Optimized Cr-nitride film on 316L stainless steel as proton exchange membrane fuel cell bipolar plate

doi:10.1016/j.ijhydene.2008.09.104

International Journal of Hydrogen Energy

Volume 34, Issue 1, January 2009, Pages 453-458

https://doi.org/10.1016/j.ijhydene.2008.09.104 Get rights and content

Abstract

Pulsed bias arc ion plating was used to form Cr-nitride films on stainless steel as bipolar plate of proton exchange membrane fuel cell. Surface micrograph, film thickness, film composition, corrosion resistance, interfacial conductivity and contact angle with water of the sample obtained at the optimal flow rate of N₂ were investigated. The atomic ratio of Cr to N was close to 2:1 and the CrN phase with crystal planes of (111), (200), (220) and (311) was found in the film. Potentiodynamic and potentiostatic tests showed that the corrosion resistance of the bipolar plate sample was greatly enhanced. The contact resistance between the bipolar plate sample and Toray carbon paper was about two orders of magnitude lower than that of 316L stainless steel. The contact angle of the sample with water was 95°, which is beneficial for water management in fuel cells.

Introduction

Bipolar plate is an important component of proton exchange membrane fuel cell (PEMFC), and it accounts for most of the total weight. The bipolar plate serves as the functions of distributing reactants uniformly over the active areas, removing heat from the active areas, collecting currents from cells, preventing leakage of reactants and coolant. An ideal bipolar plate material should have the characteristics as follows: (1) high corrosion resistance in PEMFC environment; (2) low interfacial contact resistance; (3) big contact angle with water; (4) lightweight; (5) high mechanical strength; and (6) cost-effective etc.

Forming a film with good corrosion resistance and high interfacial conductivity on stainless steel is one of the possible solutions. Metal nitrides are the promising surface modification materials for metal bipolar plate owing to their good corrosion resistance and high conductivity. Most of the researches have been focused on Cr-nitrides in recent years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. In our previous work [11], Cr-nitride gradient films were coated on 316L stainless steel by pulsed bias arc ion plating (PBAIP) as bipolar plate for PEMFC. The composition of film varied with the flow rates of N₂. Films obtained at N₂ gas flow rates from 25 to 100 sccm exhibited high interfacial conductivity, good corrosion resistance and big contact angle, which showed great potential in the application of PEMFC.

The aim of the present work was to optimize the flow rate of N₂ and obtain bipolar plate with better performance. Surface micrograph, film thickness, film composition, corrosion resistance, interfacial conductivity and contact angle with water of the bipolar plate sample prepared at the optimal flow rate of N₂ were investigated.

Section snippets

Experimental

The 316L stainless steel (bright annealed) with the size of 100 × 100 × 0.1 mm³ was chosen as the base metal of bipolar plate. Details of forming the Cr-nitride films are described in our previous paper [10]. By changing the flow rate of N₂, film with different composition could be obtained. However, the total pressure in the chamber, which is a sum of the N₂ pressure and the Ar pressure, was kept constant at 5.0 × 10⁻³ Pa. The flow rates of N₂ conducted in this study are listed in Table 1. In this

Optimization of the flow rate of N₂

The corrosion resistance and interfacial conductivity are the two main properties of metal bipolar plate materials. The parameters of passive current density (the current density under passivation potential) and interfacial contact resistance were used to evaluate theses properties. All the bipolar plate samples were prepared at different flow rates of N₂ by PBAIP. Passive current density in 0.5 M H₂SO₄ + 5 ppm F⁻ solution at 25 °C and initial contact resistance with carbon paper under 1.2 MPa of all

Conclusions

Different compositions of Cr-nitride films could be obtained by changing the flow rate of N₂ during PBAIP process. The bipolar plate sample produced at 20 sccm N₂ exhibited the best corrosion resistance and the highest interfacial conductivity simultaneously.

In the film obtained at the optimal flow rate of N₂, the atomic ratio of Cr to N was very close to 2:1 and CrN phase with crystal planes of (111), (200), (220) and (311) was found.

Potentiodynamic and potentiostatic tests performed at 70 °C

Acknowledgments

This work was financially supported by the National High Technology Research and Development Program of China (863 Program, No. 2007AA03Z221).

