Characteristics of composite bipolar plates for polymer electrolyte membrane fuel cells

As alternative bipolar plate materials for polymer electrolyte membrane fuel cell (PEMFC), two types of carbon composite were developed and characterized. Electrical and physical properties of the currently used graphite and newly developed carbon composites were evaluated in terms of bulk and contact resistance, flexural strength, density, gas tightness, water absorption, and depth deviation of the flow channel. The test results showed that the carbon composites were very promising candidates for PEMFC bipolar plate material. In single cell tests, the carbon composite bipolar plates exhibited good initial and long-term performance compared with the graphite bipolar plates.     

The electrical and corrosion properties of carbon nanotube coated 304 stainless steel/polymer composite as PEM fuel cell bipolar plates

In this study, the contact resistance and corrosion resistance of three different types of plates used as PEM fuel cell bipolar plates are investigated, viz. (1) 304 stainless steel without carbon nanotube treatment that was then sandwiched between polymer composites, (2) CNT particles placed on the surface of the 304 stainless steel that was then sandwiched between polymer composites, and (3) direct CNTs coated 304 stainless steel that was then sandwiched between polymer composites. Both treated and untreated 304 stainless steel covered with the polymer composites exhibited good corrosion resistance. The results showed that the highest improvement of the contact resistance was accomplished by the direct deposition of CNTs on the 304 stainless steel insert. The results of the potentiodynamic and potentiostatic measurements also showed that direct CNTs deposition on the 304 stainless steel insert did not degrade the corrosion performance under PEM fuel cell operating conditions.     

Electrically conductive LCP–carbon composite with low carbon content for bipolar plate application in polymer electrolyte membrane fuel cell

Lightweight polymer–carbon composites with high specific electrical conductivity at a carbon content below 40 vol.% were developed. The electrical and mechanical properties and the hydrogen permeability of carbon fiber and particle reinforced liquid crystalline polymers were examined. Vectra^® A 950, SIGRAFIL^® carbon fibers and Vulcan^® XC 72 R carbon black were employed. The composites are found to have sufficient mechanical properties and a hydrogen permeability low enough to be utilised as bipolar plate material in fuel cell applications. The density of the new composite is 20% lower than the density of commercial bipolar plates made from carbon reinforced polymeric composite materials, due to the lower carbon content. The current density at 0.5 V in an operating fuel cell is only 20% lower compared to commercial materials with more than 80 vol.% carbon content and meets the requirements for bipolar plate application.     

Development of bipolar plates for fuel cells from graphite filled wet-lay material and a thermoplastic laminate skin layer

In this paper, a method with the potential to rapidly produce thermoplastic polymer composite bipolar plates with improved formability and through-plane conductivity is described. In our earlier work, it was reported that composite bipolar plates made with graphite filled wet-lay materials exhibited excellent mechanical properties and in-plane electrical conductivity. However, the through-plane conductivity and formability of the materials needed improvement. In this work, laminate polymer composite plates consisting of a wet-lay based core and a fluoropolymer/graphite skin layer are manufactured in an effort to improve formability and through-plane conductivity. These plates are characterized by their through-plane and in-plane conductivity, half-cell resistance, and mechanical properties at ambient and elevated temperatures. The laminate plates with PPS based wet-lay core exhibited bulk conductivities of above 300 S cm⁻¹, tensile strength of up to 34 MPa, and flexural strength of up to 54 MPa. Compared to the bipolar plates consisting of wet-lay material only, the bipolar plates with laminate structure exhibited an increase in through-plane conductivity of 25–35%, as well as a decrease in half-cell resistance by a factor of up to 5. The laminate bipolar plates can be manufactured in several ways with two of them being discussed in detail in the paper.     

