Simulated Proton Exchange Membrane Fuel Cell Environment Research Articles

Temperature-relevant degradation in amorphous carbon coated SS316L bipolar plates for PEMFC

The corrosion of metallic Bipolar Plates (BPs) has become a key bottleneck in the practical application of proton exchange membrane fuel cells (PEMFCs). Environmental factors inside the PEMFCs significantly accelerate the degradation of electrical conductivity and durability of metallic BPs. In this work, we investigated the corrosion behavior and conductive properties of amorphous carbon coating (a-C) coated SS316L in a simulated PEMFC environment at various operating temperatures. The results showed that the corrosion current density (Icorr) of a-C varied in a range of 2.3–8.7 nA/cm2 when subjected to a temperature range of 40–80 °C. Additionally, the interfacial contact resistance increased from 4.36 to 9.56 mΩ/cm2 with a rise in temperature. The reasons could be ascribed to two aspects. First, the a-C maintained the good chemical stability of sp2/sp3 bonds regardless of temperature changes, favoring remarkable anti-corrosion and good conductivity. Second, the higher temperatures intensified the penetration of corrosive species, accelerating the dissolution process of a-C coated SS316L and leading to substantial corrosion failure.

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.

Screening of sealing materials for PEM fuel cell applications based on weight factor method

AbstractThe inexpensive, endurable sealing members are among the key components determining the performance and durability of proton exchange membrane fuel cells (PEMFCs). However, there is a lack of effective in situ measurement to monitor the sealing performance change in the fuel cell operation environment. Therefore, the durability of a sealing material should be assessed previously to its application. The present work investigates four types of commercially available sealing silicone rubbers, and five groups of aging tests are carried out to compare their properties and durability in a simulated PEMFC environment, including compression set, stress relaxation, compression stress–strain, solution soaking, and low‐temperature characterization. Furthermore, to comprehensively evaluate the performance of these four types of silicone rubbers and screen out the most suitable one, a comprehensive evaluation table of sealing materials selection based on weight factor was established through an expert survey method, by which the experimental results of all the silicone rubbers can be weighted and scored. This method can be widely used in the fuel cell industry.

Corrosion Behavior of Coated Low Carbon Steel in a Simulated PEMFC Environment.

Here, potential metallic bipolar plate (BP) materials were manufactured by laser coating NiCr-based alloys with different Ti additions on low carbon steel substrates. The titanium content within the coating varied between 1.5 and 12.5 wt%. Our present study focussed on electrochemically testing the laser cladded samples in a milder solution. The electrolyte used for all of the electrochemical tests consisted of a 0.1 M Na2SO4 solution (acidulated with H2SO4 at pH = 5) with the addition of 0.1 ppm F-. The corrosion resistance properties of the laser-cladded samples was evaluated using an electrochemical protocol, which consisted of the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) measurements, and potentiodynamic polarization, followed by potentiostatic polarization under simulated proton exchange membrane fuel cell (PEMFC) anodic and cathodic environments for 6 h each. After the samples were subjected to potentiostatic polarization, the EIS measurements and potentiodynamic polarization were repeated. The microstructure and chemical composition of the laser cladded samples were investigated by scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX) analysis.

Characterization and properties of NbN–Nb bilayer formed on titanium for bipolar plates

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.

NbC/Nb Film-Modified Stainless Steel Bipolar Plate for Proton Exchange Membrane Fuel Cell

