Search

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]

Bipolar plates are one of the most important components of proton exchange membrane fuel cells. With the miniaturization of bipolar plate flow channel sizes and the increasing demand for precision, springback has become a key focus of research in the bipolar plate forming process. In this paper, the hydroforming process for 316L stainless steel bipolar plates was studied, and an FEM model was built to examine the stress and strain at various locations on the longitudinal section of the plate. Modeling accuracy was validated by the comparison of experimental profile and thickness distribution. The effects of forming pressure and grain size on springback behavior are discussed. The results show that with increasing forming pressure, the springback value decreases initially, followed by an increase, but then again decreases. When the forming pressure is 80 MPa–100 MPa, the deformation of the lower element of the upper rounded corner is not uniform with more elastic regions, and the springback is positively correlated with forming pressure. The springback distribution pattern on the cross-section of the bipolar plate changes from a normal distribution to a distribution of "M" shape with increased pressure. The larger the grain size, the lower the yield strength elastic proportion, resulting in a decrease in springback of the sheet. The maximum amount of springback of the bipolar plate is 3.1 μm when the grain size is 60.7 μm. The research results provide a reference for improving the forming quality of metal bipolar plates with different flow channel shapes. [ABSTRACT FROM AUTHOR]

With the rapid development of renewable energy, redox flow battery, as a renewable energy storage system with high capacity, good flexibility, strong scalability and long cycle life, has attracted much attention in the industry. The bipolar plate, as an important part of redox flow battery stack, plays the role of supporting electrode, conducting current, connecting battery, supporting stack and separating positive and negative electrolyte. Due to the harsh working environment, the bipolar plate should have the characteristics of high electrical conductivity, good mechanical properties, good corrosion resistance, low permeability and chemical stability. Therefore, the current development of low-cost high-performance bipolar plates has become one of the key elements of the development of flow batteries. This paper focuses on the recent development status of carbon composite bipolar plates in redox flow batteries since 2010, including the influence of different flow field designs, different carbon-based materials and polymer materials on the conductivity, mechanical properties, permeability resistance, corrosion resistance and single battery performance. Finally, based on the current development requirements and key technical bottlenecks of carbon based composite bipolar plates, a brief analysis and outlook are made. [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]

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]

The channels of the graphite-based bipolar plate for hydrogen fuel cells were mainly manufactured through milling due to low forming elongation and processability. However, during the milling process, the machining precision is low due to tool wear and vibration, and there is a risk of breakage. Non-traditional laser processing can solve the problems of tool wear and vibration through non-contact processing. In this study, the interaction characteristics of the nanosecond pulsed laser and CNT composites were observed, and channels and bipolar plates were manufactured. The effect of scanning speed and pulse duration was observed for interaction characteristics. Defects were observed due to high thermal effects at low scanning speed and high pulse duration. Channels were created depending on parallel pitch distance [ΔS] and Number of Scans (NOS). The channel was evaluated for depth, top width, bottom width, channel angle, material removal rate, and surface roughness, and significant changes were observed depending on ΔS. The chemical composition, surface resistance, and contact angle of the laser-processed channel were measured. The laser processed channel was oxidized, and the surface resistance and contact angle increased. Finally, the manufacturability of the CNT composites bipolar plate using laser was examined.

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 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]

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.

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.

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.

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]

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.)

Copyright of Automobile Technology & Material is the property of Automobile Technology & Material 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.)

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]

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.)

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.

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]

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.

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.

The working temperature affects the performance of PEMFC, so a reasonable and efficient cooling channel is necessary to control the working temperature in an efficient area. In this study, the channel structure of the bipolar plate for PEMFC is analyzed using the FLUENT simulation calculation method. The influence of cell size and cooling water flow direction on cell temperature distribution is analyzed, including an examination of the channel ridge width, depth, and aspect ratio of the bipolar plate. After comparing and analyzing three ridge width sizes (0.5 mm, 1.5 mm and 2 mm) in the paper, it was found that a ridge width of 2 mm had the best heat transfer performance. And it was found that a groove depth of 0.5 mm had the best heat transfer performance when comparing three groove depth dimensions (0.5 mm, 1 mm and 1.5 mm). The aspect ratio size parameters had almost no effect on the maximum and average temperatures of the electric stacks, while the relative flow direction of cooling water had a great influence on the temperature distribution of the bipolar plate. [ABSTRACT FROM AUTHOR]

