316L Stainless Steel Bipolar Plates Research Articles

Corrosion resistance and conductivity of CrN, CrAlN, and CrTiN coatings applied to bipolar plates for proton exchange membrane fuel cells

In order to improve the corrosion resistance and conductivity of 316L stainless steel bipolar plates used for proton exchange membrane fuel cells, three Cr-containing nitride coatings were deposited on 316L stainless steel by multiarc ion plating. First, the microstructure, composition, and contact angle of the three coatings were systematically investigated. Then, electrochemical impedance spectroscopy, potentiodynamic polarization, potentiostatic polarization (PSP), and interfacial contact resistance (ICR) of the three coatings were also fully examined. The results revealed that CrN coating has the highest contact angle of 98.26°, indicating its superior hydrophobicity. Additionally, CrN coating performed the best corrosion resistance with the highest corrosion potential of 0.31 V, the lowest corrosion current density of 2.28 × 10−7 A cm−2, and the largest resistance. Furthermore, CrN coating showed the lowest current density during PSP tests and the smallest ICR value after corrosion. The superior corrosion resistance of CrN coating is mainly attributed to its decreased pore density caused by vacancylike defects and its uniform structure. This article provided evidence for the potential application of CrN coating to bipolar plates.

Improved corrosion resistance and interfacial conductivity of a-C/(Ti:C)/Ti nano-thin film for 316L stainless steel bipolar plates

To enhance corrosion resistance and electrical conductivity of metallic bipolar plates for proton exchange membrane fuel cells (PEMFCs), the film containing amorphous carbon (a-C) outer layer, titanium carbon compound (Ti:C) transition layer and titanium (Ti) seed layer has been deposited on the surface of 316L stainless steel (316L SS) by multi-arc ion plating method. Dense and uniform a-C/(Ti:C)/Ti nano-thin film is relatively hydrophobic and approximately 300 nm thick, presenting a clear multilayer structure. The interfacial contact resistance of 316L SS is effectively reduced from 124.97 mΩ·cm2 to 3.97 mΩ·cm2 at 1.4 MPa after modification. Electrochemical corrosion tests are investigated in the simulated cathodic PEMFCs environment (0.5 M H2SO4 and 2 ppm HF at 70 ℃ bubbled with air). Potentiodynamic polarization results reveal that the corrosion potential of a-C/(Ti:C)/Ti film modified sample is 0.23 V (vs. Ag/AgCl) and the corrosion current density is only 0.14 μA·cm−2. The durability of the a-C/(Ti:C)/Ti film was assessed by conducting potentiostatic polarization tests at various applied potentials. After 4 h potential of 0.6 V and 0.8 V (vs. Ag/AgCl) holding tests, the current densities of the modified 316L SS have stabilized at 0.076 μA·cm−2 and 0.098 μA·cm−2, respectively.

Corrosion Resistance, Interfacial Contact Resistance, and Hydrophobicity of 316L Stainless Steel Bipolar Plates Coated with TiN/Amorphous Carbon Double Layer under Different Carbon Target Currents

To improve the corrosion, interfacial contact resistance, and hydrophobicity of bipolar plates used in proton-exchange membrane fuel cells, a series of TiN/amorphous carbon double-layer coatings was prepared on 316L stainless steel using magnetron sputtering. The structure of the amorphous carbon was controlled with different carbon target currents. The changed rules in the coating structure and performance under different carbon target currents were studied. Due to appropriate sputtering energy, an appropriate carbon target current reduced the grain boundary of the coating, resulting in a smoother surface, and increased the content of sp2 hybrid carbon. Compared with uncoated 316L stainless steel, the samples coated with amorphous carbon showed greatly improved corrosion resistance and conductivity. At a carbon target current of 5 A, low contact resistance and high corrosion resistance were achieved simultaneously. The significant improvement in corrosion resistance is attributed to the improvement in the quality of the coating surface. Due to the appropriate carbon target current increasing the content of sp2 hybrid carbon in the coating, the contact resistance of the coating was reduced. When the carbon target current was 5 A, the interfacial contact resistance of the sample was 3.9 mΩ·cm2, which is significantly lower than that of bare 316L stainless steel. After constant potential polarization testing, the coating still exhibited good conductivity.