The NbC/Nb composite film on SS304 as the bipolar plate of proton exchange membrane fuel cell (PEMFC) was prepared by magnetron sputtering deposition. Scanning electron microscopy and x-ray diffraction were used to characterize the morphology and composition of the film. Electrochemical tests under simulated PEMFC operating conditions (pH 3 H2SO4, 0.1 ppm HF at 80°C) show that the NbC/Nb composite film can provide better corrosion resistance. Potentiodynamic polarization tests reveal that NbC/Nb/SS304 shows lower corrosion current density and more positive corrosion potential than Nb/SS304 and SS304 substrate in simulated PEMFC environments. Potentiostatic tests were also performed at the potentials of 0.84 VSHE for 24 h to simulate the cathodic PEMFC conditions. NbC/Nb/SS304 reaches the lowest polarization current density of 1.01 × 10−7 A/cm2, which is lower than Nb/SS304 (1.83 × 10−7 A/cm2) and SS304 (1.11 × 10−4 A/cm2, four orders of magnitude as low). Under the pressure of 140 N/cm2, the interfacial contact resistance value of NbC/Nb/SS is 8.76 mΩ·cm2, which is significantly lower than Nb/SS304 (14.0 mΩ·cm2) and SS304 substrate (224 mΩ·cm2). After 0.84 VSHE potentiostatic polarization for 24 h, NbC/Nb/SS304 increase by just 0.42 mΩ·cm2 (from 8.76 mΩ·cm2 to 9.18 mΩ·cm2). However, Nb/SS304 increase by 1.2 mΩ·cm2 (from 14.0 mΩ·cm2 to 15.2 mΩ·cm2) and SS304 increase by 64 mΩ·cm2 (from 224 mΩ·cm2 to 288 mΩ·cm2). Moreover, the hydrophobic angle of NbC/Nb/SS304 is 116.5°, compared to Nb/SS304 (108.8°) and SS304 substrate SS304 (67.5°), which is beneficial to the drainage of the PEMFC.

Doping and stress induced failure of Ti(Al/Pt)N films on Ti6Al4V plate in a simulated PEMFC environment

Ti(Al/Pt)N films prepared on Ti6Al4V (TC4) plates were soaked in a simulated proton exchange membrane fuel cell (PEMFC) anode environment for three weeks. The dense Ti(Al/Pt)N films exhibited various preferred orientations: TiN and TiAlN films with (111) and TiAl(Pt)N film with (200) orientations. The inner stresses of the Ti(Al/Pt)N films changed from −13 MPa for TiN, −115 MPa for TiAlN, and −66 MPa for TiAl(Pt)N. The corrosion current densities of TiN, TiAlN, and TiAl(Pt)N were of the order of 10−8, 10−7 and 10−6 A·cm−2, respectively. Their corresponding contact resistance values decreased sequentially from 29.85, 15.25 and 9.85 mΩ cm2. The appearance of second EIS impedance circles after soaking the films in the simulated PEMFC environment for 3 weeks was indicative of the corrosion failure of the Ti(Al/Pt)N films. The relatively high inner stress in the TiN film led to the formation of oxides and corrosion pits. Peeling of the TiAlN film off the TC4 occurred owing to the high inner stress. The micro-potential difference between the TiAlN columns and Pt particles that were distributed along the column boundary led to the formation of crack networks in the TiAl(Pt)N film. Al/Pt in TiN deteriorated the durability of the films, although it enhanced their conductivity.

Research on the performance of carbon film formed on thin stainless steel bipolar plates of PEMFC by laser irradiating

In order to improve the anti-corrosion performance of thin stainless steel bipolar plates of proton exchange membrane fuel cell (PEMFC), the carbon film (of about 0.82-[Formula: see text]m thickness) was fabricated on the thin stainless steel by laser direct writing technology irradiating the formed dense polydopamine (PDA) film. The results indicated that the PDA film has partially transformed into nanocrystalline graphite. Laser power and scanning speed had great effect on the anti-corrosion performance of the final obtained film in simulated PEMFC environment. When the laser power is 3.5 W and the scanning speed is 10 mm/s, the film obtained on the thin stainless steel has the best electrochemical performance in simulated PEMFC environment. Its corrosion current densities were [Formula: see text]A [Formula: see text] cm[Formula: see text]@ −0.1 V (versus SCE) and [Formula: see text]A [Formula: see text] cm [Formula: see text]@ 0.6 V (versus SCE) in simulated anode and cathode environments, respectively. Compared with the bare thin stainless steel, the corresponding corrosion current densities decreased by 45% and 62%. The results obtained in this text provide a novel strategy for modifyingPEMFC thin metal bipolar plates.

