Proton Exchange Membrane Fuel Cell Bipolar Plates Research Articles

Regulating the structure and performance of amorphous carbon-based films by introducing different interlayers for applications in PEMFC bipolar plates

In this work, the effects of inserting an interlayer on the anti-corrosion performance of amorphous carbon (a-C) films in a simulated Proton Exchange Membrane Fuel Cell (PEMFC) environment have been systematically studied. Four a-C films with different interlayers, namely CCr, C-Cr-N, CrN and Cr, were prepared on 316L stainless steel substrates using unbalanced magnetron sputtering. The surface/fractural morphologies, carbon bonding structure and the anti-corrosion performance of the 4 films were observed/characterized in detail. The nanostructure and composition evolution from the film surface down to the film-substrate interface before and after electrochemical tests were also analysed via high resolution transmission electron microscopy (HRTEM). Results indicate that a-C films with CCr and C-Cr-N interlayers display superior corrosion resistance compared to undoped samples and those lacking an interlayer, with the lowest self-corrosion current density (i.e. 2.1 × 10−7 A/cm2, C-Cr-N interlayer) being nearly two orders of magnitude lower than that of the substrate (i.e. 1.1 × 10−5 A/cm2). The doped C-Cr-N interlayer plays a vital role in the corrosion resistance of the samples by accelerating oxidation of surface defect locations, inhibiting the continuous penetration of electrolyte, and improving corrosion resistance. Additionally, a-C films with a C-Cr-N interlayer exhibited an outstanding interface contact resistance (ICR) value (~3.5 mΩ/cm2) than that with a CrN interlayer (~30 mΩ/cm2) or the 316L substrate (~100 mΩ/cm2) at a typical contact pressure of 1.5 MPa. All 4 films demonstrate obviously improved hydrophobicity (contact angles against distilled water under room temperature up to 94.2°) compared to the substrate (75.8° under identical condition). In a word, this study proves that the strategy of inserting an appropriately designed interlayer (with the ternary C-Cr-N being most promising) to a-C films could alter and enhance the anti-corrosion, ICR and hydrophobic properties of 316L, proposing valuable solutions for high-performance bipolar plates (BPs) in the PEMFC industry.

Corrosion Behavior of Ta and TiN Double-Layer-Coated SUS316L for PEMFC Bipolar Plates Using Plasma-Enhanced Atomic Layer Deposition and Magnetron Sputtering

In this study, the corrosion behavior of Ta and TiN double-layered-coated SUS316L is investigated for proton-exchange membrane fuel cells (PEMFCs) bipolar plates. The surface of SUS316L is modified by depositing 4.5 μm of Ta and 200 or 400nm of TiN using magnetron sputtering and plasma-enhanced atomic layer deposition, respectively. The experimental results reveal that this coating significantly enhances the corrosion resistance and reduces the interfacial contact resistance of the bipolar plate. Under electrochemical conditions that are 500 times more acidic than those specified by the Department of Energy (DOE), the coated SUS316L achieves a corrosion current density of only 1.0µA/cm2 at 0.6 VSCE. The corrosion current density reduces up to more than two orders of magnitude, and the interfacial contact resistance with carbon paper is below 10 mΩcm2 at compression forces below 140N/cm2, thus meeting the DOE 2025 target value for both corrosion current density and interfacial contact resistance. Our findings suggest the potential of Ta and TiN double-layered-coated SUS316L as durable bipolar plate materials for PEMFCs.

A review on key factors influencing the electrical conductivity of proton exchange membrane fuel cell composite bipolar plates

