Bipolar Plates Research Articles

Corrosion resistance and conductivity behavior of Cr-Al-N MAX phase coatings prepared by magnetron sputtering technology

Chromium aluminum nitride (CrAlN) coatings containing Cr2AlN phase were prepared by unbalanced magnetron sputtering followed by annealing at 1000 °C. The crystal structures, X-ray diffraction patterns, and selected area electron diffraction patterns of the Cr2AlN phase were modeled using computer software and compared with experimental observations. A good agreement was found between the two sets of results, thereby confirming the presence of Cr2AlN phase in the coatings. While previous studies have demonstrated the formation of Cr2AlN phase theoretically, this study presents experimental evidence of its physical existence. The potentiodynamic polarization results and interfacial contact resistance measurements show that the CrAlN coating with Cr2AlN phase has excellent corrosion resistance (a corrosion current density of 5.35 × 10−7 A/cm2 and electrical conductivity of 5.5 mΩ·cm2) and is thus a promising candidate for the protection of fuel cell bipolar plates.

Welding of thin stainless-steel sheets using a QCW green laser source

Bipolar plates are structured thin metal sheets and are, next to the membrane electrode assembly (MEA), one of the main components of polymer electrolyte membrane fuel cells. One of the production steps of such bipolar plates is the joining process of its two halves. Laser welding is a suitable method for such an application since it is fast, non-contact, automatable, and scalable. Particularly important aspects of the weld seam are the weld seam width and depth. In this paper, welding of stainless-steel material analogous to materials used in bipolar plates is examined. For this purpose, a newly developed quasi continuous wave (QCW) green laser source with higher beam quality is employed to assess the effect of the wavelength and the spot diameter on the welding of stainless-steel material. By using various focusing lens, different sized beam diameters below 20 µm are achieved and their influence on the final welding result—specifically concerning the seam width—are analyzed. With welding speeds starting at 500 mm/s, reduced weld seam widths (≤ 100 µm) are realized, particularly with a focusing lens of 200 mm focal distance. The suitability of such a process for thin channels of under 75 µm width is examined.

Development of fiber reinforced compound bipolar foils for fuel cells

In the research project "InduRex", the challenge was to produce graphite polymer bipolar plates with the thinnest possible thickness. The physical and chemical requirements were defined according to the values set by the "Department of Energy". Within the scope of the project, the continuous production of highly filled foils, which were then successfully structured as bipolar foils and operated in a fuel cell, was successfully implemented. Initial cell tests demonstrated a good cell efficiency at low and medium current densities. For this reason, the approach of creating bipolar plates from compound foils is still being pursued. Now the challenge is to produce bipolar films with a larger active area and to increase the mechanical stability to such an extent that the construction of a multicell stack can be realized. As a result, a metallic bipolar plate design was successfully transferred to a compound foil as part of the "InduRex" project. The problem is that with a larger bipolar foil there is a risk of obtaining low mechanical stability. Therefore, carbon fibers are introduced into the films as part of the research project "Faserverstaerkte Folien" in order to improve the mechanical properties. In addition to continuous production, the thin-walled foils are reinforced with carbon fibers using a hot press. The fiber-reinforced foils will be characterized in the next steps to investigate the influence of the carbon fibers. The aim is to obtain even thinner bipolar plates with consistent properties from the extruded foils in order to reduce the overall weight and volume of the fuel cell.

