Anticorrosion properties of Ta-coated 316L stainless steel as bipolar plate material in proton exchange membrane fuel cells

In order to reduce the cost, volume and weight of the bipolar plates used in the proton exchange membrane fuel cells (PEMFC), more attention is being paid to metallic materials, among which 316L stainless steel (SS316L) is quite attractive. In this study, metallic Ta is deposited on SS316L using physical vapor deposition (PVD) to enhance the corrosion resistance of the bipolar plates. Simulative working environment of PEMFC is applied for testing the corrosion property of uncoated and Ta-coated SS316L. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods (potentiodynamic and potentiostatic polarization) are also used for analyzing characteristics of uncoated and Ta-coated SS316L. Results show that, Ta-coated SS316L has significantly better anticorrosion property than that of uncoated SS316L, with corrosion current densities of uncoated SS316L being 44.61 μA cm⁻² versus 9.25 μA cm⁻² for Ta-coated SS316L, a decrease of about 5 times. Moreover, corrosion current densities of Ta-coated SS316L in both simulative anode (purged with H₂) and cathode (purged with air) conditions are smaller than those of uncoated SS316L.     

An investigation into TiN-coated 316L stainless steel as a bipolar plate material for PEM fuel cells

In order to reduce the cost, weight and volume of the bipolar plates, considerable attention is being paid to developing metallic bipolar plates to replace the non-porous graphite bipolar plates that are in current use. However, metals are prone to corrosion in the proton exchange membrane (PEM) fuel cell environments, which decreases the ionic conductivity of the membrane and lowers the overall performance of the fuel cells. In this study, TiN was coated on SS316L using a physical vapor deposition (PVD) technology (plasma enhanced reactive evaporation) to increase the corrosion resistance of the base SS316L. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods were used to characterize the TiN-coated SS316L. XRD showed that the TiN coating had a face-centered-cubic (fcc) structure. Potentiodynamic tests and electrochemical impedance tests showed that the corrosion resistance of SS316L was significantly increased in 0.5 M H₂SO₄ at 70 °C by coating with TiN. In order to investigate the suitability of these coated materials as cathodes and anodes in a PEMFC, potentiostatic tests were conducted under both simulated cathode and anode conditions. The simulated anode environment was −0.1 V versus SCE purged with H₂ and the simulated cathode environment was 0.6 V versus SCE purged with O₂. In the simulated anode conditions, the corrosion current of TiN-coated SS316L is −4 × 10⁻⁵ A cm⁻², which is lower than that of the uncoated SS316L (about −1 × 10⁻⁶ A cm⁻²). In the simulated cathode conditions, the corrosion current of TiN-coated SS316L is increased to 2.5 × 10⁻⁵ A cm⁻², which is higher than that of the uncoated SS316L (about 5 × 10⁻⁶ A cm⁻²). This is because pitting corrosion had taken place on the TiN-coated specimen.     

Improved anticorrosion properties and electrical conductivity of 316L stainless steel as bipolar plate for proton exchange membrane fuel cell by lower temperature chromizing treatment

The lower temperature chromizing treatment is developed to modify 316L stainless steel (SS 316L) for the application of bipolar plate in proton exchange membrane fuel cell (PEMFC). The treatment is performed to produce a coating, containing mainly Cr-carbide and Cr-nitride, on the substrate to improve the anticorrosion properties and electrical conductivity between the bipolar plate and carbon paper. Shot peening is used as the pretreatment to produce an activated surface on stainless steel to reduce chromizing temperature. Anticorrosion properties and interfacial contact resistance (ICR) are investigated in this study. Results show that the chromized SS 316L exhibits better corrosion resistance and lower ICR value than those of bare SS 316L. The chromized SS 316L shows the passive current density about 3E−7 A cm⁻² that is about four orders of magnitude lower than that of bare SS 316L. ICR value of the chromized SS 316L is 13 mΩ cm² that is about one-third of bare SS 316L at 200 N cm⁻² compaction forces. Therefore, this study clearly states the performance advantages of using chromized SS 316L by lower temperature chromizing treatment as bipolar plate for PEMFC.     

