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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Graphite nanoplatelets (GNPs) have been used as a secondary filler to improve the electrical conductivity of poly(phenylene sulfide) (PPS)/graphite composites for use as bipolar plates in fuel cells, and the effects of adding small quantities of GNPs on the electrical, thermal, and mechanical properties of PPS/GNP/graphite composites have been extensively studied. The GNPs were compounded with PPS to produce master batch (MB) chips that were further ground to fine MB powder (MBg). PPS/MBg/graphite powders were compressed to fabricate 10-mm thick square samples. Composites containing a large quantity of graphite (~80 wt%) were then tested for use as a bipolar plate in phosphoric acid fuel cells. When 5 wt% GNP was added to the PPS/graphite composite, the in-plane electrical conductivity increased almost twofold from 643 to 1340 S·cm−1, the through-plane electrical conductivity increased from 19 to 54 S·cm−1, the through-plane thermal conductivity increased approximately two-fold from 60 to 129 W·(mK)−1, and the flexural strength decreased slightly from 32 to 26 MPa. The fractured surface of the compressed MBg sample revealed well-dispersed GNPs in the PPS matrix, which created electrical pathways and improved the electrical conductivity of the non-conducting PPS matrix material. Thus, the PPS/GNP/graphite composite is a promising system for bipolar plate applications because a higher amount of graphite (~93 wt%) is needed in PPS/graphite composites to reach the same level of electrical conductivity as the PPS/MBg(5 wt%)/graphite (75 wt%) composite, and such a large quantity of graphite is difficult to process and leads to weaker mechanical properties. [ABSTRACT FROM AUTHOR]

Herein, we report a novel method for the fabrication of highly conductive fluorinated ethylene-propylene (FEP)/graphite nanocomposites for high-temperature bipolar plates (BPs) by incorporating the well-dispersed single-walled carbon nanotube (SWCNT) as a secondary filler in the FEP matrix. The SWCNTs were pre-dispersed with FEP powder by sonication in ethanol and subsequently mixed with graphite powder by ball milling. The composite BPs were prepared from the mixed powder by compression molding. The resulting FEP/graphite/SWCNT nanocomposite containing 80 wt% graphite (500 µm particles) and 0.1 wt% SWCNT exhibited high electrical conductivity (210 S cm−1) superior to that of the composite devoid of SWCNTs (120 S cm−1) by modulating the electrical transportation pathways between graphite particles through the SWCNTs. A small amount of the incorporated SWCNTs (0.1 wt%) also improved chemical inertness to phosphoric acid. Hence, the prepared FEP/graphite nanocomposites with SWCNTs as a secondary filler exhibited a robust performance for application as high-temperature BPs for phosphoric acid fuel cells. [ABSTRACT FROM AUTHOR]

Bipolar plates (BPs) are a major component of polymer electrolyte membrane fuel cells (PEMFCs). BPs play a multifunctional character within a PEMFC stack. It is one of the most costly and critical part of the fuel cell, and hence the development of efficient and cost-effective BPs is of much interest for the fabrication of next-generation PEMFCs in future. Owing to high electrical conductivity and chemical inertness, graphene is an ideal candidate to be utilized in BPs. This paper reviews recent advances in the area of graphene-based BPs for PEMFC applications. Various aspects including the momentous functions of BPs in the PEMFC, favorable features of graphene-based BPs, performance evaluation of various reported BPs with their advantages and disadvantages, challenges at commercial level products and future prospects of frontier research in this direction are extensively documented. [ABSTRACT FROM AUTHOR]

Cost reduction for fuel cell stainless steel bipolar plate (BPP)'s Au-coating requires in depth understanding of its corrosion behavior. To this end, this paper explores the degradation of the tensile properties of an Au-coated 316L stainless steel bipolar plate in a real fuel cell stack. 4 BPPs were randomly chosen and removed from a stack that had run for 1600 h and, along with 2 pristine BPPs, were subsequently tested for surface morphology and tensile properties. Results suggest that (1) Pristine BPPs have initial pinhole flaws on the surface, whereas corroded BPPs have punctate (on O2 side) and continual (on H2 side) corrosions. (2) The tensile ultimate elongation for a BPP significantly decreases after corrosion on both O2 and H2 sides. (3) The degradation of tensile properties is attributed to primary cell effect. [ABSTRACT FROM AUTHOR]

