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Zirconium nitride (ZrN) coatings were deposited on the stainless steel using multi-arc ion plating under varying nitrogen partial pressures (P N) ranging from 0.5 to 3.5 Pa. The effect of phase composition, microstructure, and surface morphology on the corrosion resistance and conductivity of the ZrN-coated stainless steel in a simulated proton exchange membrane fuel cell (PEMFC) cathode environment was systematically explored. XRD and TEM revealed that the columnar-structured ZrN coating mainly comprised the fcc-ZrN phase. The Zr 3 N 4 phase was discovered near the substrate during coatings prepared at low nitrogen partial pressures. Surface defects were reduced at nitrogen partial pressures exceeding 2.5 Pa. The ZrN coating exhibited enhanced corrosion resistance and conductivity (ZrN-3.5, E corr = 0.307 V, I corr = 2.085 × 10−7 A/cm2, R ct = 1.125 × 105 Ω·cm2) compared to bare stainless steel in the simulated PEMFC cathode environment. The presence of surface defects influenced the corrosion resistance, while differences in conductivity were related to the phase composition and microstructure of the coating. Thus, the findings indicate that ZrN coatings prepared under optimal deposition conditions can have potential applications in PEMFC bipolar plates. [ABSTRACT FROM AUTHOR]

Reducing the cost of PEM water electrolyzers is crucial for making green hydrogen economically viable achievable by cheaper catalysts as well as bipolar plates. This study demonstrates for the first time the use of uncoated carbon bipolar plates (C‐BPs) as an alternative to titanium bipolar plates (Ti‐BPs). The corrosion phenomena of C‐BPs versus Ti‐BPs are investigated through ex situ and in situ accelerated stress tests. The findings show that pH values, especially between 1 and 0, exponentially influence the corrosion current density of bipolar plates. Ex situ tests revealed significantly higher corrosion current densities for C‐BPs compared to Ti‐BPs (e.g., 170 times higher at pH 1 and 80 °C). Yet, tests applying C‐BPs in a Proton Exchange Membrane Electrolyzer operated for at least 567 h at alternating current densities of 1 and 3 A cm⁻2 with low degradation rates (16.41 µV h⁻¹ at 1 A cm⁻2 and 31.92 µV h⁻¹ at 3 A cm⁻2), comparable to Ti‐BPs. Contrary to general perceptions, C‐BPs are stable under application‐ready conditions and do not corrode as previously expected. This study highlights the potential of C‐BPs in electrolyzers, showcasing the potential to reduce the costs of the electrolyzers. [ABSTRACT FROM AUTHOR]

The effect of surface roughness on the interfacial contact resistance (ICR) and the corrosion behavior of 446 stainless steel in simulated anode environments for proton exchange membrane fuel cell (PEMFC) (i.e., 0.5 mol L−1 H2SO4 + 2 ppm F− and 5 × 10−4 mol L−1 H2SO4 + 0.1 ppm F− bubbled with hydrogen gas at 80 °C) was investigated by means of atomic force microscopy, potentiodynamic polarization, electrochemical impedance spectroscopy and ICR test. The surface roughness (Ra) produced by mechanical grinding increases noticeably with the decrease of sandpaper grit size from 1000# to 240#. 446 stainless steel shows the active state under free corrosion conditions in the two test solutions and the passive state at the typical anode working potential of PEMFC after the activation-passivation transition. The corrosion resistance decreases with the increase of roughness in both solutions. The corrosion product films formed in the solution with lower acidity are more protective, leading to the appearance of the diffusion process. The enlargement of surface roughness results in the gradual reduction of ICR, but the acceleration of active and passive dissolutions. [ABSTRACT FROM AUTHOR]

