Membrane Fuel Cell Bipolar Plates Research Articles

Reviewing carbon nanotube fillers for enhanced conductivity in proton exchange membrane fuel cell bipolar plates

This article reviews recent studies on carbon nanotubes (CNTs) as fillers in enhancing the electrical conductivity of composite bipolar plates (BPPs) used for Proton Exchange Membrane Fuel Cells (PEMFCs). Findings revealed that CNTs possess high-aspect ratios, which facilitate effective electron transport and promote charge-carrier mobility within the composite, thereby enhancing conductivity. In addition, strategies addressing the challenges of achieving high conductivity by optimizing filler dispersion, resin viscosity, and fiber alignment were explored.

Investigation into the Three-Stage Formation of Micro-Channels with Ultra-Thin Titanium Sheets Used for Proton-Exchange Membrane Fuel Cell Bipolar Plates.

Titanium has a low density and high corrosion resistance. In order to achieve the goal of a lightweight material, and to extend the normal working hour of proton-exchange membrane fuel cells (PEMFCs), ultra-thin titanium plates were chosen to manufacture the key components-bipolar plates (BPs). For the purpose of overcoming the challenges of manufacturing with a large depth to width ratio, a multi-stage formation process was established with characteristics such as high efficiency and a lower price. In this study, the process parameters were examined through an experimental approach. The outcomes show that the channel formed by multistage forming is deeper than that formed by single-stage forming under the same displacement conditions. To achieve greater flow depths, it is recommended to increase the displacements as much as possible during both the first- and second-stage forming processes. The implementation of three-stage forming can effectively reduce the maximum thinning rates within flow channels while improving the overall deformation uniformity. This method deviates from traditional one-stage loading processes by adopting multi-stage loading instead. By employing appropriate mold designs, material deformation and flow can be enhanced throughout gradual loading processes, thereby preventing strain concentration and enhancing the ultimate formation height accuracy within micro-flow channels. Consequently, the proposed three-stage forming process proves highly appropriate for the mass production of BPs utilizing titanium plates.

Laser powder bed fusion of micro-channels for the application of proton exchange membrane fuel cell bipolar plates

Laser powder bed fusion of micro-channels for the application of proton exchange membrane fuel cell bipolar plates

Atmospheric plasma deposition of conductive and corrosion‐resistant composite coatings for proton exchange membrane fuel cell bipolar plates

AbstractThe straightforward synthesis and application of conductive and corrosion‐protective composite coatings suitable for the preparation of bipolar plates of proton exchange membrane fuel cells (PEMFCs) are achieved by a scalable and solvent‐free atmospheric plasma deposition process. Small three‐dimensional (3D) carbon black nanoparticles and large two‐dimensional (2D) natural graphite flakes are investigated independently and together as conductive fillers. It is demonstrated that the dual‐sized conductive fillers strategy traditionally used for the preparation of composite bipolar plates is not transposable for the proposed atmospheric plasma deposition process. Only the composite coatings prepared from large 2D natural graphite flakes enable a significant decrease of the corrosion current in simulated proton exchange membrane fuel cell conditions while ensuring interfacial contact resistance in the order of several tens of mΩ·cm2.

Preparation and properties of graphite/polypropylene composite material reinforced by chopped carbon fibers for proton‐exchange membrane fuel cell bipolar plates

AbstractIn this work, chopped carbon fibers (CCFs) with different lengths were added to graphite/polypropylene (PP) composite materials to achieve high conductivity and flexural strength performances, which are required for use in proton exchange membrane fuel cells. The effects of CCF length (2–4 mm), CCF content (0–5 wt.%), graphite type‐natural flake graphite (NFG) and synthetic graphite (SG), and graphite particle size (18–106 µm) on the graphite/PP/CCFs composites are examined. The conductivities of the composites decrease significantly with increasing CCF length above 3 wt.%. CCFs improve the composite's strength, with a maximum strength of 45.8 MPa being achieved with 5 wt.% of 4 mm long CCFs. Composite with NFG exhibits superior conductivity to the one with SG but lacks flexural strength. The NFG particle size significantly affects the conductivity of the composite at high graphite contents, with a particle diameter of 75 µm resulting in maximum conductivity. An optimal composition with 38 µm/82 wt.% NFG and 2 mm/3 wt.% CCF, electrical conductivity, and flexural strength of 189.4 S/cm and 30.2 MPa, respectively, were achieved. Also, this composite exhibited interfacial contact resistance and contact angles of 111°, which showed favorable interfacial conductivity and hydrophobicity performances.