Navigating harsh ageing: Unraveling galvanostatic corrosion effects on different constituents of carbon-polymer composite bipolar plates for vanadium redox flow batteries

Bipolar plates made of carbon-polymer composites with different conductive carbon fillers, viz. graphite and carbon black, were galvanostatically corroded in a high-valence vanadium electrolyte. The harsh ageing conditions led to surface oxidation and roughening of the graphite with the formation of defective graphitic regions as revealed by X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and Raman spectroscopy. Further insight into the structural changes from the corroded surface to the bulk was gained by combining synchrotron computed tomography (CT) techniques based on X-ray diffraction (XRD) and phase contrasts. The extent of corrosion increases as the relative amount of carbon black to graphite increases. Furthermore, corrosion progresses through significant structural and chemical changes in the graphite, manifested by the expansion of graphite flakes, their exfoliation, the development of disordered graphite and the formation of graphite oxide. The bulk of the polymer remains essentially unchanged, as determined by XRD-CT. SEM studies of the cross-section and nano-CT showed decreased carbon black content in the corroded region. It can be concluded that graphite delamination and oxidation, in combination with carbon black depletion, are the main causes of corrosion of the bipolar plates investigated.

Ion Implantation Combined with Heat Treatment Enables Excellent Conductivity and Corrosion Resistance of Stainless Steel Bipolar Plates for Hydrogen Fuel Cells.

316 L stainless steel is an ideal bipolar plate material for a proton exchange membrane fuel cell (PEMFC). However, the thickening of the passivation film on the stainless steel surface and the dissolution of corrosive ions during operation will affect the durability of the PEMFC. Herein, a heterogeneous layer is prepared on the surface of 316 L stainless steel through dual ion implantation of molybdenum ion and carbon ion combined with heat treatment to promote the corrosion resistance and conductivity of the bipolar plate. The ion implantation technique resulted in a uniform distribution of Mo and C elements on the surface of 316 L stainless steel, with a modified layer depth of about 70-80 nm. The electrical conductivity of the ion implanted samples was significantly improved, and the interfacial contact resistance was reduced from 464.25 mΩ × cm2 to 42.49 mΩ × cm2. Heat treatment enhances the surface homogenization, repairs the defects of irradiation damage, and improves the corrosion resistance of stainless steel. The corrosion current density of (Mo+C)-600 samples decreased from 1.21 × 10-8 A/cm2 to 2.95 × 10-9 A/cm2 under the long-term corrosion condition of 4 h. These results can provide guidance for the modification of stainless steel bipolar plates.

Channel-to-Rib Width Ratio Optimization for the Electrical Performance Enhancement in PEMFC Based on Accurate Strain-Stress Simulation

Although a large channel-to-rib width ratio (CRWR) of the bipolar plate (BP) leads to a large electrical performance of PEMFC, an excessive CRWR leads to excessive pressure and destroys the gas diffusion layer (GDL), thus reducing the electrical performance of PEMFC. Revealing the relationship between the CRWR and GDL is of urgent necessity for improving the electrical performance of PEMFC. In this study, a three-dimensional model of PEMFC incorporating the compressed neo-Hookean theory is developed to accurately depict the stress-strain relationship. Compared with the traditional model incorporating the linear-elastic theory, the current density deviation of the proposed model is decreased from 9.81% to 2.55%. The correlation among CRWR of BP, stress, strain, and elastic modulus of GDL is fitted. The average stress deviation of the correlation from the simulated data is 3.41%. Based on the correlation, when the compressive strength of GDL is 2.5 MPa, the peak permissible CRWR is achieved at 2.91, indicating the peak value of CRWR without damaging the GDL structure. A power density enhancement of 29.04% compared to the conventional case is achieved. The strategies of this study can be used to guide the design of the channel of bipolar plates and enhance the power density of PEMFC.

Characterization and prediction of micro channel depth of ultra-thin bipolar plates for PEMFCs