This study investigates the influence of surface roughness on the performance of polymer electrolyte membrane fuel cells (PEMFCs) through computational simulations using COMSOL Multiphysics. Two distinct gas flow channel (GFC) models of serpentine and parallel GFC structures were analysed, featuring various surface roughness levels to examine their impact on gas pressure and velocity dynamics. Rough surfaces are modeled using trigonometric functions to replicate machining-induced variations. Finite element simulations were conducted, assessing the time-dependent relationship between gas pressure and velocity while considering different electrode phase potentials as a function of surface roughness. Rough surfaces generally enhance mass transport, water management, and current distribution compared to smooth surfaces. The results indicated that a surface roughness of approximately 1 µm optimizes PEMFC performance by balancing pressure and velocity, enhancing electrochemical reactions, and reducing excessive pressure drops within the cell. Notably, the 0.7 V operating voltage was found to be the most efficient, achieving rapid stabilization of pressure and velocity levels swiftly. The findings underscore the importance of precise control over GFC roughness to enhance PEMFC performance gains in commercial applications, especially when multiple cells are stacked to achieve high power outputs. [ABSTRACT FROM AUTHOR]

Flow fields are a primary component of polymer electrolyte membrane fuel cells (PEMFCs), the components supplying fuel cells with reactant gases, such as hydrogen and oxygen. However, the flow fields of fuel cells are limited by the nonuniform poor distribution of reactant gases, unintended pressure drop across channels, and poor water management, among other issues. Thus, relevant designs must focus on obtaining the lowest possible pressure drop while attaining the best possible distribution of reactant gases, further improving cell performance. In this work, the impact of novel bioinspired flow field designs on PEMFC performance was investigated. Three flow field configurations, namely, sunflower-inspired flow field (SUFF), flower of life-inspired flow field (FLFF), and palm frond-inspired flow field (PAFF), were designed, as inspired by the shape of the sunflower (i.e., flower of life and palm frond). Results revealed that the optimal operating conditions for the fuel cell were 1 L/min and 1.1 bar. The bioinspired configurations significantly affected PEMFC performance at a low voltage (< 0.645 V), but the impact was negligible at a high voltage (> 0.645 V). Furthermore, the ohmic loss region and the concentration loss region were both significantly improved by the bioinspired designs. The maximum power density was significantly increased for SUFF, FLFF, PAFF1, and PAFF2 by 16.84%, 6.07%, 6.32%, and 10.40%, respectively. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance and interfacial contact resistance (ICR) 316L stainless steel bipolar plates used in proton exchange membrane fuel cells (PEMFCs), a series of three-layer amorphous carbon films were prepared by magnetron sputtering. The corrosion resistance and ICR of 316 L stainless steels are greatly improved by the Cr, N doped amorphous carbon and multilayer film structure. Ti and CrN were basement layer and transition layer, and amorphous carbon doping with Cr and N was the top layer. Nitrogen atoms, as the variable atoms, were added into the top layer, focusing on the relation between the N content and the film properties. First principles calculations were used to analyze the bond structure by Cr, N doping into amorphous carbon structure and to determine the reasons for the structural changes in the coating after doping the elements. The results revealed that the films are about 1.05 μm thick and without apparent defects. With increasing nitrogen flow rate, Cr–N bonds and C–N bonds appeared in the coating while promoting the graphitization of amorphous carbon. Compared with that of Cr-doped amorphous carbon coated steel, the corrosion current density of Cr, N co-doped amorphous carbon decreased to 8.1 × 10−9 A/cm2 in the +0.6 V (vs. SCE) potentiostatic polarization test, and as the ICR decreased to 1.3 mΩ cm2, the film exhibited outstanding corrosion resistance and conductivity properties. The Cr, N co-doped amorphous carbon/CrN/Ti composite film formed on 316L stainless steel might be appropriate used in PEMFCs. • Cr, N co-doped amorphous carbon - CrN–Ti composite coatings are prepared. • Cr–N bonds and C–N bonds appear in the coating and influence the property. • Nitrogen addition improves coatings corrosion resistance and ICR. [ABSTRACT FROM AUTHOR]