Composite bipolar plates (BPs) hinder their application in proton exchange membrane fuel cells (PEMFC) because of their poor conductivity and mechanical properties. Nanofillers can effectively solve this problem but often have a limited effect due to their easy agglomeration. In this work, a continuous mesh carboxylated multi-walled carbon nanotube (MWCNT) coating on the surface of graphite was synthesized by chemical vapor deposition (CVD) and carboxylation modification, and the composite BPs were prepared by molding using prepared reticulated carboxylated MWCNTs, expanded graphite, and resin. By optimizing the carboxylation treatment time and the content of the nano-filler, the composite BPs had the best performance at a 15 min carboxylation treatment time and 2.4% filler content. The planar conductivity reached up to 243.52 S/cm, while the flexural strength increased to 61.9 MPa. The thermal conductivity and hydrophobicity were improved compared with the conventional graphite/resin composite BPs, and good corrosion resistance has been demonstrated under the PEMFC operating environment. This work provides a novel nanofiller modification paradigm for PBs. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of coated stainless steel as bipolar plate material in PEM fuel cell applications and its improvement through the surface modifications was investigated. A commercial SS316L stainless steel grade was deposited with thin multi-layer coatings, consisting of a carbon top layer and a chromium interlayer of two different thicknesses. Interfacial contact resistance measurements revealed that the applied Cr/C coatings are highly conductive and surpass the ICR criteria, suggested by the U.S. Department of Energy. Corrosion resistance was thoroughly analysed by potentiodynamic polarisation and cyclic voltammetry in 0.5 M H 2 SO 4 at room temperature and 80 °C, respectively, combined with numerical modelling. Electrochemical results agree well with numerical modelling, including the dissolution of metallic species, local pH-shifts and changes of electrolyte conductivity. Furthermore, the study shows that the application of a Cr/C coating significantly reduces the current density in the passive region during potentiodynamic polarisation and lowering the corrosion rate of the steel substrate by at least a factor of two. [ABSTRACT FROM AUTHOR]

The air-cooled proton exchange membrane fuel cell is widely used in unmanned aerial vehicle since its small size and high efficiency. The bipolar plate structure is an important factor affecting the performance of fuel cells. This article conducts experimental research on the impact of different channel structures on performance based on the annular bipolar plate designed by the team. A single air-cooled fuel cell with 50cm2 is used in the experiment to investigate the dynamic response under different current loading rates of 0–40 A. The test results show that the hydrogen and oxygen in different flow directions have a significant impact on the performance of the fuel cell, with a performance improvement of 8.1% by the hydrogen and oxygen in vertical and staggered flow directions for the enhancement of heat and mass transfer ability, and a decrease of about 3.5° compared with the hot spot temperature. In addition, this study further demonstrated the applicability of the annular bipolar plate structure, and verified the impact of different channels on cathode side and ridge shaped structure on performance, wind speed, temperature distribution, stability and mass power density, of which the performance of the fan channel/linear ridge is the best, which is about 8.5% higher than the output power of the worst fan channel/fan back. These test results provide basic data and technical support for the system design and application of air-cooled fuel cell of open cathode.

Fuel cell, which directly enables the generation of electricity from the conversion of the fuel through an electrochemical reaction at the electrode and electrolyte interface, without going through the heat engine process, is an incredibly powerful renewable energy technology. The electrochemical reaction in fuel cell is not restricted by the Carnot cycle, so it has high energy conversion efficiency. Proton exchange membrane fuel cell (PEMFC), in particular, has been regarded as the most promising candidate for transportations, portable equipment and fixed devices.However, there are still some problems in PEMFC, including high cost, insufficient power and poor stability, which limit the large-scale commercial application of PEMFC. The basic reason behind these problems lies in the key materials, such as cathode catalyst, gas diffusion layer, proton exchange membrane and bipolar plate in fuel cell, which can not meet the requirements of PEMFC commercialization owing to their high cost and low performance. Therefore, in order to achieve large-scale application of PEMFC, advanced cathode catalysts, gas diffusion layers, proton exchange membranes and bipolar plates are needed. For the requirement of low-cost and high-performance advanced materials for PEMFC, the research status of these key materials and main challenges in their practical application were summarized in the review, and the future development direction was pointed out: developing the technology of large-scale preparation of platinum alloy and metal-nitrogen-carbon (M-N-C) compound catalysts, preparation of proton exchange membranes with high proton conductivity and excellent mechanical property, studying the influence of modified gas diffusion layer on PEMFC performance under different working conditions, developing coatings or new metal materials with excellent corrosion resistance and electrical conductivity for bipolar plates.