In this study, a combination of experimental and statistical methods were employed to precisely determine the micro channel depth in ultra-thin metallic bipolar plates fabricated from 316 stainless steel with a thickness of 0.1 mm. The investigation centers on the rubber pad forming process and its role in the production of these critical components for Proton Exchange Membrane Fuel Cells (PEMFCs). To advance the understanding of this manufacturing process, experimental tests were designed using a Design of Experiment (DOE) technique and subsequently developed a predictive model using Response Surface Methodology (RSM). The research reveals a direct, quantifiable relationship between the channel depth in metallic bipolar plates and the magnitude of the applied force. Also, the pivotal role of rubber thickness as a dominant factor influencing channel depth was explored. Furthermore, it is revealed that augmenting the channel depth in these plates is attainable through a reduction in rubber hardness and an increase in rubber thickness. However, the benefits diminish once the rubber layer thickness exceeds a specific threshold. Moreover, the results underscore that the primary influential factors in this process include force, hardness, thickness, as well as the interplay between force and rubber thickness. The proposed model's accuracy is reaffirmed through an average error rate of approximately 5.39%, signifying its reliability in predicting microchannel depth. This research contributes novel insights into the manufacturing of ultra-thin metallic bipolar plates for PEMFCs, shedding light on the critical parameters influencing channel depth and their interrelationships. The significance and engineering value of this work lies in its potential for enhancing the design and manufacturing of metallic bipolar plates for PEMFCs. Precise control of microchannel dimensions is crucial for enhancing PEMFC performance and efficiency. This research not only advances clean energy technology but also contributes to the broader goal of achieving sustainable energy solutions, making it a noteworthy and timely contribution to the field.

A review on key factors influencing the electrical conductivity of proton exchange membrane fuel cell composite bipolar plates

AbstractFuel cells are gaining increasing importance as a promising alternative to traditional energy sources, primarily due to their exceptional efficiency and environmental advantages. The electrical performance of proton exchange membrane fuel cells (PEMFCs) largely depends on the effectiveness of proton and electron transport within the cell components. A critical factor impacting this efficiency is the electrical conductivity of polymer‐based bipolar plates (BPPs), which play a fundamental role as current collectors. BPPs in PEMFCs can be made from various materials including coated metallic materials, graphitic materials, and polymer composites. This review exclusively concentrates on polymer composite BPPs. Enhancing the overall cell performance is achievable through the integration of electrically conductive additives into the polymer matrix of these plates. Graphite (GR), carbon black (CB), carbon fibers (CF), carbon nanotubes (CNT), and graphene (Gr) all emerge as highly promising functional materials capable of substantially elevating BPPs performance. This study, among its various objectives, delves into the synergistic effects of these electrically conductive additives and their capacity to enhance the electrical conductivity within polymeric matrices. Furthermore, this review article thoroughly explores the influence of the polymeric matrix, encompassing co‐continuous morphology and processing conditions. In essence, it focuses on the improvement of BPPs electrical conductivity through innovative designs of their polymer‐based composites and nanocomposites and the particular selection of the electrically conductive fillers. The insights derived from this study significantly contribute to a more profound understanding of how to effectively harness the potential of this vital PEMFC component.

Design of bio-based adhesives for fuel cell applications

ABSTRACT Fuel cells contribute to decentralized and individually controllable energy supply. The low-temperature polymer electrolyte membrane fuel cell is ideal for both stationary and mobile use due to its low operating temperatures and superiority in discontinuous operation. Thermoplastics can be used as materials for bipolar halfplates, which have the advantage of low-cost manufacturing processes, as the components do not require cost-intensive post-processing due to their excellent corrosion resistance and electrical contacting. But the environmental conditions in operation pose a great challenge to the materials to be used: permanent humidity and sulphuric acid environment at 85°C, high required electrical conductivity and hydrogen impermeability. In order to demonstrate the potential of bio-based materials, adhesives for both sealing and conductive bonding of all joints within a fully bonded fuel cell are being developed and tested in an ongoing project. The epoxy resin systems developed can be both, one and two-component, and have different proportions of sustainable carbon. In addition, the fuel cell components, also consist of sustainable raw materials, so that bonding surfaces also pose a challenge. Results on the lap shear strength of the developed adhesives as well as on the durability of the adhesives under fuel cell environment are presented. Initial functional tests on bipolar plates bonded with proportionally bio-based raw materials show a functionality comparable to that of petroleum-based raw materials for epoxy adhesives.

