Bipolar Plate Material Research Articles

Development of Flow Fields for Zinc Slurry Air Flow Batteries

The flow field design and material composition of the electrode plays an important role in the performance of redox flow batteries, especially when using highly viscous liquids. To enhance the discharge power density of zinc slurry air flow batteries, an optimum slurry distribution in the cell is key. Hence, several types of flow fields (serpentine, parallel, plastic flow frames) were tested in this study to improve the discharge power density of the battery. The serpentine flow field delivered a power density of 55 mW∙cm−2, while parallel and flow frame resulted in 30 mW∙cm−2 and 10 mW∙cm−2, respectively. Moreover, when the anode bipolar plate material was changed from graphite to copper, the power density of the flow frame increased to 65 mW∙cm−2, and further improvement was attained when the bipolar plate material was further changed to copper–nickel. These results show the potential to increase the power density of slurry-based flow batteries by flow field optimization and design of bipolar plate materials.

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 Zr41·2Ti13·8Cu12·5Ni10Be22.5 (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.

Evaluating Current Distribution and Influence of Defect Sites for Graphitic Compound Bipolar Plate Materials

AbstractWith the growth in power and size of energy conversion devices, the consideration of current distribution inside cells and stacks becomes increasingly important. In light of understanding the effect of the material properties of graphitic compound materials on current distribution, we developed a novel measurement cell based on a segmented current feed and a segmented measurement board. Using this cell, we determined the cross‐conduction of current in three commercial graphitic compound materials used for the manufacturing of bipolar plates. The conduction behaviors, with respect to compacting pressure as well as total current density, were explained by differences in resistance of conduction pathways. Large observed differences between the materials were discussed in terms of the ratio of through‐plane and in‐plane resistivities. Additionally, we compared several methods to emulate defect sites, in order to evaluate their effect using the novel measurement cell and showed the effect of their size on the current distribution. Finally, we discuss improvements on the measurement setup.

Thermal management of edge-cooled 1 kW portable proton exchange membrane fuel cell stack

Comprehensive numerical analyses are conducted to study the influence of thermal management on performance of 1 kW edge-cooled proton exchange membrane fuel cell stack without external humidification. The experimental stack and numerical three-dimensional computational fluid dynamics model are characterized by several novelty aspects. Two numerical approaches are considered and compared for a prescribed load profile: (i) lumped model and novel (ii) real-time transient computational fluid dynamics model incorporating realistic modeling of forced air convection on the edge-cooling of the stack. The novelty of the developed computational fluid dynamics model is the capability to give insight in the transient results in only a fraction of time vs. experimental testing (40 min vs. 4 h) and other computational fluid dynamics models of fuel cells which are only capable of steady-state analysis. The developed computational fluid dynamics model is used to study the influence of (i) bipolar plate materials (ii) operating delta pressure along the flow field and (iii) different cooling fin configurations on the water and heat balance inside the stack. The results indicate that (i) maximal and average temperatures of the stack are almost linearly correlated to the thermal conductivity of bipolar plate materials and maximal temperatures can be significantly higher (ii) the operating delta pressure can be manipulated to increase the performance of the stack and (iii) the cooling fin redesign has major influence on the overall temperature uniformity across the stack. Additionally, the heat transfer between the stack and metal hydride tank is studied.

Prospects of graphite - polypropylene/epoxy blend composite for high performance bipolar plate in polymer electrolyte membrane fuel cell

Conductive polymer composites (CPCs) are very promising candidate materials for bipolar plates (BPs) in polymer electrolyte membrane fuel cells (PEMFCs). However, a major challenge facing application of CPCs in PEMFC BPs is the difficulty in achieving high electrical conductivity while maintaining adequate mechanical strength. Therefore, a good balance between electrical conductivity and mechanical strength is critical in the development of high-performance CPC BPs. In this study, CPCs consisting of polypropylene (PP)/epoxy blend filled with graphite were investigated for application as BP material, which will combine electrical conductivity and mechanical strength that meet the performance requirements for PEMFC BPs. The CPCs, with 30 – 80 wt% graphite powder, were produced by melt mixing followed by compression molding. The morphology, in-plane electrical conductivity, and flexural strength of the composites were investigated using the scanning electron microscopy, four-point probe method, and three-point bending test, respectively. The results obtained were compared with the technical targets for PEMFC BPs by the United States Department of Energy (DOE). All the PP/epoxy/graphite composites exhibited flexural strength that satisfies the DOE target of > 25 MPa while the composite with 80 wt% graphite content showed the best in-plane electrical conductivity.