Contact resistance characteristics of coated metallic bipolar plates for PEM fuel cells – investigations on the effect of manufacturing

The main purpose of this study is to understand the interfacial contact resistance (ICR) characteristics of coated metallic bipolar plates (BPP) manufactured through stamping and hydroforming. To this goal, 51 μm thick SS316L stainless steel sheet blanks were formed into BPPs using two forming techniques (stamping and hydroforming); then these formed plates were coated with three different PVD coatings (CrN, TiN, ZrN) at three different coating thicknesses (0.1, 0.5 and 1 μm). Contact resistance of the formed and coated BPP samples were measured before and after they were exposed to the proton exchange membrane fuel cells (PEMFC) operating conditions (i.e., corrosive environment). ICR tests indicated that CrN coating increased the contact resistance of the samples, unexpectedly. TiN samples showed the best performance in terms of low ICR; however, their ICR dramatically increased after short-term exposure to corrosion. ZrN coating, as well, improved conductivity of the SS316L BPP samples and demonstrated similar ICR performance before and after exposure to corrosion.     

Experimental investigations on the corrosion resistance characteristics of coated metallic bipolar plates for PEMFC

Bipolar plates (BPPs) made of stainless steels preferred in PEM Fuel Cell (PEMFC) applications due to their high electrical conductivity, low material and production costs, low weight and mechanical strength. However, their corrosion resistances are not at desired levels for real PEMFC working conditions. To overcome this issue, different coating types are suggested. In this study, corrosion resistance behavior of 51 μm-thick SS316L metallic bipolar plates that were coated with the three different PVD coatings (TiN, CrN, and ZrN) at three thicknesses (0.1 μm, 0.5 μm, and 1 μm), and then were formed with two different manufacturing processes (stamping and hydroforming) investigated. Potentiodynamic and potentiostatic corrosion experiments were performed on the coated-formed SS316L plates, and coated-unformed blanks. Corrosion test results indicate that 1 μm ZrN coating demonstrated the highest corrosion resistance among the tested cases regardless of the manufacturing process employed. Moreover, hydroformed bipolar plates exhibited higher corrosion resistance than the stamped BPPs, but lower than the blank samples. Hardness measurements were also performed on the coated samples and resulted in higher corrosion resistance for harder surfaces.     

Effect of manufacturing processes on formability and surface topography of proton exchange membrane fuel cell metallic bipolar plates

Metallic bipolar plates in PEM fuel cells offer low-volume, low-mass and low-cost stack fabrication in addition to superior durability when compared to composite bipolar plates, which suffer due to their much higher thickness and less durability. This study aims to address the formability and surface topography issues of metallic bipolar plates fabricated by stamping and hydroforming technologies. Particular emphasis was given to process repeatability, surface topology, and dimensional quality of bipolar plates that would greatly affect the corrosion and contact resistance characteristics. Thin metal sheets of several alloys (i.e., SS304, SS316L, SS430, Ni270, Ti grades 1 and 2) were used in the fabrication experiments. SS304 and SS316L were shown to possess better formability when compared to other alloys that were used in this study, while SS430 and Ti grade 2 demonstrated the worst among all. Channel formability was observed to be greatly affected by the hydroforming pressure, while it does not differ much above certain level of stamping force. The confocal microscopy analyses showed that surface roughness values of the formed samples were altered significantly when compared to the initial flat blanks. In general, increasing hydroforming pressure and stamping force yielded higher surface roughness values at channel peaks. In addition, the surface topography was shown to be influenced mainly by the pressure level rather than the pressure rate in hydroforming process.     

Surface modification and performance of inexpensive Fe-based bipolar plates for proton exchange membrane fuel cells

A reforming pack chromization with rolling pretreatment process is utilized to develop inexpensive and high-performance Fe-based metal bipolar plates (SS 420, SS 430, and SS 316 stainless steels) for PEMFC systems. Rolling process is previously performed to reduce the chromizing temperature and generate a coating possessing excellent conductivity and corrosion resistance on the steels during chromization. The power efficiencies of rolled-chromized and simple chromized bipolar plates are compared with graphite bipolar plates employed in PEMFCs. The results show that the rolled-chromized bipolar plates have a corrosion current (I_corr) of 7.87 × 10⁻⁸ A cm⁻² and an interfacial contact resistance of 9.7 mΩ cm². Moreover, the power density of the single cell assembled with rolled-chromized bipolar plates is 0.46 W cm⁻², which is very close to that of graphite (0.50 W cm⁻²), in the tested conditions of this study.     