Proton exchange membrane fuel cells (PEMFCs) (as they operate below 100 °C) must be heated when operating. The heating must be controlled not to damage the fuel cell. On the other hand, pressure from the plates and connections can cause stress and displacement. This study aimed to examine cooling, stress, and displacement from a bipolar plate under different ambient conditions (natural and forced cooling). To minimize temperature, stress, and displacement, multi-objective optimization is carried out under different conditions and the best thickness and number of plates are determined. Findings suggest as the number and thickness of bipolar plates increase, their temperature decreases. Also, using forced cooling, the temperature can reduce to more than 30 K. Moreover, optimization results can include the best temperature, minimum stress, and displacement to increase the life of the bipolar plate. Findings also suggested that natural cooling can be used to significantly increase the temperature of the bipolar plate in less time, which, however, may produce hazards to the system.

The performance of a polymer electrolyte membrane fuel cell (PEMFC) closely depends on internal reactant diffusion and liquid water removal. As one of the key components of PEMFCs, bipolar plates (BPs) provide paths for reactant diffusion and product transport. Therefore, to achieve high fuel cell performance, one key issue is designing BPs with a reasonable flow field. This paper provides a comprehensive review of various modifications of the conventional parallel flow field, interdigitated flow field, and serpentine flow field to improve fuel cells' overall performance. The main focuses for modifications of conventional flow fields are flow field shape, length, aspect ratio, baffle, trap, auxiliary inlet, and channels, as well as channel numbers. These modifications can partly enhance reactant diffusion and product transport while maintaining an acceptable flow pressure drop. This review also covers the detailed structural description of the newly developed flow fields, including the 3D flow field, metal flow field, and bionic flow field. Moreover, the effects of these flow field designs on the internal physical quantity transport and distribution, as well as the fuel cells' overall performance, are investigated. This review describes state-of-the-art flow field design, identifies the key research gaps, and provides references and guidance for the design of high-performance flow fields for PEMFCs in the future. [ABSTRACT FROM AUTHOR]

CrCx coatings (where x = 5 ~ 35 sccm is the acetylene flux) were deposited on stainless steel 316L substrates using radio frequency unbalanced magnetron sputtering. The CrC35 coating showed the highest C-sp2 content and H/E ratio of all the coatings, and thus exhibited the lowest friction coefficient and wear rate. However, the CrC25 coating showed the best anti-corrosion performance in 0.5 M H2SO4 solution due to its low surface roughness and small cluster size. The electrochemical properties of the CrC25 coating were investigated in a simulated Proton Exchange Membrane Fuel Cell (PEMFC) environment with hydrogen and oxygen purging. The coating showed a low corrosion current density in both the anode and the cathode environments. Finally, the CrC35 coating showed the lowest interfacial contact resistance (ICR) of the various coatings under a compaction force of 140 Ncm−2 due to its high C-sp2 content. [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.

The weight reduction of the bipolar plate (BP) is essential for commercializing unitized regenerative fuel cells (URFCs). In order to lighten the weight of the bipolar plate, we have used Pb/C composite powder as a cost-effective primary material, which is a mixture of low-density graphite and lead. Further, varied lead-carbon weight ratios (1: 8, 1:4, 1:1, 4:1, and 8:1) were investigated for fabricating the bipolar plate by hot-pressing process adding styrene-butadiene rubber (SBR) as a binder. The specific surface area, porosity, and microstructure characteristics corresponding to the varied lead-graphite ratio of the prepared bipolar plates were studied. The relative difference in conductivity upon the compressibility of the plates is also examined. Finally, the wettability and electrochemical properties of the prepared bipolar plates were evaluated through water contact angle and cyclic voltammetry analysis.

