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A significant challenge in many electrochemical systems is finding a stable, high‐performing current collector material that is mechanically robust, adaptable in form factor, and free of precious metals. Titanium electrodes are robust in many of these regards but exhibit poor charge transfer performance due to self‐passivation. Herein, a new materials processing paradigm based on the titanium/titanium nitride (Ti/TiN) system which allows for robust, stable, and low‐resistance current collectors of arbitrary form factor is presented. Specifically, a gas‐nitriding process for 3D‐printed titanium electrodes that results in a 20‐fold improvement of charge transfer characteristics relative to the untreated material is outlined. The ability to utilize 3D‐structured current collectors with a net 40‐fold improvement in performance over nonstructured electrodes is further demonstrated. This novel approach to creating electrochemical current collectors requires minimal laboratory resources and can be widely adapted for a variety of applications, including desalination, electrolysis, energy storage, and basic research. The work described herein provides both a means for accelerating research and opens the door to hierarchical tuneability for enhanced performance. [ABSTRACT FROM AUTHOR]

In this study, the effects of plastic deformation induced by cold-rolling on the evolution of the microstructure and the resultant corrosion resistance of 316L stainless steel in PEMFCs cathode environment are investigated. The results show that cold deformation changes grain size, grain boundary angle, low-∑ coincidence site lattice (CSL) grain boundaries and phases of the alloy. The best corrosion resistance is achieved in 316L stainless steel with 50% cold rolling deformation, mainly because the increase of low-∑ CSL grain boundaries and O2−/OH− ratio. The uniformity and compactness of the passive film also have a beneficial effect on corrosion resistance. When the cold-rolling deformation is 70 %, the dissolution of martensite accelerates the corrosion rate thus leading to poor corrosion resistance. • Grain boundary angle, low-∑ coincidence site lattice (CSL) grain boundaries and phases change by cold deformation. • Best corrosion resistance is achieved with 50% cold rolling deformation. • Dissolution of martensite by 70% cold rolling deformation accelerates corrosion rate and leads to poor corrosion resistance. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cells are gaining popularity in power-consuming devices due to their zero-emission characteristics. However, ohmic resistance, which arises from the resistance to electron flow through the electrodes and external circuit, can cause reduced efficiency and voltage drops in a fuel cell. This research aims to develop current collector plates for proton exchange membrane fuel cells with optimal design, high electrical conductivity, and thermal conductivity to mitigate ohmic resistance. Six different designs and five different materials-copper, brass, aluminum, stainless steel 316, and stainless steel 304 – were considered for this purpose. The study involved experimental electrical conductivity and fuel cell performance tests to identify the best material and design for the current collector. Results indicated that brass and copper exhibited the least resistivity and favorable material characteristics. Consequently, all six current collector plate designs were developed using brass and copper with various machining and finishing processes. Performance testing on a fuel cell test station revealed that brass current collector plate design 5, featuring open ratios, demonstrated superior performance. Ultimately, the optimum design and material selection of the current collector plates have led to the development of fuel cells with reduced ohmic resistance and improved overall performance. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolyzers (PEMWE) are being considered as a high efficiency potential option for green hydrogen production. Bipolar plates (BPPs) are a crucial element within PEMWEs serving a significant function in the sepration of product gases, distribution of flow field, electron collection, and heat conduction. This review paper aims to investigate recent research on materials used in BPPs and examine several corrosion prevention strategies aimed at enhancing their durability and performance in PEMWEs. It presents a thorough examination of the materials utilized in BPPs, encompassing both conventional metals and advanced coatings. The analysis focuses on elucidating the distinct advantages and limits associated with these materials in relation to conductivity, mechanical strength, and resistance to corrosion. The review examines electrochemical techniques and microscopy methods utilized to assess corrosion behavior, guiding the selection and optimization of materials. Ultimately, this review offers a thorough comprehension of the current advancements in BPP materials and corrosion protection strategies for PEMWEs. [Display omitted] • Consolidating recent research on BPP materials and corrosion prevention in PEMWEs. • Examining BPP materials, including traditional metals and advanced coatings. • Elucidating strengths and weaknesses of materials in conductivity and corrosion. • Investigating the physical and electrochemical characterization techniques. [ABSTRACT FROM AUTHOR]

