Long-term polarization accelerated degradation of nano-thin C/Ti coated SS316L bipolar plates used in polymer electrolyte membrane fuel cells

Dynamic potentials of polymer electrolyte membrane fuel cells (PEMFCs) lead to the corrosion of metal bipolar plates and significantly increase their interfacial contact resistance (ICR). Herein, two nano-thin C/Ti coatings with different thicknesses are prepared on SS316L (C/Ti/SS) and examined under three types of polarization potential modes. The C₁₀₀Ti₆₀ coating has improved corrosion resistance than C₂₀Ti₁₄₀ coating. The C₁₀₀Ti₆₀ coating exhibits a low ICR of 2.67 mΩ cm² and a small corrosion rate of 1.47 μA/cm², highlighting the high electrical conductivity and corrosion resistance. Moreover, C₁₀₀Ti₆₀/SS achieves a slight degradation of ICR after polarization at 0.67 V and cyclic polarization between 0.43 and 0.73 V. However, the high potential of 1.43 V induces severe delamination of C layer, resulting in a remarkable increase of ICR. Analysis suggests that the Ti layer improves the oxidation resistance and the C layer could provide effective protection when the potential is below 1.13 V.     

Investigation of acidity on corrosion behavior and surface properties of SS304 in simulated PEMFC cathode environments

This study presents the influence of acidity on the corrosion performance and surface properties of AISI 304 stainless steel (SS304) in the simulated cathode condition of proton exchange membrane fuel cells (PEMFC) with various concentrations of H₂SO₄. The electrochemical tests indicate that the corrosion resistance of SS304 samples decreases gradually with the solution acidity ascending, but the stable current densities (0.043–0.547 μA cm^?2) in the simulated solutions after polarization (0.6 V, 5 h) are all lower than that of the relevant DOE 2025 target (i_corr < 1 μA cm^?2). Obvious pitting corrosion occur in the solutions with H₂SO₄ concentration higher than 10^?3 M. The surface wettability and interfacial contact resistance (ICR) of the potentiostatically polarized SS304 show an upward trend with the solution acidity increasing, and whether the SS304 samples are polarized or not, their ICR (0.274–1.232 Ω cm²) is far higher than the latest DOE 2025 technical target (<0.01 Ω cm²). The results reveal that surface modification is indispensable for SS304 as bipolar plates, and more attention should be paid to possessing high and stable pitting resistance, hydrophobicity, and interfacial conductivity in an acid environment.     

Influence of temperature on corrosion behavior,wettability, and surface conductivity of 304 stainless steel in simulated cathode environment of proton exchange membrane fuel cells

The effects of temperature on corrosion behavior, wettability, and surface conductivity of 304 stainless steel (SS304) in simulated cathode environment of proton exchange membrane fuel cells (PEMFC) are investigated systematically using electrochemical tests and surface analyses. The results indicate that although the corrosion resistance of SS304 is decreased with the rising of solution temperature, the current density of SS304 at the working potential in the simulated PEMFC cathode environment can still meet the 2025 U.S. Department of Energy (DOE) technical target (i_corr < 1 μA cm^?2). Meanwhile, the surface wettability and ICR of SS304 samples after potentiostatic polarization show a continuous increase with the rise of the simulated solution temperature. The surface conductivity of SS304 both before and after polarization cannot reach the 2025 DOE technical target (<0.01 Ω cm²) and needs to be improved by surface modification.     

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

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

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

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

Effect of pH value on corrosion resistance and surface conductivity of plasma‐nitrided 304L bipolar plate for PEMFC

Low temperature plasma nitriding is developed to meet the requirements for corrosion resistance and interfacial contact resistance (ICR) of stainless steel 304L as the bipolar plate for PEMFC. A dense and supersaturated‐nitrogen nitrided layer has formed on the surface of the stainless steel 304L. Electrochemical behavior for the untreated and plasma‐nitrided 304L was measured in H₂SO₄ (pH=1–5)+2 ppm F^? simulating PEMFC environment, and the ICR was evaluated before and after corrosion tests. The experimental results have shown that the ICR for the plasma nitrided 304L is lower than the requirement of U.S. DOE (<10 mΩ cm² to 2010). Corrosion resistance and the ICR at the compaction force of 150–200 N cm^?2 increase with increasing pH value for the untreated and plasma‐nitrided 304L. The passive current densities for the untreated and plasma‐nitrided 304L are all lower than 16 µA cm^?2. The ICR between passive film and carbon paper are increased markedly because of passive film formed on the surface of both studied 304L. However, the passive current density and the ICR are lower for the plasma nitrided 304L than those for the untreated one at the given pH value, which results from the different composition of the stable passive film formed on the surface. The low temperature plasma nitriding provides a promising method for 304L using as bipolar plate for PEMFC. Further research is needed to evaluate the long‐term stability of passive film and the performance of single fuel cell. Copyright © 2010 John Wiley & Sons, Ltd.     