AbstractFuel cells are gaining increasing importance as a promising alternative to traditional energy sources, primarily due to their exceptional efficiency and environmental advantages. The electrical performance of proton exchange membrane fuel cells (PEMFCs) largely depends on the effectiveness of proton and electron transport within the cell components. A critical factor impacting this efficiency is the electrical conductivity of polymer‐based bipolar plates (BPPs), which play a fundamental role as current collectors. BPPs in PEMFCs can be made from various materials including coated metallic materials, graphitic materials, and polymer composites. This review exclusively concentrates on polymer composite BPPs. Enhancing the overall cell performance is achievable through the integration of electrically conductive additives into the polymer matrix of these plates. Graphite (GR), carbon black (CB), carbon fibers (CF), carbon nanotubes (CNT), and graphene (Gr) all emerge as highly promising functional materials capable of substantially elevating BPPs performance. This study, among its various objectives, delves into the synergistic effects of these electrically conductive additives and their capacity to enhance the electrical conductivity within polymeric matrices. Furthermore, this review article thoroughly explores the influence of the polymeric matrix, encompassing co‐continuous morphology and processing conditions. In essence, it focuses on the improvement of BPPs electrical conductivity through innovative designs of their polymer‐based composites and nanocomposites and the particular selection of the electrically conductive fillers. The insights derived from this study significantly contribute to a more profound understanding of how to effectively harness the potential of this vital PEMFC component.

Characterization of the performance of Ti doped α-C/α-C multilayer coating on SS316L as bipolar plates for PEMFC

In order to improve the corrosion resistance and conductivity of 316L stainless steel (SS316L) in the PEMFC (proton exchange membrane fuel cells) environment, DC-balanced magnetron sputtering was used to deposit Ti doped α-C/α-C multilayer coating on SS316L. The influence of coating structure on its micromorphology and phase composition is characterized, and the coating corrosion and conductivity were further explored. Notably, the investigation reveals that multi-layer structure can inhibit the growth of columnar crystal structure and refine the coating surface, which gradually decreased the coating porosity of from 4.54 % (1 layer) to 0.21 % (4 layers), and the passivation current density decreases to 0.22 μA/cm2 at 0.6 V, remarkably better than the targets. In addition, the introduction of Ti-doped α-C layer further promoted the sp2 hybridization of the coating, its interfacial contact resistance (ICR) value gradually decreased from 5.28 mΩ·cm2 (1 layer) to 2.28 mΩ·cm2 (4 layers) under 1.4 MPa. Therefore, the multilayer composite structure coating significantly enhances the conductivity and corrosion resistance of the SS316L bipolar plate, are more practically applied for commercialization of PEMFC technology.

Graphene-Coated Ni-Cu Alloys for Durable Degradation Resistance of Bi-Polar Plates for Proton Exchange Membrane Fuel Cells: Remarkable Role of Alloy Composition.

Bipolar plates, a critical component of proton exchange membrane fuel cell (PEMFC), are constructed out of alloys of Ti, Pt, Cr, or graphitic materials that have limitations. Electrical conductivity, cost, and corrosion resistance are among the critical considerations for bi-polar plate material. Graphene, which possesses impressive conductivity and toughness, is an attractive option as coating on metallic substrates of PEMFC bipolar plates. This study investigates corrosion resistance and its durability due to graphene developed by chemical vapor deposition on a pure Ni-Cu alloy and a commercial Ni-Cu alloy in 0.5m H2 SO4 environment, with a view to exploring use of graphene coated Ni-Cu alloys for the construction of PEMFC bipolar plates. The graphene coating on the pure alloy shows remarkably superior corrosion resistance than the commercial alloy that is attributed to the former's ability to develop considerably defect-free graphene.

High-performance polybenzoxazine based composites PEMFC bipolar plates with a multi-layer structure for surface enrichment of conductive phase

In this study, a multilayer high-performance polybenzoxazine/expanded graphite composite bipolar plate with a ‘graphite-composites-graphite’ structure was prepared by compressing molding. The surface graphite layer and the conductive network were constructed by hot compressing of graphite paper and the polybenzoxazine/expanded graphite composites. The results show that the multilayer synergy makes composite BP reach an in-plane conductivity of 278.85 S cm−1, an area specific resistance of 9.70 mΩ cm2 and a flexural strength of 75.75 MPa. The ‘graphite-composites-graphite’ structure can make the power density of a single cell assembled by the multilayer composite BP increase by 111.02% and 113.80%. In conclusion, the multilayer bipolar plate with a ‘graphite-composites-graphite’ structure is a promising polymer composite bipolar plate for the proton exchange membrane fuel cell (PEMFC).