Coated SS316L is a potential alternative to the graphite bipolar plates (BPPs) used in proton-exchange membrane fuel cells (PEMFCs) owing to their low manufacturing cost and machinability. Due to their susceptibility to corrosion and passivation, which increases PEMFC ohmic resistance, protective and conductive coatings on SS316L have been developed. However, coating adhesion is one of the challenges in the harsh acidic environment of PEMFCs, affecting the performance and durability of BPPs. This study compares mechanical polishing and the frequently adopted chemical etchants for SS316L: Adler's, V2A, and Carpenter's etchant with different etching durations and their impact on the wettability, adhesion, and corrosion resistance of a Nb-coated SS316L substrate. Contact angle measurements and laser microscopy revealed that all etching treatments increased the hydrophobicity and surface roughness of SS316L substrates. Ex situ potentiodynamic and potentiostatic polarization tests and interfacial contact resistance analysis revealed high corrosion resistance, interfacial conductivity, and adhesion of the Nb-coated SS316L substrate pretreated with V2A (7 min) and Adler's (3 min) etchant. Increased hydrophobicity (contact angle = 101°) and surface roughness (Ra = 74 nm) achieved using V2A etchant led to the lowest corrosion rate (3.3 µA.cm−2) and interfacial resistance (15.4 mΩ.cm2). This study established pretreatment with V2A etchant (a solution of HNO3, HCl, and DI water (1:9:23 mole ratio)) as a promising approach for improving the longevity, electrochemical stability, and efficiency of the coated SS316L BPPs for PEMFC application. [ABSTRACT FROM AUTHOR]

The Polymer Electrolyte Membrane Water Electrolyser (PEMWE) has gained significant interest among various electrolysis methods due to its ability to produce highly purified, compressed hydrogen. The spatial configuration of bipolar plates and their flow channel patterns play a critical role in the efficiency and longevity of the PEM water electrolyser. Optimally designed flow channels ensure uniform pressure and velocity distribution across the stack, enabling high-pressure operation and facilitating high current densities. This study uses flow channel geometry inspired by authentic vine leaf patterns found in biomass, based on various plant leaves, including Soybean, Victoria Amazonica, Water Lily, Nelumbo Nucifera, Kiwi, and Acalypha Hispida leaves, as a novel channel pattern to design a PEM bipolar plate with a circular cross-section area of 13.85 c m 2 . The proposed bipolar design is further analysed with COMSOL Multiphysics to integrate the conservation of mass and momentum, molecular diffusion (Maxwell–Stefan), charge transfer equations, and other fabrication factors into a cohesive single-domain model. The simulation results showed that the novel designs have the most uniform velocity profile, lower pressure drop, superior pressure distribution, and heightened mixture homogeneity compared to the traditional serpentine models. [ABSTRACT FROM AUTHOR]

The graphite-resin composite bipolar plates prepared by the traditional hybrid pressing process exhibit poor conductivity, processability, and wettability due to the graphite flake layer being covered by resin, hindering the formation of a continuous conductive network, which significantly constrains their promotion and application in the field of proton exchange membrane fuel cells (PEMFC). In this paper, an ultra-thin flexible graphite/epoxy composite bipolar plates (BPs) with a thickness of only 0.775 mm is prepared followed by a process of flexible graphite preforming and impregnation curing. The hydrophilicity-modified BPs surface has a contact angle of 59.01° as well as flexural and compressive strengths of 11 MPa and 4 MPa and possesses a high in-plane conductivity of 380 S/cm and a low in-plane specific resistance of 6 mΩ cm2. The electrostack test results show that the hydrophilic runner channel is more conducive to the diffusion and spreading of H 2 O generated from the cathode-side reduction reaction in the flow channel, so that O 2 smoothly passes through the gas diffusion layer to participate in the reduction reaction of O 2 , and exhibits higher electric power at high current density, while the hydrophobically modified BPs has relatively poor overall performance due to ohmic losses. [Display omitted] • A hydrophilic flexible graphite bipolar plate with a contact angle of 59.01° is prepared. • The bipolar plates with excellent flexural strength of 11 MPa and a high in-plane conductivity of 380 S/cm. • The Electricstack has the best overall monolithic voltage and total power when the current density over 1800 mA/cm2. [ABSTRACT FROM AUTHOR]