Carbon materials in composite bipolar plates for polymer electrolyte membrane fuel cells: A review of the main challenges to improve electrical performance

The technology of polymer electrolyte membrane (PEM) fuel cells is dependent on the performance of bipolar plates. There is a strong relationship between the material used in the manufacturing of the bipolar plate and its final properties. Graphite-polymer composite bipolar plates are well-established commercial products. Several other carbon based fillers are tested. Carbon nanotubes, carbon fibers, carbon black, graphite nanoplatelets and expanded graphite are examples of such materials. Structural characteristics of these particles such as morphology and size have decisive influence on the final properties of bipolar plates. Furthermore, the volumetric fraction of the filler is of prime importance. There is plenty of information on individual aspects of specific composite bipolar plates in the literature. Notwithstanding, the analysis of structure-property relationship of these materials in a comprehensive source is not found. In this paper, relevant topics on the structural aspects of carbon based fillers and how they influence the final electrical performance of composite bipolar plates are discussed. It is intended that this document contribute to the development of new and maximized products to the PEM fuel cell industry.     

Corrosion behavior of polyphenylene sulfide–carbon black–graphite composites for bipolar plates of polymer electrolyte membrane fuel cells

The aim of this work was to study the corrosion behavior of polyphenylene sulfide (PPS) – carbon black – graphite composites regarding their application as bipolar plates of polymer electrolyte membrane (PEM) fuel cells. Electrochemical impedance spectroscopy (EIS), potentiostatic and potentiodynamic polarization tests were used to characterize the electrochemical response of the composites in a simulated PEM fuel cell environment. Cross-sectional views of fractured specimens were observed by scanning electron microscopy (SEM). The results showed that the corrosion behavior depends on the carbon black content incorporated into the composite formulation. There was a trend of decreasing the corrosion resistance for higher carbon black contents. This behavior could be explained based on the porosity and electrical conductivity of the composites.     

Fabrication of high strength and a low weight composite bipolar plate for fuel cell applications

The bipolar plate is one of the most important components in a PEM fuel cell. A polymer composite bipolar plate possessing high strength (81 MPa) and high stiffness (20 GPa) has been developed by making use of carbon fiber network in a specific form as the filler component. Such high strength is very much desired, especially when the fuel cells are used for mobile applications, since it is the bipolar plate that provides mechanical support to all the other cell components. The addition of carbon black and the effect of particle size of the natural graphite flakes used as other reinforcements also play a crucial role in controlling the physical and electrical properties of the composite plates. The plate when used in the unit fuel cell assembly showed I–V performance comparable to that of the commercially available bipolar plates.     

Electrical and thermal conductivities of novel metal mesh hybrid polymer composite bipolar plates for proton exchange membrane fuel cells

This study prepares novel metal mesh hybrid polymer composite bipolar plates for proton exchange membrane fuel cells (PEMFCs) via inserting a copper or aluminum mesh in polymer composites. The composition of polymer composites consists of 70 wt% graphite powder and 0-2 wt% modified multi-walled carbon nanotubes (m-MWCNTs). Results indicate that the in-plane electrical conductivity of m-MWCNTs/polymer composite bipolar plates increased from 156 S cm⁻¹ (0 wt% MWCNT) to 643 S cm⁻¹ (with 1 wt% MWCNT) (D.O.E. target >100 S cm⁻¹). The bulk thermal conductivities of the copper and aluminum mesh hybrid polymer composite bipolar plates (abbreviated to Cu-HPBP and Al-HPBP) increase from 27.2 W m⁻¹ K⁻¹ to 30.0 W m⁻¹ K⁻¹ and 30.4 W m⁻¹ K⁻¹, respectively. The through-plane conductivities decrease from 37.8 S cm⁻¹ to 36.7 S cm⁻¹ for Cu-HPBP and 22.9 S cm⁻¹ for Al-HPBP. Furthermore, the current and power densities of a single fuel cell using copper or aluminum mesh hybrid polymer composite bipolar plates are more stable than that of using neat polymer composite bipolar plates, especially in the ohmic overpotential region of the polarization curves of single fuel cell tests. The overall performance confirms that the metal mesh hybrid polymer composite bipolar plates prepared in this study are promising for PEMFC application.     

