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Besides the fact that the Proton Exchange Membrane Fuel Cells (PEMFCs) have become the industrial norm of today, the thermal management in PEMFCs is still challenging. Therefore, the present study delves deep understanding of the issue of thermal management and summarizes the relevant research studies that evaluate the efficiency of serpentine flow fields (SFFs) to other flow configurations for thermal management in PEMFCs. The current research explores the variety of aspects of SFFs i.e., temperature uniformity, cooling efficiency, pressure drop, and overall thermal performance to guide future design optimizations and practical implementations of SFFs. The study in hand also discusses developments in SFFs such as., Multi-Pass Serpentine Flow Fields (MPSFFs) and new hybrid designs that include a combination of traditional serpentine and other flow patterns to decrease pressure drop and increase net performance. The findings of various studies show that serpentine flow fields outperform alternative designs in coolant distribution, heat transfer efficiency, and operating temperature stability. Based on the findings, the present study recommends future research options, highlighting the need to include economic and environmental concerns in flow field (FF) design, as well as investigating the use of developing materials and technologies to improve PEMFC performance.

Improving the properties of metallic bipolar plates is very crucial for high performance of proton exchange membrane fuel cells (PEMFCs). Cr–C films are prepared on the stainless steel 316L substrate by RF multi-point magnetron co-sputtering of Cr sheets and graphite target for the first time. Effect of the number of Cr sheets on the morphology, composition, corrosion resistance, conductivity, and hydrophobicity of Cr–C films are investigated systematically. With the increase of the number of Cr sheets, the ratio of sp2/sp3 hybrid in the Cr–C films is decreased, and the films become more compact and smoother. When the number of Cr sheets is 8, the ratio of sp2/sp3 hybrid is 5.01, and the Cr–C film shows the best comprehensive performance. The corrosion current densities of anode and cathode are 0.31 μA cm−2 and -0.087 μA cm−2 at constant potential, respectively, and 0.229 μA cm−2 and -0.276 μA cm−2 at galvanic potential, respectively. The corrosion resistance property of the Cr–C film is superior to DOE standards. Compared with uncoated 316L stainless steels, the properties of corrosion resistance, conductivity, and hydrophobicity of the ones coated with the Cr–C films have been improved significantly. This work opens up a new way for the preparation of metal bipolar plate films. • A method for RF multi-point magnetron co-sputtering is proposed. • The effect of the number of sheet on the properties of CrC films is studied. • CrC films with excellent corrosion resistance and hydrophobicity are prepared. • The films deposited with the number of 8 Cr sheets has the best performance. [ABSTRACT FROM AUTHOR]

Bipolar plates are the key component in polymer electrolyte membrane fuel cells (PEMFCs), which ensure the low cost of the fuel cell stack and furnish some of the important applications such as distributing the reactant gases, conducting the electrons, and removing the waste heat in PEMFCs. Thus, metallic bipolar plates (BPs), such as aluminum (Al), have attracted immense consideration and afford better performance in different machine‐driven applications and mass manufacturing opportunities. In order to increase the corrosion resistance of Al BPs, several methods are used and conducted by scientists. The corrosion behavior and surface structure analysis of pure Al were studied through the immersion process in fluoride‐sulfate solutions, assuming its use as BPs in PEMFC‐produced water. The open cell voltage, interfacial contact resistance, and polarization tests and the fuel cell operations were performed to evaluate cell voltage, current density, corrosion resistance, and the effect of fluoride and sulfate ions on the BPs in PEMFC. The hydrophobicity character of the surface of Al BPs was observed by the measurement of the wettability test. The atomic force microscopy images were taken to study the surface roughness, which was correlated with the corrosion rates of Al BPs. In addition, the amount of corrosion was calculated after 24–120 h of immersion in fluoride‐sulfate solutions. The scanning electron microscopy, transmission electron microscopy, and energy‐dispersive X‐ray spectroscopy data were analyzed to investigate the surface structure, morphology, and elemental analyses. Thus, the results found in this study revealed that Al‐based materials can be suitable for BPs in PEMFCs. Furthermore, it is noticed that the amount of corrosion was influenced by the presence of even a very small amount of fluoride ions present in the PEMFC environment, while it was suppressed efficiently by sulfate ions. [ABSTRACT FROM AUTHOR]