Effects of Nitrogen Flow Rate on the Performances of Cathodic Arc Deposited TiN Films on 316L Stainless Steels as Bipolar Plates for the Proton‐Exchange Membrane Fuel Cell

The corrosion resistance, interfacial contact resistance (ICR), and hydrophobicity of cathodic arc deposited TiN films on 316L stainless steels at different nitrogen flow rates as bipolar plates (BPs) for the proton‐exchange membrane fuel cell (PEMFC) are investigated. It is shown in the results that the TiN‐coated 316L stainless steel prepared at a moderate nitrogen flow rate (250 sccm) exhibits a low stable corrosion current density of 6.5 × 10−8 A cm−2 in the simulated corrosive cathode environment of PEMFC, and a low ICR of 8.94 mΩ cm−2 at a pressure of 1.38 MPa after corrosion, meanwhile presents a good hydrophobicity before and after corrosion. These results are discussed by considering the probable effects of the nitrogen flow rate on the substrate/coating system based on the microstructural characterization of the substrate/coating interface and the coating, which shows that the interdiffusion will be started in the deposition process and a moderate nitrogen flow rate during the coating process will promote to the broadening of interface region and lead to the formation of a robust and high‐quality coating with fewer defects that can effectively improve the performances of the 316L stainless steel substrate as the BP for PEMFC.

Nature-inspired hybrid wettability surface to enhance water management on bipolar plates of PEMFC

Proton exchange membrane fuel cell (PEMFC) requires both sufficient water in proton exchange membrane (PEM) and fast water drainage in flow channel to achieve a desirable performance, which creates a dilemma for water management. Herein, we have fabricated a nature-inspired bionic multifunctional surface (BMS) consisting of superhydrophobic coating and superhydrophilic groove. The characterizations of water contact angle, morphology and chemical composition have verified the successful preparation of hybrid wettability surface. The effects of groove width on droplet capture, storage and drainage have been investigated, which yields an optimal width of 600 μm. More importantly, BMS has been fabricated inside the flow channel of graphite bipolar plate (BMS@BP). The peak power density of BMS@BP cell is 26.3% higher than that of the cell without BMS. Under a drought-inclined condition of low current and humidity, BMS@BP mitigates the increase of internal resistance caused by PEM dry-out, whereas under a condition prone to flooding (high current and humidity), BMS@BP can reduce the voltage fluctuation and pressure drop variation incurred by flooding. Hence, BMS has demonstrated a capacity to balance the opposite needs of moisturizing PEM and draining channel water. Our work may afford an innovative hybrid-wettability-based approach to enhance water management for PEMFC.

Carbon/Graphite Sheets/PTFE-Coated Porous Titanium as the Bipolar Plate by Hydrothermal Treatment

A multilayered carbon–-Polytetrafluoroethylene/graphite sheet (C-PTFE/GS) coating is synthesized on a Ti plate by hydrothermal and immersion method. The innermost layer is composed of amorphous carbon and the outermost layer is made of a compound with PTFE, graphite sheets and nanotube. Interfacial contact resistance (ICR) decreases to 8.9 mΩ·cm−2 at the applied force of 1.4 MPa between carbon paper and the substrate with coating. The corrosive current density is only 0.49 μA/cm2 at the cathode, while the potential of 0.6 V is applied. The charge transfer resistance of the multilayer carbon coating is higher than that of a bare sample through the results of electrochemical impedance spectroscopy. Moreover, there are no obvious changes in the coating before and after potentiostatic polarization testing by X-ray photoelectron spectroscopy (XPS) analysis, which demonstrates the stability of multilayered C-PTFE/GS coating on Ti. In addition, the surface morphology of C-PTFE/GS coating is preserved without defect after potentiostatic polarization in a simulated environment of proton exchange membrane fuel cells (PEMFCs). Therefore, the C-PTFE/GS coating is potentially applied as bipolar plates in PEMFCs.

