Stainless Steel Bipolar Plates Research Articles

Influence of pH on the passivation behaviour of 904L stainless steel bipolar plates for proton exchange membrane fuel cells

The electrochemical behaviour and passive film properties of 904L stainless steel in simulated corrosive environment in proton exchange membrane fuel cells (PEMFCs) of pH ranging from 1 to 5 was evaluated by using potentiodynamic curves, EIS, Mott-Schottky approach, and ex-situ surface analytical techniques XPS and secondary ion mass spectrometry (SIMS). The results confirmed that the passive film of 904L stainless steel performs as n-type and p-type semiconductors at potentials changes around the flat band potential. The doping density decreases with increment of pH value, the passive film formed at pH 1 condition present the highest donor and acceptor density. Furthermore, a bilayer structure passive film was observed, it was mainly composed by an outer iron, molybdenum and copper oxide region, whereas the inner chromium and little molybdenum oxide. Moreover, as the pH value increased, signals of nickel oxides or hydroxides were observed in passive film.

Investigation of bipolar plate materials for proton exchange membrane fuel cells

Low-cost parts, materials, and production methods are important for effective establishment of polymer electrolyte membrane fuel cells (PEMFCs) into the commercial marketplace. The bipolar plate is one part that substantially impacts the PEMFC manufacturing cost. Metallic bipolar plates are an attractive alternative to graphite because they provide the necessary electrical and thermal conductivity and they offer good mechanical strength which supports the forces within the stack. Stainless steel, which is reasonably cheap, a good conductor, and corrosion resistant with high strength, has exhibited acceptable performance as a bipolar plate for several thousand hours of experiments. In this work, a through-mask electro-etching process was selected for fabrication of 304L and 430 stainless steel alloy bipolar plates for 25-cm2 PEMFC and they were compared against the graphite material. The key results revealed that stainless steel bipolar plates give comparable performance to graphite plates especially under well humidified conditions. At drier conditions, the resistance is the largest factor on the overall performance for all bipolar plate materials. Toray paper and Carbel CL GDLs give different performances under various bipolar plate materials and operating conditions. It is also shown that significant differences in channel depth profiles affect the overall performance.

Corrosion Investigation of Chromium Nitride and Chromium Carbide Coatings for PEM Fuel Cell Bipolar Plates in Simulated Cathode Condition

AbstractTransition metals nitrides and carbides are used as coatings on bipolar plates for proton exchange membrane fuel cells (PEMFCs) due to their suitable electrical conductivity and corrosion resistance. Chromium electroplated AISI 316L stainless steel bipolar plates were treated by plasma nitriding and solid carburizing to form chromium nitride and chromium carbide, respectively. The presence of CrN/Cr2N and Cr7C3/Cr23C6 was verified by X‐ray diffractometry (XRD) in chromium nitride and chromium carbide coatings, respectively. The corrosion behavior of coatings was investigated by potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy (EIS) in simulated cathode condition. Coated samples showed better corrosion behavior than untreated bare sample. EIS results indicated decrease in corrosion current density after 500 hours, however coatings acted as barrier against solution access to substrate. Corrosion current densities of coatings were close to targets of United Stated department of energy (DOE).

Probing Formability Improvement of Ultra-thin Ferritic Stainless Steel Bipolar Plate of PEMFC in Non-conventional Forming Process

Formability increase in non-conventional forming profiles programmed in the servo-press was investigated using finite element analysis. As an application, forming experiment on a 0.15-mm-thick ferritic stainless steel sheet for a bipolar plate, a primary component of a proton exchange membrane fuel cell, was conducted. Four different forming profiles were considered to investigate the effects of forming profiles on formability and shape accuracy. The four motions included conventional V motion, holding motion, W motion, and oscillating motion. Among the four motions, the holding motion, in which the slide was held for a certain period at the bottom dead point, led to the best formability. Finite element simulations were conducted to validate the experimental results and to probe the formability improvement in the non-conventional forming profiles. A creep model to address stress relaxation effect along with tool elastic recovery was implemented using a user-material subroutine, CREEP in ABAQUS finite element software. The stress relaxation and variable contact conditions during the holding and oscillating profiles were found to be the main mechanism of formability improvement.