Heat-assisted forming is gaining increasing attention for its potential in improving the formability and quality of metallic bipolar plate (BPP) of proton exchange membrane fuel cell (PEMFC). However, the effects of heat-assisted forming and the subsequent coating process on corrosion resistance and electrical conductivity of stainless steel BPP still remain unclear. This work proposes a way to improve simultaneously the corrosion resistance and electrical conductivity of heat-assisted forming stainless steel BPP by depositing a Cr–C coating directly on its surface without removing the oxide layer using the magnetron sputtering method. Potentiodynamic tests indicate that self-corrosion current density and corrosion current density at 1.0 V (vs. Ag/AgCl) of the Cr–C coated heat-assisted forming SS316L BPP prepared under 900 °C for 10 min are 0.021–0.040 μA cm−2 and 77.54 μA cm−2, respectively, both of which are smaller than those of coated SS316L BPP formed under room temperature. In addition, the contact resistance is close to that of the gold-plated copper plate under the same pressure. The corrosion resistant intermediate oxide layer and conductive network formed between Cr–C coating and metal substrate through defects of oxide layer may be the main reason for improvement of its corrosion resistance and electrical conductivity, respectively. [Display omitted] • A Cr–C coated heat-assisted forming bipolar plate with high performance is proposed. • Self-current densities of 0.022–0.056 μA cm−2 in fuel cell environment is obtained. • The retained intermediate oxide can contribute to a better corrosion resistance. • A lower electrical contact resistance approaching the gold coated copper is achieved. • The conductive network formed is beneficial for electrical conductivity improvement. [ABSTRACT FROM AUTHOR]

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 (BPs) are vital components in Proton Exchange Membrane Fuel Cells (PEMFCs), and their performance and cost significantly impact fuel cell stack efficiency and affordability. BPs require excellent conductivity, strength, and corrosion resistance depending on usage conditions. Common graphite and metal-based BPs offer good conductivity, but they have their drawbacks. Graphite lacks strength and is costly to process, while metal-based BPs need additional surface treatments to prevent corrosion. In recent years, composite bipolar plates have gained widespread attention due to their excellent conductivity, mechanical properties, and outstanding corrosion resistance. In this study, we used natural graphite flakes as the main conductive filler and nano-copper as the secondary conductive filler, with epoxy resin as the binder. The composite bipolar plate was prepared using a hot-pressing method. The study found that adding 1 wt% of nmCu can increase the conductivity of the composite BP by 75.2%, but it decreases the flexural strength by 26.84%. The prepared nmCu/G/EP composite BP exhibits an ASR of only 4.00 mΩ cm2 and a corrosion current density of 2.615 × 10−7 A/cm2, meeting the DOE 2025 expectations. After conducting Cu2+ leaching experiments on the prepared composite BP, single-cell performance testing showed a maximum power density of 0.556 W/cm2. This study expands the range of conductive fillers for composite BPs, no longer limited to carbon-based conductive fillers. • Prepared outstanding EP/G/Nano copper BPs with superior performance through hot-press molding. • The electrical conductivity of the prepared EP/G/Nano copper BPs reached 168.1 S/cm, with a flexural strength of 46.0 MPa. • Adding 1% nano copper raised the composite BPs' electrical conductivity by 75%, yet caused a 30% drop in flexural strength. • The composite BPs with added nano copper, under a pressure of 1.6 MPa, exhibited an ASR of 4.00 mΩ cm2. [ABSTRACT FROM AUTHOR]

Via high-throughput first principle calculations based on density functional theory (DFT), doping elements that can improve the corrosion resistance of stainless steel bipolar plates' passivation layer in PEMFCS working environment were screened. Calculation models were constructed based on the (10 12) facet of Cr2O3and 48 elements were doped and 228 doping structures were considered. According to the doping structure and displacement energy, the doping elements were divided into 4 doping types, so that different adsorption and vacancy schemes were adopted. Then the effects of each doping element on the work function, F adsorption energy and Cr/O vacancy formation energy were calculated. The calculation result shows that C, N, In, and Ru can improve all the corrosion resistance parameters of the stainless steel passivation layer; Au, Rh, Pt, Ir, Co and Ni can also effectively improve the corrosion resistance, but there are problems such as price or harm to the proton membrane; Ag, Cu, Sn, and Ge can inhibit vacancy formation and F adsorption, but reduce the work function; Zn can improve the work function and inhibit F adsorption. In addition, the calculation of the electronic density of states shows that the stable bonding formed between the doping atom and the Cr atoms is an important factor for the improvement of the corrosion resistance parameters. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) as power generators and proton exchange membrane water electrolyzers (PEMWEs) as hydrogen fuel producers play critical roles in implementing hydrogen energy. The bipolar plates (BPPs) in both PEMFC and PEMWE facilitate the distribution of reactants and products, providing electrical connectivity in a series of singular cells. Although both systems are categorized under the same PEM spectrum, the differing reaction mechanisms require specialized plate properties to achieve optimum performance. This short review analyzes the characteristics of BPPs in both PEMFC and PEMWE, with a focus on the plate material, coating, and flow field. This short review concluded that the polymer composite graphite–based BPPs are the most feasible for PEMFC with no coating needed. PEMWE needs SS316 as a BPP material with a conductive coating to withstand the highly corrosive oxygen evolution reaction at the anode. The serpentine flow field showed dominance in PEMFC stack performance due to even fluid distribution and efficient liquid water drainage. However, its high‐pressure drop contributes to greater parasitic power. PEMWEs commonly adopt the parallel flow field for its lower contact resistance and bubble formation for efficient mass transport toward the cathode. [ABSTRACT FROM AUTHOR]