Aluminum alloy bipolar plates have the merits of lightweight, favorable cold processing performance and low price, which have an extensive application prospect in proton exchange membrane fuel cells (PEMFCs). To enhance the corrosion resistance and conductivity of aluminum alloy bipolar plates, a multilayer Ni–P/Cr/CrMoAlN coating was prepared on aluminum alloy 5052 (AA5052) using electroless plating and closed field unbalanced magnetron sputtering ion plating (CFUMSIP) techniques. The research findings indicate that the outermost layer of the multilayer Ni–P/Cr/CrMoAlN coating is mainly composed of CrN, Mo2N, and AlN phases. Electrochemical and interfacial contact resistance (ICR) tests reveal that the Ni–P/Cr/CrMoAlN coating has the lowest current density (7.37 × 10−7 A cm−2) in potentiostatic polarization test and the smallest ICR (2.36 mΩ cm2). Therefore, the Ni–P/Cr/CrMoAlN coating can remarkably improve the performance of aluminum alloy bipolar plates. [ABSTRACT FROM AUTHOR]

Titanium (Ti) is generally considered as an ideal bipolar plate (BPP) material because of its excellent corrosion resistance, good machinability and lightweight nature. However, the easy-passivation property, which leads to increased interfacial contact resistance (ICR) and subsequently decreased cell performance, limits its large-scale commercial application in proton exchange membrane fuel cells (PEMFCs). In this paper, we proposed a NiTi alloy prepared by suction casting as a promising bipolar plate for PEMFCs. This NiTi alloy exhibits significantly decreased ICR values (16.8 mΩ cm2 at 1.4 MPa) compared with pure Ti (88.6 mΩ cm2 at 1.4 MPa), along with enhanced corrosion resistance compared with pure nickel (Ni). The superior corrosion resistance of NiTi alloy is accredited to the nobler open circuit potential and corrosion potential, coupled with low corrosion current densities and passive current densities. The improved ICR can be interpreted by the existence of high-proportioned metallic Ni in the passive film, which contributes to the reduced capacitance characteristic of the passive film (compared with Ti) and enhances charge conduction. This work provides a feasible option to ameliorate BPP material that may have desirable corrosion resistance and ICR. [ABSTRACT FROM AUTHOR]

The standard industrial vanadium redox flow battery (VRFB) stack is made of thick graphite bipolar plates to support the flow field required for optimal circulation of electrolyte. These thick plates suffer from electrolyte seepage, poor mechanical properties, and high machining and processing costs. In the present study, we report on the use of metallic bipolar plates for the construction of the VRFB cell. We show, through comprehensive electrochemical and hydrodynamic investigations, that Hastelloy C276, a corrosion-resistant high Nickel alloy, is a suitable bipolar plate material in VRFB cells. We show further that surface texture modification, in the form of a mix of concave and convex spherical indentations on the metallic bipolar plate, can have beneficial effects on cell performance. Comparative experiments on medium-size cells of a nominal area of 440 cm2 operating in the current density range of 75–125 mA/cm2 show that discharge energy gains of 25% or higher can be obtained together with a 10–15% reduction in pressure drop in comparison with similar cells with flat bipolar plates. It is posited that the concave indentations spread over the entire area ensure uniform electrolyte circulation while regions of low and high electrode compression create flow channeling possibilities that lead to reduced pressure drop.

This work investigates the microstructure and manufacturing control of the masked Cold Spray Additive Manufacturing (CSAM) strategy for producing of new bipolar plates (BPPs) for Proton Exchange Membrane (PEM) electrolyzers, using low-cost, lightweight, and machinable materials. CSAM is a solid-state process capable of fabricating 3D patterned parts based on a bottom-up approach using masks with a desired pattern. This study focuses on the dimensional and microstructural characteristics of pin fins fabricated with spherical (Ti-S) and irregular (Ti-I) Ti powders using the masked CSAM technology. Additionally, the performance of both Ti parts for its application in PEM electrolyzers was evaluated in terms of corrosion resistance and interfacial contact resistance (ICR). The results demonstrated that the masked CSAM technology allowed precise control and customization of the dimensions of the 3D-printed pin fins, obtaining porosity values of 6 ± 1 % for Ti-S and 4 ± 1 % for Ti-I. The evaluation of the corrosion resistance of the CSAM Ti patterned parts showed that for both Ti-S and Ti-I powders a stable oxide film at the typical operation potential (1.8 V vs Ag/AgCl) of a PEM water electrolyzer was formed without signs of pitting corrosion. Finally, at a compaction pressure of 150 N/cm2 ICR values of 42 ± 19, 40 ± 13, and 24 ± 7 mΩ·cm2 were obtained for Ti-I, Ti-S, and standard Ti Bulk, respectively. The results suggest than the masked CSAM technology shows great potential for the fabrication of Ti BPPs.

