Stainless Steel Bipolar Plates Research Articles

Characterization of the performance of CrN/Nb coated 316L stainless steel bipolar plates for PEMFC

Characterization of the performance of CrN/Nb coated 316L stainless steel bipolar plates for PEMFC

Time and Potential-Resolved Studies of Bipolar Plate Corrosion for Polymer Electrolyte Membrane Fuel Cells

Stainless steels are regarded as the reference materials for metal bipolar plates for polymer electrolyte membrane fuel cells (PEMFCs) due to their low cost and weight, high electrical conductivity, flexural strength, ease of machining, and ability to be formed into thin sheets. The main drawback is their susceptibility to corrosion in typical acidic, oxidizing environments of PEMFCs, 1,2,3 which can degrade the performance of the plate and other components of the PEMFC. The simultaneous presence of iron ions released by corrosion of the BPP and hydrogen peroxide is responsible for hydroxyl radical production, resulting in degradation of the membrane and cathode catalyst layer ionomer.4 Applying a protective coating to the metal bipolar plates is an effective way to improve its corrosion resistance.5 This work investigates corrosion rates of SS316L bipolar plates on the basis of the measured concentrations of cations (e.g., Fe, Cr, and Ni) in an aqueous electrolyte as a function of applied potential and corrosion environment.Techniques employing electrochemical flow cells (EFC) directly coupled to an inductively-coupled plasma mass spectrometer (ICP-MS) allow for more precise time- and potential-resolved detection of dissolved species. This work will report real-time data on leaching of Fe, Cr, and Ni from SS316L substrates subjected to potential cycles using a flow-through electrochemical cell coupled with an on-line ICP-MS instrument, with sub-part per billion (ppb or μg/L) sensitivity, providing the ability to resolve dissolution during potential scans. The results of this work provide a baseline for studying the efficacy of stainless steel bipolar plate coatings in mitigating degradation of PEMFCs. References Leng, P. Ming, D. Yang, C. Zhang. J. of Power Sources 451, (2020) 227783.Kumagai, S.-T. Myung, T. Ichikawa, H. Yashiro, Y. Katada, J. Power Sources 202 (2012) 92.D. Papadias, R. K. Ahluwalia, J. K. Thomson, H. M. Meyer III, M. P. Brady, H. Wang, J. A. Turner, R. Mukundan, R. Borup. J. of Power Sources 273 (2015) 1237.Elferjani, G. Serre, B. Ter-Ovanessian, B. Normand. International Journal of Hydrogen Energy 46, (2021), 32226-32241.Liu, Q. Jia, B. Zhang, Z. Lai, L. Chen. International Journal of Hydrogen Energy 47, (2022) 22915. Acknowledgements This research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the M2FCT consortium. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC under contract DE-AC-02-06CH11357.

A Simple in-situ Voltage Characterization Technique and Coating Methods for Developing Polymer Electrolyte Membrane Water Electrolysis Porous Transport Layer and Bipolar Plates