Electrochemical behavior of nanocrystalline Ta/TaN multilayer on 316L stainless steel: Novel bipolar plates for proton exchange membrane fuel-cells

Insufficient corrosion resistance and surface conductivity are two main issues that plague large-scale application of stainless steel (SS) bipolar plates in proton exchange membrane fuel cells (PEMFCs). This study explores the use of nanocrystalline Ta/TaN multilayer coatings to improve the electrical and electrochemical performance of polished 316L SS bipolar plates. The multilayer coatings have been deposited by (reactive) magnetron sputtering and characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The electrochemical behavior of bare and coated substrates has been evaluated in simulated PEMFC working environments by potentiodynamic and potentiostatic polarization tests at ambient temperature and 80 °C. The results show that the Ta/TaN multilayer coating increases the polarization resistance of 316L SS by about 30 and 104 times at ambient and elevated temperatures, respectively. The interfacial contact resistance (ICR) shows a low value of 12 mΩ × cm2 before the potentiostatic test. This ICR is significantly lower than for the bare substrate and remains mostly unchanged after potentiostatic polarization for 14 h. In addition, the high contact angle (92°) with water for coated substrates indicates a hydrophobic character, which can improve the water management within the cell in PEMFC stacks.

Electrochemical corrosion characteristics of conducting polypyrrole/polyaniline coatings in simulated environments of a proton exchange membrane fuel cell

A bilayer conducting polymer coating consisting of an inner layer of polypyrrole (Ppy) with large dodecylsulfate ionic groups and an external polyaniline (Pani) layer with small SO42− groups was electrodeposited on type 304 stainless steel bipolar plates of a proton-exchange membrane fuel cell (PEMFC). The corrosion performance of conducting Ppy/Pani bilayer coatings on 304SS in simulated cathode and anode environments (0.1 M H2SO4 solution bubbled with air or H2 at 80 °C) of a PEMFC was investigated by electrochemical impedance spectroscopy, polarization and open circuit potential measurements. The experimental results showed that the Ppy/Pani bilayer increased the free corrosion potential of the steel by about 310 mV (SCE) and 270 mV (SCE) in simulated cathodic and anodic environments of the PEMFC, respectively. Long-term exposure studies showed that the bilayer was highly stable and inhibited the corrosion of the steel effectively in simulated cathodic and anodic environments, which was attributed to its “self-healing” effect.

Numerical investigation of formed residual stresses and the thickness of stainless steel bipolar plate in PEMFC

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

Corrosion and electrical properties of carbon/ceramic multilayer coated on stainless steel bipolar plates

Abstract A carbon/ceramic multilayer is deposited onto the stainless steel to enhance the corrosion and electrical properties of metallic bipolar plates under polymer electrolyte membrane fuel cells (PEMFCs). The multilayer is composed of 1.22 μm CrN and 7 nm carbon layers. The corrosion durability tests conducted in an aggressive environments of the PEMFC reveal that a low corrosion current density of 0.12 and 0.07 μA cm − 2 is obtained for the multilayers at anodic and cathodic conditions, respectively, and the highest protective efficiency of 99.80% is recorded in the cathodic condition. Furthermore, the interfacial contact resistance of the carbon/ceramic multilayer is also reduced significantly, by seventeen times, compared to bare stainless steel. A low value of ICR is maintained even after corrosion tests. These tests show that the carbon/ceramic multilayer deposited onto the stainless steel improve the corrosion resistance of the metal substrate and lead to high surface conductivity in the aggressive environments of the PEMFC.

Multilayered Zr–C/a-C film on stainless steel 316L as bipolar plates for proton exchange membrane fuel cells

A multilayered zirconium-carbon/amorphous carbon (Zr–C/a-C) coating is synthesized by magnetron sputtering in order to improve the corrosion resistance and interfacial conductivity of stainless steel 316L (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs). Zr–C/a-C film contains an outmost pure amorphous carbon layer and a sub zirconium containing carbon layer. Interfacial contact resistance (ICR) between carbon paper and coated SS316L decreases to 3.63 mΩ cm2 at 1.4 MPa. Potentiodynamic polarization results reveal that the corrosion potential of Zr–C/a-C coated sample is more positive than pure a-C coated sample and the current density is only 0.49 μA cm−2 at the cathode applied potential 0.6 V. Electrochemical impendence spectroscopy also indicates that multilayered Zr–C/a-C film coated SS316L has much higher charge transfer resistance than the bare sample. After potentiostatic polarization, ICR values are 3.92 mΩ cm2 and 3.82 mΩ cm2 in the simulated PEMFCs cathode and anode environment, respectively. Moreover, XPS analysis of the coated samples before and after potential holding tests shows little difference, which disclose the chemical stability of multilayered Zr–C/a-C film. Therefore, the multilayered Zr–C/a-C coating exhibits excellent performance in various aspects and is preferred for the application of stainless steel bipolar plates.

