Fuel Cell Bipolar Plates Research Articles

Research on selective laser sintering process of ternary composite materials (PP/MCMB/CNT)

The composite material composed of polypropylene and conductive filler has good corrosion resistance, light weight and good conductivity, and is one of the preferred materials for fuel cell bipolar plates. The formation of ternary composite materials composed of polypropylene, mesocarbon microbeads and carbon nanotubes is realized by selective laser sintering. The influences of laser power, scanning speed, scanning spacing and defocus amount on forming quality are studied. The formability of mixed powders with different composition proportions as well as the conductivity, bending strength and hydrophobicity of the formed samples are investigated. The results show that when the input energy density is insufficient, it is easy to form defects such as spheroidized particles and worm-like structures. The parameters with good forming quality are in the following range: defocus amount is + 3 mm; line energy density is 2.94–3.85 J/mm2; peak power density is 1.13 × 104-1.48 × 104 W/mm2 and scanning spacing is 0.1–0.14 mm. The conductive filler in composite material is beneficial to improving the conductivity, but it will reduce the formability of the mixed powders and reduce the bending strength and hydrophobicity of the sample. The effect of mesocarbon microbeads on improving conductivity or on reducing hydrophobicity is smaller than that of carbon nanotubes.

Composite Graphite Bipolar Plates Under Different Working Conditions

This study uses the molding method to prepare composite graphite bipolar plates to improve the corrosion resistance and electrical conductivity of fuel cell bipolar plates, improve the conversion efficiency and service life, and test their environmental adaptability under different working conditions. In this experiment, the fuel cell test system (850e) is used to test the voltage change curve and power density change curve of the proton exchange membrane fuel cell (PEMFC). Under 200 KPa, the voltage of the fuel cell at a current density of 1000 mA/cm2 is 0.719 V. The power density reaches the maximum at 1540 mA/cm2 current density, which is 911 mW/cm 2. The radii of the three curves from 0.1 A/cm2 to 0.5 A/cm2 decrease with the increase of current density. This indicates that at the beginning, the greater the current density is, the smaller the mass transfer resistance inside the fuel cell is, and the smaller the electron transfer resistance during the electrochemical reaction is. However, when the current density increases to 1 A/cm2, the power density of the fuel cell increases slowly. In the 12-hour constant current density test, it is found that the fuel cell voltage dropped from 0.641 V to 0.611 V, and the rate of decline was 2.5 mV/h, proving that the overall performance of the fuel cell is relatively stable. The graphite bipolar plate prepared by the molding method has good adaptability under different working conditions, and the comprehensive performance is stable under long-term testing.

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

Active screen plasma nitriding of laser powder bed fusion processed 316L stainless steel for the application of fuel cell bipolar plates

ABSTRACT Laser powder bed fusion (LPBF) is capable to process complex flow field structures on 316L stainless steel (316L SS) bipolar plates, which is promising to improve the performance of proton exchange membrane fuel cell (PEMFC). However, insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) hinder the widespread of LPBF-processed 316L SS bipolar plates. In this work, active screen plasma nitriding (ASPN) was used to modify 316L SSs fabricated by the LPBF process and forging, respectively. Results showed that the nitrided layer of LPBF-processed 316L SS (2000 mm/s, 300 W) exhibited the highest surface nitrogen concentration, thickest nitrided layer and highest average hardness. The ICR values decreased significantly after ASPN treatment. The corrosion current of nitrided LPBF-processed 316L SS (2000 mm/s, 300 W) was much lower than that of the nitrided forged 316L SS. By comparing multiscale microstructures between LPBF-processed and forged 316L SS, the ASPN mechanism of LPBF-processed 316L SS was proposed.

Investigation on three-stage stamping of micro-channels with titanium ultra-thin sheet used for PEM fuel cell bipolar plates

Investigation on three-stage stamping of micro-channels with titanium ultra-thin sheet used for PEM 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.