Effect of different graphite materials on the electrical conductivity and flexural strength of bipolar plates fabricated using selective laser sintering

Selective Laser Sintering provides a way to fabricate graphite composite bipolar plates for use in fuel cells. This significantly reduces time and cost at the research and development stage of bipolar plates, as compared with the conventional fabrication methods such as compression molding and injection molding. Different graphite materials, including natural graphite, synthetic graphite, carbon black, and carbon fiber, were investigated using the selective laser sintering process to fabricate bipolar plates. The effect of each material on the electrical conductivity and flexural strength of the bipolar plates was studied experimentally. With a proper combination of these materials, bipolar plates with electrical conductivity ranging from 120 to 380 S/cm and flexural strength ranging from 30 to 50 MPa have been obtained, which satisfy the requirements set by the Department of Energy and also are comparable with those developed by compression molding and injection molding. A modified percolation model was proposed to predict the electrical conductivity of the fabricated bipolar plates with different compositions. The analytical results calculated from the proposed model agree well with the experimental results. Finally, a single PEM (Proton Exchange Membrane) fuel cell unit was assembled using the fabricated bipolar plates, and its in-situ performance was studied.     

Electrically conductive polymer composite coating on aluminum for PEM fuel cells bipolar plate

Aluminum has many advantages for commercial bipolar plate of PEM fuel cell such as light weight, low cost and easy manufacturing. However, it has a low corrosion resistance under a PEM fuel cell operation condition that is a special issue of all metal bipolar plates. In this study, polypropylene composite coated with aluminum bipolar plates were fabricated to improve the corrosion resistance. However, contact resistance of polymer composite coated aluminum bipolar plate is highly increased due to high contact resistance between aluminum substrate and composite layer. Two different types of inter layers were added to improve the contact resistance. Carbon paper attached and carbon black added samples were fabricated between aluminum substrate and composite. Polyamide-imide/carbon black composite adhesive was used for carbon paper attached on the aluminum plate. The contact resistance of carbon paper attached sample was lower than that of carbon black added sample. And, corrosion resistance was tested by potentiodynamic and potentiostatic methods. The composite coated aluminum attached to carbon paper exhibited properties suitable for PEM fuel cells.     

Effect of carbon fillers on properties of polymer composite bipolar plates of fuel cells

Bipolar plates are major components of fuel cell (FC) stacks and they make up a large portion of the stack volume and cost. In order to reduce their weight and fabrication cost, polymer composite materials with various carbon conducting fillers are tested for use as composite bipolar plates for FCs. The composite materials are prepared by using graphite with a small vol.% of carbon black (CB), multi-walled carbon nanotubes (MWNTs) or carbon fibres (CF) in an epoxy resin. The electrical conductivity and flexural properties of the composites are measured as a function of the carbon conductive filler content. The highest electrical conductivity is observed at a total conducting filler content of 75 vol.%. The addition of a small amount of hybrid conducting filler enhances the electrical conductivity up to certain threshold, viz. 5 vol.% of CB, 2 vol.% of MWNTs, and 7 vol.% of CF. Above these thresholds, the electric conductivity decreases with increasing filler content, due to the lack of sufficient resin to bind the fillers tightly. The hybrid filler system has better properties than the single filler system. The experimental results indicate that there is an optimum composition range with respect to electrical conductivity and mechanical properties.     

管理与技术并重的企业清洁生产工作研究

质子交换膜燃料电池（PEMFC）以其能量转化率高、低排放、能量和功率密度高等优点被认为是适应未来能源和环境要求的理想动力源之一。双极板是质子交换膜燃料电池组中的关键功能部件之一,而且时电池组的成本、体积和质量有直接影响。开发同时具有优良的综合性能和低成本的双极板是质子交换膜燃料电池实现产业化的必然要求。综述了目前各种双极板材料的研发现状,并对各种材料进行了比较,提出了双极板材料的发展趋势。     