Voltage fluctuations in energy input not only impact the overall hydrogen production efficiency and stability of Proton Exchange Membrane Water Electrolysis (PEMWE) systems but also pose significant challenges to the long-term service life of individual components. This study focuses on the key component − bipolar plates and investigates the response behavior of platinum-coated titanium bipolar plates under simulated fluctuating voltage conditions. By integrating surface phase analysis and electrochemical testing results, this research elucidates the response characteristics of the bipolar plates to different voltage waveforms and frequencies. And the findings hold substantial significance for the upstream energy control in hydrogen production through water electrolysis.

Proton exchange membrane fuel cells are a prime choice for substitute electricity producers. Membrane electrode assembly (MEA), bipolar electrodes, and current collectors belong to only a limited number of primary parts of the proton exchange membrane fuel cell (PEMFC). Bipolar plates are among the most famous elements in the fuel cell; they are responsible for the electrochemical reaction, as well as the flow of gases from one bipolar plate to another. A bipolar plate is to be a good electro-conducting, non-corrosive, and a high mechanical strength product. The attainability of the specification is achieved by graphite and metallic materials, each one having its own merits and demerits that are discussed in this article. Likewise, making the second pass for the flow pattern is equally important for the cell to have good performance and efficiency. The emergence of innovative and new bipolar plate designs has caused the achievement of high performance of these plates. The present review article principally focuses on the experimental study of diverse flow fields in the design of PEMFC and on the influence of various geometrical properties on the general operation of fuel cells made of PEMFC, and also on the manufacturing procedure utilized for building contemporary fuel cells. [ABSTRACT FROM AUTHOR]

The large-scale application of stainless steel (SS) bipolar plates (BPs) in proton exchange membrane fuel cells (PEMFCs) is mainly limited by insufficient corrosion resistance and electrical conductivity. In this work, Ta-Nb-N coatings were prepared on 316L SS substrates by unbalanced magnetron sputtering to improve corrosion resistance and conductivity. The Ta-Nb-N coatings had a dense structure without obvious defects. In simulated PEMFC cathode environments consisting of 0.5 M H2SO4 + 2 ppm HF at 70 ± 0.5 °C, which is harsher than the U.S. Department of Energy specification, the corrosion current density of Ta-Nb-N-coated BPs was reduced to 2.2 × 10−2  μ A · cm−2. Ta-Nb-N-coated samples showed better electrical conductivity than 316L SS, which had an excellent interfacial contact resistance of 9.2 mΩ · cm2. In addition, the Ta-Nb-N-coated samples had a water contact angle of 100.7°, showing good hydrophobicity for water management. These results indicate that Ta-Nb-N coatings could be a promising material for BPs. [ABSTRACT FROM AUTHOR]

Geleneksel fosil yakıtlar, rezervlerinin sınırlı ve ciddi zararlı kirletici sorunlarının olması önemli problemdir. Fosil yakıtlara en önemli sürdürülebilir alternatif yakıt ve enerji kaynağı hidrojendir. Hidrojenin kimyasal enerjisinin elektrik enerjisine dönüştürüldüğü sistem olan direkt hidrojenli PEM yakıt hücresi umut vaat eden bir enerji kaynağıdır. Bu çalışmada PEM yakıt hücresinin bileşenlerinin ve bazı durumların PEM yakıt hücresi performansına etkisi irdelenmiştir. Öncelikle PEM yakıt hücresinin çalışma sistemi irdelendi. Yakıt hücresinin parçaları ve bu parçaların yakıt hücresi yığın maliyetine etkisi incelendi. Son olarak membran, gaz difüzyon tabakası, bipolar tabaka ve anot-katot elektrotlarının PEM yakıt hücresi performansına etkileri araştırıldı. PEM yakıt hücresinde membran kalınlığı azaldıkça performansının arttığı görüldü. Gaz difüzyon tabakasında az veya aşırı suyun, yakıt hücresi performansı sınırlayıcı etkisi tespit edildi. Grafit gibi elektrik iletkenliği iyi olan ve korozyona dayanıklı bipolar plakanın yakıt hücresi performansını artırdığı tespit edildi. Elektrotların elektrik iletkenliği ve hidrojenin elektrotların yüzeyine tutunma kabiliyeti artıkça performansı olumlu etkilediği görüldü.

Abstract 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.