Bipolar plates play a role in electron transfer, gas distribution, water management, supporting membrane electrode assembly in the proton exchange membrane fuel cell (PEMFC) and is also a key component to ensure low cost of fuel cell stack. In this paper, bipolar plate materials (metal, graphite and composite materials), functions, advantages and challenges are reviewed. Among them, the composite graphite bipolar plate stands out with its long cycle life and high corrosion resistance, and has received high attention in recent years. The factors related to the conductive network formed by graphite (including the size and shape of filler and the auxiliary filler bridging graphite particles), the composition and curing conditions of polymer, and the influence of the molding process conditions on the properties were discussed in this paper. In the future, the development of composite graphite bipolar plates with excellent comprehensive performance, making existing formulas and forming methods suitable for large-scale production by mastering and optimizing the balance between polymer structure and reaction path on their performance, will greatly enhance the large-scale application of proton exchange membrane fuel cells in more fields.

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. [ABSTRACT FROM AUTHOR]

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Metal-core carbon nano-onions (CNOs) with uniform size ( 50 ~ 140 nm) were prepared by chemical vapor deposition (CVD) method with methane as carbon source. The synthesized CNOs were purified by microwave heating to obtain an onion carbon material with a purity of 99%, and it was used as conductive bipolar plate in proton exchange membrane fuel cells (PEMFCs) stack. The characterization and analysis of CNOs show that the synthesized CNOs are embedded with Fe-Ni nanoparticles. The contact angle test reveals that the wetting angle of the onion carbon-based bipolar plate manufactured by injection molding is less than 91°, and the hydrophilicity is enhanced compared to the commercial graphite bipolar plate, which is helpful to electron transmission. The output power of the stack formed using onion carbon-based bipolar plates reaches 58 W at 13. 2 V, which is 21% greater than that of the commercial graphite bipolar plate stack (48 W), according to the endurance and power test of the self-breathing stack. Onion carbon-based composites have been shown in studies to enhance the power density, efficiency, and longevity of PEMFCs stack. [ABSTRACT FROM AUTHOR]

In this study, a multilayer high-performance polybenzoxazine/expanded graphite composite bipolar plate with a 'graphite-composites-graphite' structure was prepared by compressing molding. The surface graphite layer and the conductive network were constructed by hot compressing of graphite paper and the polybenzoxazine/expanded graphite composites. The results show that the multilayer synergy makes composite BP reach an in-plane conductivity of 278.85 S cm−1, an area specific resistance of 9.70 mΩ cm2 and a flexural strength of 75.75 MPa. The 'graphite-composites-graphite' structure can make the power density of a single cell assembled by the multilayer composite BP increase by 111.02% and 113.80%. In conclusion, the multilayer bipolar plate with a 'graphite-composites-graphite' structure is a promising polymer composite bipolar plate for the proton exchange membrane fuel cell (PEMFC). [Display omitted] In this study, a multilayer high-performance polybenzoxazine/expanded graphite composite bipolar plate with a 'graphite-composites-graphite' structure was prepared by compress molding. The highlights of our study are summarized as follow: • Multilayer polymer composite bipolar plates are developed by in-situ efficient forming. • The surface enrichment of polymer on polymer composite bipolar plate has been solve. • Composite bipolar plates possess excellent electrical performance and mechanical performance. [ABSTRACT FROM AUTHOR]

During the operation of the proton exchange membrane fuel cell (PEMFC), the chemical reaction yields a large amount of heat. Long-term operation may cause local overheating problems which damage the proton exchange membrane structure, pull down the fuel cell performance drastically. Aiming at improving the temperature distribution and cooling capacity of PEMFC, a novel tree-shaped fractal fuel cell bipolar plate cooling flow field is proposed. The polarization curve, current density distribution, maximum temperature, temperature uniformity, cooling hydraulic pressure drop and the water content of proton exchange membrane are investigated for the fractal cooling flow field with different number of dimensions. The results show that the tree-shaped fractal cooling flow field can achieve better distributions of coolant and temperature uniformity than parallel cooling flow field. The maximum temperature reduces from 340.7 K to 337.8 K, and temperature uniformity index reduces from 1.47 to 0.45, respectively. Compared with the serpentine cooling flow field, the tree-shaped fractal cooling flow field effectively solves the problem of excessive cooling pressure drop and reduces the parasitic power loss while ensuring efficient cooling performance. This novel cooling flow field design offers an excellent solution to solve the local overheating of PEMFC.