Nanocrystalline TaCN coated titanium bipolar plate dedicated to proton exchange membrane fuel cell

To promote the corrosion resistance and surface conductivity of metal bipolar plates (BP) in proton exchange membrane fuel cells (PEMFC), a TaCN nanoceramic coating with TaN and TaC dual phase structures was engineered onto a commercially pure titanium substrate employing the double cathode glow discharge plasma (DCGDP) technique. The as-prepared TaCN coating was well-adhered to the substrate with a thickness of ∼16.5 μm. The coating exhibited a microstructure comprising equiaxed grains with an average size of ∼10.3 nm. The electrochemical behavior of the TaCN coating was evaluated in a simulated PEMFC environment containing various HF concentrations. Open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic polarization, and Mott-Schottky tests showed that the addition of HF enhanced the corrosion rate of both the Ti substrate and the TaCN coating. Nevertheless, the TaCN coating exhibited improved corrosion potential, lower corrosion current density and larger resistance than that of Ti for all HF concentrations. The Hilbert-Huang and corrosion morphology analysis indicated that the TaCN coating maintained a passive state with increasing HF concentration. First-principle calculations investigated the adsorption capacity of the F− ions on the passive film on the TaCN coating. Furthermore, the TaCN coating possesses desirable interfacial contact resistance (ICR) (about 10 mΩ cm2 under a compressive force of 140 N cm−2) and outstanding hydrophobicity (92.9° ± 2°). Overall, the TaCN coating, which can deliver appreciable enhancement relative to the performance of titanium, represents an extremely competitive candidate as a protective coating for bipolar plates.

Titanium bipolar plates augmented by nanocrystalline TiZrHfMoW coatings for application in proton exchange membrane fuel cells

A TiZrHfMoW refractory high entropy alloy (RHEA) nanocrystalline coating was engineered onto a commercially pure Ti (CP-Ti) substrate to enhance its corrosion resistance for potential application as bipolar plates for use in proton exchange membrane fuel cells (PEMFCs). The as-prepared RHEA coating possesses a single-phase BCC structure with an average grain size of ∼12 nm. The electrochemical corrosion behavior of the RHEA coating in simulated PEMFC environment, with varying HF concentrations, was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), in conjunction with detection and analysis of electrochemical noise (EN). The potentiodynamic polarization and EIS measurements of the RHEA coating indicated that, at a given HF concentration, the RHEA coating exhibits a higher Ecorr, a lower icorr and a larger resistance value compared to uncoated CP-Ti. The analysis of the EN signals indicated that the RHEA coating has low correlation dimensions (below 1.4) and small instantaneous amplitudes in the Hilbert spectra, confirming that the RHEA coating was capable of maintaining a stable passive state, regardless of the HF concentrations. Furthermore, the electron work function of TiZrHfMoW RHEA was derived by first-principles calculations to unravel the physics origin of the corrosion resistance of the RHEA coating.

Investigation of Corrosion Performance of Pure Aluminum as Bipolar Plate in PEMFC Environment