As climate change progresses, decarbonization becomes imperative, and hydrogen is gaining attention as a clean energy source alongside carbon [1]. Particularly, hydrogen obtained through electrolysis has the advantage of being carbon-free throughout the production process, known as green hydrogen. Currently, electrolysis is primarily conducted through alkaline and polymer electrolyte membrane methods. Polymer electrolyte membrane devices, operating effectively even at high pressures, offer advantages over alkaline electrolysis in efficiency and hydrogen production. Thus, polymer electrolyte membrane devices are essential for entering carbon neutrality [2]. However, the high voltage (~2V) and acidic operating environment in the operating condition causes component corrosion, forcing their uses of high price materials. The porous transport layer and bipolar plates of polymer electrolyte membrane devices utilize platinum-coated titanium [3]. Therefore, accurately measuring the voltage profile inside the device and replacing precious metal coated titanium can reduce device costs and offer commercial advantages. Although considerable research is ongoing, most studies require complex electrolyte solutions and custom membrane electrode assembly fabrication techniques.This study proposes a simple technique using commercial products to evaluate internal voltage profile in polymer electrolyte membrane devices and introduces materials that can replace titanium. Membrane Electrode Assembly from HIAT and Porous Transport Layer from Mott is utilized, and similar to Z. Kang et al. [4], voltages of the PTL, Catalyst Layer (CL), and Bipolar Plate (BP) relative to the cathode were measured. 0.001x0.005 mm² gold wire (California fine wire Co.) is used to measure voltage during the voltage. In some studies, voltage profiles of PEMWE stack were measured by applying voltage to the MEA instead of the bipolar plate [5]. In this study, voltage profiles inside of the cell and stack was measured. By simply placing a gold wire between the component, the voltage profile during device operation was observed. The measurements revealed a voltage small drop within the proton exchange membrane.On the other hand, the Ta-based stainless steel confirms the potential utilization of stainless steel coated materials as an alternative to titanium-based ones. According to Becker et al. [6], the voltage of the cathode during operation is approximately 0VvsRHE or less, and the bipolar plate's condition is electrochemically stable compared to the anode. Thus, a single-layer coating of PEALD TiN on stainless steel has been proposed for the cathode. On the contrary, the environment at the anode was harsher compared to the cathode, with a higher susceptibility to corrosion due to the application of high voltages (~2V). Therefore, a Ta based coating has been proposed for the anode. When conducting PEMWE experiments using Ta-coated stainless steel (SUS), it exhibited performance comparable to using Ti-based bipolar plates in both cell and stack performance. Moreover, in long-term performance, Ta-coated SUS demonstrated superior performance. Furthermore, coating Ta onto SUS PTL used in AEMWE confirmed the feasibility of replacing Ti-based PTL.References.[1] Y. Leng, P. Ming, D. Yang, C. Zhang, Stainless steel bipolar plates for proton exchange membrane fuel cells: Materials, flow channel design and forming processes, J. Power Sources. 451 (2020) 227783. https://doi.org/10.1016/j.jpowsour.2020.227783.[2] S.Y. Kang, J.E. Park, G.Y. Jang, C. Choi, Y.H. Cho, Y.E. Sung, Directly Coated Iridium Nickel Oxide on Porous-Transport Layer as Anode for High-Performance Proton-Exchange Membrane Water Electrolyzers, Adv. Mater. Interfaces. 10 (2023). https://doi.org/10.1002/admi.202202406.[3] H. Becker, E.J.F. Dickinson, X. Lu, U. Bexell, S. Proch, C. Moffatt, M. Stenström, G. Smith, G. Hinds, Assessing potential profiles in water electrolysers to minimise titanium use, Energy Environ. Sci. 15 (2022) 2508–2518. https://doi.org/10.1039/d2ee00876a.[4] Z. Kang, S.M. Alia, M. Carmo, G. Bender, In-situ and in-operando analysis of voltage losses using sense wires for proton exchange membrane water electrolyzers, J. Power Sources. 481 (2021) 229012. https://doi.org/10.1016/j.jpowsour.2020.229012.[5] A.J. McLeod, L. V. Bühre, B. Bensmann, O.E. Herrera, W. Mérida, Anode and cathode overpotentials under accelerated stress testing of a PEM electrolysis cell, J. Power Sources. 589 (2024). https://doi.org/10.1016/j.jpowsour.2023.233750.[6] H. Becker, E.J.F. Dickinson, X. Lu, U. Bexell, S. Proch, C. Moffatt, M. Stenström, G. Smith, G. Hinds, Assessing potential profiles in water electrolysers to minimise titanium use, Energy Environ. Sci. 15 (2022) 2508–2518. https://doi.org/10.1039/d2ee00876a.

Study on Springback Behavior in Hydroforming of Micro Channels for a Metal Bipolar Plate.