CrMoCN coatings with different carbon contents are prepared on 316L stainless steel substrates by closed-field unbalanced magnetron sputtering. The microstructure, phase composition, bonding state, corrosion properties, interfacial conductivity, and hydrophobicity of the coatings are investigated. The structural analysis shows that the nitride coating gradually changes to the coexistence of nitride phase, carbide phase, and amorphous carbon with increasing carbon content. As the phase structure transition, the CrMoCN-14 coating possesses the lowest corrosion current density of 6.28 × 10−8 A cm−2 after potentiodynamic polarization in the simulated cathodic environment. The electrochemical impedance spectroscopy also proved that the CrMoCN-14 sample has the best chemical stability. Furthermore, the CrMoCN-14 coating has a very low interfacial contact resistance value of 7.54 mΩ cm2 compared to the SS316L substrate. The analysis results demonstrated that the CrMoCN coating has excellent anti-corrosion performance and interfacial conductivity and is a potential material for bipolar plates. [ABSTRACT FROM AUTHOR]

In this research, CrN coating was applied to grade 1 titanium as a bipolar plate for PEMFC. The CrN was deposited by ion beam assisted deposition (IBAD) and the arc ion plating method (AIP). The thickness of the coating layer was about 2.5∼3 μm and it was densely deposited on the titanium substrate. The electrochemical experiments were conducted in an aqueous solution of pH 3 (H2SO4 + 0.1 ppm HF, 80°C) determined by DoE. Hydrogen gas and air were bubbled to simulate the anode and cathode environments, respectively. Various analyses (XRD, EDS, FE-SEM), electrochemical experiments (EIS, potentiodynamic polarisation, potentiostatic experiment), and interfacial contact resistance measurement were performed to evaluate the effects of the PVD deposition method. Due to the difference in the PVD method, CrN and Cr2N were formed in the IBAD specimen, whereas CrN phase was observed in the AIP specimen. The CrN coated specimens presented improved interfacial contact resistance compared to the titanium substrate. [ABSTRACT FROM AUTHOR]

Fluid distribution, conduction, and heat control are important phenomenon in the fuel cell fraternity, therefore it is crucial to develop a state-of-the-art bipolar plate (BP) to attain optimum cell performance. Metal foam (MF) and fine mesh have attracted a lot of attention in mitigating some of the challenges associated with straight, and serpentine channels. In this study, MF, 3D fine mesh, fine wire mesh (FWM) flow fields are compared with triple serpentine flow field to develop an optimum design for improved PEMFC performance. Two different foam designs are studied to attenuate the existing drawback associated with MF, mainly caused by high water retention. The 3D fine mesh is leading in performance under anodic and cathodic stoichiometry of 1 and 3 respectively. On increasing the anodic and cathodic stoichiometry to 1.2 and 3.5 respectively, the FWM took the lead. This is brought by the improved water drainage under high stoichiometry. Because FWM is already in mass production, although for other purposes, it is cost competitive over the other designs. The fine mesh and the MF have the potential to break down large water droplet making them easy to drain. They also showed symmetric fluid flow, compared to the serpentine design. • PEMFC performance strongly depends on flow field. • Bipolar plates contribute immensely to the cell volume and weight. • Stoichiometry increment improves water drainage. • Fine mesh alleviates traditional bipolar plates challenges. • Wire mesh is cheap to purchase. [ABSTRACT FROM AUTHOR]

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.

In this research, titanium nitride (TiN) was applied to grade 1 titanium as a bipolar plate for a proton exchange membrane fuel cell (PEMFC). The TiN was deposited by the arc ion plating method (AIP) to investigate the electrochemical characteristics of the anode and cathode environments in the PEMFC. The corrosion experiments were conducted in an aqueous solution of pH 3 (H2SO4 + 0.1 ppm HF, 80 °C) determined by the Department of Energy (DoE). The hydrogen gas and air were bubbled to simulate the anode and cathode environments. The potentiodynamic polarization experiment showed that there was no active peak. The potentiostatic experiment showed that the current densities of the TiN-coated specimens were less than 1 μA/cm2 in both the anode and cathode. As a result of observing the surface with an SEM before and after the potentiostatic experiment, only pinholes generated during the coating process were observed, and no corrosion damage was observed. Furthermore, electrochemical impedance spectroscopy (EIS) analysis showed that the coated specimens had a higher charge transfer resistance than the titanium substrate. In the case of interfacial contact resistance (ICR), the TiN-coated specimen displayed lower resistance than the titanium substrate and satisfied the DoE technical target of less than 10 mΩ·cm2 at 140 N/cm2. [ABSTRACT FROM AUTHOR]