Design optimization of proton exchange membrane fuel cell bipolar plate

The bipolar plate geometry design is one of the fuel cell's key features that determines the cell's power. It equally has a direct correlation to the thermal and water management of the cell as it tends to regulate the amount of by-product water that can be expunged from the fuel cell. This study, therefore, explored the development of novel bipolar plate geometry designs, namely the square baffled channel, the rectangular baffled channel, the parallel channel design, and the double serpentine geometry design. This was further compared with the traditional serpentine design to ascertain the design with the optimum fuel cell performance. With the squared baffled channel presenting the best results, varying operating conditions that will influence the performance of the novel fuel cell channel design were also evaluated. It was observed that the hydrogen mass fraction increased by 22.6% for the square baffled channel design compared with the other geometry designs considered in the present study. The square baffle channel showed 12.11% increase in power density and 14.54% increase in current density compared to the rectangular baffle channel. In terms of the parallel channel design, the square baffle showed 18.941% increase in power density and 22.278% increase in current density. The least performing channel geometry design was the double serpentine design. Comparing the double serpentine channel geometry design to the square baffle channel geometry design, there was an increase in current density by 67.72% and 77.88% in terms of power density in favour of the square baffle channel geometry design. The square baffle channel also showed 50% increase in current density and 58.23% increase in power density compared to conventional serpentine channel flow plate geometry design. An adaptive neuro fuzzy inference system (ANFIS) was also adopted to predict the output power of the cell. This was then compared with Feed Forward Back Propagation Neural Network to determine the model with the most accurate results. The adaptive neuro-fuzzy inference model accurately predicted the non-linearities associated with fuel cell performance, hence recommended as ideal for Proton Exchange membrane fuel cell prediction. The main contribution for the study is the development of optimal flow plate geometry design that will ensure maximum fuel cell performance. The current study is aimed at providing technical information to policy makers and the fuel cell industry on how optimization of the flow plate design via the introduction of baffles could increase the cell performance hence accelerates its commercialization and widen their applications in various sectors beyond the automotive industry.

Metallic Material Selection and Prospective Surface Treatments for Proton Exchange Membrane Fuel Cell Bipolar Plates-A Review.

The aim of this review is to summarize the possibilities of replacing graphite bipolar plates in fuel-cells. The review is mostly focused on metallic bipolar plates, which benefit from many properties required for fuel cells, viz. good mechanical properties, thermal and electrical conductivity, availability, and others. The main disadvantage of metals is that their corrosion resistance in the fuel-cell environment originates from the formation of a passive layer, which significantly increases interfacial contact resistance. Suitable coating systems prepared by a proper deposition method are eventually able to compensate for this disadvantage and make the replacement of graphite bipolar plates possible. This review compares coatings, materials, and deposition methods based on electrochemical measurements and contact resistance properties with respect to achieving appropriate parameters established by the DOE as objectives for 2020. An extraordinary number of studies have been performed, but only a minority of them provided promising results. One of these is the nanocrystalline β-Nb2N coating on AISI 430, prepared by the disproportionation reaction of Nb(IV) in molten salt, which satisfied the DOE 2020 objectives in terms of corrosion resistance and interfacial contact resistance. From other studies, TiN, CrN, NbC, TiC, or amorphous carbon-based coatings seem to be promising. This paper is novel in extracting important aspects for future studies and methods for testing the properties of metallic materials and factors affecting monitoring characteristics and parameters.