Effect of Crown Ether Additives on the Enhanced Performance of Metallic Bipolar Plates for Proton Exchange Membrane Fuel Cells.

One of the key components of the fuel cell stack is a metallic bipolar plate (MBP) that plays multiple roles, such as current collector, fuel and oxidant distributor, and mechanical support. However, corrosion and consequent metal elution are major drawbacks of the MBP because they diminish the efficiency and power performance of membrane-electrode assemblies (MEAs). Herein, we show that the crown ether (CE) additive can simultaneously inhibit surface corrosion of the MBP and act as a scavenger for eluted metal ions to alleviate contamination of other components. From the electrochemical measurement, high-resolution imaging, and elemental analysis, we have found that the CE undergoes electrolytic decomposition and makes an efficient protective layer in an in situ manner. This layer prevents direct contact between the MBP and electrolyte as well as the dissolution of metal ions into the electrolyte. In addition, we demonstrate that the CE can improve the recovery protocol of the MEA owing to the formation of host-guest complexes between the CE and metal cations. These results provide key insights into the design of high-performance MBPs for proton-exchange membrane fuel cells.

Model validation of hollow embossing rolling for bipolar plate forming

Hollow embossing rolling is a promising forming technology for metallic bipolar plates because of the high achievable production rates. However, the simulation-based process optimization is impeded by the incremental forming character and modeling of fine channel structures, which leads to large model sizes and long computation times. This paper presents a shell-based finite element approach validated by experimental forming tests using a miniaturized test geometry with typical discontinuities and varying channel orientations. The rolling experiments demonstrated that implementing restraining tension effectively decreases wrinkling, allowing successful forming of the selected test geometry by hollow embossing rolling. It was found that representing the manufacturing-related decreased rolling gap combined with the rolling gap changes due to roll system elasticity in the numerical model is essential for model accuracy. An optimized model approach with spring-controlled rollers was developed, which considers the effect of load-dependent rolling gap changes. With this approach the applied model achieves sufficient model accuracy for technological process simulation and optimization.

Life Cycle Assessment of a 5 MW Polymer Exchange Membrane Water Electrolysis Plant

This study performs a cradle‐to‐grave life cycle assessment of a 5 MW proton exchange membrane water electrolysis plant. The analysis follows a thorough engineering‐based bottom‐up design based on the electrochemical model of the system. Three scenarios are analyzed comprising a state‐of‐the‐art (SoA) plant operated with the German electricity grid‐mix, a SoA plant operated with a completely decarbonized energy system, and a future development plant electrolyzer with reduced energy and material demand, operated in a completely decarbonized energy system. The results display a global warming potential of 34 kg CO2‐eq. kg‐H2−1 and indicate a reduction potential of 89% when the plant is operated in a decarbonized energy system. A further reduction of 9% can be achieved by the technological development of the plant. Due to the reduced impacts of operation in a completely decarbonized energy system, the operation at locations with large offshore wind electricity capacity is recommended. In the construction phase, the stacks, especially the anode catalyst iridium, bipolar plates, and porous transport layers, are identified as dominant sources of the environmental impact. A sensitivity analysis shows that the environmental impact of the construction phase increases with a decreasing amount of operational full load hours of the plant.

High corrosion resistance and through-plane electrical conductivity of C/Ti and C/Cr coated metal bipolar plates used in PEMFC

To improve the corrosion resistance and enhance the electrical conductivity in a simulated proton exchange membrane fuel cell, carbon bound SS316L stainless steel plates were modified with titanium (Ti) or chromium (Cr). The SS316L interfacial contact resistance of 312.38 mΩ·cm2 was reduced to 1.59 mΩ·cm2 when modified with Ti and to 1.32 mΩ·cm2 when modified with Cr. The increase in potential enhanced the shedding of C films and the oxidation and dissolution of Ti and Cr buffer layers. The corrosion current density in the C/Ti coating was lower than C/Cr coating under high voltage polarization. The oxidation of Ti and Cr buffer layers led to poor appetency between the C film and the SS316L and to degradation of the through-plane electrical conductivities in the C/Ti and C/Cr coated metal bipolar plates.