The global climate changes occurred because of the emissions of greenhouse gases such as CO2, NO x and SO x that are ongoing throughout the world pose a gradually higher demand for replacing today's fossil fuel based energy system by less pollutant technologies.[1-2] Among the alternative energies available, proton exchange membrane fuel cells (PEFCs) have been considered to power transportation vehicles such as automobiles and buses due to their high power density, relatively quick start-up and low operating temperatures.[3] The bipolar plate is one of the most important parts that impacts the manufacturing cost of the PEFC.[4] The high electrical conductivity, high gas impermeability, good mechanical performance and low cost are some of the desired properties of bipolar plate materials. Also, mainly two types of materials are used as bipolar plates in PEFC as carbon and metals. Carbon materials show a very good corrosion resistance but lower performance in separating reaction gases compare with metals. Among the many candidate materials, aluminum (Al) is considered as better bipolar plate applications in PEFC due to its low cost and low density.[5] Moreover, bipolar plate is required to have sufficient corrosion resistance even with a sulfuric acid solution having a pH of around 3.0, but it is considered that Al cannot tolerate this condition without its well surface modification which is proposed by Yashiro et al.[6] Sulfuric acid solutions are widely used for aluminum anodizing operations. That’s why it was our interest to study the corrosion of Al material for using as a gas separating plate in PEFC environment. Also, the influence of sulfate and fluoride ions on the stability of films formed on Al surfaces in aqueous solutions of sulfuric acid and sodium fluoride particularly at low concentration levels through finding the amount of corrosion was examined. Scanning electron microscopic (SEM), energy dispersive x-ray (EDX) and cross-sectional analyses were also done to observe the surface morphology and elemental composition.In the present investigation, pure Al having 6 cm2 of area were used as the test pieces for immersion in 2.5×10-6M H2SO4 (pH 5.41), 5×10-6M H2SO4 (pH 5.14), 2.5×10-6M H2SO4 + 2ppm F- (pH 5.57) and 5×10-6M H2SO4 + 2ppm F- (pH 5.45) solutions using reagent grade of H2SO4 and NaF. Test pieces were polished by emery paper 4/0, 6/0, 1200 and 2000, rinsed and immersed in around 100 cm3 aqueous solutions for a period of 24h, 48h, 72h, 96h and 120h at 80°C. A potentiodynamic polarization test was performed to check the corrosion resistance of Al in the simulated PEFC environment using 0.05M SO4 2- and 2ppm F- solutions (pH 3.3 and 5.8) and high current density of Al was found. Moreover, a 500h single cell operation was also performed to investigate the corrosion of Al as the gas separating plates. A glassy carbon was used as the channel former and aluminum foil was used as the gas separating plate. The single cell results showed that the corrosion of the gas separation plate was much milder than the corrosion expected in polarization test which showed the possibility of using Al as a gas separating plate in PEFC.Additionally, the oxide film was formed in the Al surfaces because of the oxidized aluminum at the time of immersion. As a result, the corrosion products were formed and graphed as amount of corrosion versus immersion time. Firstly, the amount of corrosion was increased with increasing the concentration of sulfuric acid and increased more after the addition of 2ppmF- ions in the acid solutions. From the results found in this study, it is concluded that pure as-polished Al undergoes severe corrosion in sodium fluoride whereas sulfate ions form much lower corrosion as well as act as inhibitor when Al is used as bipolar plate in the PEFC environment. Acknowledgements This work was supported by the Ministry of Education, Sports, Science and Technology (MEXT), Japan. References Carrette, K. A. Friedrich, U. Stimming, Fuel Cells, 1 (1), 5-39 (2001).O. Collantes, Technol Forecasting Soc. Change, 74(3), 267-280 (2007).Schäfer, J. B. Heywood, M. A. Weiss, Energy, 31 (12), 2064-2087 (2006).Cunningham, D. Baird, J. Mater. Chem, 16, 4385-4388 (2006).A. A. El-Enim, O. E. Abdel-Salam, H. El-Abd, A. M. Amin, J. Power Sources, 177 (1), 131-136 (2008).Yashiro, T. Ichikawa, S. -T. Myung, M. Kumagai, S. Kozutsumi, Zairyo-to-Kankyo, 60 (10), 432-434 (2011).