We developed surface treatment method of titanium for proton exchange membrane fuel cell bipolar plate. The surface-treated titanium achieved good corrosion resistance in H2SO4 solution (pH = 3) containing 10 ppm F- at 80°C in a simulated proton exchange membrane fuel cell environment. The average corrosion current density was under 0.1µAcm-2 during potentiostatic polarization testing for 24 h. Further, the contact resistance value was 8.9mΩcm2 at a pressure of 1MPa after corrosion testing, which was very low compared to typical etching samples. [ABSTRACT FROM AUTHOR]

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.

Bipolar plates (BPPs) play an important role in PEM fuel cells in terms of weight and cost points of view. In this paper, the manufacturing of titanium BPPs with parallel flow field was experimentally and numerically studied. In this regard, a stamping die with a parallel pattern is conducted to perform the experiments. Then, the process was modeled via the finite element (FE) simulation. By comparing simulation and experiment results, it was found that the results are in good agreement and hereupon, the accuracy of the FE model was verified. To evaluate the sheet formability, a set of FE experiments was designed through the response surface methodology (RSM). The die clearance, forming velocity, and friction coefficient were considered input parameters, and the maximum thickness reduction (MTR) of the sheet was assumed to be the output. The results revealed that a lower friction coefficient causes an increase in thickness reduction and finally tearing in the formed BPPs. Moreover, changing the forming velocity has no remarkable influence on the MTR. Afterward, an Adaptive Neuro-Fuzzy Inference System (ANFIS) was trained for predicting the output of the MTR with the three mentioned inputs.

The vacuum impregnation resin method was used to prepare composite bipolar plates in fuel cell in this study. The effects of the content of epoxy resin diluent added, temperature and pore structure of graphite on the impregnation content during the vacuum impregnation process were studied. The electrical conductivity, flexural strength and airtightness of the prepared fuel cell bipolar plates were investigated. The results show that increasing the content of diluent and temperature can reduce viscosity and increase the upper limit of resin impregnation, enabling the resin to impregnate and fill into smaller pores, while there are still some pores that cannot be filled and saturated, such as the pores below 0.1 μm are difficult to fully penetrate in the expanded graphite plate, resulting in the resin being unable to completely fill the entire pores of the expanded graphite. The optimal temperature for impregnating the epoxy resin/diluent system by vacuum impregnation is 50 ℃, and the optimal addition ratio of diluent ethylene glycol diglycidyl ether is 15%(mass fraction). The obtained bipolar plate has excellent electrical conductivity of 340.12 S/cm, flexural strength of 41.52 MPa, and helium permeability of 5.4×10-7 cm3·cm-2·s-1.

The mitigation of undesired welding deformation during laser welding of metal bipolar plates (BPs), which are crucial components in proton exchange membrane fuel cells (PEMFCs), represents a significant challenge that has yet to be effectively addressed. The low weight requirements of PEMFC endow the BP with ultra-low thickness and sensitivity to processing technology. This paper introduces a study that reduces the deformation of BPs from 4 to 1 mm by implementing a novel multi-path welding process as an alternative to traditional single path welding. The research primarily investigates the weld seam space (WSS) and seven series of experiments with dissimilar WSS are conducted with the objective of minimizing deformation using specially designed welding fixtures. Following this, the weld seam stiffness and residual stress distribution are analyzed in further detail to elucidate the effects of WSS on welding deformation. Furthermore, a stress distribution indicator is proposed in this study to characterize the stress distribution. The conclusion of this study is that multi-pass welding techniques are highly effective in reducing welding deformation, particularly when the WSS is set to 0.75 mm. In principle, the stiffness of the weld seam and the distribution of residual welding stress jointly determine the welding deformation. [ABSTRACT FROM AUTHOR]