Evolutions of microstructure and mechanical properties of copper/SS304L composite micro channels during micro rolling

Manufacturing metallic micro channels is a critical issue in micro-electromechanical systems (MEMS), such as micro reactors, micro heat exchangers, micro heat sinks, and fuel cell bipolar plates. An ultra-thin metal foil rolling for the fabrication of micro composite channels was proposed in this study, which is able to improve product functions and reduce operational costs. Copper/SS304L composite foils after annealing at 900 °C were used to form micro channels under different rolling reductions (29.1%, 43.8% and 50.0%), in which the thickness of copper and SS304L are 0.3 mm and 0.1 mm, respectively. Accordingly, the microstructure evolution, material deformation behaviours and mechanical properties of the samples after micro rolling were investigated. From the characterisation of the micro channel region on the copper side, a double fibre texture is produced parallel to the rolling reduction, including a relatively strong <111> fibre and a weak <100> fibre. Moreover, a relatively strong <111> fibre and three weak <100>, <110> and α fibres along the rolling direction can be identified on the SS304L side. The hardness of copper and SS304L increases with the increase of rolling reduction, due to the strain-hardening effect for copper, and accumulated dislocation and formation of strain-induced α’ martensite for SS304L during micro rolling, respectively. It is noted that in the ridge region for all the samples, the left fillet is harder compared to the right fillet, indicating the asymmetry of material flow.

Micro rolling fabrication of copper/SS304L micro composite channels

Fabrication of micro channels is an important aspect in the development of microfluidic devices, such as microreactors, micro heat exchangers, micro heat sinks and fuel cell bipolar plates. An ultra-thin metal foil rolling for the fabrication of micro composite channels was first proposed in this study, which is able to improve product function and reduce operational cost. Copper/SS304L composite foils with the thickness of 0.3 mm for copper and 0.1 mm for SS304L after annealing at 900 °C were used to form micro channels under different rolling reductions (0.10–0.25 mm) and velocities (7.07–35.35 mm/s), and the processing characteristics, material deformation behaviours and processing mechanisms of the rolling process were investigated. The results show that the ridges and channels are asymmetrical in all samples, while the ridges become more round with the increase of rolling reduction and the decrease of rolling velocity. For the samples with different rolling reductions, the difference between set rolling reductions and the forming depth first decreases and then increases. Besides, the micro features, including micro scratches, adhesion and smooth surfaces on the surfaces of micro channels become more significant with the increase of rolling reduction, and thus the roughness increase with increased rolling reduction. For the samples with different rolling velocities, a lower velocity would be conducive to fabricating the micro channels with a higher forming accuracy. As the rolling velocity increases, the micro scratches, adhesion and smooth surfaces on the surfaces of micro channels can be reduced during rolling process.

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.

Coating and laser processes for mass production of fuel cell bipolar plates

Coating and laser processes for mass production of fuel cell bipolar plates

Contact resistance measurement methods for PEM fuel cell bipolar plates and power terminals

The electrical contact resistance is a key parameter for optimising both the bipolar plate of the polymer electrolyte membrane fuel cell (PEMFC) and the electrical contact of the power terminal of the stack. The contact resistance is affected by the conductivity, roughness, and hardness of the two contacting surfaces. Here, new, application-specific contact resistance measurement methods are proposed for both the stack power terminal, and the bipolar plate. The proposed methods are compared to methods from references as well as standards, and it is concluded that the uncertainty of the measurements can be reduced by changing the measurement setup, and that the influence of probe resistance on measurement results can be eliminated. Furthermore, the effect of different accelerated durability tests on the contact resistance of the power terminal is examined both on test coupons and on a prototype screw connection with an electroless NiP and an electroplated NiSn coatings. As expected, the NiSn coupons gives lower contact resistance after ageing as compared to the NiP. However, the increase in contact resistance seen on coupons after ageing is not observed on the prototype screw connection.

Carbon nanotube (CNT) modified carbon fiber/epoxy composite plates for the PEM fuel cell bipolar plate application

Light structures of the composite materials are prominent outcomes for reducing the total stack weight. However, the poor electrical properties of the composite structures pose an obstacle to wide employment as a bipolar plate for the PEMFC systems. In the current study, the carbon fiber/epoxy composite laminates were modified with the multi-walled carbon nanotube superconductor materials to overcome conductivity issues. The effects of CNTs additives in a range of 0.25–1.25% wt on the electrical, mechanical, and performance features of the carbon fiber/epoxy laminates were investigated. Electrical conductivities of the nonconductive carbon fiber/epoxy plates increased with the rising additive ratio, as expected, and reached 120 S/cm for the 1.25% CNT reinforcement. Although the mechanical strength of the pristine composite BP is already satisfactory, CNTs can increase the flexural strength and flexural modulus of the BP up to 42% and 27%, respectively. Each composite plate was subjected to the single-cell performance test. 1.25% wt CNT modified plate was executed pretty close performance compared to the aluminum alloy (AA 3105) bipolar plate under the same conditions.