Review on current research of materials, fabrication and application for bipolar plate in proton exchange membrane fuel cell

Bipolar plate (BP) in proton exchange membrane (PEM) fuel cells provides conducting paths for electrons between cells, distributes and blocks the reactant gases, removes waste heat, and provides stack structural integrity. It is a key component to ensure the aforementioned functions while maintaining a low cost of fuel cell stack. This paper presents a comprehensive review about the BP materials (metallic, non-porous graphite and composite materials) and the corresponding fabrication methods, flow field layouts, and PEM fuel cells applications. Among the materials, the metallic BP has attracted high attention in automotive application due to its superior mechanical and physical properties, competitive cost compared with non-porous graphite and composite materials, but the fabrication technology and corrosion resistance are the major concerns for metallic bipolar plates. In recent studies, the protective coatings reported such as the conductive polymer, metal nitride/carbide and noble coatings have become the hot topics. They have been widely applied in different kinds of metallic bipolar plates, and the metal nitride coatings exhibit relatively low corrosion current and moderate interfacial contact resistance in comparison to other coatings. In future, developing excellent corrosion resistance and electrical conductivity coatings or novel metallic materials for bipolar plates will greatly enhance PEM fuel cells application in transportation field.

Characteristics of Metallic Bipolar Plate for Polymer Electrolyte Membrane Fuel Cells

The bipolar plate is one of the most significant key components in polymer electrolyte membrane fuel cells (PEMFCs). Bipolar plate (BPP) weight and cost are determining factor for future commercialisation of PEMFC technology. To overcome this major hurdle, metallic bipolar plates are used as a BPP in large number of commercial PEMFCs due to their advantages such as excellent mechanical strength, good electrical and thermal conductivities, low cost, ease of fabrication, gas impermeability, and possibility to make thin plates [1, 2]. However, corrosion remains a major anxiety for metallic bipolar plates use in real PEMFC operating conditions. Further, the formation of passivation layers reduces not only the electrical conductivity but also the overall performance. The aim of this present research is to characterise metallic bipolar plate with respect to corrosion behaviour, surface area and roughness changes and its level of success to meet the DOE requirements for BPPs. Especially, electrochemical stability was investigated in terms of corrosion measurements within a three electrode cell system. Active exposure area of 1 cm2 bipolar plate material was used as working electrode (WE). A platinum wire with an activated carbon felt, and reversible hydrogen electrode employed as a counter electrode (CE), and reference electrode (RE), respectively. Bipolar plates were subjected to chemical storage in 0.5 M H2SO4 at 80 ºC as a function of time. Further, electrochemical stability were evaluated in term of potentiostatic conditions such as open circuit potential (OCV), anodic and cathodic polarisation conditions. Finally, a corrosion analysis is presented using atomic force microscopy (AFM), confocal microscopy and/or µ-computed tomography (µ-CT) as well as inductively coupled plasma with mass spectrometry (ICP-MS) as an attempt to know the surface area changes of corrosion in metallic bipolar plates and their degradation products in acid. Figure 1: Three-electrode set-up for corrosion measurements (left), AFM picture of metallic BPP (right) Figure 1

Preparation and performance of nanometric Ti/TiN multi-layer physical vapor deposited coating on 316L stainless steel as bipolar plate for proton exchange membrane fuel cells

The current research mainly focuses on surface properties, corrosion resistance and interfacial contact resistance (ICR) of nanometric titanium/titanium nitride (Ti/TiN) multi-layer coating deposited on 316L stainless steel via physical vapor deposition (PVD) technique for using in proton exchange membrane fuel cell (PEMFC) bipolar plate (BPP) application. The phase and microstructure of the coated BPPs is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle examinations. The performance of the BPPs is investigated by electrochemical corrosion tests including electrochemical impedance spectroscopy (EIS), potentiodynamic and potentiostatic polarization tests at two conditions including at ambient temperature and in the simulated PEMFC cathode environment. Electrochemical test results reveal that the Ti/TiN coating increases the polarization resistance of 316L stainless steel by 26 orders of magnitude at ambient temperature and by 1000 orders of magnitude in the simulated PEMFC cathode environment. The corresponding ICR of the BPPs is measured ex-situ in a PEMFC set-up. It is observed that the coated BPP has ICR value of 11 and 18 mΩ cm2 before and after potentiostatic polarization, respectively. Hence, the Ti/TiN coating studied in this work has promising properties as BPP material and is potentially suitable alternative to replace the graphite BPP in PEMFC.

Corrosion Behavior and Conductivity of TiNb and TiNbN Coated Steel for Metallic Bipolar Plates

To improve corrosion resistance and electronic conductivity of bipolar plates for proton exchange membrane fuel cell (PEMFC), coatings of TiNb and TiNbN on 316L stainless steel (SS) were prepared by magnetron sputtering. X-ray diffraction (XRD) measurements confirmed the existence of metallic nitrides in the TiNbN coating. Scanning electron microscope (SEM) tests showed that the deposited coatings provided smooth surfaces. Further electrochemical measurements indicated that the corrosion resistance of TiNb coating was significantly higher than that of substrate. At 0.19 V vs MSE, the long-term stabilized current density of TiNb/316L SS was lower than 1 μA·cm−2. The interfacial contact resistance (ICR) values between coating and carbon paper suggested that TiNb and TiNbN films had better contact conductivity than 316L SS substrate. In conclusion, TiNb coated 316L SS metallic bipolar plate material is a promising option for PEMFC.