Corrosion resistance characteristics of stamped and hydroformed proton exchange membrane fuel cell metallic bipolar plates

Metallic bipolar plates have several advantages over bipolar plates made from graphite and composites due to their high conductivity, low material and production costs. Moreover, thin bipolar plates are possible with metallic alloys, and hence low fuel cell stack volume and mass are. Among existing fabrication methods for metallic bipolar plates, stamping and hydroforming are seen as prominent approaches for mass production scales. In this study, the effects of important process parameters of these manufacturing processes on the corrosion resistance of metallic bipolar plates made of SS304 were investigated. Specifically, the effects of punch speed, pressure rate, stamping force and hydroforming pressure were studied as they were considered to inevitably affect the bipolar plate micro-channel dimensions, surface topography, and hence the corrosion resistance. Corrosion resistance under real fuel cell conditions was examined using both potentiodynamic and potentiostatic experiments. The majority of the results exhibited a reduction in the corrosion resistance for both stamped and hydroformed plates when compared with non-deformed blank plates of SS304. In addition, it was observed that there exist an optimal process window for punch speed in stamping and the pressure rate in hydroforming to achieve improved corrosion resistance at a faster production rate.     

Arc ion plated Cr/CrN/Cr multilayers on 316L stainless steel as bipolar plates for polymer electrolyte membrane fuel cells

Arc ion plating (AIP) is applied to coat sandwich-like Cr/CrN/Cr multilayers on stainless steel 316L (SS316L) as bipolar plates for polymer electrolyte membrane fuel cell (PEMFC). Phase structure, hardness, adhesion property, interfacial contact resistance (ICR) between bipolar plates and carbon papers, and electrochemical corrosion property in the simulated PEMFC conditions are investigated. Cr phase with crystal plane of (1 1 0), (2 1 1), (3 2 2), and CrN phase with (3 2 1) are observed in the multilayer. The coating is found smooth, continuous and dense in cross-sectional observation by SEM, and the sandwiched structure of the coating is also confirmed by EDX results. Scratch tests show that the multilayer exhibits strong adhesion strength with steel substrate, which is beneficial to prevent layers from peeling off mechanically. After the coating treatment, the performance of the bipolar plate is greatly improved. Knoop hardness of the bipolar plates increases from 324 HK to 692 HK. The ICR decreases by one order of magnitude; furthermore, the corrosion resistance was also enhanced. Our analysis indicates that the improvement is attributed to high adhesion force of the smooth and dense coating and the synergistic function of Cr/CrN/Cr multilayer structure.     

Ex situ evaluation of nanometer range gold coating on stainless steel substrate for automotive polymer electrolyte membrane fuel cell bipolar plate

The bipolar plate in polymer electrolyte membrane (PEM) fuel cell helps to feed reactant gases to the membrane electrode assembly (MEA) and collect current from the MEA. To facilitate these functions, the bipolar plate material should exhibit excellent electrical conductivity and corrosion resistance under fuel cell operating conditions, and simultaneously be of low-cost to meet commercialization enabling targets for automotive fuel cells. In the present work, we focus on the benchmarking of 10 nm gold coated SS316L (a.k.a. Au Nanoclad^®) bipolar plate material through ex situ tests, which is provided by Daido Steel (Japan). The use of nanometer range Au coatings help to retain the noble properties of gold while significantly reducing the cost of the bipolar plate. The area specific resistance of the flat sample is 0.9 mΩ cm² while that for the formed bipolar plate is 6.3 mΩ cm² at compaction force of 60 N cm⁻². The corrosion current density was less than 1 μA cm⁻² at 0.8 V/NHE with air sparge simulating cathodic conditions. Additionally, gold coated SS316L showed anodic passivation of SS316L, thereby exhibiting robustness towards coating defects including surface scratches that may originate during the manufacturing of the bipolar plate. These series of ex situ tests indicate that 10 nm gold coated SS316L has good potential to be considered for commercial bipolar plates in automotive fuel cell stack.     

