W kg^–1 at the output voltage of 0.6 V. This study may propose a possible means to meet the DOE's 2010 technical target that volumetric power density is 2,000 W L^–1 and specific power is 2,000 W kg^–1 for stack.     

Fabrication of Aluminum Bipolar Plates by Semi‐solid Forging Process and Performance Test of TiN Coated Aluminum Bipolar Plates

Aluminum bipolar plates that can replace graphite bipolar plates for PEM fuel cells are made by applying a semi‐solid forging process. A semi‐solid slurry is made using electromagnetic stirring (EMS), and the resulting slurry is injected into a forging die attached to a 200 ton hydraulic press. The slurry is then compressed with a punch, flowed into a die cavity, and solidified into the bipolar plate form. A356 (cast Al alloy), A6061 (wrought Al alloy), and A1100 (pure Al) are used to make the plates. Titanium nitride (TiN) coating is deposited on the aluminum bipolar plates. An atomic force microscope (AFM) is used to measure the surface roughness of the plates. TiN coated A356 and A1100 plates have a surface roughness of R_a < 1.2 μm. The plate thickness is 1.2 mm. The active area of the channel is 70 mm × 70 mm, with a depth and width of 0.3 and 1.0 mm, respectively. The three TiN‐coated aluminum plates are combined with a unit cell for a performance test. Our results show that a current density value of 473 mA cm^–2 (about 41% of the current density value of commercial graphite plates) can be obtained.     

Automated and Continuous Production of Microstructured Metallic Plates via Cold Embossing

Many critical issues need to be addressed when microstructured reactors are manufactured in large unit volumes. The most crucial of these are cost, ease of production, and reliability. The lack of breakthrough manufacturing technology to provide high‐efficiency, low‐cost, high‐precision plates is a hindrance to the early market implementation of systems requiring metallic microstructured plates. This contribution focuses on the development and optimization of a combined embossing and bending tool for the quick and continuous manufacture of easily machined plates.     

Performance Improvement of Wave‐Like PEMFC Stack with Compound Membrane Electrode Assembly

The novel architecture of wave‐like proton exchange membrane fuel cell (PEMFC) stack developed in our previous work achieved peak volumetric power density and specific power of 2,715.9 W L^–1 and 2,157.9 W kg^–1, respectively. However, there still existed perforated bipolar plates and the carbon fiber gas diffusion layer (GDL) was easy to cause damage during the fabrication process of undulate membrane electrode assembles (MEAs). In the present study, sintered stainless steel fiber felt (SSSFF) was employed to work as metallic GDL (MGDL) and bipolar plates simultaneously. Compound membrane electrode assembles (CMEAs) with serpentine and interdigitated flow channels were designed and fabricated using stamping process. A single cell with CMEA was assembled in house and the output performance was evaluated systemically. The results indicated that the peak volumetric power density and specific power of wave‐like PEMFC single with CMEA are 5,764.0 W L^–1 and 4,693.5 W kg^–1 respectively. This study achieved a significant performance improvement due to the concept of CMEA and may propose a possible means to meet the DOE's 2020 technical target that volumetric power density is 2,500 W L^–1 and specific power is 2,000 W kg^–1 for stack.     

Carbon coated stainless steel bipolar plates in polymer electrolyte membrane fuel cells

The desirable properties of the metallic bipolar plates in polymer electrolyte membrane fuel cells (PEMFC) are good corrosion resistance, high electrical conductance, hydrophobicity, and low cost. In this study, carbon films are deposited on stainless steel 316L (SS316L) samples by close field unbalanced magnetron sputtering. The AFM, SEM, and Raman results show that the carbon film is dense, continuous, and amorphous. The corrosion resistance, hydrophobicity, and interfacial contact resistance (ICR) of the carbon coated steel are investigated and compared to those of uncoated SS316L. The deposited carbon film has high chemical inertness thereby significantly enhancing the corrosion resistance of the coated SS316L. Furthermore, the carbon coated SS316L is more hydrophobic and the resulting ICR is elevated to that of graphite. Our results indicate that the properties of the carbon coated SS316L are better than those of conventional graphite bipolar plates.     

高温车用燃料电池的发展及现状综述

燃料电池车以其能量转化效率高、绿色环保、噪音低等优点,被认为是替代传统化石能源汽车最有前景的新能源汽车。目前车用燃料电池的工作温度一般都低于80℃,低温的工作环境使其面临着诸多问题,如复杂的水管理和CO中毒等。通过提高质子交换膜燃料电池（PEMFC）的工作温度可以缓解这些问题,提高燃料电池的性能。然而,高温的工作环境也会对燃料电池带来诸多挑战,如膜脱水、催化剂团聚、冷启动速度缓慢等。要促进高温（90～120℃）车用燃料电池的快速发展,需要对其问题及解决方法进行分析。本文从电堆比功率、膜电极、双极板、进气方式、加湿方式等方面,介绍燃料电池的发展现状及存在的问题,包括Nafion膜和催化剂的热稳定问题、双极板的耐腐蚀问题、流道的气体分配问题、进气方式和加湿方式的优化以及冷启动问题。指出通过掺杂亲水性氧化物改善Nafion膜的高温性能;将Pt合金化及采用介孔炭提高催化剂的稳定性和电化学活性;镀层不锈钢金属双极板可以增强耐腐蚀性;3D流场等新型流场结构及提高进气温度、速度可以提高气体的均匀性;采用自增湿方式可以简化电堆结构等解决方法,以期对燃料电池车的进一步发展起到引导作用。     