Effect of carbon doping on corrosion resistance and conductivity of CrMoN-coated 316L stainless steel bipolar plates

Effect of carbon doping on corrosion resistance and conductivity of CrMoN-coated 316L stainless steel bipolar plates

Performance and structure of Ti-doped amorphous carbon/CrN/Ti multilayer coating deposited on 316L stainless steel for use as bipolar plate in proton exchange membrane fuel cell

In order to improve the corrosion resistance and conductivity of stainless steel bipolar plates, three-layer Ti-doped amorphous carbon/CrN/Ti films were deposited on 316L stainless steel used for bipolar plates in PEMFCs. Titanium as the doped element added into amorphous carbon. Magnetron sputtering technology was used to deposit the films and control the titanium doped content by different titanium target currents. The structure transformation law of Ti content in amorphous carbon coating was studied. The application principle of corrosion resistance and conductivity of bipolar plates during the transformation of the coating structure from amorphous carbon to carbide was analyzed. With increasing Ti-doped content, the sp2/sp3 ratio increased, and the amorphous carbon film gradually transformed to titanium carbide matrix film. Characterization of the electrochemical corrosion confirmed that the anti-corrosion property of the films was closely related to the Ti-C phase and sp2/sp3 ratio. Ti-doped amorphous carbon/CrN/Ti film, which is built at 1A Ti target current, has the best corrosion current density. The interfacial contact resistance (ICR) first decreased and then increased with increasing Ti content. When excessive doping of titanium atoms makes the coating become a TiC matrix, the corrosion resistance and ICR property of the coating worsen. The film’s state of chemical bonds after electrochemical corrosion was tested by XPS to study the ICR increase mechanism. The Ti-doped amorphous carbon/CrN/Ti multilayer film can be used as a modified coating of 316L stainless steel bipolar plates for PEMFCs.

Effect of cold deformation on corrosion behavior of selective laser melted 316L stainless steel bipolar plates in a simulated environment for proton exchange membrane fuel cells

This work studied the influence of cold deformation on the microstructure evolution and corrosion behavior of selective laser melted (SLMed) 316L stainless steel in a simulated cathode environment for proton exchange membrane fuel cells (PEMFCs). Results indicated that at < 50% deformation levels, the corrosion resistance was improved with an increase in deformation level, which was attributed to the deformation twins, refining sub-grains, and the formation of stable passive films. At 70% deformation level, martensite nucleation decreased the stability of the passive film and consequently reduced the corrosion resistance.

Corrosion resistance and conductivity of NbN-coated 316L stainless steel bipolar plates for proton exchange membrane fuel cells

NbN coatings were deposited by multi-arc ion plating at different nitrogen partial pressure (PN) to improve the corrosion resistance and conductivity of metallic bipolar plates. With increasing PN, the phase composition of the coating transformed from a mixture of β-Nb2N and δ’-NbN to δ-NbN, which was accompanied by grain refinement. The coating deposited at a relatively high PN (3.5 Pa) exhibited the lowest ICR and corrosion current density of 12.75 mΩ·cm2 and 2.619 × 10−6 A/cm2, respectively. The influence of the phase composition, microstructure, and surface morphology on the anti-corrosion behavior and conductivity of the coating were analyzed in detail.

Additive manufacturing of bipolar plates for hydrogen production in proton exchange membrane water electrolysis cells

Water electrolysis is a process that can produce hydrogen in a clean way when renewable energy sources are used. This allows managing large renewable surpluses and transferring this energy to other sectors, such as industry or transport. Among the electrolytic technologies to produce hydrogen, proton exchange membrane (PEM) electrolysis is a promising alternative. One of the main components of PEM electrolysis cells are the bipolar plates, which are machined with a series of flow distribution channels, largely responsible for their performance and durability. In this work, AISI 316L stainless steel bipolar plates have been built by additive manufacturing (AM), using laser powder bed fusion (PBF-L) technology. These bipolar plates were subjected to ex-situ corrosion tests and assembled in an electrolysis cell to evaluate the polarization curve. Furthermore, the obtained results were compared with bipolar plates manufactured by conventional machining processes (MEC). The obtained experimental results are very similar for both manufacturing methods. This demonstrates the viability of the PBF-L technology to produce metal bipolar plates for PEM electrolyzers and opens the possibilities to design new and more complex flow distribution channels and to test these designs in initial phases before scaling them to larger surfaces.