Improvement of corrosion resistance and electrical conductivity of 304 stainless steel using close field unbalanced magnetron sputtered carbon film

Carbon film has been deposited on 304 stainless steel (SS304) using close field unbalanced magnetron sputter ion plating (CFUBMSIP) to improve the corrosion resistance and electrical conductivity of SS304 acting as bipolar plates for proton exchange membrane fuel cells (PEMFCs). The corrosion resistance, interfacial contact resistance (ICR), surface morphology and contact angle with water of the bare and carbon-coated SS304 are investigated. The carbon-coated SS304 shows good corrosion resistance in the simulated cathode and anode PEMFC environment. The ICR between the carbon-coated SS304 and the carbon paper is 8.28-2.59 mΩ cm² under compaction forces between 75 and 360 N cm⁻². The contact angle of the carbon-coated SS304 with water is 88.6°, which is beneficial to water management in the fuel cell stack. These results indicate that the carbon-coated SS304 exhibits high corrosion resistance, low ICR and hydrophobicity and is a promising candidate for bipolar plates.     

Effect of fluoride ions on corrosion behavior of SS316L in simulated proton exchange membrane fuel cell (PEMFC) cathode environments

In order to determine the suitability of SS316L as a bipolar plate material in proton exchange membrane fuel cells (PEMFCs), its corrosion behavior is studied under different simulated PEMFC cathode corrosion conditions. Solutions of 1 × 10⁻⁵ M H₂SO₄ with a wide range of different F⁻ concentrations at 70 °C bubbled with air are used to simulate the PEMFC cathode environment. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to study the corrosion behavior. Scanning electron microscopy (SEM) is used to examine the surface morphology of the specimen after it is potentiostatic polarized under simulated PEMFC cathode environments. Auger electron spectroscopy (AES) analysis is used to identify the composition and the depth profile of the passive film formed on the SS316L surface after it is polarized in simulated PEMFC cathode environments. Photo-electrochemical (PEC) method and capacitance measurements are used to characterize the semiconductor passive films. The results of both the potentiodynamic and potentiostatic analyses show that corrosion currents increase with F⁻ concentrations. SEM examination results indicate that pitting occurs under all the conditions studied and pitting is more severe with higher F⁻ concentrations. From the results of AES analysis, PEC analysis and the capacitance measurements, it is determined that the passive film formed on SS316L is a bi-layer semiconductor, similar to a p-n heterojunction consisting of an external n-type iron oxide rich semiconductor layer (electrolyte side) and an internal p-type iron-chromium oxide semiconductor layer (metal side). Further analyses of the experimental results reveal the electronic structure of the passive film and shed light on the corrosion mechanisms of SS316L in the PEMFC cathode environment.     

Chromium nitride/Cr coated 316L stainless steel as bipolar plate for proton exchange membrane fuel cell

Chromium nitride/Cr coating has been deposited on surface of 316L stainless steel to improve conductivity and corrosion resistance by physical vapor deposition (PVD) technology. Electrochemical behaviors of the chromium nitride/Cr coated 316L stainless steel are investigated in 0.05 M H₂SO₄ + 2 ppm F⁻ simulating proton exchange membrane fuel cell (PEMFC) environments, and interfacial contact resistance (ICR) are measured before and after potentiostatic polarization at anodic and cathodic operation potentials for PEMFC. The chromium nitride/Cr coated 316L stainless steel exhibits improved corrosion resistance and better stability of passive film either in the simulated anodic or cathodic environment. In comparison to 316L stainless steel with air-formed oxide film, the ICR between the chromium nitride/Cr coated 316L stainless steel and carbon paper is about 30 mΩ cm² that is about one-third of bare 316L stainless steel at the compaction force of 150 N cm⁻². Even stable passive films are formed in the simulated PEMFC environments after potentiostatic polarization, the ICR of the chromium nitride/Cr coated 316L stainless steel increases slightly in the range of measured compaction force. The excellent performance of the chromium nitride/Cr coated 316L stainless steel is attributed to inherent characters. The chromium nitride/Cr coated 316L stainless steel is a promising material using as bipolar plate for PEMFC.     