Proton exchange membrane (PEM) electrolyzers are promising devices for hydrogen production from water splitting, but their performance and stability are still limited by various factors. This paper studies the effects of different structures on the performance of PEM electrolyzers, focusing on the working temperature, water conductivity, and the structure of bipolar plate. The results show that higher temperature and lower water conductivity enhance the electrolyzer performance, by increasing the catalyst activity and the proton transport. Moreover, a novel structure using a platinum-coated titanium mesh-based bipolar plate is proposed and tested. This structure improves the performance of the electrolyzer, by optimizing the mass transport, pressure drop, and water management in the electrolyzer. A 23-cell electrolyzer with this structure is developed and demonstrated. The electrolyzer achieves a high performance and stability, with a cell voltage of 1.742 V, a voltage efficiency of 85.0%, and a hydrogen production rate of 1.14 Nm3/h at 0.99 A/cm2. The observed cell voltage for the PEM electrolyzer is consistent with the documented range, typically spanning from 1.55 to 1.90 V at a current density of 0.99 A/cm2. This suggests that our bipolar plate design simplifies PEM electrolyzer manufacture while maintaining comparable performance to existing electrolyzers. [Display omitted] • Performance of PEM electrolyzers affected by different structures. • Higher temperature and lower water conductivity enhance performance. • Platinum-coated titanium mesh as flow field plate improves performance. • 23-cell electrolyzer with novel structure achieves high performance and stability. [ABSTRACT FROM AUTHOR]

The ability to manipulate rheological and electrical properties of colloidal carbon black gels makes them attractive in composites for energy applications such as batteries and fuel cells, where they conduct electricity and prevent sedimentation of 'granular' active components. While it is commonly assumed that granular fillers have a simple additive effect on the composite properties, new phenomena can emerge unexpectedly, with some composites exhibiting a unique rheological bi-stability between high-yield-stress and low-yield-stress states. Here we report such bi-stability in suspensions of non-Brownian graphite and colloidal carbon black in oil, a model system to mimic composite suspensions for energy applications. Steady shear below a critical stress elicits a transition to a persistent mechanically weak and poorly conducting state, which must be 'rejuvenated' using high-stress shear to recover a stronger, high-conductivity state. Our findings highlight the highly tunable nature of binary granular/gel composite suspensions and present new possibilities for optimising mixing and processing conditions for Li-ion battery slurries. [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]

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

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Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

This review summarized the characteristics and preparation technology of metallic BPPs of fuel cells. Metal bipolar plates have many properties required for fuel cells, such as mechanical properties, thermal and electrical conductivity, and versatility. The main shortcoming of metal is its vulnerability to corrosion in the fuel cell operating environment. During this process, the formation of the passivation layer causes an unavoidable increase in the interfacial contact resistance. With an appropriate deposition method, a suitable coating system can effectively deal with this shortcoming. In this review, we summarize the classification and preparation methods of metallic BPPs coatings that are currently being studied by scholars around the world and compare the differences between the different coatings through various types of tests. It also provides relevant experience on performance test methods for fuel cell bipolar plates and the factors affecting performance and test parameters.

In this study, the corrosion behavior and degradation mechanism of Ti–Pt-coated stainless steel bipolar plates were investigated through electrochemical tests and surface analysis in a polymer electrolyte membrane water electrolysis (PEMWE) operating environment. The coated bipolar plate has a corrosion current density of only 1.68 × 10−8 A/cm2, which is an order of magnitude lower than that of the bare SS316L substrate (1.94 × 10−7 A/cm2), indicating that its corrosion resistance is superior to that of bare SS316L substrate. However, in the PEMWE operating environment, the protection efficiency of the coating and the corrosion resistance of the coated bipolar plate decreased. The degradation of the coated bipolar plate can be attributed to electrolyte penetration into the blistering areas of the coating layer with micro voids. Defects in the coating layer occur because of the pressure of oxygen gas generated within the coating layer under high-potential conditions, thereby exposing the substrate to the electrolyte and corrosion.