Investigation of high potential corrosion protection with titanium carbonitride coating on 316L stainless steel bipolar plates

In order to improve the durability of stainless steel bipolar plates at high potential during the start-up/shut-down process of proton exchange membrane fuel cell (PEMFC), TiN and TiCN coatings with different C element contents are deposited on the 316L stainless steel substrates by using Closed Field Unbalanced Magnetron Sputter Ion Plating. The electrochemical test results show that the TiCN-2sccm sample possesses excellent corrosion resistance compared to other samples. The results of interfacial contact resistance (ICR) measurements show that the minimum ICR value of the TiCN-2sccm sample is 10 mΩ cm2, which meets the Department of Energy targets.

Bilayer CrN/Cr coating-modified 316L stainless steel bipolar plates for high temperature polymer electrolyte fuel cells

In this work, a bilayer CrN/Cr coating was deposited on the surface of a 0.1 mm-thick SS316L specimen with a size of 60 × 60 mm2 by means of a reactive magnetron sputtering method. Using a specially-designed electrochemical cell for simulating the HT-PEFC environment, various electrochemical tests, including potentiodynamic polarization, potentiostatic polarization and EIS, were performed in order to evaluate the anti-corrosion properties and stability of the bilayer CrN/Cr coating in simulated HT-PEFC environments. Additionally, ex-situ characterizations using XRD, SEM + EDX and ICR were carried out to investigate the crystal structure and composition of CrN/Cr coating, surface morphologies and the interfacial contact resistance of samples before and after corrosion tests. The results show that the bilayer CrN/Cr coating could provide a more than 99.9% protective effect on the substrate (SS316L) in the simulated HT-PEFC environment at RT and 130 °C, and reduce the corrosion rates of BPPs more than 600 times in both the simulated cathodic and anodic environments of a HT-PEFC. Furthermore, an ICR value of CrN/Cr SS316L (5.5 mΩ cm2) is around one order of magnitude lower than that of the bare SS316L substrate (47 mΩ cm2) in a typical pressing force for assembling fuel cells (140 N cm−2).

Preparation and performance of electrically conductive Nb-doped TiO2/polyaniline bilayer coating for 316L stainless steel bipolar plates of proton-exchange membrane fuel cells.

A bilayer coating composed of an inner layer of Nb-doped TiO2 obtained by the sol–gel method and an external polyaniline layer with small SO42− groups obtained by galvanostatic deposition was prepared to protect 316L stainless steel bipolar plates of proton-exchange membrane fuel cells. The corrosion resistances of bare 316L and 316L with single polyaniline coating and Nb-doped TiO2/polyaniline bilayer coating were investigated. The experimental results indicated that both single and bilayer coatings increased the corrosion potential and decreased the corrosion current density compared with bare 316L stainless steel. A thirty-day exposure experiment indicated that the Nb-doped TiO2/polyaniline bilayer showed high stability, and it protected 316L more effectively from the penetration of the corrosive ions.

Performance of a PEM Fuel Cell Using Electroplated Ni–Mo and Ni–Mo–P Stainless Steel Bipolar Plates

The performance and durability of 316L stainless steel bipolar plates (BPP) electroplated with Ni–Mo and Ni–Mo–P coatings are investigated in a proton exchange membrane fuel cell (PEMFC), using a commercial Pt/C Nafion membrane electrode assembly (MEA). The effect of the BPP coatings on the electrochemical performance up to 115 h is evaluated from polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy together with interfacial contact resistance (ICR) measurements between the coatings and the gas diffusion layer. The results show that all the coatings decrease the ICR in comparison to that of uncoated 316L BPP. The Ni-Mo coated BPP shows a low and stable ICR and the smallest effects on MEA performance, including catalyst activity/usability, cathode double layer capacitance, and membrane and ionomer resistance build up with time. After electrochemical evaluation, the BPPs as well as the water effluents from the cell are examined by Scanning Electron Microscopy, Energy Dispersive and Inductively Coupled Plasma spectroscopies. No significant degradation of the coated surface or enhancement in metal release is observed. However, phosphorus addition to the coating does not show to improve its properties, as deterioration of the MEA and consequently fuel cell performance losses is observed.