Bipolar Plate Flow Field Structure Research Status and Trends for Hydrogen Fuel Cell Vehicles

The bipolar plate is the fundamental structural element of the hydrogen fuel cell, and its flow field design has a significant impact on the performance of the fuel cell. The hydrogen fuel cell is employed as an important energy supply source for vehicle power. The classification and operation of hydrogen fuel cells, as well as the benefits and drawbacks of conventional flow fields, are discussed in this paper and contrasted with the state of bipolar plate flow field research in recent years. Comprehensive analysis is done on the optimization of the fuel cell bipolar plate flow field based on the conventional flow field. All are favorable to enhancing fuel cells' ability to generate electricity and aid in the progressive development of a full set of structural design guidelines.

Multiwalled Carbon Nanotube-Filled Polymer Composites for Direct Injection Molding of Bipolar Plates

Fuel cell bipolar plates are commonly fabricated from graphite and stainless steel, however machining intricate channels into these materials can be a costly and time-consuming process. For this reason, we are exploring injection molding of polymer composite bipolar plates. Polymer composites offer the potential for lightweight, low-cost plates [1]. Several factors impact the ability of a polymer composite to conduct electricity. The geometry, filler weight percentage, dispersion, and the physical properties of the fillers are important in forming an electrical pathway through the composite. In this study, polymer composites based on nylon were injection molded with different weight percentages of conductive filler. Initially, carbon fiber was added to nylon at weight percentages ranging from 10 to 50%. Results show that the percolation threshold for carbon fiber in nylon occurs around 25 wt%. While carbon fiber loadings beyond 50 wt% would further increase conductivity, the increased viscosity of the polymer blends can inhibit proper injection molding.Multiwalled carbon nanotubes were then added to the direct injection-molded nylon/carbon fiber composites to investigate the synergistic effects of multiple conductive fillers [2]. By introducing carbon nanotubes into the polymer matrix, the nanotubes act as a bridge between the carbon fibers. SEM images show that the MWCNTs fill the void between each fiber due to their smaller size and their ease of dispersion. This bridging creates more conductive pathways within the composite, thereby increasing the electrical conductivity. Samples with MWCNTs reached conductivities nearing the United States Department of Energy technical target for bipolar plate conductivity (> 100 S/cm). Mighri, F.; Huneault, M. A.; Champagne, M. F., Electrically conductive thermoplastic blends for injection and compression molding of bipolar plates in the fuel cell application. Polymer Engineering and Science 2004, 44 (9), 1755-1765.Zameroski, R.; Kypta, C. J.; Young, B. A.; Sanei, S. H. R.; Hollinger, A. S., Mechanical and Electrical Properties of Injection-Molded MWCNT-Reinforced Polyamide 66 Hybrid Composites. Journal of Composites Science 2020, 4 (4), 14. Figure 1

3D Printing and Injection Molding of Polymer Composites for Fuel Cell Bipolar Plates

Electrically conductive polymer composites offer the potential for manufacturing lightweight, low-cost, fuel cell bipolar plates. In this work, we explore 3D printing and injection molding of these composites. The primary objective of this research is to fabricate polymer composites that will meet the United States Department of Energy technical target for bipolar plate electrical conductivity (> 100 S/cm). Samples were 3D printed with various filaments, in various printing orientations, and injection molded samples utilized various weight percentages of conductive filler. Sample compositions were then compared by measuring electrical conductivity using a four-point probe method. Conductivities greater than 250 S/cm were achieved, exceeding the DOE technical target. In addition to experimental efforts, we also develop a micromechanical model to predict conductivity based upon direction in the material, fiber alignment, fiber length and diameter, fiber concentration, and fiber conductivity. Modeling predictions show good correlation within 10% of experimental conductivity data.