Bipolar plates in proton exchange membrane fuel cells (PEMFCs) are confronted by the dilemma of low contact resistance and high corrosion resistance; this study aimed to simultaneously satisfy these dimensions in a harsh environment. Using thick multilayer coatings can improve the corrosion resistance, but the contact resistance would be largely compromised. To address this challenge, we propose compatible tantalum/titanium-based coatings on 316L stainless steel (SS316L) as bipolar plates for PEMFCs. With the transition layer, the optimal TaN/(Ta,Ti)N/TiN/Ti coating exhibits an ultralow corrosion current density of 0.369 μA·cm−2 (at +0.6 V vs. SCE) and a contact resistance of 6 mΩ cm2 at 138 N/cm2 after 5 h of potentiostatic polarization, both of which meet the standard of the U.S. Department of Energy. Electrochemical impedance spectroscopy (EIS) and an equivalent electrical circuit model further elucidated that TaN/(Ta,Ti)N/TiN/Ti coating significantly impedes the oxidation reaction and dissolution of metals and provides good protection for the SS316L. [ABSTRACT FROM AUTHOR]

Abstract The effect of the presence of a microporous layer on the propensity for corrosion of metallic bipolar plates in an operating polymer electrolyte membrane fuel cell is investigated using an in situ reference electrode array. The local potential at the surface of the cathode bipolar plate is significantly more negative in the presence of the microporous layer, which is attributed to the higher ionic resistance of the aqueous phase in the reactant transport layer associated with more effective removal of water from the catalyst layer/reactant transport layer interface. As a result the bipolar plate is effectively shielded from elevated potentials that may be present at the cathode electrode, even during start-up and shutdown of the cell. Revision of ex situ test protocols for candidate bipolar plate materials, surface treatments and coatings is recommended to reduce unnecessary conservatism in testing. Highlights • In situ mapping of local potential at a fuel cell metallic bipolar plate. • Demonstrated beneficial effect of MPL on corrosion of metallic bipolar plates. • More effective water removal increases ionic resistance in reactant transport layer. [ABSTRACT FROM AUTHOR]

A low-temperature proton exchange membrane fuel cell (LT-PEMFC) is a promising clean and effective technology for power generation because of its simplified water and heat management. Due to the non-uniform of H 2 and air distributions within fuel cells, the stack design is one of the key factors to enhance the performance and efficiency of LT-PEMFC. In this study, a single, two cells, 6 cells and 11 cells LT-PEMFC stack was investigated with cell active area 114 cm 2 , Nafion membrane 112 and catalyst loading 0.4 mg/cm 2 working at 25 °C and atmospheric pressure using hydrogen and air as a fuel and oxidant, respectively. The power output that is obtained from each stack is presented and the overall power output is compared with single cell stack. The stack prototype has been fabricated, constructed and tested producing a maximum value of 70 W electrical power using 11 cells stack. [ABSTRACT FROM AUTHOR]

Clamping load impacts the contact area, resistance, sealing and heat generation of fuel cell stacks, the uneven distribution of clamping load decreases the durability of PEMFC stacks, therefore it is essential to quantitative modeling the pressure distribution and improve the imbalance distribution issue. In this paper, a quantitative model is proposed to characterize the pressure distribution on bipolar plates. A theoretical model is established based on both finite element modeling (FEM) and measurement, and the flexible pressure sensors are applied in the established test systems. Furthermore, a nacre-inspired optimization approach is applied to improve the uneven pressure distributions based on the quantitative model. Results indicate that the optimized design can significantly improve the uneven clamping load, and it provides an effective approach for the design of durable PEMFC stacks. • A non-uniformity clamping pressure model in PEMFC is established quantitatively. • A precise test bench is established to validate the quantitative model. • Bio-inspired design is adopted to optimize the pressure distribution. • The optimization procedure is proposed to improve pressure distribution. [ABSTRACT FROM AUTHOR]