References (11)

G. Bertrand et al.
A study of the corrosion behaviour and protective quality of sputtered chromium nitride coatings
Surf Coat Technol
(2000)
M.P. Brady et al.
Preferential thermal nitridation to form pin-hole free Cr-nitrides to protect proton exchange membrane fuel cell metallic bipolar plates
Scripta Mater
(2004)
I.E. Paulauskas et al.
Corrosion behavior of CrN, Cr₂N and π phase surfaces on nitrided Ni-50Cr for proton exchange membrane fuel cell bipolar plates
Corros Sci
(2006)
H. Wang et al.
Thermally nitrided stainless steels for polymer electrolyte membrane fuel cell bipolar plates: part 2. Beneficial modification of passive layer on AISI446
J Power Sources
(2004)
H. Wang et al.
Thermally nitrided stainless steels for polymer electrolyte membrane fuel cell bipolar plates: part 1: model Ni-50Cr and austenitic 349™ alloys
J Power Sources
(2004)

There are more references available in the full text version of this article.

Cited by (77)

Effect of aging temperature on corrosion resistance of 316L stainless steel in simulated proton exchange membrane fuel cell cathode environment
2024, International Journal of Hydrogen Energy
The effects of aging temperature on the corrosion behavior of 316 L stainless steel in a simulated cathodic environment of a proton exchange membrane fuel cell (PEMFC) were investigated by potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), double-loop electrochemical potential response (DL-EPR). The results show that the corrosion resistance of 316 L is significantly degraded after aging at 750–900 °C for 1 h in the simulated cathodic environment of PEMFC. A strong sensitivity to intergranular corrosion takes place after aging at 850 °C, and chromium rich M₂₃C₆ carbides precipitate on grain boundaries. The precipitation of M₂₃C₆ leads to discontinuity of the passivation film near the grain boundaries, resulting in Cr-depleted zones at the grain boundaries, increasing intergranular corrosion, and decreasing corrosion resistance. When the aging temperature exceeds 950 °C, grain boundary precipitation of M₂₃C₆ does not occur and the corrosion resistance is improved. At an aging temperature of 1050 °C, a dense Cr₂O₃ film is formed on the surface of the alloy during the polarization test, giving it the best corrosion resistance in the simulated cathodic environment of PEMFC.
High corrosion resistance and conductivity of Al<inf>2</inf>O<inf>3</inf>/CrN coating for metal bipolar plates in PEMFCs: Al<inf>2</inf>O<inf>3</inf> hinders CrN columnar crystals growth
2024, International Journal of Hydrogen Energy
An excellent corrosion-resistant and good conductivity coating is desired for metal bipolar plate (BP) in proton exchange membrane fuel cell (PEMFC). In this view, a novel strategy to achieve this aim by introducing Al₂O₃ into CrN film. Al₂O₃/CrN nanocomposite coatings are first prepared by co-sputtering. Subsequently, the microstructure, electrochemical corrosion resistance, interfacial contact resistances (ICR) and contact angle are systematically investigated. As a result, Al₂O₃/CrN nanocomposite coating shows a low corrosion current density of 0.084 μA/cm² in room temperature and a low corrosion current density of 0.39 μA/cm² at 70 °C, which highly meets the requirement of U.S. DOE 2025 targets. Besides, Al₂O₃/CrN nanocomposite coating displays a superior durability to pure Au film. It is revealed that Al₂O₃ can hinder the growth of CrN columnar crystals and result in coating amorphization, which is the mechanism of Al₂O₃-promoted the CrN corrosion resistance. Furthermore, Al₂O₃/CrN coating also exhibits an excellent electrical conductivity, featuring a smaller ICR of 3.09 mΩ cm². Inspired by these results, introducing Al₂O₃ into CrN coatings can provide enlightening insights to design new non-noble-metal coatings for metal BP in future PEMFC manufacturing.
Adjustable TiN coatings deposited with HiPIMS on titanium bipolar plates for PEMFC
2022, International Journal of Hydrogen Energy
TiN coatings were deposited by HiPIMS at different N₂ flow rate to improve the corrosion resistance and conductivity of metallic bipolar plates. The results show that the surface microstructure of TiN coating depends strongly on the N₂ flow rate, all the samples (N₂ flow rate: 4 to10 sccm) meet the DOE 2025 standard and exhibit good hydrophobicity, which has great potential for industrial application. Among them, at the N₂ flow rate of 8 sccm, the TiN coating shows high compactness and the optimum surface microstructure with the lowest surface roughness of 1.083 nm and the highest hardness of 31.172 GPa. The optimized TiN coating exhibits excellent corrosion resistance with corrosion current density of 0.278 μA cm⁻² and a low interfacial contact resistance value of 3.51 mΩ cm². This work has opened a new way for the large-scale preparation of high-performance metal bipolar plate coatings.
Characterization and properties of NbN–Nb bilayer formed on titanium for bipolar plates
2022, Materials Chemistry and Physics