Materials and design development for bipolar/end plates in fuel cells

Bipolar/end plate is one of the most important and costliest components of the fuel cell stack and accounts to more than 80% of the total weight of the stack. In the present work, we focus on the development of alternative materials and design concepts for these plates. A prototype one-cell polymer electrolyte membrane (PEM) fuel cell stack made out of SS-316 bipolar/end plate was fabricated and assembled. The use of porous material in the gas flow-field of bipolar/end plates was proposed, and the performance of these was compared to the conventional channel type of design. Three different porous materials were investigated, viz. Ni–Cr metal foam (50 PPI), SS-316 metal foam (20 PPI), and the carbon cloth. It was seen that the performance of fuel cell with Ni–Cr metal foam was highest, and decreased in the order SS-316 metal foam, conventional multi-parallel flow-field channel design and carbon cloth. This trend was explained based on the effective permeability of the gas flow-field in the bipolar/end plates. The use of metal foams with low permeability values resulted in an increased pressure drop across the flow-field which enhanced the cell performance.     

Bipolar plates for PEM fuel cells: A review

Bipolar plates (BPs) are a key component of proton exchange membrane (PEM) fuel cells with multifunctional character. They uniformly distribute fuel gas and air, conduct electrical current from cell to cell, remove heat from the active area, and prevent leakage of gases and coolant. BPs also significantly contribute to the volume, weight and cost of PEM fuel cell stacks. Hence, there are vigorous efforts worldwide to find suitable materials for BPs. The materials include non-porous graphite, coated metallic sheets, polymer composites, etc. This paper reviews various types of materials, in use and proposed, for BPs and critically examines their physical and chemical properties.     

Design,fabrication, and initial testing of a miniature PEM fuel cell with micro-scale pyrolyzed carbon fluidic plates

Carbonization of machined polymers is a method of creating carbon structures with small feature sizes without having to directly machine carbon (a difficult and expensive process). Pyrolyzed carbon fluidic plates with feature sizes less than 1 mm are used to create a miniature fuel cell. Epoxy is used to seal the fuel cell and water is directly applied to exposed Nafion^® to hydrate the membrane. The use of miniature carbon fluidic plates will allow for fabrication of 3D (non-planar) proton exchange membrane fuel cells utilizing carbon bipolar plates. Initial test results of the fuel cell are given.     

Development of bipolar plates for fuel cells from graphite filled wet-lay material and a compatible thermoplastic laminate skin layer

In this paper a method with the potential to lead to the rapid production of thermoplastic polymer composite bipolar plates with improved mechanical properties, formability, and half-cell resistance is described. In our previous work it was reported that laminate structure composite bipolar plates made with a polyphenylene sulfide (PPS) based wet-lay material as the core and a polyvinylidene fluoride (PVDF)/graphite mixture as the laminate exhibited improved formability, through-plane conductivity, and half-cell resistance over that of wet-lay based bipolar plates. However, the mechanical strength of the laminate plates needed improvement. In this work laminate polymer composite plates consisting of a PPS/graphite-based laminate mixture and a PPS based wet-lay core are manufactured in an effort to improve mechanical strength. Additionally, our existing channel design has been altered to reduce the channel depth from 0.8 to 0.5 mm in an effort to improve the half-cell resistance by reducing the total plate thickness. The plates are characterized by their half-cell resistance and mechanical properties at ambient and elevated temperatures. The PPS based laminate plates exhibited half-cell resistances as low as 0.018 Ω cm², tensile strength of up to 37 MPa, and flexural strength of up to 60 MPa at ambient temperature. The laminate bipolar plates can be manufactured in several ways with two of them being discussed in detail in the paper.     