Insufficient corrosion resistance and surface conductivity are two main issues that plague large-scale application of stainless steel (SS) bipolar plates in proton exchange membrane fuel cells (PEMFCs). This study explores the use of nanocrystalline Ta/TaN multilayer coatings to improve the electrical and electrochemical performance of polished 316L SS bipolar plates. The multilayer coatings have been deposited by (reactive) magnetron sputtering and characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The electrochemical behavior of bare and coated substrates has been evaluated in simulated PEMFC working environments by potentiodynamic and potentiostatic polarization tests at ambient temperature and 80 °C. The results show that the Ta/TaN multilayer coating increases the polarization resistance of 316L SS by about 30 and 10 4 times at ambient and elevated temperatures, respectively. The interfacial contact resistance (ICR) shows a low value of 12 mΩ × cm 2 before the potentiostatic test. This ICR is significantly lower than for the bare substrate and remains mostly unchanged after potentiostatic polarization for 14 h. In addition, the high contact angle (92°) with water for coated substrates indicates a hydrophobic character, which can improve the water management within the cell in PEMFC stacks. [ABSTRACT FROM AUTHOR]

Stainless steel bipolar plates are regarded as a good substitute for traditional graphite bipolar plates in proton exchange membrane fuel cells. Stamping is a first selection for the manufacture of stainless steel bipolar plates. In addition to paying more attention to the stamping channel shape, a good prediction, and an efficient evaluation of the formed residual stress and thinning of bipolar plates are necessary. In this paper, the formed stress and deformation of SS304 stainless steel BPP with a thickness of 0.1 mm was investigated by a 2D plane strain FE model. Numerical results showed that formed BPP has a large residual stress, especially in the bending zone. Residual stresses distribution along the inner surface, outer surface, and direction of thickness was non-uniform. Geometrical dimensions have a great effect on residual stress and formed thickness. With an increase of the upper die width and die depth, the peak residual stress increased, and the formed thickness became less uniform. With an increase of the curve radius, the residual stress decreased, and the formed thickness became more uniform. [ABSTRACT FROM AUTHOR]

The carbon/epoxy composite bipolar plate is an ideal substitute for the brittle graphite bipolar plate for proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs) because of its high mechanical properties and easy manufacturing. However, due to the resin-rich area that forms on its surface, the carbon/epoxy composite bipolar plate requires an expanded graphite coating to decrease the areal specific resistance (ASR). The expanded graphite coating not only increases the manufacturing costs but also has very low mechanical properties. In this work, an innovative manufacturing method that exposes carbon fibers on the surface of the carbon/epoxy composite bipolar plate was developed. Soft release films were inserted between the mold and the composite to prevent the formation of a resin-rich area and to expose carbon fibers on the surface of the bipolar plate. The developed method considerably decreased the ASR of the carbon composite bipolar plate without an expanded graphite coating, which satisfied the target established by the Department of Energy (DOE) of United States. The effects of the soft layer on the mechanical and electrical properties of the carbon composite bipolar plate were investigated. [ABSTRACT FROM AUTHOR]

The primary components of proton exchange membrane fuel cell (PEMFC) systems are bipolar plates, end plates, membrane electrode assemblies (MEAs), gas diffusion layers (GDLs), and gaskets. The PEMFC composed of many components induces sealing problem of the stack, which affects the fuel efficiency, reliability, and maintenance costs of the system. Conventional PEMFCs are sealed with numerous elastomeric gaskets to seal the stack, which increases the manufacturing and assembly costs. To reduce the assembly time and to increase the sealing reliability without the use of gaskets, a gasket-integrated carbon/silicone elastomer composite bipolar plate is developed. Silicone elastomer is employed rather than conventional glassy thermoset or thermoplastic polymers for the matrix of the composite bipolar plate, where the silicone elastomer works as gaskets due to its resilience. The mechanical and electrical properties of the developed carbon/silicone elastomer composite are investigated at both room temperature and operating temperature of high-temperature PEMFCs (HT-PEMFCs). The sealability of the gasket integrated composite bipolar plate is tested. [ABSTRACT FROM AUTHOR]