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).

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.

Low-nickel austenitic stainless steel as an alternative to 316L bipolar plate for proton exchange membrane fuel cells

Suitability of low Ni austenitic stainless steel (201 SS) as an effective alternative to 316L stainless steel bipolar plates for proton exchange membrane fuel cells (PEMFC) was investigated. Polarization studies showed 201 SS behaved similar to 316L in the cathodic environment of fuel cell, but performed poorly in the anodic environment. Electrochemical impedance spectroscopy (EIS) studies revealed that in the anodic environment the oxide thickness and resistance of 201 SS is lower than 316L, whereas in the cathodic environment both steels showed similar behavior. Mott–Schottky analysis revealed that the defect concentration in oxide layer is higher for 201 SS at the anodic environment, whereas the oxide stability is better than 316L at the cathodic environment. The interfacial contact resistance (ICR) for both the steels was similar.

Electrochemical Synthesis of PANI on 316L Stainless Steel Bipolar Plates of PEMFC and its Corrosion Performance

PANI conducting polymer coating was electrochemically deposited on 316L stainless steel bipolar plates of PEMFC in the bath of 0.5M H2SO4 and 0.5M aniline. PANI coating could be synthesized with optimal conditions presenting in smooth and dense feature when the voltage was from 0.75V to 0.85V(Vs.SCE). The anti-corrosion performance of the coating was evaluated by electrochemical technique in the medium of 1M H2SO4 and 2ppM NaF at 70°C to simulate the working environment of PEMFC. It was found that the anodic branch of polarization curves presented in passivation character. EIS results indicated that the radius of the capacity impedance for PANI coating increased distinctly, which validated the excellent corrosion resistance of the coating. The surface morphology of the coating was observed by SEM, and the results showed that the surface of 316L stainless steel bipolar plates was covered by claviform shape coating. The chemical composition of the coating was investigated by FTIR and the results illustrated that the coating were composed of PANI.

The effect of pH and halides on the corrosion process of stainless steel bipolar plates for proton exchange membrane fuel cells

Abstract Stainless steel is attractive as material for bipolar plates in proton exchange membrane fuel cells, due to its high electrical conductivity, high mechanical strength and relatively low material and processing cost. Potentiostatic and potentiodynamic tests were performed in H2SO4 solutions on AISI 316L stainless steel bipolar plates with etched flow fields. The effect of pH and presence of small amounts of fluoride and chloride on the corrosion rate and interfacial contact resistance of the stainless steel bipolar plate were investigated. The tests performed in electrolytes with various pH values revealed that the oxide layer was thinner and more prone to corrosion at pH values significantly lower than the pH one expects the bipolar plate to experience in an operating proton exchange membrane fuel cells. The use of solutions with very low pH in such measurements is thus probably not the best way of accelerating the corrosion rate of stainless steel bipolar plates. By use of strongly acidic solutions the composition and thickness of the oxide layer on the stainless steel is probably altered in a way that might never have happened in an operating proton exchange membrane fuel cell. Additions of fluoride and chloride in the amounts expected in an operating fuel cell (2 ppm F− and 10 ppm Cl−) did not cause significant changes for neither the polarization- nor the contact resistance measurements. However, by increasing the amount of Cl− to 100 ppm, pitting was initiated on the stainless steel surface.