Coated stainless steel as bipolar plate material for anion exchange membrane fuel cells (AEMFCs)

Low-temperature anion-exchange membrane fuel cells (AEMFCs) are gathering increased attention because they facilitate the use of non-precious metal catalysts, which might drastically reduce costs compared to low-temperature proton exchange membrane fuel cells (PEMFCs). Metallic, e.g., stainless steel, bipolar plates (BPPs) present a cost-efficient solution for this type of cell. However, anodic film formation at high positive potentials (approx. +1.5 V vs. RHE) on uncoated metals/stainless steels leads to high interfacial contact resistance (ICR) of the BPP once exposed to such a potential. A potential of +1.5 V vs. RHE is commonly reached under local and global hydrogen starvation, which rules out the use of uncoated metals in AEMFCs. We have investigated the ICR change and oxide film formation of several materials under simulated fuel cell operating conditions and found that suppression of anodic film formation and, in turn, low ICRs can be achieved by carbon coating of stainless steels.

Electrolyzer Components and Coatings: Methods for Ex-Situ Accelerated Stress Testing

Lowering electrolyzer capital costs and increasing material durability are key efforts toward furthering the commercial penetration of PEM electrolysis technology. This work focuses on bipolar plate and porous transport media materials, typically consisting of a titanium alloy coated with a protective thin-film of Pt, Au, or Ir. The titanium alloy serves as a corrosion-resistant base material and the coating material is selected with the purpose of delaying titanium oxidation that leads to increasing contact resistance and performance decline during operation. Potential alternative, lower-cost materials and coatings exist and/or could be developed. To avoid time, equipment, and labor intensive in-situ durability testing, accelerated high-throughput screening methods are desirable and explored in this work.. The explored ex-situ testing methodologies involve the preparation of coated material samples which are used as oxygen evolution electrodes. The materials are submersed in liquid electrolyte and degradation stressors such as temperature, pH, and potential are directly controlled. By varying each stressor independently, the influence that each has on the rate of degradation can be quantified. Such an approach may ultimately be useful in translating ex-situ results toward predicting in-situ performance. Periodic measurement of contact resistance and coating thickness during durability testing are also used toward this end. We further developed the use of time-lapse microscopy monitoring and analysis for our ex-situ testing setup. This technique allows identification and comparison of distinct corrosion modes and enables visual observations to be related to electrochemical durability data, which can improve its interpretation. We will first present results that have guided our methodology development, in which electrode surface preparation and mounting variants were evaluated using a model system of sputtered Pt coatings on Ti coupons. With improved electrode preparation, we then evaluate some common Pt deposition techniques that include evaporation, sputtering, and electrodeposition. We also make a direct comparison between sputtered Pt and Ir coatings while using time-lapse microscopy to identify the corrosion modes of each. Coatings of Pt show a progression of yellowing, blistering, and peeling while Ir corrodes via darkening and dissolution. By processing the time-lapse microscopy to determine the change in apparent active area with time, we show that performance decline trends closely with the loss of active area. Some discrepancy at the beginning and end of the durability test have yet to be explained and additional analyses of the time-lapse data are ongoing. We will also present results of work in progress that includes investigation of Pt and Ir coating thickness, adhesion layers, and post-deposition annealing.

Investigation of Faradaic Contributions from Bipolar Plates to Areal Current Density in Vanadium Redox Flow Batteries