In order to obtain films with high corrosion resistance and excellent interfacial contact resistance (ICR) on 316L stainless steel used for bipolar plates in proton-exchange membrane fuel cells (PEMFCs), Cr, Ti co-doped amorphous carbon films were prepared on 316L stainless steel. The preparation method for the coating was magnetron sputtering. The doping amount of the Ti element was controlled by a Cr target and a Ti target current. The change in the structure and properties of the coating after the change from Cr single-element doping to Cr and Ti co-doping was studied. The change rule of the structure and properties of the coating from Cr single-element doping to Cr and Ti co-doping was studied. An increase in the Ti content led to a decreased grain boundary, a flatter surface, and a higher sp2-hybridized carbon content. TiC and CrC nanocrystals were formed in the amorphous carbon structure together. The amorphous carbon films doped with Cr and Ti simultaneously achieved a low ICR and high corrosion resistance compared with single-Cr-doped amorphous carbon. The enhanced corrosion resistance was attributed to the decreasing grain boundary, the formation of the TiC crystal structure, and the smaller grain size. The best performance was obtained at a Ti target current of 2A. Compared with bare 316L stainless steel, the corrosion resistance of Cr, Ti co-doped amorphous carbon (Icorr = 5.7 × 10−8 A/cm2, Ti-2 sample) was greatly improved. Because Ti doping increased the content of sp2-hybridized carbon in the coating, the contact resistance of the coating decreased. Moreover, the interfacial contact resistance was 3.1 mΩ·cm2 in the Ti-2 sample, much lower than that of bare 316L stainless steel. After the potentiostatic polarization test, the coating still had excellent conductivity. [ABSTRACT FROM AUTHOR]

Cost reduction in bipolar plates in proton exchange membrane water electrolyzers has previously been attempted by substituting bulk titanium with austenitic stainless steels protected with highly conductive and corrosion-resistant coatings. However, austenitic steels are more expensive than ferritic steels due to their high nickel content. Herein we report on the corrosion resistance of two high chromium ferritic stainless steels, AISI 442 and AISI 446, as an alternative material to manufacture bipolar plates. Electrochemical corrosion tests have shown that AISI 442 and AISI 446 have similar corrosion resistance, while AISI 446 reveals more noble corrosion potential and performs better during potentiostatic stress tests. The current density obtained during polarization at 2 V versus the standard hydrogen electrode (SHE) is 3.3 mA cm−2, which is more than two times lower than on AISI 442. Additionally, surface morphology characterization demonstrates that in contrast to AISI 442, AISI 446 is not sensitive to intercrystalline or pitting corrosion. Moreover, EDX energy dispersion analysis of AISI 446 reveals no differences in the chemical composition of the surface layer compared to the base material, as a confirmation of its high corrosion resistance. The results of this work open up the perspective of replacing austenitic stainless steels with less expensive ferritic stainless steels for the production of components such as bipolar plates in proton exchange membrane water electrolyzers. [ABSTRACT FROM AUTHOR]

We study the role of filler concentration and microphysics on the rheology of polydisperse flake-graphite particles suspended in Newtonian mineral oil. Under steady shear, our samples exhibit shear thinning, and yielding behavior is observed for volume fractions ϕ > --> 0.18. Time-temperature superposition was observed using an Arrhenius-type horizontal shift factor, giving a flow activation energy that is dependent on the graphite volume fraction, suggesting concentration-dependent contributions to relaxation processes in the suspensions. The flow curves are fitted by a constraint-based model, indicating that the flow behavior is controlled by frictional and adhesive contacts, with the model suggesting that the adhesive stress is temperature dependent. [ABSTRACT FROM AUTHOR]

Bipolar plate is one of the key components of proton exchange membrane fuel cell. It can smoothly transport fuel to catalyst layer and discharge water generated inside the fuel cell. At the same time, bipolar plate also plays a supporting role. In view of the importance of bipolar plates, this paper mainly studies the cathode variable cross-section flow channel. Through the research, it was found that under humidity of 100%, the performance of flow field structure calculation model of case 4 was best, and case 4 was improved by 7.3% compared with traditional bipolar plate, which indicates that the design of the flow channel can improve fuel cell performance. Further analysis found that variable cross-section flow field structure designed can better improve pressure drop, and the distribution of water and gas is more uniform, which ultimately makes current density more uniform. [ABSTRACT FROM AUTHOR]

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]

• Nonprecious metal-filled Pt-based coatings were prepared by magnetron sputtering. • Conductivity is influenced by coating morphology and oxidation state of Pt. • Ta as Filler Metal Exhibits Superior Corrosion Resistance and Conductivity. • The incorporation of filler metals significantly reduced the coating cost. In proton exchange membrane water electrolyzer (PEMWE), coatings based on Pt demonstrate outstanding performance; however, their elevated cost restricts broader utilization. The application of nonprecious metal coatings frequently compromises either conductivity or corrosion resistance. In this investigation, a range of nonprecious metal-filled Pt-based coatings was fabricated on TA1 through magnetron sputtering. The application of thinner coatings and filler materials led to a significant reduction in Pt usage to 0.051 mg cm−2. The conductive Pt surface, along with the wire-like Pt structure integrated within the coating, contributes to remarkable electronic transmission capabilities. The dense and stable oxides generated by the filler metals ensure excellent corrosion resistance. Following a 48-h durability assessment, the application of the coating decreased the interfacial contact resistance of the Ti plate from 90.5 mΩ cm2 to 2.48 mΩ cm2, while the dissolution of Ti ions in the corrosive solution reduced from 13.45 ppb to 0.53 ppb. This effective nonprecious metal-filled Pt-based coating presents a novel strategy for minimizing the cost associated with PEMWE bipolar plates. [ABSTRACT FROM AUTHOR]