The bipolar plate is of critical importance to the efficient and long lasting operation of a polymer electrolyte fuel cell (PEMFC) stack. With advances in membrane electrode assembly design, greater attention has been focused on the bipolar plate and the important role it plays. Although carbon composite plates are a likely candidate for the mass introduction of fuel cells, it is metallic plates made from thin strip materials which could deliver significant advantages in terms of part cost, electrical performance and size. However, there are some disadvantages. Firstly, interfacial stability of the metal interconnect is difficult to achieve. Secondly, and the issue addressed here, is the difficultly and cost in developing new plate designs when there are very significant tooling costs associated with manufacture. The use of selective laser melting (SLM: an additive manufacturing technique) was explored to produce metallic bipolar plates for PEMFC as a route to inexpensively test several plate designs without committing to tooling. Crucial to this was proving that, electrically, bipolar plates fabricated by SLM behave similarly to those produced by conventional manufacturing techniques. This research presents the development of a small stack to compare the short term performance of metallic plates made by machining against those made by SLM. Experimental results demonstrate that the cell performance in this case was unaffected by the manufacturing method used and it is therefore concluded that additive manufacturing could be a very useful tool to aid the rapid development of metallic bipolar plate designs. [ABSTRACT FROM AUTHOR]

Currently stainless steel is the material on which extensive research interest is being focused for the purpose of using it as bipolar plates (Bp) for Proton Exchange Membrane Fuel Cell (PEMFC) because of its suitable physical and mechanical properties. In the present study TiN, TiAlN mono-layer and TiN/TiAlN bi-layer coatings were developed on 316L stainless steel (SS) by physical vapourvapour deposition (PVD) technique. The X-ray diffraction (XRD) patterns and Raman spectrum confirmed TiN cubic structure was formed for all the coatings. An increased surface roughness determined by atomic force microscopy (AFM) and high contact angle value with water for TiN/TiAlN qualify the Bp for the wet operating conditions in PEMFC. The electrochemical corrosion behaviour of the uncoated and coated specimens have been studied by Electrochemical impedance spectroscopy (EIS) as well as Potentiodynamic and Potentiostatic polarization studies in 0.5 M H 2 SO 4 with 2 ppm of fluoride ions at 80 °C purged with air to simulate the PEMFC environment. The corrosion protection performance is in the order of TiAlN < 316L SS < TiN/TiAlN < TiN and the corrosion current (i corr ) density obtained for TiN and TiN/TiAlN are less than 1 μA/cm 2 . Surface resistance measurements showed that TiN has 0.8 m Ω cm 2 and exhibits more conductivity after the polarization studies. [ABSTRACT FROM AUTHOR]

Metallic bipolar plates are of increasing interest to automotive polymer electrolyte membrane fuel cell (PEMFC) manufacturers due to their low cost, high power density, ease of manufacture, high conductivity and good mechanical properties but minimising the undesirable effects of corrosion remains a key challenge. Unfortunately, reliable assessment of the applicability of stainless steels with a range of coatings and surface treatments has been hampered by a lack of representative ex situ test methods. Here we characterise the local environment experienced by a bipolar plate during fuel cell operation via in situ measurement of pH and corrosion potential for an uncoated 316L stainless steel bipolar plate in a single cell PEMFC. We demonstrate that the degradation mode is more akin to corrosion in relatively dilute thin liquid layers, rather than the fully immersed conditions employed in conventional ex situ screening tests. A key observation is that the corrosion potential of the bipolar plate is only weakly coupled to the potential of the nearest Pt electrode due to the low ionic conductivity of the discontinuous aqueous phase in the gas diffusion layer (GDL). However, localised polarisation of the steel can occur in the presence of oxygen as a result of galvanic coupling with the carbon GDL at wetted interfaces, a process which may be enhanced by the creviced geometry. The implications for development of more representative ex situ test protocols are discussed. [ABSTRACT FROM AUTHOR]

In order to realize the fuel cell (FC) operation with higher power density, researchers have made various attempts to it. The innovative design of bipolar plate (BPP) can contribute about 20% to the volumetric power density increase. Mass transfer and drainage capacity are two keys of plate design. In order to improve its mass transfer capacity, many improvements have been made, such as baffle flow field (FF) and biomimetic FF. These FFs have their own advantages and disadvantages. For facilitate comparison, this article summarizes the influence of various FF designs, structures, flow patterns and other parameters on FC performance, and gives the BPP's development direction in the future. The effects of different FF structures, geometric parameters and arrangement forms on the uniformity of i distribution are summarized. The effects of contact area, channel design parameters such as channel width/rib ratio, fillet radius and channel size on the BPP's interfacial contact resistance are reviewed. Guidance is provided for designing FFs that can achieve more uniform i distribution and smaller contact resistance. The main manufacturing processes of BPPs are reviewed, and then the difficulties that need to be overcome in order to manufacture higher performance BPPs are pointed out. • The influences of various BPP flow field designs on FC performance are summarized. • The effects of BPP on current distribution and contact resistance are summarized. • The fabrication process of BPPs and existing difficulties are summarized. • The development directions of BPP fabrication and flow field design are predicted. [ABSTRACT FROM AUTHOR]

