Bipolar Plate Material Research Articles

Sintered Stainless Steel for Interconnectors for PEM Fuel Cell

Polymer electrolyte membrane fuel cell performance strongly depends on properties of the fuel cell stack bipolar plates (BPs). Bipolar plates are a key component of fuel cells. Functions of materials used for fuel cells include even distribution of gas fuel and air, conduction of electricity between the adjacent cells, heat transfer from the cell as well as prevention of gas leakage and cooldown. Due to multifunctionality of fuel cell plates, choice of materials used for plates is immensely difficult. This paper presents opportunities of application of a new technology of powder sintering for creation of parts for electricity and heat generators. Sintered stainless steel 316LHD was investigated as a candidate material for bipolar plate materials. 316L powders were compacted with the following load: 700MPa, 550MPa, and 200MPa, and then sintered at the temperature of 1250 °C in hydrogen medium. The main criterion for selection of a particular material for components of fuel cells is their corrosion resistance in operating conditions of hydrogen fuel cells. In order to determine resistance to corrosion in the environment of operation of fuel cells, potentiokinetic curves (as a function of temperature) were registered in synthetic solution 0.1M H2SO4 + 2 ppmF- at 80°C. The investigations also covered measurements of mechanical properties and microstructural testing of sinters with austenitic structure.

Polymer Composites Bipolar Plates for PEMFCs

In order to improve their commercial liability, many scientific and technological efforts are being performed on fuel cell systems. The bipolar plates represent a major part of the stack with about 80% of the total weight and 30 to 40% of cost. On the technical point of view, bipolar plates should fulfill functional challenges besides ensuring the mechanical strength of the stack. As a result an optimal material for bipolar plate application should present an unusual balance of properties, essentially high electrical conductivity and good mechanical strength. To date, many different materials for bipolar plates have been investigated and an alternative solution consists in polymer composite that com-bine the processability and mechanical properties of the polymeric phase and the conductivity of the carbon fillers. This communication provides a state-of-the-art review of the current development, manufacturing and structure-property re-lationship of polymer composites designed for bipolar plates applications. Both thermoset resins and thermoplastics were considered and combined to many different carbon fillers: graphite, carbon fibers, carbon black, carbon nanotubes. The interests and limitations of these formulations are presented in terms of processability and most relevant properties. A debate on the optimization of electrical and mechanical properties is presented.

The Effects of Compression Pressure Applied on the Manufacture of Carbon Composite Bipolar Plate for PEMFC by Utilizing Graphite Waste Products

Proton electrolyte membrane fuel cells (PEMFC) have near zero carbon dioxide and hazardous pollutant emission. Thus, it is considered as one of energy sources for transportation and other application which can improve environmental performance by decreasing the emission of greenhouse gases and other air pollutant. In accordance with its environmental preservation values, graphite waste product from electric arc furnace (graphite EAF) was chosen as a potential candidate material for bipolar plate for PEMFC. The utilization of graphite waste product is expected to result in light-weight and cost-effective bipolar plates. In this paper, we used graphite EAF as a filler together with carbon black and epoxy resin as a binder. We examined the effects of differential pressure applied on compression molding process on density, porosity, flexural strength and electrical conductivity of the resulting carbon polymer composite bipolar plate. Pressure was applied from 30 MPa - 60 MPa in increments of 5 MPa while maintaining constant temperature operation at 700C for 4 hours. Maximum value of bipolar plate density was achieved at application 55 MPa, of 1.69 g/cm3. At this condition, the flexural strength was measured to be 48 MPa with the porosity of 0.7%, and electrical conductivity of 1.03 S/cm. Taken together, we demonstrated that graphite EAF is a good candidate for the manufacturing of polymer composite bipolar plates.