Electrical and mechanical properties of polypropylene/epoxy blend-graphite/carbon black composite for proton exchange membrane fuel cell bipolar plate

Conductive polymer composites (CPCs) exhibit favorable density and corrosion resistance for application as bipolar plate (BP) in proton exchange membrane fuel cell (PEMFC). However, achieving CPCs that combine the required level of electrical conductivity and mechanical strength is a challenge that has limited their application in PEMFC BPs. This study explored the potential of achieving CPC BPs with high electrical and mechanical performance by using carbon black (CB) as a secondary filler in graphite-polymer composites. Polypropylene (PP)/epoxy blend was selected as the matrix due to its good combination of strength and toughness as well as its potential to form a co-continuous morphology, which promotes the formation of more continuous conducting networks within the composite, leading to enhanced electrical performance. The PP/epoxy/graphite/CB composites were prepared by melt mixing in a Rheomixer at 190 °C and 60 rpm for 10 min, followed by compression molding at 200 °C and 6 metric tonnes for 10 min. The electrical conductivity of the composites increased from 49.26 Scm−1 to 90.34 Scm−1 (in-plane) and from 0.37 Scm−1 to 9.34 Scm−1 (through-plane) as the total filler content increased from 50 to 85 wt%. The flexural strength initially increased from 45.57 MPa at 50 wt% to 51.84 MPa at 60 wt% total filler content. Further increase in total filler content led to a decrease in flexural strength. The nanosize CB particles, used as a minor filler, filled the voids between the graphite particles, leading to the formation of more conducting pathways and higher electrical conductivities compared to the PP/epoxy/graphite composites without CB fillers. The PP/epoxy/graphite/CB composite with 80 wt% total filler content exhibited the most promising in-plane conductivity (88.5 Scm−1), through-plane conductivity (8.52 Scm−1), and flexural strength (28.53 MPa) for BP application.

Proton exchange membrane (PEM) fuel cell bipolar plates prepared from a physical vapor deposition (PVD) titanium nitride (TiN) coated AISI416 stainless-steel

Metal nitrides (and particularly TiN) are among the most extensively investigated proton exchange membrane fuel cell bipolar plates (BP) coatings. The most employed methods of nitrides coating deposition are various modifications of physical vapor deposition (PVD), while different types of stainless steels are the most common BP materials coated with TiN PVD films. In the current work, we report on the integrity maintenance of TiN PVD coating of AISI416, considering this as a clue to the sustainability of such a film. The advantage of this combination lies in the fact that the coefficients of thermal expansion (CTE) of this alloy is close to the CTE of the TiN film. Thus, the thermal stresses of such coating are expected to be minimal, as well as related coating cracks. We conducted a thorough surface analysis of roughness evolution in the course of BP corrosion process, investigating different initial surface pretreatments. Finally, we found that fine mirror-like polished BP substrate prior to deposition is essential for TiN film’s integrity during corrosion analysis time.

Performance of surface chromizing layer on 316L stainless steel for proton exchange membrane fuel cell bipolar plates

Stainless steels as proton exchange membrane fuel cell bipolar plates have received extensive attention in recent years. The pack chromizing layer was fabricated on 316L stainless steel to improve the corrosion resistance and electrical conductivity. The corrosion properties were investigated in 0.5 M H2SO4 + 2 ppm HF solution at 70 °C purged with hydrogen gas and air. Higher electrochemical impedance and more stable passive film were obtained by chromizing the 316L stainless steel. Potentiodynamic polarization results showed the corrosion current densities were reduced to 0.264 μA cm−2 and 0.222 μA cm−2 in two simulated operating environments. In addition, the interfacial contact resistance was decreased to 1.4 mΩ⋅cm2 under the compaction force of 140 N⋅cm−2 and maintained at low values after potentiostatic polarization for 4 h. The excellent corrosion and conductive performances could be attributed to the chromium carbides and high alloying element content in chromizing layer.