A graphene–polymer composite is used in the manufacture by 3D printing of bipolar plates for fuel cells. This composite is formed by a PVDF matrix with graphene. The thermal and dynamic mechanical characterization of this composite is studied, as well as the density of printed composite. The study finds that the material studied is a semicrystal polymer and is thermally stable. Density depends on filler in 3D printing, decreasing with fill percentage. The mechanical properties of these materials are good for fuel cell applications. [ABSTRACT FROM AUTHOR]

Metal bipolar plates are prone to corrosion in the acid environment of fuel cells. It is necessary to deposit protective films with excellent corrosion resistance on the surface of metal bipolar plates. In this study, LaB 6 -doped carbon films with strong corrosion resistance were deposited on 316L stainless steel by magnetron sputtering ion plating using graphite composite targets with different contents of LaB 6. The effects of bias voltage and content adjusting on the corrosion resistance of obtained films were investigated. The results show that doping LaB 6 is benefit to adjust the structure and improve the corrosion resistance of a-C matrix. The carbon film with moderate LaB 6 doping possesses compact structure with no columnar defects and exhibits excellent corrosion resistance, providing good protection for 316L stainless steel bipolar plates. • LaB 6 can emit abundant energetic particles, which give higher energy to the plasma during magnetron sputtering process and thus suppress the growth of columnar structure in a-C matrix. • Doping LaB 6 is benefit to promote the graphitization of carbon films and increase the content of sp2-C in a-C matrix. • The most compact structure with no columnar defects is observed for the La-5-100 film, which inhibit the corrosion solution invading into substrates and provide good protection. • The corrosion current density of La-5 films is less than 1 µA·cm-2, and the lowest value can reach 0.33 µA·cm-2. [ABSTRACT FROM AUTHOR]

As one core component in hydrogen fuel cells and water electrolysis cells, bipolar plates (BPs) perform multiple important functions, such as separating the fuel and oxidant flow, providing mechanical support, conducting electricity and heat, connecting the cell units into a stack, etc. On the path toward commercialization, the manufacturing costs of bipolar plates have to be substantially reduced by adopting low-cost and easy-to-process metallic materials (e.g., stainless steel, aluminum or copper). However, these materials are susceptible to electrochemical corrosion under harsh operating conditions, resulting in long-term performance degradation. By means of advanced thermal spraying technologies, protective coatings can be prepared on bipolar plates so as to inhibit oxidation and corrosion. This paper reviews several typical thermal spraying technologies, including atmospheric plasma spraying (APS), vacuum plasma spraying (VPS) and high-velocity oxygen fuel (HVOF) spraying for preparing coatings of bipolar plates, particularly emphasizing the effect of spraying processes on coating effectiveness. The performance of coatings relies not only on the materials as selected or designed but also on the composition and microstructure practically obtained in the spraying process. The temperature and velocity of in-flight particles have a significant impact on coating quality; therefore, precise control over these factors is demanded. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, we present a series of innovative single-layer TaC/α-C coatings designed for integration into proton exchange membrane fuel cells (PEMFC). These coatings are fabricated on stainless steel (SS316L) substrates employing the magnetron sputtering technique. We systematically explore the influence of varying TaC content and the current applied to the tantalum target on the composition, morphology, and properties of these coatings. Notably, the investigation reveals that the coatings exhibit remarkably low values for interfacial contact resistance (ICR), amounting to 0.56 mΩ cm2, and corrosion current density, measuring at 10.7 nA cm−2. Subsequently, Single-cell performance of PEMFC test shows that the highest peak power density of TaC/α-C coated SS316L bipolar plates is 1003 mW cm−2 slightly higher than that of graphite bipolar plates, which is 948 mW cm−2. All the results show that the novel TaC/α-C coating is a prospective coating for PEMFC metal bipolar plates. [Display omitted] • A novel single layer TaC/α-C coating is designed for SS316L bipolar plates. • The lowest corrosion current density at 0.84 V is 10.7 nA cm−2. • The lowest ICR at 1.4 MPa is 0.56 mΩ cm2. • The highest peak power density is slightly higher than graphite bipolar plates. [ABSTRACT FROM AUTHOR]

[Display omitted] Expanded graphite–polyimide composites for fuel cells containing from 0 to 23 wt% expanded graphite were produced by direct compression molding after pre-mixing the binder and filler. The percolation threshold in this system was determined to be 2.5%, while the corrosion current was 3 × 10−2 μA cm−2, and the composites were thermally stable up to 400 °C. [ABSTRACT FROM AUTHOR]