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

Enhanced corrosion resistance and electrical conductivity of stainless steel bipolar plates by molybdenum ion implantation

Enhanced corrosion resistance and electrical conductivity of stainless steel bipolar plates by molybdenum ion implantation

Nanostructured multilayer Cr/CrN coatings on 316L stainless steel for proton exchange membrane fuel cell bipolar plates

Nowadays, hybrid surface modification approaches offer tailored solutions for improving the corrosion resistance and electrical conductivity of the bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs). In the present study, a combination of plasma nitriding and physical vapor deposition (PVD) processes was used to apply a nanometric Cr/CrN multilayer coating onto 316L stainless steel (SS316L) bipolar plates. The performance of the resulting plasma nitrided, PVD-coated, and combined plasma nitriding/PVD-coated SS316L BPPs was examined by phase and morphological characterizations, surface wettability measurements, interfacial contact resistance (ICR), and electrochemical investigations. Potentiodynamic and potentiostatic polarization evaluations, electrochemical impedance spectroscopy (EIS) and Mott-Schottky asessments were conducted on the coated samples in a simulated PEMFC cathode environment at temperatures of 25 °C and 75 °C. Results indicated that the Cr/CrN multilayer coating deposited on the plasma-nitrided 316L BPP exhibited a remarkable 100-fold improvement in corrosion resistance compared to the uncoated substrate. Also, the combination of nitriding and PVD resulted in a significant reduction of the ICR from 186 mΩ cm2 for the uncoated SS316L to 10.2 mΩ cm2 for the coated sample. Multilayer coatings based on the combination of plasma nitriding and PVD treatment can identified as promise candidates for BPP applications.

Coating Titanium Transport Layers for Enhanced Short and Long Term Performance in PEM Water Electrolysis Cells

The ageing of titanium porous transport layers (PTL) affects the longevity of polymer electrolyte membrane water electrolysis systems by the formation and thickening of a weakly conductive oxide layer. The evolving oxygen on the anode in combination with the high electrical potential provides a challenging environment in which a low electrical contact resistance to the catalyst layer (CL) needs to sustain over a long period. One previous approach is a precious metal coating of the PTL with platinum or iridium [1], which can prevent oxidation of the titanium. A cost-effective alternative is a hydrochloric acid treatment, which forms titanium hydride (TiH). [2] Titanium nitride (TiN) promises better electrical conductivity with similar corrosion resistance, but has not yet been tested as a coating. The same is true for niobium, which performed well as a coating for stainless steel bipolar plates. [3] In our studies, all these candidates face the same conditions aside an untreated PTL in one unique series of measurements. All types are repeated three times to ensure reproducibility. The mean polarization curves (figure 1 left) show that the two precious metals, iridium and platinum, significantly improve the cell voltage at a current density of 2A/cm² by 80mV and 95mV, respectively. Titanium hydride achieves an even higher reduction of 100mV without the use of precious metals. The high frequency resistance plots in figure 1 right determine that the improvement of up to 20% or 30mΩ∙cm² is attributable to a reduced contact resistance to the CL. This assumption is proven by the fact that a PTL that is only coated with iridium on the side facing the CL behaves identically to a PTL that is coated on both sides. The ohmic losses in contact with the BPP are therefore negligible in these experiments. Titanium nitride and niobium coated PTLs behave in the same way as the reference measurement. In addition to the measurements shown, long-term experiments (>1000 hours) are currently running for all types of coating, and corrosion measurements in sulphuric acid are being carried out in parallel. The joint results will determine the suitability of the various coatings for long-term use in electrolysers.[1] Liu, C., Shviro, M., Gago, A. S., Zaccarine, S. F., Bender, G., Gazdzicki, P., Morawietz, T., Biswas, I., Rasinski, M., Everwand, A., Schierholz, R., Pfeilsticker, J., Müller, M., Lopes, P. P., Eichel, R.-A., Pivovar, B., Pylypenko, S., Friedrich, K. A., Lehnert, W., Carmo, M., Exploring the Interface of Skin-Layered Titanium Fibers for Electrochemical Water Splitting. Adv. Energy Mater. 2021, 11, 2002926. https://doi.org/10.1002/aenm.202002926[2] Bystron, T., Vesely, M., Paidar, M. et al. Enhancing PEM water electrolysis efficiency by reducing the extent of Ti gas diffusion layer passivation. J Appl Electrochem 48, 713–723 (2018). https://doi.org/10.1007/s10800-018-1174-6[3] Stiber, S., Hehemann, M., Carmo, M., Müller, M., Ayers, K.E., Capuano, C., Danilovic, N., Morawietz, T., Biswas, I., Gazdzicki, P., Heger, J.-F., Gago, A.S. and Friedrich, K.A. (2022), Long-Term Operation of Nb-Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Water Electrolyzers. Adv. Energy Sustainability Res., 3: 2200024. https://doi.org/10.1002/aesr.202200024 Figure 1