Improving channel depth of stainless steel bipolar plate in fuel cell using process parameters of stamping

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.

The residual stress in a brazed joint of metallic bipolar plates of PEMFC: A numerical model

Bipolar plates are regarded as the core of the proton exchange membrane fuel cell. In order to obtain a connected stainless steel bipolar plate with low residual stress and small deformation, the brazing process is commonly used for bipolar plate connection. In this study, a numerical model was developed to calculate the residual stress in a brazed joint. Clamp pressure, brazing gap, and solder type were investigated. The results showed that clamping pressure had little influence on residual stress and the residual stress decreased with an increase in the brazing gap, which provided a reference for controlling brazed residual stresses for stainless steel bipolar plates.

Protective coatings on stainless steel bipolar plates for proton exchange membrane (PEM) electrolysers

Proton exchange membrane (PEM) electrolysis is a promising technology for large H2 production from surplus electricity from renewable sources. However, the electrolyser stack is costly due to the manufacture of bipolar plates (BPP). Stainless steel can be used as an alternative, but it must be coated. Herein, dense titanium coatings are produced on stainless steel substrates by vacuum plasma spraying (VPS). Further surface modification of the Ti coating with Pt (8 wt% Pt/Ti) deposited by physical vapour deposition (PVD) magnetron sputtering reduces the interfacial contact resistance (ICR). The Ti and Pt/Ti coatings are characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). Subsequently, the coatings are evaluated in simulated and real PEM electrolyser environments, and they managed to fully protect the stainless steel substrate. In contrast, the absence of the thermally sprayed Ti layer between Pt and stainless steel leads to pitting corrosion. The Pt/Ti coating is tested in a PEM electrolyser cell for almost 200 h, exhibiting an average degradation rate of 26.5 μV h−1. The results reported here demonstrate the possibility of using stainless steel as a base material for the stack of a PEM electrolyser.

Corrosion kinetics of 316L stainless steel bipolar plate with chromiumcarbide coating in simulated PEMFC cathodic environment

Stainless steel with chromium carbide coating is an ideal candidate for bipolar plates. However, the coating still cannot resist the corrosion of a proton exchange membrane fuel cell (PEMFC) environment. In this work, the corrosion kinetics of 316L stainless steel with chromium carbide is investigated in simulated PEMFC cathodic environment by combining electrochemical tests with morphology and microstructure analysis. SEM results reveal that the steel’s surface is completely coated by Cr and chromium carbide but there are pinholes in the coating. After the coated 316L stainless steel is polarized, the diffraction peak of Fe oxide is found. EIS results indicate that the capacitive resistance and the reaction resistance first slowly decrease (2–32h) and then increase. The potentiostatic transient curve declines sharply within 2000s and then decreases slightly. The pinholes, which exist in the coating, result in pitting corrosion. The corrosion kinetics of the coated 316L stainless steel are modeled and accords the following equation: i0=7.6341t−0.5, with the corrosion rate controlled by ion migration in the pinholes.

Effects of Substrate Temperature on the Corrosion Behaviour of Nanochromium Coatings Deposited by Direct Current Magnetron Sputtering

Nanochromium coatings were deposited on 316L stainless steel bipolar plates of a proton-exchange membrane fuel cell (PEMFC) by a direct current magnetron sputtering technique. The effect of substrate temperature on the corrosion resistance of nanochromium coatings was investigated. The corrosion performance of the bare and chromium-coated steel in a simulated environment of PEMFC (0.5 M H2SO4+ 2 ppm F−) was studied using electrochemical impedance spectroscopy, polarisation, and open circuit potential measurements. The results showed that the corrosion rates of two nanochromium coatings deposited at 300°C and 500°C were lower than those of uncoated steel by more than one order of magnitude. Electrochemical impedance spectra of both nanochromium coatings exhibited distinct characteristics in corrosive solution. The nanochromium coating deposited at 500°C showed superior stability in the corrosive solution.