Efficiency enhancement of hydrogen based electric powertrain is becoming highly relevant for medium to heavy duty transportation due to advantages of eminent electrochemical cell design and advances in infrastructure accessibility. Herein, a facile and highly effective fabrication process has been reported for the first time to demonstrate an outstanding mechanical strength and electrical conductivity simultaneously in the carbon rich composite designed to enhance the fuel cell performance. Improvement of composites with different advanced reinforced materials such as carbon veil, recycled carbon fiber as well as functional additives such as carbon black, multiwalled nanotube, etc. Was investigated through a holistic approach of optimized parameters. Advanced composite plates have been designed to be mechanically flexible, electrically conductive and cost effective; this newly designed composite for bipolar plate supersedes by far the US Department of Energy (DOE) target for fuel cell bipolar plate with a flexural strength of over 64 MPa and exceeding electrical conductivity of 200 S/cm. Notably, tuned process parameters as well as novel architecture of materials such as continuous carbon fiber and carbon veil can facilitate the fabrication of a light-weight high-performance carbon polymer composite for a wide range of applications including battery electrodes, supercapacitors, fuel cells and solar cell.

As a promising carbon-neutral technology, the polymer electrolyte membrane fuel cell (PEMFC) is gaining considerable attention over the past decades. Many problems in PEMFC performance and durability can be ultimately ascribed to the flow-field design, which is a complex and systematic work owing to the inherent sophisticated nature of the PEMFC with multicomponent mass transportation and multiphysics field coupling. This paper presents a critical review of the state-of-the-art flow-field designs and an in-depth analysis of the key problems involved from a perspective of efficient mass transport within the PEMFC. In particular, flow-optimization principles are discussed specifically for the enhancement in reactant mass transfer, water management, optimized opening ratio, uniformity of flow distribution, and choice of appropriate numerical approaches assisting the flow-field design. The material formability and forming accuracy and their effects are also discussed for metallic bipolar plates. The objective of this review work is to present a comprehensive overview of the problems, progresses, and perspectives of the flow-field designs for bipolar plates in PEMFC and provide a general theoretical instruction for present and future relevant R&D activities that aim at high-performance, durable, and low-cost fuel cells.

CrAl alloy coating has advanced potential to improve corrosion inhibition, hydrophobicity, and electrical conductivity for metallic BPs. The feasibility of CrAl coating for surface modification of the BPs is thoroughly examined through comparative analysis with stainless steel 316L (SS316L). The coated specimen can reach high polarization resistance (R p) and 93% inhibition efficiency (η) from Tafel plots. Based on the various surface properties of CrAl coating, corrosion resistance mechanisms for substitutional solid solution and nanograin structures containing hydrophobic and low surface free energy are proposed. [Display omitted] • Designed as a BCC solid solution, CrAl protects the SS316L BPs in PEMFC environments. • Corrosion resistance mechanisms of CrAl are discussed in terms of the crystal structure and grain boundary diffusion. • The CrAl coated surface is more hydrophobic than SS316L and forms a lower surface free energy. • CrAl possesses lower interfacial contact resistance than bare SS316L both before and after the CA test. [ABSTRACT FROM AUTHOR]

Bipolar plates are recognized as an important component of proton exchange membrane fuel cells (PEMFCs) because of their critical duties of separating reactant gas, cooling medium, conducting electricity, as well as discharging heat and product water. Recognizing the importance of bipolar plates to the functioning of PEMFCs, researchers have been committed to create bipolar plates with high conductivity, good air tightness, appropriate mechanical qualities, corrosion resistance, and cheap cost. In this review, we provide an overview of the functional requirements and parameter specifications for bipolar plates, followed by a detailed analysis of research developments in recent years for three categories of bipolar plates: graphite, metallic, and composite. Meanwhile, the influence of physicochemical parameters, such as the morphologies, internal structure and composition, on the corrosion-resistance ability, mechanical strength, electrical and thermal conductivities of bipolar plates are examined and reported. This review covers various research directions and highlights the most promising avenues for future research. The objective of this review is to give guidelines for researchers who intend to create high-performance bipolar plates for use in PEMFCs. [Display omitted] • The article summarizes the development trends of materials in bipolar plates (BPs). • High conductivity, good air tightness and corrosion resistance are important for BPs. • The inherent properties of graphite BPs limit further development. • Composite BPs focus on the physical and chemical properties of conductive fillers. • Metallic BPs focus on coating technology and metal components. [ABSTRACT FROM AUTHOR]