An investigation of Zr-based bulk metallic glasses as bipolar plates for proton exchange membrane fuel cells

The electrochemical properties and interfacial contact resistance (ICR) of four Zr-based bulk metallic glasses with different compositions are evaluated for PEMFC applications. Based on the results and market demands, the corrosion behavior of the Zr_41·2Ti_13·8Cu_12·5Ni₁₀Be_22.5 (numbers indicate at.%) BMG and 304 stainless steel (SS304) in accelerated simulated anode and cathode environments, such as 0.5 M H₂SO₄ and 2 ppm HF solutions bubbled with pure hydrogen and air at 80 °C, respectively, is further investigated through potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. The performance tests of the single cell with the Zr-based BMG as BPPs are conducted and the maximum power density of the single cell has exceeded 470 mW/cm². The combination of these results and other properties demonstrate that the Zr-based BMG can be used as the anode or cathode material for metallic bipolar plates.     

Effect of plasma nitriding on behavior of austenitic stainless steel 304L bipolar plate in proton exchange membrane fuel cell

A dense and supersaturated nitrogen layer with higher conductivity is obtained on the surface of austenitic stainless steel 304L by the low temperature plasma nitriding. The effect of plasma nitriding on the corrosion behavior and interfacial contact resistance (ICR) for the austenitic stainless steel 304L was investigated in 0.05 M H₂SO₄ + 2 ppm F⁻ simulating proton exchange membrane fuel cell (PEMFC) environment using electrochemical and electric resistance measurements. The experiment results show that the stable passive film is formed after the potentiostatic polarization at the specified anodic or cathodic potentials under PEMFC operation condition, and the plasma nitriding improves slightly the corrosion resistance and decreases markedly the ICR of 304L. The ICR of the plasma nitrided 304L increases after the potentiostatic polarizations for 4 h, and lower than 100 mΩ cm² at the compaction force of 150 N cm⁻².     

Rapid coating preparation strategy for chromium nitride coated titanium bipolar plates of proton exchange membrane fuel cells

It is critical to develop a coating with sufficient comprehensive performances and efficient preparation strategy for the commercial application of metallic bipolar plate in proton exchange membrane full cell (PEMFC). In this work, chromium nitride coatings prepared by a rapid multi-arc ion plating (MIP) process with various nano thicknesses are investigated in the simulated PEMFC cathodic environments. Both the corrosion resistance and conductivity of the coatings increase with the growth of the coating thickness, which can be attributed to the increasing equivalent diameter, density, and area fraction of the droplets formed on the coating surfaces. The chromium nitride coating with a thickness of approximately 1.0 μm has the lowest I_0.6 V (0.594 μA cm^?2) and interfacial contact resistance (ICR, 6.54 mΩ cm²@1.4 MPa after corrosion test), achieving the 2025 technical targets proposed by the US Department of Energy for bipolar plates. This work shows that rapid preparation by MIP within 12 min is a potential strategy for chromium nitride coated titanium bipolar plates of PEMFCs at industrial scale.     

Investigation of corrosion properties with Ni–P/TiNO coating on aluminum alloy bipolar plates in proton exchange membrane fuel cell

Aluminum alloy bipolar plates have unique application potential in proton exchange membrane fuel cell (PEMFC) due to the characteristics of lightweight and low cost. However, extreme susceptibility to corrosion in PEMFC operation condition limits the application. To promote the corrosion resistance of aluminum alloy bipolar plates, a Ni–P/TiNO coating was prepared by electroless plating and closed field unbalanced magnetron sputter ion plating (CFUMSIP) technology on the 6061 Al substrate. The research results show that Ni–P interlayer improves the deposition effect of TiNO outer layer and increase the content of TiN and TiO_xN_y phases. Compared to Ni–P and TiNO single-layer coatings, the Ni–P/TiNO coating samples exhibited the lowest current density value of (1.10 ± 0.02) × 10^?6 A·cm^?2 in simulated PEMFC cathode environment. Additionally, potential cyclic polarization measurements were carried out aiming to evaluate the durability of the aluminum alloy bipolar plate during the PEMFC start-up/shut-up process. The results illustrate that the Ni–P/TiNO coating samples exhibit excellent stability and corrosion resistance.     