An experimental feasibility study of vanadium oxide films on metallic bipolar plates for the cold start enhancement of fuel cell vehicles

An experimental study of vanadium oxide polycrystalline films deposited onto 316L stainless steel bipolar plates as an efficient Joule heating source for fuel cell vehicles was conducted by carefully modulating the negative temperature coefficients of the electrical resistance of the films at subzero temperatures. To fabricate the thin films, a well-mixed precursor solution of vanadium alkoxide and organic cosolvent was prepared by the hydrolytic sol-gel route and then coated on the pre-cleaned flat surface of 316L stainless steel plates with natural passive oxide layers by a dip-coating method. Subsequently, the variation of the nonlinear electrical resistance of the thin film was measured simultaneously over a wide temperature range of −20 to 80 °C, allowing direct detection of the surface temperature of the thin films. In addition, the adhesion, microstructures, compositions, and morphologies of the vanadium oxide thin films were investigated using the ASTM D3359 method, XRD, FE-SEM, and XPS analyses. A remarkable result from this study was that a temperature increase of 41.65 °C was induced by significant Joule heating of the vanadium sesquioxide films on metallic bipolar plates, i.e. approximately 1.8-folded more than the minimum requirement of Joule heating, at a current density of 0.1 A·cm −2 at −20 °C. Thus, it was concluded that thermal dissipation from the resistive vanadium oxide films with a negative temperature coefficient can be effectively used as a self-heating source to melt frozen water at subzero ambient temperatures, particularly for fuel cell vehicles.

Deposition of gold–titanium and gold–nickel coatings on electropolished 316L stainless steel bipolar plates for proton exchange membrane fuel cells

The effects of electropolishing and coating deposition on electrical resistance and chemical stability were studied for the stainless steel bipolar plates in proton exchange membrane fuel cell (PEMFC). A series of 316L stainless steel plates, selected as the substrate for a proton exchange membrane fuel cell (PEMFC) bipolar plate, were electropolished with a solution of H 2SO 4 and H 3PO 4 at temperatures ranging from 70 to 110 °C. The surface regions of the two electropolished stainless steel plates were coated with gold and either a titanium or nickel layer using electron beam evaporation. The electropolished stainless steel plates coated in 2-μm thick gold with a 0.1-μm titanium or nickel interlayer showed remarkably smooth and uniform surface morphologies in AFM and FE-SEM images compared to the surfaces of the plates that were coated after mechanical polishing only. The electrical resistance and water contact angle of the deposited stainless steel bipolar plates are strongly dependent on the surface modification treatments (i.e., mechanical polishing versus electropolishing). ICP-MS and XPS results indicate that after electropolishing, the coating layers show excellent chemical stability after exposure to an H 2SO 4 solution of pH 3. Finally, it was concluded that before coating deposition, the surface modification using electropolishing was very suitable for enhancing the electrical property and chemical stability of the stainless steel bipolar plate.

Electrochemical Performance Testing and Characterization of Silver-Plated and Graphite-Coated 316L Stainless Steel Bipolar Plates

316L stainless steels are the most promising materials for use as bipolar plates in proton exchange membrane fuel cells (PEMFC) because of their low cost,light weight,convenience of machining,ease of shaping into thin sheets,excellent electrical conductivity,and their heat exchange properties.However,the interfacial contact resistance (ICR) between carbon paper and stainless steel was found to increase because of passive film formation in a PEMFC cathodic environment.Additionally,the catalyst was poisoned by the corrosion products of the bipolar plate in the PEMFC anodic environment and the output power of the cell decreased.We added a conductive graphite coating onto the surface of 316L stainless steel and found the ICR of the sample reached 80.6 mΩ·cm2.The ICR was only 19.8 mΩ·cm2 when a thin layer of silver was present between the 316L stainless steel and the graphite layer.Various electrochemical tests,such as Tafel curves and oxidation curves using steady potential,were used to study the corrosion behavior of the three samples (316L stainless steel,silver-plated 316L stainless steel,silver-plated and graphite-coated 316L stainless steel) in PEMFC environments.Results showed that compared to 316L stainless steel,the corrosion potential of the silver-plated and graphite-coated 316L stainless steel increased by 0.49 and 0.35 V,respectively and the corrosion current density decreased to 10-6-10-7 A·cm-2.The silver-plated sample was easily damaged as small holes in the silver-layer allowed parts of the stainless steel substrate to be exposed.