An anti-corrosive and conductive NbTaMoW medium entropy alloy (MEA) coating was deposited on 304 stainless steel using a dual-cathode glow discharge technology. This MEA coating exhibits a single body-centered cubic phase with about 10 nm grains, and forms a passivation film with significantly enhanced corrosion resistance at any given HF concentration. The lower adsorption energy of Nb atoms for oxygen atoms leads to the enrichment of Nb oxides in the passivation film, which is beneficial for hindering the rapid diffusion of F− ions. These findings underscore the potential of NbTaMoW MEA coatings to improve the durability and efficiency of PEMFCs. [Display omitted] • The MEA coating consists of a single BCC phase and exhibits nanoscale grain size. • The i corr values of MEA coating are two orders of magnitude lower than that of 304 SS. • MEA coating exhibits enhanced corrosion resistance in HF containing environments. • The strong adsorption between Nb and O leads to the enrichment of Nb oxide in the passivation film. • The heterojunction interface containing Nb 2 O 5 effectively hinders the diffusion of F−. [ABSTRACT FROM AUTHOR]

Nitrogen ions were implanted into the coated Nb layer by plasma immersion ion implantation to improve resistance to corrosion of a metal bipolar plate. Due to nitrogen implantation, the corrosion behavior of the Nb layer was enhanced. The electron microscope observation reveals that the microstructure of the Nb layer became denser and had fewer defects with increasing implantation energy. As a result, the densified structure effectively prevented direct contact with the corrosive electrolyte. In addition, at a higher implantation rate (6.40 × 1017 N2/cm2), a thin amorphous layer was formed on the surface, and the implanted nitrogen ions reacted at neighboring Nb sites, resulting in the localized formation of nitrides. Such phase and structural changes contributed to further improve corrosion resistance. In particular, the implanted Nb layer at bias voltage of 10 kV exhibited a current density more than one order of magnitude smaller with a two times faster stabilization than the as-deposited Nb layer under the PEMFC operating conditions. [ABSTRACT FROM AUTHOR]

Aluminum AA5052 is an inexpensive and lightweight metal that has been used in a variety of applications, including the Bipolar Plate in Proton Exchange Membrane Fuel Cells (BPs PEMFC). The alloy has good electrical conductivity and low corrosion. Corrosion rate (CR) increases during PEMFC operation with increasing temperature. Inorganic dyes, such as chromate, are commonly used to reduce metal corrosion. Unfortunately, they are toxic and have a negative impact on the environment. Chitosan, which is a green, cheap, non-toxic, and environmentally friendly organic solvent, can be used to solve this problem. Electrophoretic Deposition (EPD) technique was used to coated the surface of AA5052 with chitosan. CR was measured using electrochemical and weight loss methods (in 0.5 M H2SO4). The best research results are as follows. The lowest CR values were obtained at the EPD time of 20 min at a chitosan concentration of 0.5% wt. The results of the study using the weight loss method indicated that after soaking for 72 h, the chitosan inhibitor can reduce the corrosion rate (CR) with an inhibitor efficiency of 87.89%, while the electrochemical method obtained a higher efficiency of 95.12%. An increase in temperature will result in a decrease in the efficiency of the inhibitor. Testing with SEM-EDX, after being coated with chitosan inhibitor, the metal surface looks smoother and the Al composition is reduced and it is detected that there is adsorption of O, N and S elements that coated the metal to form insoluble complex compounds, so the corrosion rate decreases. [ABSTRACT FROM AUTHOR]