Biomimetic Microchannels for the Passive Management of Water in PEM Fuel Cells

In polymer electrolyte membrane (PEM) fuel cells, the bipolar plates (BPPs) are responsible for the transport of reactants (via embedded flow fields), heat, and electrons, and account for 18-28% of the cost of fuel cell systems1. Thus, there is a great opportunity to improve the energy density of PEM fuel cells by improving the functions of BPPs, such as providing liquid water management, which affects reactant delivery and heat distribution. Previous work has shown that mass transport losses due to liquid water accumulation under the lands and channels of PEM fuel cell flow fields limit the power density of fuel cells2. Previous work has demonstrated that water will preferentially flow in a desired direction by implementing biomimetic wicking structures3; however, such wicking structures have not been previously implemented into a fuel cell. Furthermore, the design of BPPs has not been tailored to target areas of water accumulation.In this work, biomimetic geometries that promote passive unidirectional water wicking were implemented in a PEM fuel cell flow field to enhance liquid water removal and the distribution of reactant gases. The BPPs were characterized via constant current electrochemical testing and electrochemical impendence spectroscopy (EIS) to elucidate the dominant losses observed during operation. Operando synchrotron X-ray radiography was performed during the electrochemical testing in order to quantify the liquid water accumulation on the cathode side of the PEM fuel cell. The spatial distribution of liquid water was combined with EIS characterizations to explain the performance of the designs at high current densities, where mass transport losses typically dominate. The results from this work can be used to further optimize the design of PEM fuel cell bipolar plates in order to produce more efficient fuel cell stacks and drive PEM fuel cells into the global energy market. References Y. Wang, D. F. Ruiz Diaz, K. S. Chen, Z. Wang, and X. C. Adroher, Materials Today, 32, 178–203 (2020).N. Ge et al., Electrochimica Acta, 328, 135001 (2019).J. Feng and J. P. Rothstein, Journal of Colloid and Interface Science, 404, 169–178 (2013).

Multiwalled Carbon Nanotube-Filled Polymer Composites for Direct Injection Molding of Bipolar Plates

Fuel cell bipolar plates are commonly fabricated from graphite, however the associated machining costs are a major limitation to fuel cell commercialization. A promising alternative approach to bipolar plate manufacturing is injection molding of polymer composites. Injection molding is well-suited for mass production and polymeric materials can significantly reduce the weight of the bipolar plate. In this study, polymer composites based on nylon were injection molded with different weight percentages of conductive filler. Initially, carbon fiber was added to nylon 6,6 at weight percentages ranging from 10 to 50%. Results show that the percolation threshold for carbon fiber in nylon occurs around 25 wt%. Multiwalled carbon nanotubes (MWCNTs) were then added to the direct injection-molded nylon/carbon fiber composites to investigate the synergistic effects of multiple conductive fillers. By introducing carbon nanotubes into the polymer matrix, the nanotubes act as a bridge between the carbon fibers. SEM images show that the MWCNTs fill the void between fibers due to their smaller size and their ease of dispersion. This bridging creates more conductive pathways within the polymer matrix, increasing the electrical conductivity of the composite. Samples with MWCNTs reached conductivities of 64 S/cm, nearing the United States Department of Energy technical target for bipolar plate conductivity (>100 S/cm).

Tribological, Anti-corrosion, and Electrical Conductivity Properties of CrCx Coatings Deposited on Stainless Steel 316L and Used as Metal Bipolar Plates for Fuel Cells

Tribological, Anti-corrosion, and Electrical Conductivity Properties of CrCx Coatings Deposited on Stainless Steel 316L and Used as Metal Bipolar Plates for Fuel Cells

Shape and position design of two-step micro-channel on plate during rubber pad forming process based on simulation

Rubber pad forming is an advanced processing technology to form the metal sheet. The micro-channel on the plate can be formed by both rubber pad and the metal mold. With the development of micro-channel, a two-step micro-channel has been applied in more and more fields such as fuel cell bipolar plate. However, little attention was given to the forming strategy for these unique channels. In this paper, the rubber pad forming process is used to form the entire SS304 sheet with two-step channels. In order to design the micro-channel structure with good formability, the main parameters of the two-step micro-channel are discussed through finite element modeling (FEM) and forming experiment. Not only for the geometric parameters for structures like length, width, edge chamfer, and the height ratio of first to second step, but also for the spatial distribution like the number and distance of two-step micro-channels in the entire plate. In addition, MATLAB is used to study the influences on the final forming results because of the various parameters. And then, the plates can be precisely formed when the structure is suitable, while micro-channels with unsuitable structure cannot be formed as designed. Finally, based on the FEM and forming experiment results, a design strategy is provided in the conclusions.