Abstract: In this research, the synthesis of a suitable nanocomposite in terms of properties and economics for use in bipolar plates in proton-exchange membrane fuel cells (PEMFCs) has been carried out successfully. Nowadays, bipolar plates play a significant role in fuel cells which is absolutely important in renewable energy industry. So, epoxy/graphite/nano-copper nanocomposite bipolar plates are prepared by bulk molding compound process. Graphite and nano-copper were added as primary and secondary fillers to the composite, respectively. Epoxy resin was selected since fabrication bulk molding can be done with ease and also because of its lower cost compared to other materials. Although graphite could increase conductive characteristics, it is not sufficient for bipolar plates. Therefore, we boost the conductive properties by increasing nano-copper. Due to the small size of nanoscale copper, it can be well dispersed in polymer and graphite matrix; nano-copper can release conductive properties perfectly throughout the composite. Different percentages of nano-copper, graphite and constant percentage of epoxy are used for this purpose. The electrical resistance, flexural strength, and density of composites were measured according to the applicable standards. The morphology of the prepared plate was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) found that fillers disperse well in the matrix. Innovations in this work include improving properties and increasing the efficiency of the nanocomposite by adding metal nanoparticles (copper).Graphical Abstract: [ABSTRACT FROM AUTHOR]

This article reported the electrochemical deposition of polyaniline (PANI) on 316-L stainless steel (316LSS) to improve the anti-corrosion performance as PEMFC metal bipolar plates. The results indicate that PANI can increase the corrosion potential of 316LSS by more than 410.57 mV and effectively decrease the corrosion current density by four orders of magnitude in comparison with the uncoated 316LSS. The experimental results showed that the PANI increased the open-circuit potential of the steel by about 140 mV. The polarization current value of PANI-coated 316LSS reduced to 2.3 × 10−7 A/cm2 under the PEMFC cathode working condition. During exposure for 12 h, Nyquist plots of PANI-coated 316LSS did not change substantially. This indicates that the PANI coating was an effective barrier against the inward penetration of corrosive species. [ABSTRACT FROM AUTHOR]

In order to efficiently operate the alkaline water electrolyzers with renewable energy, behaviors of the electrolyzer during start-up or shut-down must be unveiled, because they might be suffered by reverse current that naturally flows. The mechanism of the reverse current in alkaline water electrolyzer having relation between the electrolyzer operating conditions and cell voltage has been investigated using a bipolar-type electrolyzer which consists of two cells. The electrodes were nickel mesh, which are conventional electrodes for alkaline water electrolyzer. The amount of natural reverse current measured during off-load was proportional to the current loaded until just before stopping the operation. The increase in the charge would result from the increasing oxide on the anode of the bipolar plate. Cell voltages were above 1.4 V at all cases just when the electrolyzer is forcibly opened the circuit to stop. The major redox couple of the reverse current would be [NiO/NiOOH] and [H/HO] due to the cell voltage and the redox couples. The open circuit cell voltage of the cathode terminal side cell gradually decreased to 0.3 V, while that of the anode terminal side cell was maintained above 1.1 V. Therefore, nickel oxides on the anode of the bipolar plate would be reduced, and the cathodic active material of hydrogen and nickel for the cathode side of the bipolar plate would be oxidized during the reverse current flows. Ultimately, the reverse current would stop when the redox state of both sides of the bipolar plate had the same oxidation state. [ABSTRACT FROM AUTHOR]

In this research, the parameters of pulsed Nd:YAG laser welding on the lap-joint of a 316L stainless steel foil were optimized through the response surface methodology with the aim of enhancing the tensile-shear strength. For this purpose, the effects of peak power, pulse-width, and frequency were investigated. The results showed that the analysis of welding parameters in the form of a simple combination of pulse energy could not completely predict welding properties, and the above-mentioned statistical method could appropriately be employed to balance the parameters by modeling and presenting a second-order polynomial. In this model, with the increased power and pulse-width, the strength first increased and then it decreased, and its maxima occurred at a power of 260 W and a pulse-width of 3 ms. The most important parameters affecting this model have been found to be power and pulse-width with impacts of 65 and 25%, respectively. In addition, microscopic studies showed that decrease in strength was because of the undercut and lack of penetration. [ABSTRACT FROM AUTHOR]