Electrochemical behavior and surface conductivity of NbC modified Ti bipolar plate for proton exchange membrane fuel cell

The drawback of corrosion resistance and surface conductivity is the main deficiency to restrict the widespread application of Ti bipolar plate in proton exchange membrane fuel cell (PEMFC). A NbC modified layer has been prepared on the surface of Ti plate by plasma surface modification technology to improve the performance of bipolar plate. The NbC modified layer possesses dense, continuous microstructure and exhibits well interface bonding with substrate. The electrochemical characteristic of NbC-Ti bipolar plate is investigated in simulated PEMFC environment (0.5 M H2SO4 + 3 ppm HF solution at 75 °C). The NbC modified bipolar plate exhibits more positive corrosion potential and lower current density at anode and cathode potential. The interfacial contact resistance (ICR) of NbC-Ti bipolar plate shows a low value of 16.6 mΩ cm2 at compaction force of 140 N cm−2, lower than that of bare Ti plate (91.9 mΩ cm2). In addition, the ICR of NbC modified bipolar plate only exhibits slight increase after potentiostatic test of 4 h in both anode and cathode environment. Thus, the NbC modified Ti bipolar plate can act as candidate supplies for PEMFC.

Durable degradation resistance of graphene coated nickel and Monel-400 as bi-polar plates for proton exchange membrane fuel cell

Degradation/corrosion of metallic bi-polar plates in proton exchange membrane fuel cell (PEMFC) environment is a vexing problem in durable performance of PEMFCs. Graphene coatings have been demonstrated to provide robust and durable corrosion resistance in PEMFC environment, without compromising the essential criterion, i.e., high electric conductivity. Multilayer graphene coatings were deposited on nickel and a commercial Ni–Cu alloy by chemical vapour deposition technique. Time dependent electrochemical tests carried out in the simulated PEMFC environment (0.5 M H2SO4 solution) showed up to two orders of magnitude improvement in corrosion resistance of the metal substrate, and this resistance sustained for the entire test duration of 750 h. The magnitude of corrosion resistance of graphene-coated Ni was considerably superior than that for graphene-coated Monel 400 (investigated in this study) or graphene-coated Cu (reported in an earlier study). As suggested by the post-corrosion scanning electron microscopy, the graphene coatings on Ni and Monel 400 remained largely intact after long exposures to the aggressive H2SO4 solution. The durable corrosion resistance of nickel and a nickel-copper alloy due to graphene coating is attributed to the ability of nickel to develop multilayer graphene (however, the nickel-copper alloy is less efficient in developing a robust multilayer graphene).

Study on the Properties of Vertical Carbon Nanotube Films Grown on Stainless Steel Bipolar Plates.

Research on the conductivity and corrosion resistance of stainless steel bipolar plates in a proton exchange membrane fuel cell (PEMFC) is commonly performed in a normal-temperature environment (about 20 °C). However, these fuel cells must function in low-temperature environments (lower than 0 °C) in some conditions, such as in vehicle fuel cells and in portable power supplies that operate during the winter in northern China. Stainless steel bipolar plates have higher requirements in terms of their hydrophobic and anti-icing properties, in addition to needing high conductivity and corrosion resistance. In this study, carbon nanotubes (CNTs) are grown on the surface of 304 stainless steel (304 SS) without a catalyst coating by plasma-enhanced chemical vapor deposition (PECVD), which is a simple and cheap method that allows stainless steel to be used as bipolar plates in low-temperature environments. The Raman spectroscopy and scanning electron microscopy (SEM) results show that the CNTs grown on the surface of 304 SS have different morphologies. The stainless steel samples with different CNT morphologies are tested by hydrophobicity and in situ icing experiments to prove that vertical CNTs can achieve a superhydrophobic state and have good anti-icing properties. The interfacial contact resistance (ICR) of the bare 304 SS and the 304 SS with vertical CNTs is compared by voltammetry, and then the corrosion resistances of both types is compared in a simulated PEMFC environment via a three-electrode system. Consequently, the ICR of the 304 SS with vertical CNTs was lower than the bare 304 SS. The corrosion potential was positive, and the corrosion current density was greatly reduced for the stainless steel with vertical CNTs grown directly on its surface when compared with the bare 304 SS. The experimental results show that vertical CNTs have good application prospects as bipolar plates for PEMFCs in low-temperature environments.