The graphite-Ni/C particles are prepared by Closed-Low Oxygen Pyrolysis Method (CLOPM), in which the graphite particles are coated by colloid of Ethylenediaminetetraacetic Acid (EDTA)-Ni (II) ligands that bound Ni. These graphite-Ni/C particles are dried, sized and compacted in a crucible and closed in low-oxygen state, then pyrolyzed at a temperature of 900oC. Ni/C particles as precursors have been investigated separately by SEM/EDS, HR-TEM, FTIR, PSA, XRF and Raman spectroscopy. Ni/C particles are 9.6 nm in size and consist of 40.7% of Ni, 52.4% of NiO, and 6.8% of C. The electrical properties of graphite-Ni/C powder have been measured in a compacted solid state. The electrical conductivity of graphite material coated with 10% Ni/C is 7.64 S/cm, which means an increase of 84% over the electrical conductivity of pure graphite, 4.15 S/cm, which has been achieved. These graphite-Ni/C particles will be used as a filler in bipolar plates for PEM fuel cells. [ABSTRACT FROM AUTHOR]

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In the proton exchange membrane water electrolysis (PEMWE), the titanium bipolar plate coated with noble metals is usually used, which puts forward higher requirements for costs. This study investigates the cathode plasma electrolytic deposition (CPED) for the titanium and obtains TiN and TiN/CrN coatings. The TiN coating exhibits the diffusion resistance in the anode PEMWE environment, resulting in an increase in the interfacial contact resistance (ICR). The denser TiN/CrN coating eliminates the diffusion resistance and increases the polarization resistance (R p) value from 3873 Ω cm2 of TiN coating to 12,320 Ω cm2 of TiN/CrN. After long-term potentiostatic polarization, the ICR of TiN/CrN coating is 8.5 mΩ cm2, which is 3.5 times lower than that of TiN coating. Therefore, the low-cost TiN/CrN coating obtained by CPED has brought a good application prospect for bipolar plates in PEMWE. • The TiN and TiN/CrN coatings improve electrical conductivity after long-time service. • The dense TiN/CrN coating avoids the diffusion resistance of the TiN coating. • The corrosion mechanism of TiN/CrN coating in PEMWE environment was revealed. • The passive film properties of TiN and TiN/CrN coatings on TA1 were studied. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of different channel geometries on the performance of Proton Exchange Membrane Fuel Cells (PEMFCs). The study employs computational fluid dynamics (CFD) coupled with thermal and electrochemical simulations to analyze five channel geometries (cases A to E) of bipolar plates. A thorough study on this topic is not found in the literature and aims to identify designs that optimize performance and align with cost-effective production methods. Among the various studied geometries, case D, featuring a trapezoidal cross-section, exhibited the most favorable performance compared to the others, with a current density value of 2.01 A/cm2 and a maximum temperature of 74.89 °C at 0.3 V, leading to an increase in generated power of 4.46%, compared to base case A. The trapezoidal shape enhanced the contact area with the reacting region, resulting in higher reaction rates and an improved overall performance. However, the study also highlights the relevance of velocity and turbulence, with case B demonstrating an enhanced performance due to its higher velocity, and case E benefiting from localized higher velocity regions and turbulence created by baffles. Case B can increase generated power at its peak by around 3.21%, and case E can improve it by 1.29%, with respect to case A. These findings underscore that contact area has a major impact on the PEMFC performance, but velocity and turbulence also play relevant roles. Additionally, trapezoidal channels can be easily manufactured through sheet metal-forming techniques, aligning well with new market trends of weight and cost reduction on bipolar plates. Fuel and oxygen utilization percentages, 38.14% and 62.96% at 0.3 V, respectively, further confirm the superiority of trapezoidal channels, providing insights into optimizing the PEMFC performance. This exhaustive study contributes valuable information for designing efficient metallic bipolar plates and advancing the development of practical fuel cell technologies. [ABSTRACT FROM AUTHOR]