Protective graphite coating on metallic bipolar plates for PEMFC applications

A new design of metallic bipolar plates with pure graphite coating on metal substrates has been developed. The top layer was a continuous graphite sheet made by the expanded graphite flakes. The pure and layered graphite surface provides high electrical conduction and high chemical inertness in PEMFC environments. Between the graphite sheet and the metal substrate was a binder layer, which mainly consisted of ester resin and conductive fillers. It functions as a binder for the graphite layer and as the second protection layer from acid solution as well. The results from the potentiodynamics tests showed rather low corrosion current densities for our proposed materials, even after soaking tests for over 2000 h. The graphite-coated 316L revealed negative (cathodic) current densities either in the PEMFC cathodic or in the anodic environment for the whole polarization period in the potentiostatic experiments. Thus, the graphite-coated SS316L could potentially be used as a bipolar plate material in the PEM fuel cell applications.

Electrodeposition of ruthenium oxide on ferritic stainless steel bipolar plate for polymer electrolyte membrane fuel cells

The effect of RuO2 electrodeposition on ferritic stainless steel as a bipolar plate is evaluated in terms of the surface morphology, interfacial contact resistance (ICR), potentiostatic polarization, contact angle, and X-ray photoelectron spectroscopy. The surface morphology of deposited RuO2 is greatly stabilized by addition of HNO3 in 10 mM RuCl3·xH2O solution. The RuO2-deposition on stainless steel shows a high contact angle indicating the high surface energy and hydrophobic characteristics. The ICR measurement indicates that the deposition of conductive RuO2 on stainless steel is very effective in decreasing ICR value. Moreover, after potentiostatic polarization, the ICR value shows only 2.4 and 2.2 mΩ cm2 at 150 N/cm2 under air and H2 purged environments, respectively. In electrochemical test, even though the current density of RuO2-deposited stainless steel is slightly higher than that of bare stainless steel, it is acceptable value for the relevant DOE 2015 target for metallic bipolar plates (less than 1 μA/cm2). Because the RuO2-deposition on stainless steel shows a low ICR value and good corrosion resistance and high contact angle, the RuO2-deposition is a sufficiently feasible method for the bipolar plate material of PEMFC.

고분자 전해질막 수소 연료 전지 분리판 용 고분자/흑연 복합 재료의 혼합 및 유변학적 특성에 관한 연구

이 연구에서는 고분자 전해질 막 연료전지의 분리판 용 고분자/흑연 복합소재의 혼합 특성 및 점도 측정 방법에 관하여 연구하였다. 분리판은 전도성이 있어야 하기 때문에 흑연의 함량이 매우 높고 이 때문에 제조된 복합재료의 점도가 높아 점도 측정이 어려운 문제가 있다. 일반적으로 캐필러리 레오메터에서 사용되는 다이로 점도를 측정한 결과 압력이 시간에 따라서 계속 변하고 정상상태의 값을 보이지 않아서 점도 측정이 불가능 했다. 다이의 디자인을 변경하여 측정하면 압력이 정상상태를 보이는 것을 관찰할 수 있었으나, 흑연과 PET를 단순 용융 혼합하여 점도를 측정하는 경우에는 측정된 점도 값이 재현성이 없는 결과를 나타냈다. 여러 차례의 시행 오차 끝에 흑연과 PET를 작은 입자로 분쇄한 후 용융 혼합하면 재현성 있는 점도를 측정할 수 있고, 제조된 복합재료의 전기전도도 값도 재현성 있는 결과를 보임을 관찰하였다. 【In this paper, studies on a mixing characteristic and viscosity measurement of polymer/graphite composites for a bipolar plate of the polymer electrolyte membrane fuel cell were presented. Since the materials for the bipolar plate should be electrically conductive, contents of solid graphite in the composite are very high. As a consequence, a viscosity of the polymer/graphite composite used for the bipolar plate is very high and the measurement of the viscosity is difficult. Viscosity measurements of the polymer/graphite composites were not possible because pressure drops were continuously fluctuated during the viscosity measurements when a conventional capillary die was used. After the die design was optimized, the steady state pressure drop could be achieved, but the viscosity thus measured was not reproducible. After many trials with different experimental techniques, it was found that melt blending of the grinded powder mixtures of both PET and graphite provides reproducible viscosity measurements and electric conductivities of the polymer/graphite composites.】