Chromium-containing carbon film on stainless steel as bipolar plates for proton exchange membrane fuel cells

A series of chromium-containing carbon films are deposited on 316L stainless steel (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs) by pulsed bias arc ion plating (PBAIP). The film characterizations are evaluated by X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD). Interfacial contact resistance (ICR) between the coated SS316L samples and carbon paper is measured. Potentiodynamic and potentiostatic tests in the simulated corrosive circumstance of PEMFC are conducted to evaluate the corrosion resistance of the coated SS316L samples. The results indicate the films are primarily composed of pure carbon atoms with amorphous structure, including sp³ and sp² carbon atoms. The contents of sp³ and sp² carbon atom are remarkably influenced by the doping chromium. ICR and corrosion resistance of the coated SS316L sample are greatly improved owing to the surface film. The lowest ICR between the coated SS316L sample and carbon paper is only 2.8 mΩ cm² at the compaction force of 120 N cm⁻². The ICR has a close relationship with the contents of sp³ and sp² carbon atom, and the lowest ICR is obtained for the Cr_0.23C_0.77 film with the lowest sp³ carbon atom content and highest sp² carbon atom content. The SS316L sample with Cr_0.23C_0.77 film also exhibits the best corrosion resistance. Finally, the variations of ICR and surface morphology of the coated sample before and after corrosion testing are discussed.     

Coated stainless steels evaluation for bipolar plates in PEM water electrolysis conditions

Proton exchange membrane water electrolysis (PEMWE) is a promising technology to be incorporated in the production of green hydrogen, but one of its limitation to market penetration is the cost of bipolar plates (BPP).Aiming to reduce the cost of PEMWE stack, different surface engineered coating systems based on CrN/TiN, Ti/TiN, Ti and TiN deposited by physical vapor deposition on SS 316L, SS 904L and SS 321 were tested, as potential cost effective solutions to be implemented on bipolar plates. A corrosion evaluation has been carried out in anodic PEMWE conditions in order to determine the best substrate/coating combination for bipolar plates. Ti/TiN multi-layered coating on SS 321 shown the best performance with ?0.02% weight loss, current at 2 V_SHE to 436 μA cm^?2 and ICR after corrosion test to 9.9 mΩ cm².     

NiFe LDH/Ti3C2Tx/nickel foam as a binder-free electrode with enhanced oxygen evolution reaction performance

In this work, NiFe LDH/Ti₃C₂T_x/Nickel foam (NF) was successfully prepared as a binder-free electrode by depositing NiFe layered double hydroxide (LDH) nanosheets on Ti₃C₂T_x/NF substrate through electrodeposition approach. The strong electrostatic interactions between the negatively charged surface of MXene and positively charged NF substrate enabled the direct growth of NiFe LDH nanosheets on Ti₃C₂T_x/NF substrate. As a result, the as-prepared NiFe LDH/Ti₃C₂T_x/NF electrode exhibited an excellent OER performance, fast catalytic reaction kinetics and good chemical stability. Its overpotential reached 200 mV at a current density of 10 mA cm^?2, and the cycling tests suggested a good cycling stability.     

Pt nanowire/Ti3C2Tx-CNT hybrids catalysts for the high performance oxygen reduction reaction for high temperature PEMFC

The activity of catalyst could be enhanced by the temperature rising, so it is a suitable way to reduce the noble metal loading for the catalyst. However, the corrosion of carbon supports will be remarkable in the high temperature proton exchange membrane fuel cells (HT-PEMFC, >100 °C). This report demonstrated a novel Ti₃C₂T_x and CNT hybrid material as the catalytic support, and Pt nanowires (Pt NWs) is loaded on the hybrid support to construct the catalyst for HT-PEMFC. The Pt NWs/Ti₃C₂T_x-CNT performs higher electrochemical activity, better stability than that of commercial Pt/C. The mass activity and specific activity of Pt NWs/Ti₃C₂T_x-CNT catalysts are 3.89 and 3.02 times as that of Pt/C, respectively. The power densities of HT-PEMFC showed 155.4 mW cm⁻² and 182 mW cm⁻² at 150 and 180 °C, respectively.     