Effect of molding temperature on the properties of phenolic resin/carbon black/graphite composite bipolar plates

Effect of molding temperature on the properties of phenolic resin/carbon black/graphite composite bipolar plates

Effect of Mo content on the corrosion resistance of (CoCrFeNi)1−xMox thin films in sulfuric acid

(CoCrFeNi)1−xMox thin films with various Mo content (0–10 at.%) were grown by magnetron sputtering on a stainless steel substrate. The films with 0–2 at.% presented two crystal structures: one FCC phase and one sigma phase, while films with higher Mo content only had the FCC structure. All films have a (111) texture and follow the topography of the substrate. The corrosion resistance of the films was evaluated in 0.05 M H2SO4 at room temperature and at 80 °C. It was observed that the corrosion current densities considerably decreased for Mo > 2 at%, and that the current densities were higher at the elevated temperature. Scanning Kelvin Probe Force Microscopy showed a large potential difference between the main FCC phase and sigma phase for the Mo0–2 films. This would suggest that preferential dissolution of the FCC phase occurs over the sigma and reduces the corrosion resistance. Such preferential dissolution does not occur for the higher Mo content films with only the FCC phase. The high corrosion resistance was also attributed to the inhibition of Fe and Cr dissolution by Mo and the stabilisation of the Cr enriched oxide by incorporating Mo oxides into the passive film, identified by X-ray photoelectron spectroscopy. The low corrosion current densities (below 1 µA/cm2) make these thin films possible candidates for protective coatings of bipolar plates in PEM fuel cells.

Optimisation of bipolar plate through computational fluid dynamic simulation and modelling using nickle open pore cellular foam material

Bipolar plates remain one of the key components in PEM fuel cells. It serves as the medium (Channel) in which the reactive substances (Hydrogen and oxygen/air) finally converge on the catalyst layer where the electrochemical reaction leading to the release of electron (electricity) occurs. Its optimization would eventually have an immense impact on the performance of the fuel cell. Simulation and modelling is a key tool in the engineering industry as it saves engineers time and money before the manufacturing of any engineering product. It helps manufacturers have firsthand information about the design feasibility before the manufacturing process in a workshop.This paper reports the modelling and simulation of the bipolar plate in fuel cell using nickel Open Pore Cellular Foam material through computational fluid dynamics software (Ansys CFX). The modelled bipolar plate was validated through design of experiments (DOE) in Ansys and compared with other flow plate design (serpentine) in the fuel cell industry.

Parametric Analysis on Formability of SS304 Metal Bipolar Plate with Wave Flow Field Structure

The main production method of metal bipolar plate is stamping, and the size parameters of the flow field structure can not only change the performance of the fuel cell, but also affect the stamping quality of the metal bipolar plate. In the case of ensuring the performance of the fuel cell, it is necessary to study the stamping of the metal bipolar plate with different flow field structures. In the past, there were few studies on the wave flow field stamping forming. This paper analyzed the wave flow field, formulated several sets of bipolar plate structural dimension parameters, and evaluated the stamping forming quality of the reaction zone of SS304 metal bipolar plate through finite element simulation. By reducing the rib height ΔH=0.075mm in the corner part, the maximum thinning rate can be reduced from 34.833% to 24.689% and the thickness can reach 0.0753mm when the flow channel width S=1.0mm, the rib width W=1.5mm and the forming depth H=0.5mm. It provides some guidance for optimizing the structural dimension parameters of metal bipolar plates.