A Competitive Design and Material Consideration for Fabrication of Polymer Electrolyte Membrane Fuel Cell Bipolar Plates

The bipolar plate is one of the most significant components of a polymer electrolyte membrane (PEM) fuel cell, and contributes substantially to the cost structure and the weight of the stacks. A number of graphite polymer composites with different fabrication techniques have been reported in the literature. Graphite composites show excellent electromechanical properties and chemical stability in acidic environments. Compression and injection molding are the most common manufacturing methods being used for mass production. In this study, a competitive bipolar plate design and fabrication technique is adopted in order to develop a low-cost and light-weight expanded graphite (EG) polymer composite bipolar plate for an air-breathing PEM fuel cell. Cutting molds are designed to cut fuel flow channels on thin expanded graphite (EG) sheets (0.6 mm thickness). Three separate sheets, with the flow channel textures removed, are glued to each other by a commercial conductive epoxy to build a single bipolar plate. The final product has a density of 1.79 g/cm3. A bipolar plate with a 20 cm2 active area weighs only 11.38 g. The manufacturing cost is estimated to be 7.77 $/kWe, and a total manufacturing time of 2 minutes/plate is achieved with lab-scale fabrication. A flexural strength value of 29 MPa is obtained with the three-point bending method. A total resistance of 22.3 milliohms.cm2 is measured for the three-layer bipolar plate. We presume that the suggested design and fabrication process can be a competitive alternate for the small-scale, as well as mass production of bipolar plates.

Surface modification of multiwall carbon nanotubes and its effect on mechanical and through‐plane electrical resistivity of PEMFC bipolar plate nanocomposites

In this work, we showed how the functionalization of multiwall carbon nanotubes (MWCNT) by nitric acid (HNO3) and their predispersion into poly (butylene terephthalate) (PBT) improved the through‐plane electrical conductivity and mechanical properties of co‐continuous morphology polyvinylidene fluoride (PVDF)/poly (ethylene terephthalate) (PET)/carbon black (CB)/graphite (GR)/MWCNT nanocomposites. First, when MWCNT were functionalized with HNO3 then premixed with PBT, they showed no aggregations inside the PBT matrix due to their improved interfacial interactions and chemical compatibility with the PBT matrix. Then, when PBT/(HNO3‐functionalized MWCNT) mixture was added in small quantities to (PET/PVDF)/(CB/GR) composites, it decreased significantly their through‐plane resistivity and enhanced their impact and flexural properties. Its synergistic effect also led to the best proton exchange membrane fuel cell bipolar plate prototypes (smoother surface, without any cracks).

Corrosion Behavior of Stainless Steel Coated Graphene Layers for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates

Metallic materials such as stainless steel are considering as a bipolar plate for polymer electrolyte membrane fuel cells (PEMFCs) due to their low bulk electrical resistivity, high heat conductivity, high mechanical strength, gas impermeability, low cost, and ability to produce thin sheets or foil (0.1 - 1 mm thick) form to achieve high power densities [1]. However, its corrosion resistance in working conditions of PEMFCs is still far from satisfaction. In addition, metal ions produced during the corrosion process decrease the ionic conductivity of Nafion®membrane and reduce the overall efficiency of a cell due to contamination of the catalysts [2]. Various coating materials such as ceramic-like nitride, carbides, conducting polymers, and surface modification of a substrate using thermal nitridation have been investigated to satisfy the requirements for bipolar plates [3]. Especially, carbon coating materials have received significant attention, because such materials supply excellent corrosion resistance, electrical conductivity and chemical stability in working conditions of PEMFCs [4]. In this study, carbon layers were coated on the surface of stainless steel plates to be used as bipolar plates in PEMFCs by spin coating system. Graphene oxide composite suspensions were used as coating materials. The graphene oxide layers were thermally reduced to increase the electrical conductivity. Microstructural analysis of the reduced graphene oxide layers were investigated by means of Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). For in-depth analysis of the corrosion properties, the electrochemical performance of the graphene coating layers was evaluated by the poteniodynamic method under simulated working conditions of PEMFCs, and the mechanism on corrosion resistance is discussed in detail.