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.

Unitized regenerative proton exchange membrane fuel cell (URPEMFC) as a self-sufficient hydrogen energy system offers a unique proposition for achieving a net zero emissions future. The system combines the operation of water. Due to the design parameters and operating conditions of URPEMFC, the potential cycling from the mode switching, high temperature, humidified environment and the long exposure of metallic components to hydrogen are the primary factors causing degradation to the system. Consequently, the conventional graphite bipolar plate (BP) suffers heavily under such an environment while giving rise to alternative metallic base materials, such as titanium, stainless steel, and aluminum. Various surface treatment and coating methods are currently under investigation to provide the required corrosion resistance while maintaining feasible manufacturing process and cost. This paper presents an overview into the degradation phenomena of URPEMFC that contributes to the corrosion of BP that is affecting the performance and future commercialization of the system. The operating condition of the system is summarized in terms of fuel cells and water electrolyzers respectively, along with the integration of both operations as a system. Next, the paper outlines the degradation phenomena observed on BP and the behavior of various materials under such conditions. The performances of various base and coating materials have been compiled as have characterization methods that are useful in measuring corrosion resistance. This paper aims to provide a better understanding on the overall degradation of BP in URPEMFC and overview of various material choices to identify the optimal corrosion mitigation solution. [Display omitted] • Breakdown of the URPEMFC operating parameters from the respective operation modes. • System design approaches allowing integration of fuel cell and electrolyzer modes. • Identification of the main degradation mechanism on the BP. • Tabulated data of various base materials and coatings performance. • Discussion of current experimental and modeling methods for corrosion resistance characterization. [ABSTRACT FROM AUTHOR]

This study explores impact of novel parallel S-type flow channels on ammonia decomposition and thermal-electric performance of direct ammonia solid oxide fuel cells (DA-SOFC). Four channel arrangements were numerically studied using single cell models: conventional unbent channels (UC–SOFC) and proposed single S-type channels (SSC–SOFC), double S-type channels (DSC-SOFC), triple S-type channels (TSC-SOFC). Cells with parallel S-type channel configurations outperformed unbent channel. Particularly, TSC-SOFC demonstrated the highest electrical performance, followed by DSC-SOFC, SSC-SOFC, and UC-SOFC, with power density improvements of 33.6%, 28.9%, and 28.9%, respectively, compared to UC-SOFC. Further results show that S-type channels exhibit self-heating effects, namely heat released from electrochemical reactions in the rear supplies ammonia decomposition in the front part of channel, enhancing H 2 concentration and electrochemical reactions. Quantitatively, back-heat supplied to primary ammonia decomposition region increases by 33.3% in TSC-SOFC compared to UC-SOFC. Moreover, higher velocities in S-type channels enhance species diffusion towards rib underside, finally reducing concentration polarization and, improving power density. Besides of electrical performance, recycling waste heat from exhaust gases also improve the temperature uniformity cell, potentially benefiting the stability and lifetime of cell. [Display omitted] • Mathematical modeling of large-scale DA-SOFC single cells. • Cell performance optimization considering in-cell ammonia decomposition. • Promoting in-cell ammonia endothermic decomposition via a novel parallel S-type channel. • Both self-heating feedback and enhanced velocity toward the underside of the ribs are observed in the novel channel. [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. [ABSTRACT FROM AUTHOR]

Stainless steel bipolar plates (BPs) fabricated using innovative additive manufacturing techniques can improve fuel cell performance and reduce costs. A high current density can be obtained using a low‐cost membrane electrode assembly (MEA) with low platinum (Pt) loading at the anode, along with BPs with rectangular micro channels. Three types of BPs of serpentine flow field are designed after varying the width of the rectangular channel. Two types of MEAs are used. First is 0.12 mg cm−2 Pt loading at anode, and the second is 0.50 mg cm−2. Wherein MEA with Pt loading at 0.12 mg cm−2 is used, a high current density is obtained as the channel width decreases. The BP with 300 µm channels has a current density of 1.205 A cm−2, which is higher by 31.4% than that of BP with 500 µm channels and higher by 70.2% than that of the BP with 940 µm channels. However, when the MEA with Pt loading at 0.50 mg cm−2 is applied to the test, the opposite results are obtained: As the channel width becomes narrow, the current density decreases. In the long‐term operation, a similar trend in the current density as that of the short‐term operation is observed. [ABSTRACT FROM AUTHOR]