Structure and performance of N-doped amorphous carbon films (a-C: N) on stainless steel surfaces for bipolar plates in proton exchange membrane fuel cells

Stainless steel bipolar plates (BPPs) are anticipated to supersede traditional graphite BPPs in proton exchange membrane fuel cells (PEMFCs) owing to their superior machinability, enhanced mechanical strength, and cost-effectiveness. Nevertheless, stainless steel BPPs are susceptible to corrosion and dissolution in acidic environments over extended periods, leading to the formation of a passivation film that diminishes conductivity. In this study, amorphous carbon (a-C) films with varying N doping contents were deposited onto 304L stainless steel foil using the cathodic arc ion plating technique. This was achieved by manipulating the N2 flow rate. The research investigated the impact of N doping on the microstructure, corrosion resistance, interfacial contact resistance (ICR), and hydrophobicity of the a-C films on stainless steel surfaces. The findings reveal that the various a-C films significantly enhance the performance of 304L stainless steel under simulated PEMFCs operating conditions. While N-doped a-C (a-C: N) films are advantageous for reducing ICR, incorporating N results in a decrease in C-sp3 content and density, ultimately leading to a decrease in the corrosion resistance of films. Additionally, the hydrophobicity of the a-C films diminishes with increasing N content. Consequently, N doping is not conducive to improving the overall performance of a-C films on the surface of 304L stainless steel bipolar plates under simulated PEMFCs operating conditions.

Corrosion behavior of Ti–Pt-coated stainless steel for bipolar plates in polymer electrolyte membranes under water electrolysis conditions

In this study, the corrosion behavior and degradation mechanism of Ti–Pt-coated stainless steel bipolar plates were investigated through electrochemical tests and surface analysis in a polymer electrolyte membrane water electrolysis (PEMWE) operating environment. The coated bipolar plate has a corrosion current density of only 1.68 × 10−8 A/cm2, which is an order of magnitude lower than that of the bare SS316L substrate (1.94 × 10−7 A/cm2), indicating that its corrosion resistance is superior to that of bare SS316L substrate. However, in the PEMWE operating environment, the protection efficiency of the coating and the corrosion resistance of the coated bipolar plate decreased. The degradation of the coated bipolar plate can be attributed to electrolyte penetration into the blistering areas of the coating layer with micro voids. Defects in the coating layer occur because of the pressure of oxygen gas generated within the coating layer under high-potential conditions, thereby exposing the substrate to the electrolyte and corrosion.

Improving corrosion and conductivity of Ti-doped amorphous carbon film coated on 316L stainless steel bipolar plates by nitrogen atoms doping

Amorphous carbon films have recently attracted extensive attention as surface functional films for bipolar plates with excellent conductivity and anti-corrosion properties. In this research, to determine the influence of the amorphous carbon film doped with titanium and nitrogen on the efficiency of proton exchange membrane fuel cells (PEMFCs) and clarify the effect of N atoms on Ti doped amorphous carbon, a series of Ti, N co-doped amorphous carbon films are built on 316L stainless steel at different N2 flow rates. This study provides detailed research about the influence of N atoms content on the microstructure, morphology evolution, corrosion resistance and interfacial contact resistance (ICR) of Ti, N co-doped amorphous carbon films. The results reveal that the N doping of the Ti-doped amorphous carbon film has the potential to enhance the C-sp2 content and refine the grain. The characterization results indicate that introducing N atoms into Ti doped amorphous carbon can reduce the ICR of the film to 2.38 mΩ cm2. The introduction of N atoms can also enhance the anti-corrosive characteristics of the titanium singly doped amorphous carbon film. The Ti, N co-doped film can be used as candidate materials applied to metal bipolar plates.