Corrosion behavior of tantalum coatings on AISI 316L stainless steel substrate for bipolar plates of PEM fuel cells

Corrosion resistance of tantalum coatings 30 μm thick deposited by chemical vapor deposition on SS316L coupons has been evaluated by electrochemical impedance spectroscopy (EIS). To this end, anodic and cathodic operating conditions of proton exchange membrane fuel cells (PEMFC) have been simulated in a three-electrode heated corrosion cell. Interfacial contact resistance (ICR), contact angle and durability tests have been performed in long-term tests (>100 h) polarizing the electrode to 1.193 V vs. Ag/AgCl. Results obtained by different experimental techniques show a dense coating structure with a high polarization resistance, mainly formed by surface crystals of α-Ta (bcc), Ta₂O₅ and carbon. An atomic ratio (in %) of oxide to metallic species (Ta_ox/Ta_met) of 4.8 was verified from XPS spectra, which is slightly increased to 6.23 after the anodizing treatment. The modified surface composition yielded a coating capacity higher than the amorphous oxide, favoring the in-plane electrical conduction. After the treatment, no noticeable changes were observed neither in surface morphology nor in contact angle (>90°). ICR values in the range of 22.3–32.6 mΩ cm² were obtained for a clamping pressure of 140 N cm⁻². No morphological changes or loss of coating adherence were observed during the long-term tests.     

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

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

Quasi zero-dimensional MoS2 quantum dots decorated 2D Ti3C2Tx MXene as advanced electrocatalysts for hydrogen evolution reaction

Developing advanced noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is still a great challenge. Herein, a novel HER catalyst with quasi zero-dimensional (0D) MoS₂ quantum dots (QDs) supported on two-dimensional (2D) Ti₃C₂T_x MXene nanosheets is facilely synthesized. The MoS₂ QDs/Ti₃C₂T_x nanohybrid retains the unique layer structure, and the MoS₂ QDs are in situ formed and distributed uniformly. The obtained MoS₂ QDs/Ti₃C₂T_x catalyst exhibits superior electrocatalytic activity due to its excellent conductivity, abundant of active sites exposed and a high percentage of 1T metallic phase (～76%) of MoS₂ QDs. Remarkably, an early HER overpotential of 220 mV at 10 mA cm^?2 and a small Tafel slope of 72 mV dec^?1 of MoS₂ QDs/Ti₃C₂T_x are achieved in 0.5 M H₂SO₄ solution. In addition, the exchange current density of MoS₂ QDs/Ti₃C₂T_x is ～5 times larger compared with pure MoS₂, thus demonstrating an accelerated charge transfer during the electrocatalytic process.     

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

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

Effect of Ni content on the electrical and corrosion properties of CrNiN coating in simulated proton exchange membrane fuel cell

In this paper, CrNiN coatings with various Ni content are deposited on 304ss bipolar plates by closed field unbalanced magnetron sputter ion plating from CrNi alloy targets. Simulative working environment of proton exchange membrane fuel cell (PEMFC) is applied to test the electrical and corrosion properties of uncoated 304ss and CrNiN-coated samples. The influence of Ni content on microstructure, phase structure, contact angle with water and electrochemical performance is investigated. Results show that all the coated samples significantly enhanced the corrosion resistance of the 304ss, and the CrN-coated 304ss sample without Ni has the best corrosion resistance of 153.8 and ?141.9 mV in the simulated anodic and cathodic environments, respectively. Electrochemical impedance spectroscopy (EIS) studies reveal that the resistance of CrN coating is higher than that of other coated samples and 304ss in the cathodic environment. Furthermore, Interfacial contact resistance (ICR) studies revealed that CrN coating has a superior ICR of 11 mΩ cm² at a compaction force of 160 N cm^?2. In addition, the contact angle of the CrNiN coatings with water is approximately 114°, which is beneficial for water management in PEMFC. Analysis result indicates that the enhanced performance of the coated 304ss bipolar plates is related to the high film density determined by closed field unbalanced magnetron sputter ion plating, and the synergistic function of the CrNiN layered structure.     

Durability and degradation of CrMoN coated SS316L in simulated PEMFCs environment: High potential polarization and electrochemical impedance spectroscopy (EIS)

The high potential on the cathode side originated from the start-up/shut-down processes is the one that cannot be ignored, which will accelerate degradation of the bipolar plates and increase the interfacial contact resistance (ICR) eventually degrade the performance of PEMFCs. Therefore, the coating with corrosion resistance and conductivity is in urgent need of development. CrMoN coating is deposited on SS316L by closed field unbalanced magnetron sputter ion plating (CFUMSIP) with an aim to improve corrosion resistance and conductivity of SS316L under PEMFCs at shut-up/shut-down stages. In terms of high potential polarization test, the corrosion current density and ICR values are found to increase as the applied potential increases. The electrochemical degradation of CrMoN coated SS316L is investigated by electrochemical impedance spectroscopy (EIS). After 40 days of immersion, the charge transfer resistance (R_ct) of the CrMoN-4A coated SS316L is approximately 14 times greater than that of the uncoated SS316L and the ICR values are 11.2 mΩ cm², indicating that the CrMoN-4A coating still has high corrosion resistance and well conductivity after long time immersion.