Overcoming the Dilemma between Low Electrical Resistance and High Corrosion Resistance Using a Ta/(Ta,Ti)N/TiN/Ti Multilayer for Proton Exchange Membrane Fuel Cells

Bipolar plates in proton exchange membrane fuel cells (PEMFCs) are confronted by the dilemma of low contact resistance and high corrosion resistance; this study aimed to simultaneously satisfy these dimensions in a harsh environment. Using thick multilayer coatings can improve the corrosion resistance, but the contact resistance would be largely compromised. To address this challenge, we propose compatible tantalum/titanium-based coatings on 316L stainless steel (SS316L) as bipolar plates for PEMFCs. With the transition layer, the optimal TaN/(Ta,Ti)N/TiN/Ti coating exhibits an ultralow corrosion current density of 0.369 μA·cm−2 (at +0.6 V vs. SCE) and a contact resistance of 6 mΩ cm2 at 138 N/cm2 after 5 h of potentiostatic polarization, both of which meet the standard of the U.S. Department of Energy. Electrochemical impedance spectroscopy (EIS) and an equivalent electrical circuit model further elucidated that TaN/(Ta,Ti)N/TiN/Ti coating significantly impedes the oxidation reaction and dissolution of metals and provides good protection for the SS316L.

Superhydrophobic Cobalt–Graphene Composite for the Corrosion Protection of Copper Bipolar Plates in Proton Exchange Membrane Fuel Cells

Abstract Superhydrophobic cobalt and cobalt–graphene films were fabricated on copper bipolar plates (BPPs) using potentiostatic electrodeposition to improve their corrosion resistance and surface conductivity. A scanning electron microscope (SEM) was used to study the surface morphology of the prepared superhydrophobic films. The results show that the cobalt film modified by stearic acid (Co-SA) and cobalt–graphene composite modified by stearic acid (Co–G-SA) exhibit micro–nano structures. The results of the Fourier transforming infrared (FTIR) spectrophotometer confirm that the copper substrate was coated by Co-SA and Co–G-SA films. The wettability results of the prepared superhydrophobic films demonstrate that the films display superhydrophobicity, where the fabricated Co-SA and Co–G-SA films have contact angles (CAs) of 159 deg and 165 deg, respectively. Chemical stability, mechanical abrasion resistance, surface conductivity, and corrosion resistance in a simulated proton exchange membrane fuel cells (PEMFCs) environment are significantly higher for copper coated by Co–G-SA film. Because the copper coated with Co–G-SA has a low interfacial contact resistance (ICR) value and a high corrosion resistance, it is thought to be a good choice for PEMFC bipolar plates.

Nb–Cr–C coated titanium as bipolar plates for proton exchange membrane fuel cells

Herein, a ternary Nb–Cr–C film is successfully prepared by arc ion plating for surface modification of titanium using as proton exchange membrane fuel cell (PEMFC) bipolar plates. Film morphology, composition as well as corrosion behavior, conductivity and performance of single cell are investigated. As results revealed, the Nb–Cr–C film is about 500 nm thick without obvious defects. Compared with the bare titanium, the corrosion current density of Nb–Cr–C coated titanium lowered to 0.022 μA/cm 2 and -0.051 μA/cm 2 in simulated PEMFC cathode and anode environments, respectively, accompanied with the interfacial contact resistance lowered to 1.15 mΩ cm 2 , indicating outstanding anti-corrosion and conductivity performance. The single cell with Nb–Cr–C coated titanium bipolar plates reaches its peak power density 1.167 W/cm 2 at 2.2 A/cm 2 , which is comparable with that of graphite bipolar plates and apparently better than that of bare titanium bipolar plates. The remarkable improvements in both ex-situ tests and single cell tests suggest that the Nb–Cr–C coated titanium might be a proper material for PEMFC bipolar plates. • A novel Nb–Cr–C film is designed to modify titanium for PEMFC bipolar plates. • Corrosion current density at 0.6 V in cathode is 0.022 μA/cm 2 . • ICR with carbon paper at 1.5 MPa is 1.15 mΩ cm 2 .