Fabrication and characterization of micro PEM fuel cells using pyrolyzed carbon current collector plates

A novel fabrication technique for micro proton exchange membrane fuel cells (μPEMFCs) based on carbon-MEMS (C-MEMS) was optimized to yield higher performance cells. Polymer manufacturing is relatively easy compared to directly patterning graphite as is typically done to make fuel cell bipolar plates. In a C-MEMS approach, fuel cell bipolar plates are fabricated by first patterning polymer Cirlex^® sheets. By subsequently pyrolyzing the machined polymer sheets at high temperature in an inert atmosphere, carbon bipolar plates with intricate groove structures to distribute the reactants are obtained. Using an improved assembly technique such as polishing the carbonized plates to minimize the contact resistance between gas diffusion layers (GDL) and bipolar plates, better pyrolysis temperature control and a better end plate design, a μPEMFC with a 0.64 cm² active surface was fabricated using the newly developed bipolar plates. At 1 atm and 25 °C a maximum power density of ∼76 mW cm⁻² was obtained, and at 2 atm and 25 °C ∼85 mW cm⁻² was achieved. These data are comparable with data reported in the literature for μPEMFCs and are a dramatic improvement over earlier results reported for the same C-MEMS based fuel cell. Electrochemical Impedance Spectroscopy (EIS) and cyclic voltammetry were carried out to characterize steady-state and transient characteristics of the novel C-MEMS fuel cell.     

The preparation technique optimization of epoxy/compressed expanded graphite composite bipolar plates for proton exchange membrane fuel cells

Vacuum resin impregnation method has been used to prepare polymer/compressed expanded graphite (CEG) composite bipolar plates for proton exchange membrane fuel cells (PEMFCs). In this research, three different preparation techniques of the epoxy/CEG composite bipolar plate (Compression-Impregnation method, Impregnation-Compression method and Compression-Impregnation-Compression method) are optimized by the physical properties of the composite bipolar plates. The optimum conditions and the advantages/disadvantages of the different techniques are discussed respectively. Although having different characteristics, bipolar plates obtained by these three techniques can all meet the demands of PEMFC bipolar plates as long as the optimum conditions are selected. The Compression-Impregnation-Compression method is shown to be the optimum method because of the outstanding properties of the bipolar plates. Besides, the cell assembled with these optimum composite bipolar plates shows excellent stability after 200 h durability testing. Therefore the composite prepared by vacuum resin impregnation method is a promising candidate for bipolar plate materials in PEMFCs.     

Highly filled graphite/graphene/carbon nanotube in polybenzoxazine composites for bipolar plate in PEMFC

This research aims to develop polybenzoxazine (PBA) based composites suitable for bipolar plates in proton exchange membrane fuel cells (PEMFCs). PBA composites filled with carbon derivatives i.e. graphite, graphene, and multiwall carbon nanotubes (CNTs) were prepared. The effects of CNT contents from 0–2 wt% at an expense of graphite with constant content of graphene and benzoxazine on properties of the obtained composites were investigated. It was found that the composite with 2 wt% of CNTs exhibited through-plane thermal conductivity as high as 21.3 W/mK which is 44 times higher than that of the composite without CNTs. Also, this composite showed electrical conductivity of 364 S/cm, Flexural Strength of 41.5 MPa and Modulus 49.7 GPa, respectively. These values meet the requirements suggested by the Department of Energy, USA and confirm that these composites are great candidates as bipolar plates for PEMFCs.     

A graphite-coated carbon fiber epoxy composite bipolar plate for polymer electrolyte membrane fuel cell

A PEMFC (polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell) stack is composed of GDLs (gas diffusion layers), MEAs (membrane electrode assemblies), and bipolar plates. One of the important functions of bipolar plates is to collect and conduct the current from cell to cell, which requires low electrical bulk and interfacial resistances. For a carbon fiber epoxy composite bipolar plate, the interfacial resistance is usually much larger than the bulk resistance due to the resin-rich layer on the composite surface.In this study, a thin graphite layer is coated on the carbon/epoxy composite bipolar plate to decrease the interfacial contact resistance between the bipolar plate and the GDL. The total electrical resistance in the through-thickness direction of the bipolar plate is measured with respect to the thickness of the graphite coating layer, and the ratio of the bulk resistance to the interfacial contact resistance is estimated using the measured data. From the experiment, it is found that the graphite coating on the carbon/epoxy composite bipolar plate has 10% and 4% of the total electrical and interfacial contact resistances of the conventional carbon/epoxy composite bipolar plate, respectively, when the graphite coating thickness is 50 μm.