NiCrCN coatings are deposited on the surfaces of 316 L stainless steel (SS316L) substrates via closed field unbalanced magnetron sputtering ion plating (CFUMSIP) to improve the corrosion resistance and electrical conductivity of proton exchange membrane fuel cell (PEMFC) bipolar plates. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results show that CrN, Cr 2 N, Ni, and Cr 7 C 3 phases exist in NiCrCN coatings. As the Cr target current grows from 2 A to 6 A, the Cr 7 C 3 content in the carbon compounds increases from 3.39% to 11.46%, and the interfacial contact resistance (ICR) value is reduced from 18.0 mΩ cm2 to 11.2 mΩ cm2. When the Cr target current reaches 4 A, the NiCrCN coating shows the most intensive cross-sectional growth pattern by cold-field scanning electron microscopy (CFSEM) results, and the current density after prolonged polarization (0.11 μA cm−2) is much lower than that of SS316L (1.86 μA cm−2). • A novel NiCrCN coating is designed to modify SS316L for PEMFC bipolar plates. • Corrosion current density reaches 0.11 μA cm−2 after 4 h polarization. • NiCrCN coatings greatly improve the hydrophobicity of SS316L. • The value of ICR decreases with the increase of Cr 7 C 3 content in the coating. [ABSTRACT FROM AUTHOR]

Carbon fiber-polymer blend composite bipolar plate is developed using epoxy resin and polypropylene as the polymer blend (PB) and short carbon fiber (CF) as conductive reinforcements by melt mixing and compression molding technique. A PB results in a lower percolation threshold, known as the double percolation threshold, compared to a single polymer which requires a high filler concentration. Via thermodynamic and kinetic factors, the selective localization of CF at the interface in the PB was predicted and later confirmed through SEM analysis. The electrical conductivity, flexural properties, tensile properties, impact strength, and water absorption are the characteristics used to evaluate the developed bipolar plates. The electrical conductivities of the prepared composites increased with the addition of CF and reached 16.7 S/cm for the 70 wt% CF reinforcement, as expected. The results showed that the flexural and tensile strength were decreasing with the rising additive ratio of CF. At 30 wt% of CF, PP/Epoxy/CF recorded the highest tensile strength (30 MPa) and flexural strength (72.7 MPa). On the other hand, the impact strength increased as the CF concentration increased from 30 to 60 wt%, reaching the highest value of 7.49 kJ/m2 at 60 wt%. However, at 70 wt%, the impact strength significantly decreased. The water absorption of the composites increased slightly as the CF content increased from 30 to 60 wt%, but significantly increased at 70 wt%. The developed composites met the DOE targets for mechanical properties and water absorption. However, the electrical conductivity of the composites still falls below the targets. [ABSTRACT FROM AUTHOR]

Nano Cr–N/Ti–N multilayers coating is deposited on the SS304 surface by cathodic arc-PVD to enhance electrical conductivity and corrosion resistance of SS304 applied as a bipolar plate in PEMFCs. Afterward, the thickness, composition, corrosion rate, interfacial contact resistance and hydrophobicity of the samples are identified. According to the findings, the nano Cr–N/Ti–N multilayer can considerably increase the corrosion resistance due to the enhanced numbers of interfaces and preparing dense coating. The corrosion current density of the coating in the experimentally prepared cathodic solution of the fuel cell is 0.187 μA cm–2, which satisfies targets set by the DOE 2025 (i.e., <1 μA cm−2). The total porosity of coating is 0.0033% which illustrates the very dense nano multilayer PVD deposition. Moreover, the contact angle results indicate that Cr–N/Ti–N can enhance the hydrophobicity of electrode surface. The ICR measurements between the carbon paper and Cr–N/Ti–N coating before and after polarization shows very low value, which is in accordance with the U.S. DOE requirement (≤10 mΩ cm2). [ABSTRACT FROM AUTHOR]

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To improve the corrosion, interfacial contact resistance, and hydrophobicity of bipolar plates used in proton-exchange membrane fuel cells, a series of TiN/amorphous carbon double-layer coatings was prepared on 316L stainless steel using magnetron sputtering. The structure of the amorphous carbon was controlled with different carbon target currents. The changed rules in the coating structure and performance under different carbon target currents were studied. Due to appropriate sputtering energy, an appropriate carbon target current reduced the grain boundary of the coating, resulting in a smoother surface, and increased the content of sp2 hybrid carbon. Compared with uncoated 316L stainless steel, the samples coated with amorphous carbon showed greatly improved corrosion resistance and conductivity. At a carbon target current of 5 A, low contact resistance and high corrosion resistance were achieved simultaneously. The significant improvement in corrosion resistance is attributed to the improvement in the quality of the coating surface. Due to the appropriate carbon target current increasing the content of sp2 hybrid carbon in the coating, the contact resistance of the coating was reduced. When the carbon target current was 5 A, the interfacial contact resistance of the sample was 3.9 mΩ·cm2, which is significantly lower than that of bare 316L stainless steel. After constant potential polarization testing, the coating still exhibited good conductivity. [ABSTRACT FROM AUTHOR]