This study is dedicated to overcome the poor formability problem of thin stainless steel sheets used as bipolar plates of proton exchange membrane fuel cells (PEMFCs). Different parameters such as the sheet type (SUS 304 and SUS 316), sheet direction (rolling and transverse), load condition (static and dynamic), and heat treatment can be varied to adjust the channel depth in the bipolar plate. The channel of a bipolar plate is formed using static and dynamic loads and along different directions (rolling and transverse). The depth of the formed channel is about 0.18 mm, and the difference in channel depth from static and dynamic loads is small regardless of the sheet direction. The forming limitations due to the stainless steel hardening during the process can be solved through heat treatment. The channel of a bipolar plate formed with a heat-treated sheet is more than twice as deep as the one formed from a sheet without heat treatment and is more uniform. The formed channel is deeper with a dynamic load than a static load and in the transverse to rolling direction than in the rolling direction of sheet. [ABSTRACT FROM AUTHOR]

A polypropylene electrode filled with carbon black, graphite, and carbon nanotubes (CNTs) was successfully prepared by sheet extrusion to serve as the bipolar plate for a zinc/bromine redox flow battery. The electrical conductivity, mechanical properties and charge-discharge performance of the carbon plastic composite electrode with various added amounts of CNTs for the zinc/bromine redox flow battery were investigated. The volume resistivity of the carbon plastic composite electrode was 1.12 Ocm when the CNT content was 5 wt%. The voltage efficiency (VE) and the energy efficiency (EE) of the cell stack with 5 wt% CNT were measured to be 80.7% and 73.2%, respectively, during charge-discharge cycling. In addition, the zinc/bromine redox flow battery equipped with the carbon plastic composite electrode with added CNTs had good mechanical strength and chemical stability. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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

In this study, SUS316L is selected as an ideal material because of its easy workability and excellent corrosion resistance. The press equipment used in this study is a material testing system with a rated load of 25 t. Bipolar plates are manufactured, and their formabilities are evaluated according to various parameters (type of load, load size, die radius (R), and number of cycles) for dynamic load stamping. The bipolar plate formed using a sine-wave dynamic load (17 cycles, load of 50-120 kN) with a die radius of 0.3 mm has 15.0 % deeper channels than one formed with a static load of 120 kN. Moreover, when R is 0.1 mm, the bipolar plate formed using a square-wave dynamic load has 26 % deeper channels than one formed with a static load. Plates formed using sine-wave dynamic loads with R values of 0.1 and 0.3 mm have channel depths of 0.320 and 0.445 mm, respectively. Compared to an R value of 0.1 mm, the use of an R value of 0.3 mm produces channels that are 28 % deeper. [ABSTRACT FROM AUTHOR]

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

The effects of graphite content, compression molding conditions, and types of catalysts on the mechanical and electrical properties and corrosion resistance of a graphite composite based on benzoxazine resin for the bipolar plate of polymer electrolyte membrane fuel cells (PEMFC) are provided in this study. Four kinds of catalysts based on imidazole (Im) acting as catalysts are investigated in order to enhance the physicochemical properties of the graphite/polybenzoxazine composites. The characteristics of the graphite composites based on benzoxazine resin with 85 wt% graphite content prepared via compression molding satisfy the US DOE targets for the bipolar plate of a PEMFC. A graphite composite based on polybenzoxazine with an Im-based catalyst having a relatively long alkyl chain shows the best performance in terms of flexural strength and corrosion resistance without sacrificing electrical conductivity. This graphite/polybenzoxazine composite can be successfully molded as a bipolar plate with excellent physicochemical properties through a compression molding process. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This research study focuses on the manufacturing of a bipolar plate used in proton exchange membrane fuel cells. In particular, the authors investigate the manufacturing of the part by means of warm hydroforming, adopting an aluminium alloy (AA6061) as sheet material. Both the channel profile (the reagent channel width and the die upper radius), and the bipolar plate geometries (in terms of channel layouts) are investigated by means of finite element simulations. Preliminary experimental investigations were carried out in order to define both the mechanical (flow curves) and strain behaviours (forming limit curves) of the adopted aluminium alloy according to temperature and strain rate. Subsequent finite element investigations aimed to define the channel profile by means of 2D models: a statistical approach was used to evaluate the dimension of the reagent channel width, the die upper radius and the sheet thickness. Finally, proposed bipolar plate geometries were investigated by running 3D simulations at different working temperatures and oil pressures in order to evaluate: (1) the bipolar plate geometry able to avoid regions with critical thinning and (2) suitable parameters for the warm hydroforming process. [ABSTRACT FROM AUTHOR]