The structure evolution of austenite stainless steel with pre-shot peening during plasma nitriding

Abstract Austenitic stainless steel is a very promising metal bipolar plate for proton exchange membrane fuel cells (PEMFC), which has advantages such as high mechanical strength, easy processing, and low cost. However, it is prone to corrosion in the acidic environment of PEMFC, which can have adverse effects on its lifespan and conductivity. By adopting a composite modification method to generate a dense nitride structure on the surface of 304 stainless steel bipolar plates, the corrosion resistance of the bipolar plate substrate can be improved. In this paper, shot peening pretreatment and plasma nitriding hybrid modification methods were employed to improve nitriding efficiency and reduce nitriding critical temperature, which generated a modified layer with good corrosion resistance on the surface of 304 austenitic stainless steel.

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.

Improvement of corrosion resistance and electrical conductivity of a Cr–C coated heat-assisted forming stainless steel bipolar plate for proton exchange membrane fuel cell

Heat-assisted forming is gaining increasing attention for its potential in improving the formability and quality of metallic bipolar plate (BPP) of proton exchange membrane fuel cell (PEMFC). However, the effects of heat-assisted forming and the subsequent coating process on corrosion resistance and electrical conductivity of stainless steel BPP still remain unclear. This work proposes a way to improve simultaneously the corrosion resistance and electrical conductivity of heat-assisted forming stainless steel BPP by depositing a Cr–C coating directly on its surface without removing the oxide layer using the magnetron sputtering method. Potentiodynamic tests indicate that self-corrosion current density and corrosion current density at 1.0 V (vs. Ag/AgCl) of the Cr–C coated heat-assisted forming SS316L BPP prepared under 900 °C for 10 min are 0.021–0.040 μA cm−2 and 77.54 μA cm−2, respectively, both of which are smaller than those of coated SS316L BPP formed under room temperature. In addition, the contact resistance is close to that of the gold-plated copper plate under the same pressure. The corrosion resistant intermediate oxide layer and conductive network formed between Cr–C coating and metal substrate through defects of oxide layer may be the main reason for improvement of its corrosion resistance and electrical conductivity, respectively.

Ex-situ Characterization of Nb-Ti Alloy/Pt Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Fuel Cells

Metallic bipolar plates are crucial for the development of compact and lightweight proton exchange membrane fuel cell stacks; however, most of them encounter durability and conductivity challenges in the fuel cell environment. In this study, Nb-Ti alloy/Pt coatings are deposited on SS316L plates to enhance corrosion resistance, surface wettability, electrical and thermal conductivity, with reduced interfacial contact resistance. Corrosion resistance is assessed by exposing test samples to a 1M H2SO4 acidic environment at 25 °C and 80 °C, respectively, via potentiostatic and potentiodynamic polarization tests. It is found that Nb-Ti alloy/Pt coatings exhibit exceptional stability, with corrosion potential increased by 2.5 (at 25 °C) and 0.5 (at 80 °C) times and corrosion current density reduced by orders of magnitude; and their anti-corrosion performance far exceeds the technical targets set by the US Department of Energy, with a protective efficiency of 99.98 % at both temperatures tested. The coated samples have reduced water affinity, indicated by significantly larger contact angle values compared to the uncoated samples in both pre-and post-corrosion tests. The incorporation of Nb-Ti alloy/Pt coatings on SS316L increases the in-plane electrical conductivity by 42.6 % and thermal conductivity by 3.5 %; surpassing the US Department of Energy's technical targets in these categories as well. At a compaction force of 140 N/cm2, the interfacial contact resistance for the coated samples is about 2.5 times lower than the Department of Energy's requirements. These results indicate the viability of Nb-Ti alloy/Pt coated SS316L bipolar plates for fuel cell applications.