Bipolar plate cell design for a lithium air battery

The performance and cost of a bipolar plate cell design for a 40 kWh lithium-air battery was estimated and compared to USABC goals. A bipolar plate cell design for a lithium-air battery can meet the cell performance goals, provided certain cell design targets are met. In particular, the excess lithium should be <2×, the current density should be >40 mA cm −2, the cathode capacity should be >1650 mAh g −1 carbon, and the bipolar plate material density should be <5 g cm −3. Meeting the above targets, the specific and volumetric energy densities for the lithium-air cell were estimated at 640 Wh kg −1 and 600 Wh l −1, respectively; the specific and volumetric power densities were estimated at 1310 W kg −1 and 1220 W l −1, respectively. However, the system cost goal of $100 kWh −1 for electric vehicles was not met; the cost of a 40 kWh lithium-air battery system using a bipolar plate design was estimated at $238 kWh −1.

Effects of Low-Cost Salt Bath Nitrification Method on the Stainless Steel as Bipolar Plates for PEMFC

Stainless steel has attracted interest as a bipolar plate material for PEMFC due to its excellent mechanical properties and low cost. However, this problem is worse corrosion resistance under PEMFC operating condition. So, the difficult surface treatment technologies and process cost is very expensive. In this study, salt bath nitrification with pre-oxidation of stainless steel was performed in order to improve both the corrosion resistance and the electrical conductivity.

Characterization of Uncoated Stainless Steel as Proton Exchange Membrane Fuel Cell Bipolar Plates Material

AbstractThanks to their high conductivity, important gas tightness, good corrosion resistance, and low‐cost manufacturing pathways, stainless steels are considered as good candidates for proton exchange membrane fuel cell (PEMFC) bipolar plates materials. In this study, a proprietary alloy was identified as very promising: its initial electrical contact resistance (ECR) with the gas diffusion layer was low, while its corrosion resistance in simulated PEMFC environment was sufficient. Furthermore, the ECR did not increase dramatically during long‐term potentiostatic and potentiodynamic polarizations in simulated PEMFC cathode and anode environments. Finally, the stainless steel was successfully tested for 3,000 h in a commercial system using a 16‐cell stack, without detrimental cell voltage losses.

Effect of Chemical Treatment on Interfacial Contact Resistance of Ferritic Stainless Steel as Bipolar Plate for PEMFC

Ferritic stainless steel is a good candidate material for bipolar plate, however stainless steel is limited to use as a bipolar plate due to its high ICR. In order to reduce ICR value, chemical treatment is performed by immersion in the acidic and alkali solutions. Immersion in the HCl solution makes the specimen surface rougher because of metal dissolution. The rough surface decreases the ICR value since the real contact area between the specimen surface and carbon paper increases. Immersion in the NaOH solution do not result any change in the surface topology. However, the ICR value decreases because the passive film immersed in NaOH solution enriches in Cr oxy-hydroxide with the bound water acting as a donor-type impurity.

Expanded Graphite Epoxy Composite Bipolar Plates for PEM Fuel Cells

Light weight, flexible and thin single layer epoxy impregnated expanded graphite bipolar plates were manufactured and evaluated as a PEM fuel cell bipolar plate material. Mechanical strength values up to 17.41 MPa, in-plane electrical conductivity values up to 136.6 S/cm, through-plane electrical resistance of 0.027 Ohm-cm and flexibility (deflection at mid-span) values up to % 4.38 were obtained with epoxy impregnation in expanded graphite foams. The low thickness (~0.5 mm) and density (~1.2 g/cm3) values of the prepared composite plates put them one step ahead for mobile applications which require high mass and volumetric power density (W/kg, W/L). On the other hand, corrosion current and contact angle values of these composite plates couldn't achieve desired values.

Sintered Materials for Bipolar Plates

Sintered Materials for Bipolar PlatesThis study presents an analysis of opportunities of the application of stainless steel for interconnectors in fuel cells. The investigations also included microstructural analysis of sintered materials in terms of use of them as interconnectors in proton exchange membrane fuel cells (PEMFC). Corrosion resistance in sinters made of a stainless steel was analysed in sulphate solutions; general corrosion resistance and pitting corrosion resistance were tested in the presence of chloride ions. Due to the multifunctionality of materials for interconnectors, selection of these materials is extremely difficult. Results of the investigations of corrosion resistance prove that corrosion resistance is connected with the structure of material and chemical composition of sinters.