Bipolar plates are one of the crucial components of proton exchange membrane fuel cells. Because of the expensive production costs of traditional graphite bipolar plates, which require a few millimeters thickness over the space, the resulting metal bipolar plate reduces the cost, and the thickness can be reduced to the micron range. This study explored the application of micro-stamping technology to produce thin metal bipolar plates with the relevant process parameters. In this study, the channel design was 0.8 ×0.75 mm for the use of a rigid punch on a 50-μm-thick stainless steel sheet (SUS 304) for micro-channel stamping processes. The finite element method and the experimental results were used to analyze the main parameters of the micro-stamping process. The traditional material model and the scale factor modified material model were used for simulation. The experimental results verified that the modified material model is more realistic for products and has superior similarity because the punch load is relatively small. This study used updated Lagrangian formulation concept to establish an elastic-plastic deformation finite element analysis model and scale factor to modify the calculation to effectively simulate the micro-stamping process for metal bipolar plates. [ABSTRACT FROM AUTHOR]

A bipolar plate is one of the crucial components that strongly influence the power density of the proton exchange membrane fuel cell stack. Especially, an aluminium bipolar plate not only has better mechanical properties such as density, electrical resistivity and thermal conductivity but also has more corrosion resistance than bipolar plates made of stainless steel and graphite composites. Furthermore, the use of aluminium reduces the cost and weight of the plates, and the plates are easily machinable. This study presents the results of experiments conducted to investigate the feasibility of developing bipolar plates made of aluminium that consist of microchannels. This paper explains experimental investigations performed to investigate the formability of an aluminium sheet. The effects of forming velocity and die temperature on the microchannels in thin sheets of Al5052 having a thickness of 0.3 mm are investigated. The roundness of the core-die channels ranged from 0.3 to 0.1 mm, and the height is 0.6 mm. Formability tests are conducted for forming velocities of 0.1 and 1.0 mm/s and die temperatures in the range from room temperature to 300°C. The experimental results indicate the feasibility of the proposed technique for manufacturing the bipolar plates of aluminium. [ABSTRACT FROM AUTHOR]

The effects of a hybrid hardener on the mechanical and electrical properties and corrosion resistance of conductive graphite based epoxy composites for the bipolar plate of polymer electrolyte membrane fuel cells (PEMFC) is investigated. Diaminodiphenylsulfone (DDS) is used as an additional hardener in order to enhance the physicochemical properties of graphite-based bisphenol type epoxy-cresol novolac phenol resin composites. The characteristics of the graphite composites, based on epoxy resin respectively with and without DDS, are compared in order to shed light on the curing behaviors of the epoxy/graphite composites. The tensile strength and conductivity of the epoxy/graphite composites with DDS are much higher than those without DDS. From the results of the scanning electron microscope and optical microscope analyses, the morphology of the epoxy/graphite composite with DDS was evaluated and is shown to be more compact than that without DDS. This is attributed to the strong crosslinking effect of DDS. This epoxy/graphite composite can be successfully molded as a real bipolar plate, with fairly good physicochemical properties through a compression molding process. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ti(N,C,O) thin films were deposited by means of metal-organic chemical vapor deposition using a glow discharge with the aim of enhancing the corrosion resistance and electrical contact conductivity of austenitic stainless steel as a candidate materials for the bipolar plates used in polymer electrolyte membrane fuel cells. The corrosion properties were found to be dependent on the composition, i.e., the precursor source, and on the thickness of the thin films. Tetrakis(diethylamino) titanium used as a liquid metal organic source for the deposition of thin Ti(N,C,O) layers onto austenitic stainless steel provided a significant improvement of the corrosion resistance, which resulted in superior interfacial electrical conductivity after corrosion tests. [ABSTRACT FROM AUTHOR]