Increase in the corrosion resistance of stainless steel bipolar plates by the formation of thermally-induced Cr-nitride

Cr-nitride layer is formed on the surface of Cr-electroplated stainless steel to use metallic bipolar plates of polymer electrolyte membrane fuel cell (PEMFC). The dense and continuous Cr-nitride layer is confirmed by scanning electron microscope (SEM) results. The corrosion resistance results in aggressive environments of PEMFC reveal that the corrosion current density of 0.5 μA cm−2 and 0.5 μA cm−2 are presented in anodic and cathodic environments of PEMFC, respectively. The highest protective efficiency of 99.9% is recorded in the cathodic condition. The dense Cr-nitride layer provides sufficient corrosion resistance. Moreover, the interfacial contact resistance (ICR) of Cr-nitride layer is significantly decreased up to 15 mΩ cm−2 compared with pure stainless steel and the ICR is maintained after corrosion tests. This analysis indicates that the improvement is originating solely from dense Cr-nitride layer on the surface.

Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Electrolyzers

Given its rapid response to fluctuating currents and wide operation range, proton exchange membrane (PEM) water electrolysis is utmost suitable for generation of hydrogen from renewable power. However, it is still hindered by the high cost of the stack components compared to those used in the alkaline technology. In particular, the titanium bipolar plates (BPP) are an issue and the replacement of this metal by stainless steel is a challenge, due to the highly corrosive environment inside PEM electrolyzer stack. Herein, we coat stainless steel BPPs with 50–60 μm Ti and 1.5 μm Pt coatings by vacuum plasma spraying (VPS) and magnetron sputtering physical vapor deposition (PVD), respectively. The BPPs are evaluated at constant 1 A cm−2 for more than 1000 h. The thermally sprayed Ti coatings fully protect the stainless steel substrate during this period of time, and the Pt surface modification allows achieving a cell performance comparable to the baseline.

Corrosion resistance of a tungsten modified AISI 430 stainless steel bipolar plate for proton exchange membrane fuel cells

A W-modified layer is prepared on 430 SS via plasma surface diffusion alloying to improve its corrosion resistance in marine PEMFCs.

Influence of Cr-C film composition on electrical and corrosion properties of 316L stainless steel as bipolar plates for PEMFCs

Stainless steel (SS) has received much attention in recent years as an alternative material for bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs). However, stainless steel BPPs are still required to combat corrosion in the acid environment without forming oxidants, passive layers and metal ions. In this study, multilayered chromium-carbon (Cr-C) film is deposited on SS316L sheet as BPPs using closed field unbalanced magnetron sputter ion plating (CFUBMSIP). Five films with different composition are deposited and the influence of chromium content adjusted by sputtering current is characterized by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Interfacial contact resistance (ICR) between coated SS316L sheets and gas diffusion layer (GDL) is measured. Potentiodynamic and potentiostatic tests are conducted to evaluate the corrosion resistance of the coated samples. Experimental results show that Cr-C film with content of Cr0.75C5 presents the optimal performance, i.e. the interfacial contact resistance(ICR) reduces to 1.4 mΩ cm2 under a compaction pressure of 1.4 MPa, and the corrosion current density reaches 1.046 μA cm−2 in the PEMFCs cathodic environment (0.5 M H2SO4 + 5 ppm HF solution at 70 °C, 0.6 V vs. SCE). The performance variation of five films can be preliminarily explained by the crystallographic structure and chemical composition analysis.

Performance of electrocatalytic gold coating on bipolar plates for SO2 depolarized electrolyser

One of the largest obstacles for SO2 depolarized electrolyser (SDE) commercialization is the material stability in rough operating conditions. In this work stainless steel bipolar plates have been coated with thin Au layer having bifunctional role: providing electrocatalytic surface for both electrode reactions and simultaneously improves the stainless steel support corrosion tolerance at the potential window of SDE. The stability and performance of the coated bipolar plates were tested in a bench-scale electrolyser set-up and the results indicate that these plates can be utilized as economic catalyst for SDE, moreover, they show corrosion resistance in SDE operation.

Study on the Properties of Fuel Cell 304 Stainless Steel Bipolar Plates with Flow Channels Milled Using Different Methods

Study on the Properties of Fuel Cell 304 Stainless Steel Bipolar Plates with Flow Channels Milled Using Different Methods