Niobium Sputter Coated Stainless Steel as a Bipolar Plate Material for Polymer Electrolyte Membrane Fuel Cell Stacks

Niobium Sputter Coated Stainless Steel as a Bipolar Plate Material for Polymer Electrolyte Membrane Fuel Cell Stacks

Synthesis of mesoporous carbon-silica-polyaniline and nitrogen-containing carbon-silica films and their corrosion behavior in simulated proton exchange membrane fuel cells environment

In this study, polyaniline is deposited onto mesoporous carbon-silica-coated 304 stainless steel using electropolymerization method. Variation of the electropolymerization time and applied potential can affect the growth of polyaniline, and lead to different structural and electrochemical properties of the films. Nitrogen-containing groups are successfully introduced onto the mesoporous carbon-silica film by pyrolyzing treatment under N 2 atmosphere and the electrical conductivity is improved observably compared with the carbon-silica film. The electrochemical properties of the mesoporous carbon-silica-polyaniline films and nitrogen-containing carbon-silica composite films are examined by using potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy. The corrosion tests in 0.5 M H 2SO 4 system display that the carbon-silica-polyaniline films show the optimal protective performance. However, according to potentiostatic polarization process, nitrogen-containing carbon-silica film with a water contact angle 95° is extremely stable and better for the protection of stainless steel in simulated fuel cell environment compared to carbon-silica-polyaniline film. Therefore, the nitrogen-containing carbon-silica-coated 304 stainless steel is a promising candidate for bipolar plate materials in PEMFCs.

Influence of fluoride ions on corrosion performance of 316L stainless steel as bipolar plate material in simulated PEMFC anode environments

Corrosion performance of 316L stainless steel as a bipolar plate material in proton exchange membrane fuel cell (PEMFC) is studied under different simulated PEMFC anode conditions. Solutions of 1 × 10−5 M H2SO4 with a wide range of different F− concentrations at 70 °C bubbled with hydrogen gas are used to simulate the PEMFC anode environments. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to study the corrosion behavior. Scanning electron microscope (SEM) and atomic force microscope (AFM) are used to examine the surface morphology of the specimen after it is potentiostatic polarized in simulated PEMFC anode environments. X-ray photoelectron spectroscopy (XPS) analysis is used to identify the compositions and the depth profile of the passive film formed on the 316L stainless steel surface after it is polarized in simulated PEMFC anode environments. Mott–Schottky measurements are used to characterize the semiconductor passive films. The results of potentiostatic analyses show that corrosion currents increase with F− concentrations. SEM examinations show that no localized corrosion occurs on the surface of 316L stainless steel and AFM measurement results indicate that the surface topography of 316L stainless steel becomes slightly rougher after polarized in solutions with higher concentration of F−. From the results of XPS analysis and Mott–Schottky measurements, it is determined that the passive film formed on 316L stainless steel is a single layer n-type semiconductor.

Corrosion properties and cell performance of CrN/Cr-coated stainless steel 316L as a metal bipolar plate for a direct methanol fuel cell

CrN/Cr-coated stainless steel (STS) 316L is investigated as the material for a metal bipolar plate for a direct methanol fuel cell (DMFC) under actual operating circumstances. Protective coating layers of CrN/Cr are formed on STS 316L using an unbalanced magnetron (UBM) DC sputter via Cr target in an effort to improve the corrosion resistance and long-term stability of the STS 316L. In a corrosion resistance test, the CrN/Cr-coated STS 316L shows much better corrosion resistance than bare STS 316L in simulated electrolytic environments under anodic and cathodic potentials relevant to DMFCs. The interfacial contact resistance (ICR) between CrN/Cr-coated 316L and carbon paper decrease to 4 mΩ cm 2 at a compaction force of 150 N cm −2 compared to bare STS 316L (570 mΩ cm 2). The CrN/Cr-coated STS 316L cell has better cell performance compared to the bare STS 316L cell. Furthermore, the CrN/Cr-coated STS 316L cell exhibit low voltage losses of 38.2 μV h −1 under long-term operation of 760 h. These results show that the CrN/Cr-coated STS 316L, demonstrating its feasibility for use as a metal bipolar plate in a DMFC under actual operating circumstances.