Corrosion behavior and interfacial conductivity of amorphous hydrogenated carbon and titanium carbide composite (a-C: H/TiC) films prepared on titanium bipolar plates in PEMFCs

In this work, amorphous hydrogenated carbon and titanium carbide composite (a-C: H/TiC) films are deposited on titanium bipolar plates which are used in proton exchange membrane fuel cells (PEMFCs). It was fabricated by high power pulsed magnetron sputtering (HiPIMS) with TiN and TiCN transition layers. The microstructure results indicated that the titanium element was introduced in the films with a form of titanium carbide, and the increasing ID/IG values imply the graphitization of films. Amorphous carbon with a large content of sp2 hybrid bonds leads to an excellent conductivity of 1.6 mΩ·cm2 at 1.4 MPa and improves the corrosion resistance by inhibiting the growth of columnar crystal. In addition, a number of sp2-riched clusters on the surface enhance the hydrophobicity of the film. The a-C: H/TiC films prepared in this work significantly improved the hydrophobicity, corrosion resistance and interfacial conductivity of titanium bipolar plates, showing a great potential for applications in PEMFCs.

Research progress in surface modification of metal bipolar plates for proton exchange membrane fuel cells

<p indent=0mm>Bipolar plates are the core components of proton exchange membrane fuel cells (PEMFC), and their quality directly determines the output power and service life of the battery stack. Metal bipolar plates have attracted intensive attention and become the research focus of bipolar plates in PEMFC due to their excellent mechanical and electrical performances. Unfortunately, bare metal bipolar plates are prone to corrosion in PEMFC. After the corrosion of metal bipolar plates, the released metal ions could poison the catalyst, and the formed dense oxide film could increase the interface contact resistance, affecting the output power and service life of the PEMFC. Surface modification of metal bipolar plates can effectively tackle the aforementioned problems. In this review, firstly, the types, merits and disadvantages of bipolar plates are introduced. Subsequently, preparation methods, performances and the latest research progress of surface modified coatings, such as metallized coating, carbon based coating and conducting polymer coating, for metal bipolar plates are systematically summarized. Finally, the commercialization challenges of modified coatings in China and current industrialization situation at home and abroad are analyzed. Furthermore, the development direction of surface modification of metal bipolar plates is prospected from the point of view of cost and service life.

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).

Evaluation of vacuum heat-treated α-C films for surface protection of metal bipolar plates used in polymer electrolyte membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) assembled with metal bipolar plates (BPPs) is a promising power source for new energy vehicles. However, metal BPPs have serious corrosion issues and the surface electrical performance degrades in the harsh PEMFC environment. Amorphous carbon (α-C) films exhibit improved properties with both high corrosion resistance and electrical conductivity. Subsequent vacuum heat treatment of the as-coated α-C films can change their phase composition and film structure, modifying their performance. This study prepared α-C films with a titanium interlayer on a SS316L substrate by DC balance magnetron sputtering and then subjected them to vacuum heat treatment at different temperatures (400–700 °C). These treated α-C films are systemically analyzed in terms of surface and cross-sectional morphologies, sp bond hybridization, interfacial electrical conductivity, and corrosion resistance. The results indicate that the conversion of sp3 to sp2 and the compact density of α-C films are greatly enhanced with an increase in temperature, greatly improving the corrosion resistance and surface conductivity of the films. These promising results lead to a potential direction for the post-coating treatment of α-C films on metal BPPs in PEMFCs.

High-Performance Graphene Coating on Titanium Bipolar Plates in Fuel Cells via Cathodic Electrophoretic Deposition

In this article, we proposed a facile method to electrophoretically deposit a highly conductive and corrosion-resistant graphene layer on metal bipolar plates (BPs) while avoiding the oxidation of the metal substrate during the electrophoretic deposition (EPD). p-Phenylenediamine (PPD) was first grafted onto negatively charged graphene oxide (GO) to obtain modified graphene oxide (MGO) while bearing positive charges. Then, MGO dispersed in ethanol was coated on titanium plates via cathodic EPD under a constant voltage, followed by reducing the deposited MGO with H2 at 400 °C, gaining a titanium plate coated with reduced MGO (RMGO@Ti). Under the simulated environment of proton exchange membrane fuel cells (PEMFCs), RMGO@Ti presents a corrosion current of &lt; 10−6 A·cm−2, approximately two orders of magnitude lower than that of bare titanium. Furthermore, the interfacial contact resistance (ICR) of RMGO@Ti is as low as 4 mΩ·cm2, which is about one-thirtieth that of bare titanium. Therefore, RMGO@Ti appears very promising for use as BP in PEMFCs.