Differences in physico-mechanical behaviors of resol(e) and novolac type phenolic resin based composite bipolar plate for proton exchange membrane (PEM) fuel cell

Composite bipolar plates for Proton Exchange Membrane Fuel Cell (PEMFC) are prepared by compression molding technique using polymer as binder and graphite as electric filler material with some other reinforcements. Study on the effect of resole and novolac type phenolic resin on the properties of composite bipolar plate, such as bulk density, porosity, bulk conductivity, hardness, flexural strength, etc. shows that both of the resin shows different physico-mechanical properties. Moreover, single cell performance analysis also shows variation for resole and novolac based composites. A novel concept of triple continuous structure to provide graphite polymer blends with high electrical conductivity, high shore hardness, high flexural strength, less porosity and low density has been proposed and study on the effect of different types of phenolic resin on the properties and performance of bipolar plate reveals that novolac type powdered phenolic resin gives better mechanical properties than resole type phenolic resin. However, resole type phenolic resin compound has slightly higher electrical conductivity due to more number of polar -OH group presents on its cured form. But due to the less porosity and higher mechanical strength, bipolar plates with novolac type phenolic resin gives better performance in I-V analysis than bipolar plates with resole type phenolic resin.     

Nanosized TiN-SBR hybrid coating of stainless steel as bipolar plates for polymer electrolyte membrane fuel cells

In attempt to improve interfacial electrical conductivity of stainless steel for bipolar plates of polymer electrolyte membrane fuel cells, TiN nanoparticles were electrophoretically deposited on the surface of stainless steel with elastic styrene butadiene rubber (SBR) particles. From transmission electron microscopic observation, it was found that the TiN nanoparticles (ca. 50 nm) surrounded the spherical SBR particles (ca. 300-600 nm), forming agglomerates. They were well adhered on the surface of the type 310S stainless steel. With help of elasticity of SBR, the agglomerates were well fitted into the interfacial gap between gas diffusion layer (GDL) and stainless steel bipolar plate, and the interfacial contact resistance (ICR), simultaneously, was successfully reduced. A single cell using the TiN nanoparticles-coated bipolar plates, consequently, showed comparable cell performance with the graphite employing cell at a current density of 0.5 A cm⁻² (12.5 A). Inexpensive TiN nanoparticle-coated type 310S stainless steel bipolar plates would become a possible alternate for the expensive graphite bipolar plates as use in fuel cell applications.     

Fabrication of electrically conductive polymer composites for bipolar plate by two‐step compression molding technique

Electrically conductive polymer composites for bipolar plate were fabricated by two‐step compression molding technique. Raw materials consisted of natural graphite flakes (G), expanded graphite (EG), carbon black (CB), and phenol resin (PF). The G/EG/CB/PF composites were first compressed at a temperature lower than curing point (100°C) and then cured at a high temperature above curing point (150°C) and high pressure (10 MPa). Results showed that G and EG are oriented in the direction parallel to the composite plate surface. CB is dispersed not only in the phenol resin matrix but also in the packing and porous space of G and EG. The addition of EG and CB significantly increases number of the electrical channels and thus enhances the electrical conductivity of the composite. Under optimal conditions, electrical conductivity and flexural strength of the composite were 2.80 × 10⁴ S/m and 55 MPa, respectively, suggesting that the dipolar plates prepared by two‐step compression molding technique are adequate to meet the requirement of proton exchange membrane fuel cells. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2296–2302, 2013     

Thermal conductivity models for carbon/liquid crystal polymer composites

Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of four different types of polyacrylonitrile carbon fillers (Ketjenblack carbon black, Thermocarb synthetic graphite, Fortafil 243 carbon fiber, and Panex 30 carbon fiber) were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer), with the resulting resins tested for through‐plane and in‐plane thermal conductivity. There are two unique contributions of this work. The first contribution is the use of the Nielsen model for the through‐plane thermal conductivity as a function of the single filler volume fraction. The model fits the data for all composites well. The second contribution is the development of a new, accurate, empirical model to predict the in‐plane thermal conductivity for all resins containing synthetic graphite or carbon fiber. Both of these models will form the basis for the development of new thermal conductivity models for composites with multiple fillers for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

表面改性金属双极板在直接甲醇燃料电池中的应用

石墨双极板由于制作成本高、易碎等不利因素严重制约直接甲醇燃料电池（DMFC）的发展。表面改性后的金属材料由于具备接触电阻低，加工强度高等优点而受到广泛关注。但是，迄今为止，国内少见改性金属双极板在DMFC中的研究报道。本文分别对金属及其氧化物、导电高分子、碳膜及金属碳化物、金属氮化物作为金属材料表面改性膜层进行了详述。基于改性金属双极板在模拟DMFC运行环境中的腐蚀原理，重点分析了表面改性前后金属双极板的抗腐蚀性能、接触电阻、表面涂层的成分及形态等关键参数，分析比较了改性涂层金属双极板对燃料电池运行中的电化学行为和寿命的影响。展望了表面改性金属双极板在DMFC中应用的研究趋势，为实现DMFC便携式发展奠定了良好的基础。