To gain high hardness, good thermal stability and corrosion resistance, multicomponent TiAlSiN coating has been developed using different deposition methods. In this study, the influence of Al and Si on the electrochemical properties of TiN-coated 316L stainless steel as bipolar plate (BP) materials has been investigated in simulated proton exchange membrane fuel cell environment. The deposited TiN, TiAlN and TiAlSiN possess high hardness of 23.9, 31.7, 35.0 GPa, respectively. The coating performance of the TiN coating is enhanced by Al and Si addition due to lower corrosion current density and higher Rcoating and Rct values. This result could be attributed to the formation of crystalline-refined TiN(200), which improves the surface roughness, surface resistance, corrosion performance, and decreased passive current density. [ABSTRACT FROM AUTHOR]

Silica impregnated expanded graphite-epoxy composites are developed as bipolar plates for proton exchange membrane (PEM) fuel cells. These composite plates were prepared by solution impregnation, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance, and contact angles were determined as a function of impregnated content. The plates show high flexural strength with 5% methyltrimethoxysilane (MTMS) addition 20 MPa) and in-plane conductivity of 131 S cm-1 that meet the DOE target (>100 S cm-1). Corrosion current values as low as 1.09 µA cm-2 were obtained. The contact angle was found to be 80°. Power density of 1 W cm-2 was achieved with custom made expanded graphite-polymer composite plates. High efficiency values were obtained at low current regions. [ABSTRACT FROM AUTHOR]

The effect of operational parameters on the performance of PEMFCs by using serpentine flow field channels with different (rectangular and trapezoidal) cross-section shape has been investigated. More than cell temperature and pressure, reactant humidification temperature (Tha,c) has a significant influence on the effect of serpentine channels with trapezoidal cross-section on cell performance. The high capability of water removal by serpentine channels with trapezoidal cross-section positively affects the fuel cell performance when the water content in the system is high, as in the case of the reactant humidification temperature higher than cell temperature (Tc). On the contrary, when the water content in the cell is low, as in the case of Tha,c = Tc, the high ability of water removal of serpentine channels with trapezoidal cross-section results in a less effective membrane/cathode hydration. Conversely, the effect of Tha,c on the performance of the cell with serpentine channels with rectangular cross-section is negligible. [ABSTRACT FROM AUTHOR]

Metallic bipolar-plates have advantages over non-porous graphite ones due to their higher mechanical strength and better electrical conductivity. However, corrosion resistance and interfacial contact resistance are major concerns that remain to be solved, since metals such as stainless steels may develop oxide layers that decrease electrical conductivity, thus lowering fuel cell efficiency. In this study, multi-layered nitride coatings consisting of Ti and TiN were deposited on 316L stainless steel (SS316L) by a D.C magnetron sputtering method to enhance the corrosion resistance and to lower the interfacial contact resistance (ICR) of metallic bipolarplates for a polymer electrolyte membrane fuel cell (PEMFC). Electrochemical methods were conducted and ICRs of the coated specimens were measured to investigate the potential of the coated metallic bipolar-plate for use in PEMFCs. The multi-layered Ti/TiN coating deposited on SS316 showed lower ICR values than the single-layered TiN coating, and improved corrosion resistance when the PEMFC was not in operation while the degradation of the coating layer was observed in both cathodic and anodic working environments. [ABSTRACT FROM AUTHOR]

Abstract: Diverse CAD (Computer aided-Design) 3D bipolar plates model are presented. By using the OpenFOAM software, an open source CFD (Computational Fluid Dynamic), hydrogen flow simulations were carried out, obtaining velocities and pressure maps for each model. Main objective resides on predict the flow behavior in response to the modifications proposed on the bipolar plate geometry, such as width, depth and shape of the distributing channels (collectors) as over the main channels. Channelers fins are also besought with the purpose of direct the flow towards different zones, in order to homogenize the flow distribution. [Copyright &y& Elsevier]