In-situ electrodeposition of conductive polypyrrole-graphene oxide composite coating for corrosion protection of 304SS bipolar plates

The enhancement in long-term corrosion resistance of conductive polymer coating is essential for the practical application, particularly to protect metallic bipolar plates in the aggressive environment of proton exchange membrane fuel cell (PEMFC). In this study, graphene oxide (GO) was introduced to polypyrrole (PPY) matrix, furthermore, PPY-GO composite coatings with different GO content were in-situ electrodeposited on 304 stainless steel (SS) bipolar plates to protect them from corrosion in the aggressive working environment. The electrochemical results imply that the conductive PPY-GO composite coatings significantly decrease the polarization current density of 304SS during potentiostatic polarization in the simulated PEMFC environment. The existence of GO in PPY matrix enhances the coatings adhesion strength and makes the diffusion pathway of corrosive species longer and more circuitous, further restricts their inward penetration. The PPY-GO coating with the optimized GO content of 1 mg mL−1 in the electrodeposition electrolyte shows the best corrosion resistance among the prepared coatings. This enhanced long-term corrosion protection of the PPY-GO composite coating in comparison with the pristine PPY coating is resulting from the enhanced physical barrier and anodic protection.

Degradation of Silicone Rubbers as Sealing Materials for Proton Exchange Membrane Fuel Cells under Temperature Cycling.

Gaskets are compressed in proton exchange membrane fuel cells (PEMFCs) to keep fuel, oxidant and coolant within their respective regions and are very important for sealing and maintaining electrochemical performance of fuel cells during their long-term operation. It has been proved that the gas leakage caused by the failure of the gaskets following long-term operation is one of the main reasons for PEMFC performance degradation. In this work, degradation of silicone rubbers, the potential gasket materials for PEMFCs, were investigated in the simulated PEMFC environment solution, weak acid solution, de-ionized water and air, respectively, under alternating temperature cycling from −20 °C to 90 °C. The changes in hardness, weight, chemical properties, mechanical behavior and surface morphology of the samples of silicone rubbers were studied after a certain number of temperature cycles. The results show that with the increase in temperature cycles, the hardness of the samples increases and the weight of the samples decreases gradually. Scanning electron microscopy reveals that cracks and caves constantly appear on the surface of the samples. Attenuated total reflection Fourier transform infrared spectra (ATR-FTIR) results demonstrate that the surface chemistry changes via de-crosslinking and chain scission in the backbone due to the exposure of samples to the environments over time under alternating temperature cycles.

Ex-situ evaluation of PTFE coated metals in a proton exchange membrane fuel cell environment

Metallic-based bipolar plates exhibit several advantages over graphite-based plates, including higher strength, lower manufacturing cost and better electrical conductivity. However, poor corrosion resistance and high interfacial contact resistance (ICR) are major challenges for metallic bipolar plates used in proton exchange membrane (PEM) fuel cells.Corrosion of metallic parts in PEM fuel cells not only increases the interfacial contact resistance but it can also decrease the proton conductivity of the Membrane Electrode Assembly (MEA), due to catalyst poisoning phenomena caused by corrosive products. In this paper, a composite coating of polytetrafluoroethylene (PTFE) was deposited on stainless steel alloys (SS304, SS316L) and Titanium (G-T2) via a CoBlast™ process. Corrosion resistance of the coated and uncoated metals in a simulated PEM fuel cell environment of 0.5M H2SO4+2ppm HF at 70°C was evaluated using potentiodynamic polarisation. ICR between the selected metals and carbon paper was measured and used as an indicator of surface conductivity. Scanning Electron Microscopy (SEM), 3D microscopy, Energy Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and contact angle measurements were used to characterise the samples. The results showed that the PTFE coating improved the hydrophobicity and corrosion resistance but increased the ICR of the coated metals due to the unconductive nature of such coating. Thus, it was concluded that it is not fully feasible to use the PTFE alone for coating metals for fuel cell applications and a hybrid coating consisting of PTFE and a conductive material is needed to improve surface conductivity.