Microstructure evolution and its effect on corrosion behavior during cold rolling of Ti–Nb–Ni sheet as bipolar plates substrate for PEMFC

In this work, hot rolled Ti–Nb–Ni sheet with thickness of 1.8 mm was subjected to cold rolling with different reductions (20 %, 40 %, 60 %, 75 % and 85 %). Microstructure evolution and corrosion resistance of sheets with and without being cold rolled were investigated. Mechanical twins are generated for 20 % and 40 % cold rolled sheets, while dislocation slip becomes dominant for reductions larger than 40 %. Typical TD-split basal texture was observed in all of specimens. Corrosion resistance of the sheets in solution of pH = 3 H2SO4 with 0.1 ppm F− at 80 °C were evaluated. All the sheets possessed corrosion current densities lower than 1 μA cm−2, meeting the requirement of Department of Energy. Hot rolled sheet possessed the noblest OCP (−0.212 V), lowest corrosion current density (0.15 μA cm−2) and steady state current density (0.012 μA cm−2), as well as the largest polarization resistance of all the sheets (749.1 kΩ cm2). Besides, corrosion resistance for cold rolled sheets becomes inferior with reduction increasing. This can be attributed to increased dislocation density which provides more available active sites and deteriorates corrosion resistance with reduction increasing. Therefore, to obtain desirable corrosion resistance in PEMFC environment, Ti–Nb–Ni sheets with microstructure possessing massive dislocations should be avoided.

Electrochemical performance of metal nitride coated titanium bipolar plate for proton exchange membrane water electrolyser

In order to improve corrosion resistance and electric conductivity of titanium bipolar plate (BPP) for proton exchange membrane water electrolyser (PEMWE), three different metal nitride (i.e.Ta/TaN, Cr/CrN and Nb/NbN) coated titanium bipolar plates are prepared by magnetron sputtering. The coated BPP is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscope (AFM), and their electrochemical performance is assessed by electrochemical corrosion tests including open circuit voltage (OCP), potentiodynamic and potentiostatic polarization tests in the simulated PEMWE anode environment. It is revealed that the surface roughness of titanium substrates is decreased after coating, implicating the reduced interfacial contact resistance (ICR). Potentiodynamic and potentiostatic tests demonstrate that Ta/TaN and Nb/NbN coatings can significantly improve the corrosion resistance of titanium bipolar plate. The corrosion current density of coated substrate is reduced by approximately 67 % upon coating with Ta/TaN and Nb/NbN under the simulated PEMWE anode environment. However, the ICR of Ta/TaN coating is the lowest (3.9 mΩ × cm2), which is reduced by 74 % compared with pristine titanium substrate (14.9 mΩ × cm2). Hence, the Ta/TaN coated BPP is tested in single electrolytic cell and demonstrates significantly improved electrolysis efficiency.

Effects of sub-distribution zone structure of bipolar plate on the mass transport of large-area proton exchange membrane fuel cells

Sub-distribution zone of the flow field plays an important role in distributing gas reactants and removing liquid products in large-active area proton exchange membrane (PEM) fuel cells. This study evaluates the effects of sub-distribution zone of PEM fuel cells with the active area of 300 cm2 based on a three-plus-one-dimensional (3D+1D) model. A new structural design of sub-distribution zone, namely, mixed structure distribution zone (MSDZ) is proposed and compared with the classic dot matrix distribution zone (DMDZ) and forced shunt distribution zone (FSDZ) design regarding pressure drop, gas distribution uniformity and cell performance. It is found that FSDZ and MSDZ design distribution uniformities are improved by 90.4 % and 55.5 %, compared to DMDZ design. The cell with the MSDZ design reaches an optimal value of 0.647 V, attributed to the reduction in mass transport voltage loss. Subsequently, based on structure characteristics of FSDZ and MSDZ designs, the effects of the rib/channel width ratio in sub-distribution zone are explored. It is found that primary shunt affects the overall distribution and secondary shunt regulates the localization. Finally, the cell performance of the three types of sub-distribution zones is compared under different humidification conditions. Results show that the cell with MSDZ design demonstrates a power density increased by 4.0 % (0.05 W cm−2) and 7.6 % (0.09 W cm−2) compared with that with DMDZ design at high and low humidification conditions, respectively.