In polymer electrolyte fuel cell (PEFC) system, ideal structural integrity design takes into account the end-to-end load transfer mechanism. Hence, structural durability of cell is dependent of individual layers response to the external clamp loading. Since failure modes of each layer differ from another, multidisciplinary approach is needed to innovative designs. Bipolar plate (BPP) of PEFC is multi-functional layer that has a significant potential for research to avoid its structural failure as well as neighboring layers. To this end, present work investigates the effect of BPP materials on the stress transfer as well as distribution in cell layers based on theoretical investigation for clamping load. Gas-diffusion layer (GDL) / BPP interface has drawn considerable interest among researchers due to its susceptibility for damage failure and other related losses. Hence, investigating the interfacial behavior and relating this to the electrical contact resistance is the key feature in proposed investigation. [ABSTRACT FROM AUTHOR]

This research studied the preparation of graphite composite using liquid thermosetting plastic such as polyester resin (POE), phenolic modified alkyd resin (PhA) and mixed resin (POE with 10% PhA) as a binder. The morphology, physical, electrical and mechanical properties of the graphite composites were analyzed. The results showed that POE could combine with graphite powder (the 66% wt. saturated of graphite powder) better than PhA and mixed resin and gave higher electrical conductivity (4.52 S/cm). It was also found that epoxy resin could improve the mechanical property of composite plate. The addition of TiO2 and ZnSt slightly decreased the electrical conductivity and the water absorption. Moreover, it was proposed that TiO2 could improve the mechanical property. Carbon fiber can increase electrical and mechanical properties and water absorption of the composite with POE as a binder. The mixing of wet-lay mixture with graphite, carbon fiber and POE composite improved the mechanical property and decreased the water absorption. [ABSTRACT FROM AUTHOR]

This paper is devoted to the numerical optimization of the dimensions of channels and current transfer ribs of bipolar plates as well as the thickness and porosity of gas diffusion layers. A mathematical model of the transfer processes in a PEM fuel cell has been developed for this purpose. The results are compared with experimental data. Recommendations of the values of operating parameters and some design requirements to increase PEM fuel cell efficiency are suggested. [ABSTRACT FROM AUTHOR]

Numerical simulation of flow through a three-dimensional serpentine microchannel, subjected to a voltage perpendicular to the flow direction is presented here. Commercial CFD software CFD-ACE+ is used for the numerical analysis. A parametric study is conducted to investigate the effect of radius of curvature, Reynolds number, zeta potential and Debye length on the pressure drop and friction factor. Each case is compared with flow without electroosmotic effect. It is found that electroosmosis induces secondary flow patterns in the straight portion of the channel in addition to secondary vortices at bends. This electroosmosis-induced secondary flow causes additional pressure drop as compared to flow without electroosmosis. For flow with and without electroosmosis, the pressure drop increases with Reynolds number and the nature of variation is qualitatively similar in both the cases. It is also found that the pressure drop increases as the Debye length is reduced. [ABSTRACT FROM AUTHOR]

Bipolar plates for proton exchange membrane fuel cell (PEMFC) where polymer is used as binder and graphite is used as electric filler were prepared by means of compression molding technology. Study on the effects of graphite particle size and shape on the bipolar plate performance, such as electrical conductivity, strength, etc. showed that with decrease of graphite particle size, bulk electrical conductivity and thermometric conductivity decreased, but that flexural strength was enhanced. After spherical graphite occurrence in flake-like form, the flexural strength of the bipolar plate was enhanced, electrical conductivity increased but thermal conductivity decreased in direction paralleling pressure direction, and both electrical conductivity and thermometric conductivity reduced in direction perpendicular to pressure direction. [ABSTRACT FROM AUTHOR]

The interfacial ohmic losses between the bipolar plate and the MEA can significantly reduce the overall power output from a SPFC. For graphitic bipolar plate materials, these losses are insignificant relative to stainless steel, where the existence of a passive film on the surface greatly reduces electrical conductivity. In this paper we have evaluated different bipolar plate materials, and present long-term fuel cell data for Poco® graphite, titanium, 316 and 310 stainless steel. The properties of the passive film on the surface of 316 and 310 stainless steel are markedly different. Although both were adequately corrosion resistant in a fuel cell environment, 310 tended to produce higher fuel cell performance and like 316, no degradation was observed after 1400 h testing. Analysis of the passive film indicated that this increased performance was related to the decreased thickness of the oxide film. [ABSTRACT FROM AUTHOR]