For the high performance of a fuel cell where a bipolar plate (BP) is applied, rectangular channel, microchannel width, micro-rib, enough channel quantity, adequate channel depth, and innovative flow field design should be realized from a configuration standpoint. In this study, a stainless-steel BP with a microchannel flow field is fabricated with a powder bed fusion (PBF) 3D printer to improve fuel cell performance. A BP with a triple serpentine flow field, rectangular channel, 300 μm channel width, 300 μm rib, and 500 μm channel depth is designed. The print is completed perfectly until the flow field. The bending phenomenon due to thermal deformation does not occur in the BP fabricated by designing the thickness at 2 mm. Performance tests are conducted using fabricated stainless-steel BPs. The current density value is 1.2052 A/cm2 at 0.6 V. This value is higher by 52.8% than the BP with 940 μm channels (rectangle, 940 μm ribs, and 500 μm channel depth). In addition, the value is higher by 24.9% than a graphite BP with 940 μm channels (rectangle, 940 μm ribs, and 1000 μm channel depth). The current density values are measured at 0.6 V for 260 h. [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., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Muhammad Ahmed reports financial support, article publishing charges, equipment, drugs, or supplies, and writing assistance were provided by the Student’s Innovation Center at the College of Energy Engineering, 10.13039/501100004835Zhejiang University, Zhejiang, China and Jianbing Leading Goose Project (Grant Number: 2023C01239) in Zhejiang Province, China. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Ltd.)

Proton exchange membrane water electrolyzer (PEMWE) represents a promising technology for the sustainable production of hydrogen, which is capable of efficiently coupling to intermittent electricity from renewable energy sources (e.g., solar and wind). The technology with compact stack structure has many notable advantages, including large current density, high hydrogen purity, and great conversion efficiency. However, the use of expensive electrocatalysts and construction materials leads to high hydrogen production costs and limited application. In this review, recent advances made in key materials of PEMWE are summarized. First, we present a brief overview about the basic principles, thermodynamics, and reaction kinetics of PEMWE. We then describe the cell components of PEMWE and their respective functions, as well as discuss the research status of key materials such as membrane, electrocatalysts, membrane electrode assemblies, gas diffusion layer, and bipolar plate. We also attempt to clarify the degradation mechanisms of PEMWE under a real operating environment, including catalyst degradation, membrane degradation, bipolar plate degradation, and gas diffusion layer degradation. We finally propose several future directions for developing PEMWE through devoting more efforts to the key materials.

Films for bipolar plates deposited from PVD are always restricted by narrow parameters’ widow, which restrict the robust quality of high conductivity and anticorrosion due to the fluctuation of deposition plasma naturally. In this study, CrN films with high conductivity and strong corrosion resistance was deposited on Ti plates by high power impulse magnetron sputtering in wider Ar/N2 ratios. The results show that the CrN film prepared by this method effectively inhibits the columnar structure and forms a dense structure of amorphous wrapped nano Cr2N clusters, providing good protection for Ti plate. Meanwhile, First-principal calculations shown Cr2N has stronger metallicity than CrN, resulting in lower ICR. This work has opened up a new way for the large-scale preparation of metal bipolar plate films.

The working temperature affects the performance of PEMFC, so a reasonable and efficient cooling channel is necessary to control the working temperature in an efficient area. In this study, the channel structure of the bipolar plate for PEMFC is analyzed using the FLUENT simulation calculation method. The influence of cell size and cooling water flow direction on cell temperature distribution is analyzed, including an examination of the channel ridge width, depth, and aspect ratio of the bipolar plate. After comparing and analyzing three ridge width sizes (0.5 mm, 1.5 mm and 2 mm) in the paper, it was found that a ridge width of 2 mm had the best heat transfer performance. And it was found that a groove depth of 0.5 mm had the best heat transfer performance when comparing three groove depth dimensions (0.5 mm, 1 mm and 1.5 mm). The aspect ratio size parameters had almost no effect on the maximum and average temperatures of the electric stacks, while the relative flow direction of cooling water had a great influence on the temperature distribution of the bipolar plate.

Composite bipolar plates (BPs) hinder their application in proton exchange membrane fuel cells (PEMFC) because of their poor conductivity and mechanical properties. Nanofillers can effectively solve this problem but often have a limited effect due to their easy agglomeration. In this work, a continuous mesh carboxylated multi-walled carbon nanotube (MWCNT) coating on the surface of graphite was synthesized by chemical vapor deposition (CVD) and carboxylation modification, and the composite BPs were prepared by molding using prepared reticulated carboxylated MWCNTs, expanded graphite, and resin. By optimizing the carboxylation treatment time and the content of the nano-filler, the composite BPs had the best performance at a 15 min carboxylation treatment time and 2.4% filler content. The planar conductivity reached up to 243.52 S/cm, while the flexural strength increased to 61.9 MPa. The thermal conductivity and hydrophobicity were improved compared with the conventional graphite/resin composite BPs, and good corrosion resistance has been demonstrated under the PEMFC operating environment. This work provides a novel nanofiller modification paradigm for PBs.