SUMMARY Corrosion behaviors of Fe-26Mn-3A1-7Cr alloy are investigated in the solution of 0.05 M H2SO4 + 2 ppm F-, and interfacial contact resistances (ICRs) are measured before and after potentiostatic polarization at operation potentials. The results show that passive current densities of Fe-26Mn-3A1-7Cr alloy are about 10-5 A cm-2. Stable passive film forms on the surface of Fe-26Mn-3A1-7Cr alloy in the cathodic side, and no pit is observed, while serious dissolution occurs in the anodic one. The ICR of Fe-26Mn-3A1-7Cr alloy in anode side is about three times higher than that in cathode one. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

AISI446 stainless steel was electrochemically nitrided at room temperature. X-ray photoelectron spectroscopy (XPS) analysis indicated that the nitrided steel was covered with surface ammonia and a layer of nitrides (mainly of mixed chromium nitrides). The nitride layer for 4 h nitrided steel at -0.9 V was about 2.5 nm thick. Dominating oxides appear on the steel's surface, so nitrogen incorporated oxides is a suitable term to describe the nitrided surface. The nitrided surface showed very low interfacial contact resistance (ICR) and excellent corrosion resistance in simulated polymer electrolyte membrane fuel cell (PEMFC) environments. The excellent stability of the nitride steel was confirmed by XPS depth profiling before and after testing in the PEMFC environments. Electrochemical nitridation provides an economic way for modifying the steel's surface to approach the U.S. Department of Energy 2015 goal for bipolar plates. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, we elucidate the possible reasons for high voltage retention during operation when a Ni-saving high nitrogen stainless steel (hereafter referred as to Ni-saving HNS) was used as bipolar plates for PEMFCs. A typical type 316L was also employed as bipolar plates to compare the cell performance. The Ni-saving HNS bipolar plate adopting cell obviously exhibited better cell performance at various current densities. After 1000h of cell operation, the tested metallic bipolar plates were analyzed by scanning electron microscopy, inductively coupled plasma-mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and transmission electron microscopy–electron energy loss spectroscopy to prove the superiority of the Ni-saving HNS bipolar plates. As a result, the surface state of the bipolar plates exposed to the PEMFCs environment is the critical factor that affects cell performance. Protection of the metal surface mainly with chromium oxide-based surface layer, which was induced from a reaction of N from the Ni-saving HNS and H2O generating proton, H+, that lowers local surface pH, was thus substantially effective to retain the voltage upon operation. [Copyright &y& Elsevier]

Abstract: Tribological variations, surface conditions (roughness, hardness, coating) and surface interactions between micro-stamping dies and bipolar plate blanks play a critical role in determining the surface quality, channel formation and precision of bipolar plates. This study is aimed to understand the cause, mechanism and consequences of interactions between micro-stamping process conditions and bipolar plate quality. A total of 2000 repeated micro-stamping of 51 μm-thick uncoated and 1 μm-thick ZrN coated SS316L sheet blanks into an array of 750 μm micro-channels were performed using 175–220 kN force levels with constant stamping speed of 1 mm/s. Microscopic examinations were conducted periodically on both die and coated & uncoated plate surfaces to observe topographic variations. In addition, corrosion and contact resistance tests were carried out in the same intervals. Analysis of variance (ANOVA) technique was used to determine the significance of the process parameters on channel height, roughness, corrosion and contact resistance differences. The results revealed similar roughness trends for die and plate surfaces during 2000 micro-stampings. ZrN coating with 1 μm thickness dramatically improved corrosion and contact resistance behavior of plates. [Copyright &y& Elsevier]

Abstract: AISI446 steel has been electrochemically nitrided in 0.1 M HNO3 + 0.5 M KNO3 solution at room temperature. XPS analysis revealed surface NH3 and a deeper nitride layer. The surface layer of the stainless steel modified by electrochemical nitridation was thus composed of a nitrogen-incorporated oxide film. The nitrided steel showed very low interfacial contact resistance (ca. 18 mΩ cm2 at 140 N/cm2) and excellent corrosion resistance in simulated PEMFC environments. Electrochemical nitridation provides an economic way to modify the stainless steel’s surface, and is very promising for application to fuel cell bipolar plates. [Copyright &y& Elsevier]