Nanocomposite-carbon coated at low-temperature: A new coating material for metallic bipolar plates of polymer electrolyte membrane fuel cells

A nanocomposite-carbon layer is coated onto the surface of 316L stainless steel (SS316) using a beam of accelerated C₆₀ ions at low temperature. The coating is composed of textured graphite nanocrystals ranging in size from 1 to 2 nm, with the graphene plane normal to the coating plane; the nanocrystals are separated by amorphous carbon. This orientation of the graphene layer provides low film resistivity in the direction of the substrate normal. Corrosion resistance tests performed in aggressive anodic and cathodic environments of a polymer electrolyte membrane fuel cell (PEMFC) show that the nanocomposite-carbon coated SS316L exhibits better anticorrosion properties than does bare SS316L. The interfacial contact resistance (ICR) of the nanocomposite-carbon coated SS316L is 12 mΩ cm², which is similar to that of graphite at a compaction force of 150 N cm⁻² and lower than a target of ∼20 mΩ cm². A low value of ICR is maintained even after corrosion tests in aggressive anodic and cathodic environments. The fabricated nanocomposite-carbon coated SS316L exhibits excellent corrosion resistance and low interfacial contact resistance under simulated PEMFC bipolar plate conditions.     

The effect of temperature on corrosion behavior of SS316L in the cathode environment of proton exchange membrane fuel cells

The effect of temperature on the corrosion behavior of SS316L in simulated proton exchange membrane fuel cell (PEMFC) environments has been systematically studied. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to characterize the corrosion behavior. Atomic force microscope (AFM) is used to examine the surface morphology and X-ray photoelectron spectroscopy (XPS) analysis is used to identify the composition and the depth profile of the passive film. Photo-electrochemical (PEC) measurements are also performed to determinate the band gap energy of the passive film semiconductor. Interfacial contact resistances (ICR) between polarized SS316L and carbon paper are also measured. The experimental results show that corrosion resistance decreases with temperatures even though the thickness of passive film increases with temperature, at a given cell potential, the corrosion behavior of SS316L can be significantly different at different temperatures in PEMFC cathode environments, and the band gap of passive films decrease with temperature. The results also show that within the temperature range studied (25-90 °C), after different passivation time, the corrosion current densities of SS316L are all lower than the US DOE 2015 target value of 1 μA cm⁻², but the ICR between the carbon paper and polarized SS316L does not satisfy the US DOE 2015 target.     

Evaluation of anticorrosion and contact resistance behavior of poly(orthophenylenediamine)- coated 316L SS bipolar plate for proton exchange membrane fuel cell

The present work was focused on the corrosion properties and contact resistance behavior of poly(orthophenlyenediamine) (PoPD) coating on 316L SS bipolar plates. To reduce the corrosion rate and increase the interfacial conductivity of 316L SS bipolar plates, PoPD coating was deposited using an electropolymerization technique by the various monomer concentration of orthophenlyenediamine (oPD) on its surface. The presence of 1, 2, 4, 5- tetra substituted benzene nuclei of phenazine units in the polymer coating was confirmed by infrared spectroscopy. X-ray photoelectron spectroscopy analysis has confirmed the (%) of chemical composition in PoPD coating. The results of scanning electron microscopy analysis revealed that the uniform and compact coating with complete cover on 316L SS. The corrosion properties were investigated in 0.5 M H₂SO₄ and 2 ppm HF solution at 80 °C. The polarization test results showed that the PoPD coating reduced the corrosion current density both in the PEMFC anode and cathode environments. The charge transfer resistance values were in the order of 316L SS ? 0.02 M PoPD ? 0.06 M PoPD ? 0.04 M PoPD. A very low interfacial contact resistance and good adhesion strength was observed for 0.04 M PoPD coating. The higher contact angle of 0.04 M PoPD coating explained the hydrophobic property and more benefit of water management in the PEMFC environment. The results of the analysis of total metal ion releases clearly explained that the low level of metal ions released for 0.04 M PoPD coating. The overall studies revealed the PoPD coating with optimized 0.04 M oPD concentration showed best performance and provided more anodic protection to 316L SS bipolar plates.     

Optimization of the polypyrrole-coating parameters for proton exchange membrane fuel cell bipolar plates using the Taguchi method

In order to overcome the high price, weight and volume of non-porous graphite bipolar plates, metallic bipolar plates are being investigated as a substitute material. However, metallic materials can corrode under proton exchange membrane fuel cell (PEMFC) working conditions, leading to a degradation in the performance of the membrane. Previous work had shown that a polypyrrole coating on SS316L can significantly increase the corrosion resistance of the base material. In this study, a Taguchi design of experiment method was used to optimize the process parameters for the polypyrrole coating so as to produce the maximum corrosion resistance. Potentiodynamic and potentiostatic tests were used to determine the corrosion resistance of the polypyrrole-coated SS316L. Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) was used to characterize the coating thickness and coating appearance. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to determine the metal ion concentration in the solution after corrosion. The interfacial contact resistance of SS316L with carbon paper was measured both before and after coating with polypyrrole.     