Corrosion Resistance and Conductivity of Ta-Nb-N-Coated 316L Stainless Steel as Bipolar Plates for Proton Exchange Membrane Fuel Cells

The large-scale application of stainless steel (SS) bipolar plates (BPs) in proton exchange membrane fuel cells (PEMFCs) is mainly limited by insufficient corrosion resistance and electrical conductivity. In this work, Ta-Nb-N coatings were prepared on 316L SS substrates by unbalanced magnetron sputtering to improve corrosion resistance and conductivity. The Ta-Nb-N coatings had a dense structure without obvious defects. In simulated PEMFC cathode environments consisting of 0.5 M H2SO4 + 2 ppm HF at 70 ± 0.5 °C, which is harsher than the U.S. Department of Energy specification, the corrosion current density of Ta-Nb-N-coated BPs was reduced to 2.2 × 10−2 μA·cm−2. Ta-Nb-N-coated samples showed better electrical conductivity than 316L SS, which had an excellent interfacial contact resistance of 9.2 mΩ·cm2. In addition, the Ta-Nb-N-coated samples had a water contact angle of 100.7°, showing good hydrophobicity for water management. These results indicate that Ta-Nb-N coatings could be a promising material for BPs.

A novel carbon coating by electrochemical deposition in deep eutectic solvent with the assistance of ammonium chloride for stainless steel bipolar plates

In this work, pulse electrodeposition method was proposed to directly deposit amorphous carbon coating (ACC) onto 316L stainless steel substrate in choline chloride-ethylene glycol deep eutectic solvent (DES) mixed with ammonium chloride (NH4Cl) to fabricate bipolar plates. The obtained dense ACC has a thickness of ∼400 nm. Potentiodynamic and potentiostatic polarization tests demonstrated that the corrosion current density of ACC coated 316L steel was of the order of 10−7 A cm−2 in the simulated proton exchange membrane fuel cells (PEMFC) working environment, and the self-corrosion potential of the coating positively shifted by 0.4V, indicating a significant improvement on corrosion resistance of the coated steel plate due to excellent electrochemical stability of ACC. The Rockwell C indentation test showed that the as-obtained ACC was strongly bonded to the substrate and also had high in-plane strength. Further numerical simulation and comparison experiments showed that C was chemically bonded with Fe in the substrate, which was boosted by the assistance of NH4Cl. The intact and strong bonding between ACC and the substrate is highly helpful to improve corrosion resistance. The success in coating stainless steel plate with ACC by pulse electrodeposition method provides a promising alternation for coating of proton exchange membrane electrolyzer cell (PEMEC) and PEMFC metal bipolar plates.

Fabrication of (TiZrNbSiMo)1-xNx high entropy alloy coatings using a high power impulse magnetron sputtering technique: Effects of nitrogen addition

Due to the outstanding mechanical and physical properties of high entropy alloy (HEA) coatings, the global academic and industrial communities have made significant research efforts in recent years, aiming to expand their industrial applications. In this study, TiZrNbSiMo and (TiZrNbSiMo)1-xNx HEA nitride coatings with different nitrogen contents were fabricated using a high power impulse magnetron sputtering (HiPIMS) system. By varying the nitrogen flow rates, the nitrogen contents of coatings increased from 0 to 48.8 at. %. The deposition rate decreased with increasing nitrogen content due to the target poisoning effect. Very fine and dense microstructure can be seen for each coating. The amorphous structure was obtained as the nitrogen content was lower than 19.1 at.%, whereas a nanocrystalline FCC structure was formed when the nitrogen content reached 34.9 at. %. Furthermore, the corrosion resistance of TiZrNbSiMo and four TiZrNbSiMoN HEA coatings in 0.5 M H2SO4 aqueous solution were superior to uncoated 304 stainless steel. We can conclude that the nanocrystalline TiZrNbSiMoN HEA coatings with a nitrogen content of 34.9 at. % exhibited a high hardness of 15.6 GPa, an electrical resistivity of 766.5 μΩ·cm, and an excellent corrosion polarization resistance of 9.71 × 105 Ω·cm2, 610.7 times higher than 304SS. This study provides valuable insights for future promising applications of (TiZrNbSiMo)1-xNx HEA nitride coatings in severely corrosive environments, such as the protective coatings on stainless steel bipolar plates in proton exchange membrane fuel cells.