Effect of chemical and heat treatment on the interfacial contact resistance and corrosion resistance of 446M ferritic stainless steel as a bipolar plate for polymer electrolyte membrane fuel cells

The bipolar plate is an important component of the polymer electrolyte membrane fuel cell (PEMFC) because it supplies the pathway of the electron flow between each unit cell. The ferritic stainless steel is considered a good candidate material for bipolar plate, but it is limited to use as a bipolar plate due to its corrosion problem and high interfacial contact resistance (ICR). To explore a cost-effective method of surface modification, various chemical and heat treatments are performed with 446M ferritic stainless steel to understand the effect of the surface modifications on the ICR and the corrosion resistance. The ICR and corrosion resistance of 446M stainless steel can be effectively controlled by a proper surface modification with combined treatment of immersion in the acidic solution, followed by heat treatment. The combined chemical and heat treatment not only improves the corrosion resistance but also reduces the ICR value.

Preparation of carbon-coated stainless steels and their properties as bipolar plate materials of polymer electrolyte fuel cells

In order to develop metal bipolar plates for polymer electrolyte fuel cells (PEFC), various grades of stainless steels (SUS304, SUS316, and SUS430) were coated with carbonaceous thin films by plasma-assisted chemical vapor deposition method. The resulting carbon-coated stainless steels were characterized by Raman spectroscopy, interfacial contact resistance (ICR) measurement, and scanning electron microscopy (SEM). Corrosion properties were examined by dynamic polarization measurement in H2SO4 solution. ICR values were decreased by carbon coating due to the deposition of a conductive carbonaceous thin film. The corrosion resistance of carbon-coated SUS304 and SUS430 was superior to that of carboncoated SUS316 at ambient temperature. Based on the SEM images obtained after dynamic polarization measurements, it was found that carbonaceous thin-film layers on SUS304 and SUS430 were dense and did not peel. At 80°C (simulated operating temperature of PEFCs), corrosion resistance of carbon-coated SUS304 was superior to that of carbon-coated SUS430. The influence of the stainless steel grade on the corrosion properties provided by carbon-coating was discussed in relation to the carbon deposition mechanism.

Corrosion resistance and interfacial contact resistance of TiN coated 316L bipolar plates for proton exchange membrane fuel cell

TiN coating is successfully deposited on 316L by multi-arc ion plating. Corrosion behavior of TiN coated 316L is studied in 0.05 M H 2SO 4 + 2 ppm F − simulating proton exchange membrane fuel cell (PEMFC) environments using electrochemical method, and interfacial contact resistance (ICR) is measured before and after potentiostatic polarization at operation potential for PEMFC. The TiN coated 316L exhibits promising ICR and improved corrosion resistance in simulated aggressive PEMFC environments. Only general overall corrosion is observed after potentiostatic polarization. Stable passive film has formed on the surface of the TiN coated 316L after potentiostatic polarization at the operation potential and results in a slight increase in the ICR. These results indicate that the TiN coated 316L is a candidate bipolar plate material for PEMFC stacks.

Surface modification by carbon ion implantation for the application of ni-based amorphous alloys as bipolar plate in proton exchange membrane fuel cells

Ni-based amorphous alloys with surface modification by carbon ion implantation are proposed as an alternative bipolar plate material for polymer electrolyte membrane fuel cells (PEMFCs). Both Ni60Nb20Ti10Zr10 alloys with and without carbon ion implantation have corrosion resistance as good as graphite as well as much lower contact resistance than 316L stainless steel in the PEMFC environment. The formation of conductive surface carbide due to carbon ion implantation results in a decrease in the contact resistance to a level comparable to that of graphite. This combination of excellent properties indicates that carbon ion implanted Ni-based amorphous alloys can be potential candidate materials for bipolar plates in PEMFCs.