Performance and long-term stability of Ti metal and stainless steels as a metal bipolar plate for a direct methanol fuel cell

In this study, STS 316L (Stainless Steel 316L), STS 430, and Ti metal are investigated as metal bipolar plates for a direct methanol fuel cell (DMFC). The corrosion resistance of these materials is investigated by potentiodynamic and chronoamperometry tests. Their cell performance and long-term stability are then studied under a real fuel cell test. The corrosion resistance of the metal bipolar plates is in the order of Ti > STS 316L > STS 430. However, the results of the real fuel cell test differ from the results of the corrosion resistance. Ti shows the lowest performance due to a sharp performance decrease in ohmic loss regions, while STS 430 shows a lower performance decrease in ohmic loss regions. Although STS 430 has less resistance to corrosion than STS 316L in the simulated environment, STS 430 performs better as a metal bipolar plate for a DMFC than STS 316L, particularly, with regard to cell performance, cell resistance, and durability.     

Coating of stainless steel and titanium bipolar plates for anticorrosion in PEMFC: A review

Anticorrosion coating for stainless steel (SS) and titanium bipolar plates were evaluated to improve the corrosion resistance and electrical conductivity in PEMFC. The PEMFC offers clean and environmentally friendly usage in electrical power systems. The bipolar plates contribute 60%–80% of the total components of PEMFC stack with electrical conductivity >100 S cm^?1. Therefore, high conductivity and corrosion resistance are observed for long-term operations in PEMFC. Recent works has developed the cost-effective and feasible alternative materials to replace graphite bipolar plates. Metallic materials, such as SS and titanium, possess good electrical conductivity but poor corrosion resistance. Coating of SS and titanium bipolar plates can improve the corrosion resistance of metallic bipolar plates. Excellent performance of bipolar plates was recorded by using NbC coating for stainless steel materials. The ICR value using plasma surface alloying method was 8.47 mΩ cm² with a low current density (I_corr) between 0.051 and 0.058 μA cm^?2. The criteria for both current densities (<1 μA cm^?2) and electrical conductivity (<10 mΩ cm²) met the DOE's 2020 technical targets. In addition, conventional air brush method can be used for fabricating multilayer coatings onto substrates because it is self-cleaning, low cost and offers high volume and large area production. Vapor deposition method, a highly advanced coating technology using PVD, suitable for coating bipolar plates because it is environmentally friendly and can be used in high temperatures, producing materials with good impact strength and excellent abrasion resistance. PEMFC cost is still too high for large scale commercialization, which is the cost of raw material and processing to allow fabrication of thinner plates contributes substantially to the total PEMFC cost. Some future works on fuel cell anticorrosion research with reasonable coating method is suggested to reduce the cost in order to facilitate the move toward commercialization especially for SS and titanium bipolar plates.     

Thin chromium nitride PVD coatings on stainless steel for conductive component as bipolar plates of PEM fuel cells: Ex-situ and in-situ performances evaluation

In this paper, two types of chromium PVD coatings (100 nm) have been elaborated on 316L stainless steel (SS) by adjusting the nitrogen flow rate. The first coating is a mixture of Cr₂N and Cr, the second one is a single phase CrN. It is shown that the performances of the material are strongly dependant of the nature of the passive film formed on the chromium nitride layers due to the galvanic coupling between the coating and the substrate. The CrN coated SS shows very good corrosion resistance in simulated PEMFC media. The surface conductivity of the SS is also greatly improved and the CrN coated SS shows an interfacial contact resistance of 10 mΩ cm² at 140 N cm⁻². Five single cells of stainless steel bipolar plates coated with the CrN film were assembled for performance test. This 5 cell stack does not show any mean voltage degradation over 200 h dynamic cycling. Moreover, the performances of the CrN coated SS bipolar plates are very close to the Au-coated SS bipolar plates.