Graphene grown on stainless steel as a high-performance and ecofriendly anti-corrosion coating for polymer electrolyte membrane fuel cell bipolar plates

In this study, the growth of graphene by chemical vapor deposition (CVD) on SUS304 stainless steel and on a catalyzing Ni/SUS304 double-layered structure was investigated. The results indicated that a thin and multilayered graphene film can be continuously grown across the metal grain boundaries of the Ni/SUS304 stainless steel and significantly enhance its corrosion resistance. A 3.5 wt% saline polarization test demonstrated that the corrosion currents in graphene-covered SUS304 were improved fivefold relative to the corrosion currents in non-graphene-covered SUS304. In addition to enhancing the corrosion resistance of stainless steel, a graphene coating also ameliorates another shortcoming of stainless steel in a corrosive environment: the formation of a passive oxidation layer on the stainless steel surface that decreases conductivity. After a corrosion test, the graphene-covered stainless steel continued to exhibit not only an excellent low interfacial contact resistance (ICR) of 36 mΩ cm2 but also outstanding drainage characteristics. The above results suggest that an extremely thin, lightweight protective coating of graphene on stainless steel can act as the next-generation bipolar plates of fuel cells.

Evaluation of CoBlast Coated Titanium Alloy as Proton Exchange Membrane Fuel Cell Bipolar Plates

We investigated the potential of graphite based coatings deposited on titanium V alloy by a low-cost powder based process for bipolar plate application. The coatings which were deposited from a mixture of graphite and alumina powders at ambient temperature, pressure of 90 psi, and speed of 20 mm were characterised and electrochemically polarised in 0.5 M H2SO4 + 2 ppm HF bubbled with air and hydrogen gas to depict the cathode and anode PEM fuel cell environment, respectively. Surface conductivity and water contact angles were also evaluated. Corrosion current in the 1 μA/cm2 range in both cathodic and anodic environment at room temperature and showed negligible influence on the electrochemical behaviour of the bare alloy. Similar performance, which was attributed to the discontinuities in the coatings, was also observed when polarised at 0.6 V and −0.1 V with air and hydrogen bubbling at 70∘C respectively. At 140 N/cm2, the coated alloy exhibited contact resistance of 45.70 mΩ·cm2 which was lower than that of the bare alloy (66.50 mΩ·cm2) but twice that of graphite (21.29 mΩ·cm2). Similarly, the wettability test indicated that the coated layer exhibited higher contact angle of 99.63° than that of the bare alloy (66.32°). Over all, these results indicated need for improvement in the coating process to achieve a continuous layer.

Alloy Selection and Die Design for Stamped Proton Exchange Membrane Fuel Cell (PEMFC) Bipolar Plates

Proton exchange membrane fuel cells have benefits over heat engines and batteries as an energy system for transportation, stationary power, and portable electronics. Before fuel cells can replace current energy systems, their manufacturing cost to performance ratio must be improved. The bipolar plate is a fuel cell component that contributes significantly to fuel cell manufacturing costs and is a key driver of performance. Metallic bipolar plates, with characteristic flow dimensions below the standard 1 mm, were fabricated using direct machining. Hydrogen/air fuel cells constructed of these plates were tested to ensure performance gains, using interdigitated flow operation and automobile-representative channel lengths. Finite Element Modelling (FEM) was used to investigate the manufacture of bipolar plates using low cost sheet metal stamping. Multiple bipolar plate alloys were compared based on their stampability, and die design parameters needed to stamp submillimeter channels were determined. Springback analysis was performed, and the effect of springback on fuel cell stack stresses was investigated.