Fuel 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. [ABSTRACT FROM AUTHOR]

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An excellent corrosion-resistant and good conductivity coating is desired for metal bipolar plate (BP) in proton exchange membrane fuel cell (PEMFC). In this view, a novel strategy to achieve this aim by introducing Al 2 O 3 into CrN film. Al 2 O 3 /CrN nanocomposite coatings are first prepared by co-sputtering. Subsequently, the microstructure, electrochemical corrosion resistance, interfacial contact resistances (ICR) and contact angle are systematically investigated. As a result, Al 2 O 3 /CrN nanocomposite coating shows a low corrosion current density of 0.084 μA/cm2 in room temperature and a low corrosion current density of 0.39 μA/cm2 at 70 °C, which highly meets the requirement of U.S. DOE 2025 targets. Besides, Al 2 O 3 /CrN nanocomposite coating displays a superior durability to pure Au film. It is revealed that Al 2 O 3 can hinder the growth of CrN columnar crystals and result in coating amorphization, which is the mechanism of Al 2 O 3 -promoted the CrN corrosion resistance. Furthermore, Al 2 O 3 /CrN coating also exhibits an excellent electrical conductivity, featuring a smaller ICR of 3.09 mΩ cm2. Inspired by these results, introducing Al 2 O 3 into CrN coatings can provide enlightening insights to design new non-noble-metal coatings for metal BP in future PEMFC manufacturing. Al 2 O 3 can hinder CrN columnar crystals growth and results in a high-performance Al 2 O 3 /CrN nanocomposite coating for metal bipolar plates in PEMFC. [Display omitted] • Al 2 O 3 /CrN coatings are first prepared to protect metal bipolar plates in PEMFCs. • Al 2 O 3 /CrN coated Ti plates shows a low corrosion current density of 0.084 μA/cm2. • The ICR value of Al 2 O 3 /CrN coated Ti plates is 3.09 mΩ cm2 under 150 N/cm2. • Al 2 O 3 /CrN coating shows a more excellent durability than pure Au film. • Al 2 O 3 incorporation can hinder the columnar crystals growth of CrN. [ABSTRACT FROM AUTHOR]

Direct ammonia SOFCs (DA-SOFCs) are numerical studied to investigate the effects of bipolar plate flow channel configuration on thermal-electric performance. This study establishes a planar DA-SOFC model and investigates triangular, quadrangular, and oval flow channel configurations' impact using numerical simulations. Results reveal oval cross-section channels outperform trapezoidal and triangular ones, achieving power density increases of 15.6%, 16.1%, and 18.6%, respectively, compared to rectangular channels at 0.6V. The oval channel displays superior velocity and vorticity, enhancing mass transfer between the main flow and reaction zone. Increasing channel width reduces rib width, promoting O 2 distribution, temperature improvement via exothermic reactions, NH 3 decomposition into H 2 , and improved cell performance. Rib width increase shortens diffusion and reduces concentration polarization, but increases ion transport and ohmic polarization. A theoretical formula for optimal rib width (W rib0) to minimize polarization loss is provided. These findings offer a comprehensive reference for optimizing DA-SOFC design. [Display omitted] • Strategy for flow channel shape and size optimization in DA-SOFCs is presented. • Theoretical formula to determine rib width for the minimum polarization is derived. • Effects of channel cross-sectional on DA-SOFC is comprehensively investigated. [ABSTRACT FROM AUTHOR]

A suitable channel structure can lead to efficient gas distribution and significantly improve the power density of fuel cells. In this study, the influence of two channel design parameters is investigated, namely, the ratio of the channel width to the bipolar plate ridge width (i.e., the channel ridge ratio) and the channel depth. The impact of these parameters is evaluated with respect to the flow pattern, the gas composition distribution, the temperature field and the fuel cell output capability. The results show that a decrease in the channel ridge ratio and an increase in the channel depth can effectively make the distributions of velocity, temperature and concentration more uniform in each channel and improve the output capability of the fuel cell. An increase in the channel ridge ratio and depth obviously reduces the flow resistance and improves the flow characteristics. [ABSTRACT FROM AUTHOR]