Electrochemical Properties of Tungsten-Alloying-Modified AISI 430 Stainless Steel as Bipolar Plates for PEMFCs used in Marine Environment

To improve the corrosion resistance and surface electrical conductivity of AISI 430 stainless steel (430 SS) as bipolar plates for proton exchange membrane fuel cells (PEMFCs) used in marine environment, a tungsten alloying layer has been successfully prepared on 430 SS substrate via the plasma surface diffusion alloying technique. The tungsten-modified (W-modified) 430 SS displays a 7–8 μm tungsten alloying layer with a body-centered-cubic structure. The W-modified surface also shows a better hydrophobicity with contact angle of 93.5° and a lower interfacial contact resistance compared with the untreated 430 SS. The potentiodynamic and potentiostatic polarization and electrochemical impedance spectroscopy measurements show that the corrosion resistance of 430 SS is obviously improved in simulated PEMFC environment (0.05 M H2SO4 + 2 ppm HF + 0.01 M NaCl solution at 70 °C), after the plasma surface diffusion alloying process.

Optimisation of pack chromised stainless steel for proton exchange membrane fuel cells bipolar plates using response surface methodology

Stainless steels, as low cost materials, are attractive for proton exchange membrane fuel cells (PEMFC) bipolar plates. However, these metallic alloys require surface coatings or treatments to enhance its corrosion resistance and surface conductivity in PEMFC environments. In this study, response surface methodology based on Box–Behnken design was employed to investigate the influence of time, activator content and temperature on corrosion current density of pack chromised 304 stainless steel in simulated PEMFC environment of aerated 0.5 M H2SO4 + 2 ppm HF at 70 °C. These process parameters were optimised and the performance of the optimised coatings in simulated and real PEMFC environments was investigated. The results indicated that temperature had the most significant influence on the performance of chromised coatings in the selected PEMFC environment. The optimised coating produced at 1040 °C for 3 hours with powder containing 6.84 wt% activator content exhibited better corrosion resistance than the substrate in typical PEMFC cathode and anode environments respectively as well as about six fold decrease in the contact resistance of the substrate at 150 N/cm2. Hence, the single fuel cell assembled with the bipolar plate coated with the optimised process parameters exhibited a two-fold increase in the maximum power density of the cell with the uncoated bipolar plates.

An investigation on corrosion protection of chromium nitride coated Fe–Cr alloy as a bipolar plate material for proton exchange membrane fuel cells

The corrosion properties of chromium nitride (CrN) coating are investigated to assess the potential use of this material as a bipolar plate for proton exchange membrane fuel cells (PEMFCs). Conductive metallic ceramic CrN layers are firstly deposited onto Fe–Cr alloy using a multi-arc ion plating technique to increase the corrosion resistance of the base alloy. Electrochemical measurements indicate that the corrosion resistance of the substrate alloy is greatly enhanced by the CrN coating. The free corrosion potential of the substrate is increased by more than 50 mV. Furthermore, a decrease in three orders of magnitude of corrosive current density for the CrN-coated alloy is observed compared to the as-received Fe–Cr alloy. Long-term immersion tests show that the CrN layer is highly stable and effectively acts as a barrier to inhibit permeation of corrosive species. On the contrary, corrosion of the Fe–Cr alloy is rather severe without the protection of CrN coating due to the active dissolution. Finally, the corresponding electrochemical impedance models are proposed to elucidate the corrosion process of the CrN/Fe–Cr alloy submerged in a simulated PEMFCs environment.