Investigation on the Optimal Angle of a Flow-Field Design Based on the Leaf-Vein Structure for PEMFC

As a critical component, the bipolar plate appreciably affects the performance of proton exchange membrane fuel cell (PEMFC). The flow field structure on the bipolar plate is significant in transporting the internal reaction gas and excess water. In the nature, the leaf veins provide efficient branch networks to the plant, contributing to distribute the nutrients in the whole system. By bionic means, a similar branching structure can be used to design flow channels on the bipolar plates for PEMFC, which helps distribute the reactant gas evenly and manage the water better. In this paper, a three-dimensional isothermal single phase model of the bio-inspired flow channel design based on the leaf vein pattern was presented. The effect of the angle between the main channel and sub-channels on the performance of PEMFC was studied at various cases. A PEMFC of 10.24cm2 activation area was assembled and examined experimentally. The results showed that increasing the angle appropriately was beneficial to improving the uniform oxygen distribution and excess water removal. After comprehensively analyzing the electrochemical performance, species distribution, and power loss of PEMFC, the optimal angle was presented.

Study on conductivity and corrosion resistance of N-doped and Cr/N co-doped DLC films on bipolar plates for PEMFC

In order to obtain films with good conductivity and high corrosion resistance for proton exchange membrane fuel cell (PEMFC) bipolar plate applications, N-doped and Cr/N co-doped diamond-like carbon (DLC) were deposited on stainless steel 316L and silicon wafer with constant nitrogen flow rate (4 sccm) and different Cr target power (0, 60, 90, 120 W). The electrical properties and corrosion resistance of the uncoated stainless steel and coated samples were tested under the simulated working environment of PEMFC. Scanning electron microscope (SEM) results show that the surface of Cr/N co-doped DLC film is smoother. Through the analysis of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results, it is found that Cr/N co-doing DLC film is a combination of amorphous C, CrC, CN, Cr2N and nanocrystalline CrN. Contact resistance test indicates that the Cr/N co-doped DLC film (with Cr target power of 90 W) has the best electrical conductivity (9.20 mΩ cm2 at 150 N/cm2 pressure). Potentiodynamic polarization test shows that both N-doped DLC and Cr/N co-doped DLC films had better corrosion resistance (the corrosion current density could reach E−6 ~ E−7 A/cm2) than uncoated SS316L. To sum up, Cr/N co-doped DLC film (with Cr target power of 90 W) shows outstanding performance in both electrical conductivity and corrosion resistance, which is suitable for the surface treatment of stainless steel bipolar plates.

Thin Niobium and Niobium Nitride PVD Coatings on AISI 304 Stainless Steel as Bipolar Plates for PEMFCs

In this paper, Nb, NbN, and Nb/NbN thin films were successfully deposited on AISI 304 stainless steel (304 SS) as the bipolar plate (BPP) for proton-exchange membrane fuel cell (PEMFC) by employing a radio-frequency (RF) magnetron sputtering system. Corrosion assessments in simulated PEMFC operating conditions (1 M H2SO4 + 2 mg/kg HF, 70 °C) revealed that the Nb and NbN coatings significantly improved the corrosion resistance of the 304 SS substrates. The Nb and NbN deposited samples at 350 °C exhibited superior corrosion resistance compared to those coated at 25 °C. Potentiostatic tests were also performed at the constant potentials of +0.644 and −0.056 V vs. Ag/AgCl to simulate the cathodic and anodic PEMFC conditions, respectively. The minimum current densities were recorded for the Nb coating in both anodic and cathodic conditions. Compared with the 304 SS substrate, all coatings showed lower interfacial contact resistance (ICR) and higher hydrophobicity. Among the tested coatings, the Nb coating exhibited the smallest ICR (9 mΩ·cm2 at 140 N/cm2). The results of this investigation revealed that the Nb and NbN coatings deposited by RF magnetron sputtering on 304 SS can be regarded as promising candidates for BPPs in PEMFCs.