The composite materials based on a thermosetting binder mark SFP and thermally expanded graphite and containing 50–70% of the filler are prepared by the method of hot pressing. It is studied how the physicochemical and mechanical characteristics of the composite depend on the method of filler introduction. The materials prepared by mixing air-dry components are shown to exhibit the high conductivity (up to 195 S/cm) and strength (above 25 mPa), the low interface contact resistance (less than 10 mΩ cm2), and the corrosion current not exceeding 1 µA/cm2, which allows the high efficiency of energy conversion in SPFC to be reached. [ABSTRACT FROM AUTHOR]

This study investigates the influence of surface roughness on the performance of polymer electrolyte membrane fuel cells (PEMFCs) through computational simulations using COMSOL Multiphysics. Two distinct gas flow channel (GFC) models of serpentine and parallel GFC structures were analysed, featuring various surface roughness levels to examine their impact on gas pressure and velocity dynamics. Rough surfaces are modeled using trigonometric functions to replicate machining-induced variations. Finite element simulations were conducted, assessing the time-dependent relationship between gas pressure and velocity while considering different electrode phase potentials as a function of surface roughness. Rough surfaces generally enhance mass transport, water management, and current distribution compared to smooth surfaces. The results indicated that a surface roughness of approximately 1 µm optimizes PEMFC performance by balancing pressure and velocity, enhancing electrochemical reactions, and reducing excessive pressure drops within the cell. Notably, the 0.7 V operating voltage was found to be the most efficient, achieving rapid stabilization of pressure and velocity levels swiftly. The findings underscore the importance of precise control over GFC roughness to enhance PEMFC performance gains in commercial applications, especially when multiple cells are stacked to achieve high power outputs.

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

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, three carbon-based coating variants were deposited onto stainless steel substrates, and the process pressure during the carbon layer deposition was varied. We conducted Raman spectroscopy, transmission electron microscopy, interfacial contact resistance measurements, and potentiodynamic polarization tests to examine the effect of the process pressure on the properties of the coatings. The structural characterization revealed that all specimens exhibit a highly sp2-bonded structure. However, some structural differences could also be identified. In the TEM cross-section images of the carbon layer variants, these structural differences could be observed. The carbon layer deposited at 0.98 Pa has some distortions in the mainly perpendicular graphitic structure, which agrees with the Raman results. Almost completely vertically oriented graphitic layers exhibit the 0.1 Pa coating variant with a d-spacing similar to pure graphite. Regarding the contact resistance, the process pressure has only minor influence. All coatings variants have very low resistance values below 3 m Ω cm2, even at a compaction force of 50 N cm−2, which can be attributed to the graphite-like structure. The polarization tests show that the corrosion resistance increases with increasing process pressure. The best coating variant has a corrosion current density of approximately 10 − 8 A cm−2 and almost 10 − 6 A cm−2 at room temperature and 80 ° C, respectively. [ABSTRACT FROM AUTHOR]

The demand for polymer composite solutions in bipolar plates for polymer electrolyte membrane fuel cells (PEMFCs) has risen due to advantages over metal plates such as longer lifetime, weight reduction, corrosion resistance, flexible manufacturing, freedom of design, and cost-effectiveness. The challenge with polymer composites is achieving both sufficient electrical conductivity and mechanical stability with high filler content. A carbon fiber fleece as reinforcement in a graphite-filled polypropylene (PP) matrix was investigated for use as bipolar plate material with increased mechanical and sufficient conductive properties. Plates with a thickness of 1 mm containing four layers of fleece impregnated in the PP-graphite compound were produced in a compression molding process. Particle and fiber interactions were investigated via microscopy. The plates were characterized with respect to the electrical conductivity and mechanical stability. High electric conductivity was reached for fiber-reinforced and plain PP-graphite compound plates, with increased filler content leading to a higher conductivity. The contact resistance remained largely unaffected by surface etching as no polymeric skin layer formed during compression molding. Fiber-reinforced plates exhibit twice the tensile strength, a significantly higher tensile modulus, and an increased elongation at break, compared to PP filled only with graphite. [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]

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]