In this study, the NbN/Nb bilayer structure was prepared by duplex-treatment (plasma surface alloying + nitriding) on titanium used as bipolar plates for proton exchange membrane fuel cells (PEMFCs). Niobium coating was deposited on titanium by means of double glow plasma surface alloying technique. Then, a thin NbN layer was created by plasma nitriding. The corrosion resistance and electrical conductivity of samples were measured in simulated PEMFCs environments. The result shows that at an applied potential of 0.6 V the corrosion current density of duplex-treated sample is two orders lower than that of untreated titanium. After corrosion testing at 0.6 V for 4 h, the interfacial contact resistance is 5.1 mΩ cm² compared with 29.7 mΩ cm² for untreated titanium.
Roles of H<inf>2</inf> evolution overpotential, materials porosity and cathode potential on mineral electro-precipitation in microfluidic reactor – New criterion to predict and assess interdependency
2022, Electrochimica Acta
Citation Excerpt :
It is also interesting to link the hydrophobicity of the cathode material with the occurring electro-precipitation. The increase of contact angles values from stainless steel (73°; [51]) to graphite (78°; [39]) and carbon paper (∼150°, according to a similar carbon paper characteristic (280 µm, no PTFE treatment, 80% of porosity; [52]), highlights the increase of hydrophobicity with the increasing cathodic electro-precipitation. This could be explained by the increase of O2 gas affinity towards the most hydrophobic material (i.e., carbon paper), which then increases the possibility of its subsequent reduction that lead to higher OH− generation.
The influence of cathode materials including carbonaceous electrode on the cathodic mineral scaling behavior in a context of wastewater treatment is investigated for the first time and particularly in thin film microfluidic reactors. The kinetics of CaCO₃ and Mg(OH)₂ electro-precipitations were evaluated with different cathode materials (with distinct porosities, electroactive surface area (S_elec) and hydrogen (H₂) evolution overpotential (HEP)) and by varying the applied current densities and interelectrode distances (d_elec). Three electrode materials were tested, carbon paper (porosity = 89%; S_elec = 175 cm²), graphite (porosity = 15%; S_elec = 85 cm²), stainless steel (porosity = 0%; S_elec = 80 cm²). An optimal condition to minimize the mineral deposition could be found in microfluidic configuration (100 µm d_elec) and by using graphite material being able to increase cathodic potential (E_C) so to decrease OH⁻ production. At higher d_elec, stainless steel led to less electro-precipitation compared with graphite. These results newly highlight that the electro-precipitation rate strongly depends on E_C values, which vary with current density and d_elec, as well as with the materials properties (porosity, S_elec, HEP). A new criterion, namely E_C/HEP, has been introduced to assess the interdependency of those parameters. Interestingly, a maximal electro-precipitation was noticed at E_C/HEP ≈ 1.3 for porous and non-porous materials. This further announces the possibility to predict the range of required E_C according to the electro-precipitation objective, which is crucial in real applications of electrolysis for wastewater treatment.
A comprehensive review on assembly design strategies on proton exchange membrane applications
2022, International Journal of Hydrogen Energy
Proton exchange membranes (PEMs) are widely used in fuel cells, electrolyzers, and electrolytic dehumidifiers. Despite significant improvements in material preparation, operational performance and durability for these applications remain impractical, mainly due to poor multilayer structures and component design. This paper reviews recent ideas on improving the assembly design for three types of PEM applications, focusing on aspects of configuration optimization of the membrane electrode assembly and microstructured anode/cathode materials. Well-designed interfaces in catalyst layers (CLs) and diffusion layers (DLs), and between multilayers, are critical for reducing contact resistance and enhancing water management. Modification of catalyst/ionomer interfaces, such as order-structured CLs and patterned PEM/CLs, can improve catalyst utilization and notably reduce loading. Combining multiple CLs and DLs with different porosity or hydrophobicity, or using metal-based DLs (metal fiber or foam) is also feasible. Another approach receiving much attentions is to improve the common plate-and-frame structure to a plate-less one. Eliminating bipolar plates with ridge grooves or integrating the flow field with DLs can improve the reaction, and reduce mass transfer and interface ohmic resistances. Stack compactness can also be enhanced. From the microstructure of materials to the macrostructure of assembly configurations, this review pointed out systematical guidance for further research to achieve well-designed PEM assemblies.

View all citing articles on Scopus

View full text

Optimized Cr-nitride film on 316L stainless steel as proton exchange membrane fuel cell bipolar plate

Abstract

Introduction

Section snippets

Experimental

Optimization of the flow rate of N2

Conclusions

Acknowledgments

Surf Coat Technol

Scripta Mater

Corros Sci

J Power Sources

J Power Sources

Optimization of the flow rate of N₂