Effect of magnetron sputtering C-doped CrN film on the conductivity and corrosion resistance of 304 stainless steel bipolar plates

Using a high-power impulse and direct current (DC) magnetron sputtering approach, C-doped CrN films with various C-target pulse frequencies are created on the surface of SS 304. The microstructure, corrosion resistance and conductivity of the films are examined. With the decreases of C-target pulse frequency, the roughness of the CrCN films decreases and the density increases. The results of XPS and TEM analyses demonstrate that C atoms are either present in CrN lattice as interstitial atoms or precipitate at grain boundaries to form amorphous carbon, which facilitates the increase of film density and conductivity. In the potentiodynamic tests, the CrCN-1000 Hz film exhibits the lowest corrosion current density 0.54 μA/cm2 at 0.6 V vs. Ag/AgCl potential. The values of icorr and Ecorr are 0.11 μA/cm2 and 0.427 V, respectively. Furthermore, the CrCN-1000 Hz film has the lowest interface contact resistance (ICR) under a compaction force of 140 N/cm2 after potentiostatic polarization test, indicating that C doping is beneficial to improve the corrosion resistance and conductivity of CrN film.

Investigation of evolution of γ N phase and its effect on conductivity and corrosion resistance of plasma-nitrided 316 L stainless steel bipolar plate for proton exchange membrane fuel cell

In this work, the evolution of γ N phase and its effect on conductivity and corrosion resistance of plasma-nitrided 316 L stainless steel bipolar plate was investigated. The results shows that a certain thickness of uniform γ N phase layer was formed after plasma-nitriding treatment. As the increasing in plasma-nitriding time, the thickness of γ N phase layer and nitrogen atoms in γ N phase layer was increased gradually. As the plasma-nitriding time was larger than 10 h, a large amount of cracks was formed in γ N phase layer because the nitrogen atoms were diffused into γ phase to cause the serious lattice distortion. When the plasma-nitriding time was reached to 24 h, the Fe4N compound was found on the sample surface. After plasma-nitriding treatment, the conductivity and corrosion resistance of the sample was obviously enhanced compared with the untreated sample. With the increasing in the thickness of γ N phase layer, the interfacial contact resistance (ICR) and corrosion current of the sample was gradually reduced. The ICR of the sample was reduced to 7 mΩ under 10 h condition. However, the formation of Fe4N compound and high roughness contributed to the increase of ICR of the sample under 24 h condition, its value was reached to 15 mΩ. When the plasma-nitriding time was larger than 10 h, the corrosion resistance of the sample became poor. The formation of cracks in γ N phase layer and the high surface roughness resulted in the degradation of corrosion resistance of the sample. Under 5 h condition, the comprehensive properties of the sample were the best. The ICR and corrosion of the sample were current conductivity and corrosion resistance of the sample were 15 mΩ and 5.1 μA cm−2, which were low 4 times and 15 times compared with the untreated sample.

Performance of Stainless-Steel Bipolar Plates (SS-BPPs) in Polymer Electrolyte Membrane Water Electrolyser (PEMWE): A Comprehensive Review

Bipolar Plates (BPPs) play a critical role in Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) for effective hydrogen generation. The performance and longevity of the system can be considerably impacted by choosing the suitable material for these components. Polymer electrolyte membrane water electrolysis technology relies on cost-effective and corrosion-resistant BPPs. Tantalum, niobium, and titanium are low-cost, easy-to-machine materials that have good electrical and thermal conductivity; however, they exhibit low corrosion resistance. Noble metal and metal nitride coatings are usually investigated to minimize corrosion and interfacial contact resistance. Because of its performance-to-cost ratio, Stainless Steel (SS) based materials are among the most popular materials for BPP development. This study recommends material and operating parameters to improve PEMWE systems for sustainable hydrogen production’s efficiency, durability, and economic viability.