Corrosion characteristics and interfacial contact resistances of TiN and CrN coatings deposited by PVD on 316L stainless steel for polymer electrolyte membrane fuel cell bipolar plates

In a polymer membrane fuel cell stack, the bipolar plate is a key element because it accounts for over 50% of total costs of the stack. In order to lower the cost of bipolar plates, 316L stainless steels coated with nitrides such as TiN and CrN by physical vapor deposition were investigated as alternative materials for the replacement of traditional brittle graphite bipolar-plates. For this purpose, interfacial contact resistances were measured and electrochemical corrosion tests were conducted. The results showed that although both TiN and CrN coatings decreased the interfacial contact resistances to less than <TEX>$10m{\Omega}{\cdot}cm^2$</TEX>, they did not significantly improve the corrosion resistance in simulated polymer electrolyte membrane fuel cell environments. A CrN coating on 316L stainless steel showed better corrosion resistance than a TiN coating did, indicating the possibility of using modified CrN coated metallic bipolar plates to replace graphite bipolar plates.

Surface Characteristic of Chemically Converted Graphene Coated Low Carbon Steel by Electro Spray Coating Method for Polymer Electrolyte Membrane Fuel Cell Bipolar Plate

Graphene was coated on low carbon steel (SS400) by electro spray coating method to improve its properties of corrosion resistance and contact resistance. Exfoliated graphite was made of the graphite by chemical treatment (Chemically Converted Graphene, CCG). CCG is distributed using dispersing agent, and low carbon steel was coated with diffuse graphene solution by electro spray coating method. The structure of the CCG was analyzed using XRD and the coating layer of surface was analyzed using SEM. Analysis showed that multi-layered graphite structure was destroyed and it was transformed in to fine layers graphene structure. And the result of SEM analysis on the surface and the cross section, graphene layer was uniformly formed with 3-5 microm thickness on the surface of substrate. Corrosion resistance test was applied in the corrosive solution which is similar to the polymer electrolyte membrane fuel cell (PEMFC) stack inside. And interfacial contact resistance (ICR) test was measured to simulate the internal operating conditions of PEMFC stack. As a result of measuring corrosion resistance and contact resistance, it could be confirmed that low carbon steel coated with CCG was revealed to be more effective in terms of its applicability as PEMFC bipolar plate.

Computational Fluid Dynamics of Water Droplet Formation and Detachment from Gas Diffusion Layer

Liquid water removal from a polymer electrolyte membrane fuel cell bipolar plate channel is critical for optimal performance and durability. A two-dimensional, two-phase computational fluid dynamics (CFD) model was created to simulate water droplet formation and removal. The numerical domain consist of a gas diffusion layer (GDL) and channel. The polytetrafluoroethylene (PTFE) loading in the GDL was varied by changing the surface tension and contact angle. The effect of 10%, 15%, and 20% PTFE loading on the droplet detachment velocity and penetration pressure was studied. It was found that increasing the PTFE loading decreased the detachment velocity due to lower wetting at the GDL surface. However, increasing the PTFE loading had the consequence of raising the required capillary pressure to penetrate the GDL. This was due to initial spreading of the water below the GDL and the formation of local water paths, which was observed for the higher PTFE loadings.

Design and Simulation on Polymer Electrolyte Membrane Fuel Cell Bipolar Plates with Hilbert Patterns

Polymer Electrolyte Membrane fuel cell converts directly electrochemical energy into electricity. Channels in bipolar Plate, a critical component of fuel cell, is designed with Hilbert pattern, which are obtained through offsetting Hilbert curves to both sides according to working size. Polarization curve expresses the same characteristics between Hilbert channel and traditional serpentine and parallel channel. Output current densities of Hilbert channel are equivalent to that of the serpentine channel but larger than that of parallel channel. Simulation demonstrates that fluid flowing states in Hilbert channel are similar to that in serpentine channel and investigates that pressure drop changes with composite Hilbert channel arrangement. Temperature is an important factor influencing fuel cell performance and optimal temperature is close to 333K in this research.