All-vanadium redox flow batteries (VRFBs) have been identified as a promising technology for bridging the gap to integrating renewables onto grids as well as improving grid-level power generation efficiency. VRFBs are prime candidates for this role on account of their modularity, scalability, and relatively high performance. [1] There are still, however, many design parameters that can be more highly optmized to improve and specialize the aspects of this technology. Capacity fade is a parasitic loss that occurs in all electrochemical enery storage systems and is one of the parameters that can be most improved in VRFBs. Fading capacity is due to a host of variables in the system, such as membrane permeability and electroactive species concentration.[2] Degradation of cell components (electrodes and membranes) can also contribute to capacity decay in the form of increased overpotentials throughout the systems operating range. The kinetics at the negative electrode (V(II) ↔ V(III)) are generally understood to be more sluggish than at the positive electrode [3] as well as being less stable (i.e. degrading more rapidly with respect to time). Several high performance materials have been identified for the negative electrode [4] [5], however extended cycling data on the order of years is uncommon in the literature. Mitigation of this degradation on this time scale is one such optimization that can improve voltage efficiency and mitigate capacity fade. In this work we present our most recent experimental work in which the Faradaic current that can be supported by the plates is quantified on different sets of VRFB hardware and isolated from the current on the combined plates with GFD 2.5 mm carbon felt electrodes. For this work symmetric cells were utilized, to isolate crossover effects, in conjunction with electrochemical impedance spectroscopy and polarization curves to quantify the contributions from the different processes at each overpotential. Likewise, experiments were also performed on a symmetric cell where the plates served as the electrodes to quantify the parallel contribution. The data were assessed via statistical tests in order to determine significance. The results of this study show that, graphitic bipolar plates can support 35-50% of the current density on the negative electrode at low overpotentials and 20 and 30% at higher overpotentials. The open circuit impedance data also show that the ASR of the cell with felt electrodes is increasing at a rate of around 25 mΩ cm2 min−1 at this stage in the electrode’s life. This degradation is nonlinear and asymptotes to a stable ASR, however, this implies that the percentage measured in this context is smaller than the steady state percentage. These combined results suggests a material oriented approach to improving the bipolar plate material in order to achieve a more stable negative electrode.

Carbon-based materials for bipolar plates for low-temperatures PEM fuel cells — A review

The PEMFC (Polymer Exchange Membrane Fuel Cell) is one of the most researched generators in hydrogen technology. The PEMFCs offer low emissions, several applications in industry with high power density. The basic material for the construction of components in low-temperature fuel cells is carbon or its allotropic forms and carbon nanomaterials. Carbon materials are used to build diffusion layers of electrodes, as catalyst carriers, for the construction of covers/interconnectors and as fuel. In this work, the carbon materials used to build a single cell have been reviewed taking into account various methods of fabrication and modification of materials.

Influence of microporous layer on corrosion of metallic bipolar plates in fuel cells

The effect of the presence of a microporous layer on the propensity for corrosion of metallic bipolar plates in an operating polymer electrolyte membrane fuel cell is investigated using an in situ reference electrode array. The local potential at the surface of the cathode bipolar plate is significantly more negative in the presence of the microporous layer, which is attributed to the higher ionic resistance of the aqueous phase in the reactant transport layer associated with more effective removal of water from the catalyst layer/reactant transport layer interface. As a result the bipolar plate is effectively shielded from elevated potentials that may be present at the cathode electrode, even during start-up and shutdown of the cell. Revision of ex situ test protocols for candidate bipolar plate materials, surface treatments and coatings is recommended to reduce unnecessary conservatism in testing.

Cr2N coated martensitic stainless steels by pack cementation process as materials for bipolar plates of proton exchange membrane fuel cells

Bipolar plates in proton exchange membrane fuel cells must have corrosion resistance in an acidic environment and also high electrical conductivity. For steels to be used as bipolar plate materials, surface treatment process suitable for volume production must be developed so that both of these two key property requirements can be met within cost limit. Cr2N is both corrosion resistant in acidic environment and electrically conductive, but it is technically challenging to produce Cr2N-coated steels by thermochemical process such as gas-nitriding, which is suitable for volume production purpose. Here, it is shown that the pack cementation process, which is another form of thermochemical process, can be applied to form a pinhole free Cr2N surface layer on martensitic stainless steels, providing a novel method for producing Cr2N-coated steels for use as bipolar plate materials for proton exchange membrane fuel cells. The corrosion resistance and the pinhole free feature of such Cr2N-coated steel are both confirmed by immersion test in H2SO4 solutions at 60 °C in which the Cr2N-coated steel shows no mass change whereas the uncoated steel exhibits rapid mass loss.

Measuring In Situ Interfacial Contact Resistance in a Proton Exchange Membrane Fuel Cell

Interfacial contact resistance (ICR) is one of the remaining hurdles for successful implementation of stainless steel bipolar plates in PEM fuel cells. We have developed a reliable method, using thin gold wires, to measure the interfacial contact resistance between the bipolar plate material and the porous transport layer during fuel cell operation. The ICR values were found to be in the same range as the ICR values measured ex situ after fuel cell operation. Local ex situ ICR measurements on tested plates indicate uneven current distribution during fuel cell operation. Consequently, an average between three measuring points was used for the in situ measurements, which enabled consistent monitoring of the ICR development alongside fuel cell performance. For almost all of the tests, the largest ICR changes took place within the first two hours of operation, showing the importance of early ICR measurements. Non-coated stainless steel and titanium-coated steel BPPs experienced a higher ICR compared to the gold coated stainless steel.

Evaluation of Ni-Cr-P coatings electrodeposited on low carbon steel bipolar plates for polymer electrolyte membrane fuel cell

Polymer electrolyte membrane fuel cell (PEMFC) stacks suffer from the high cost and low volumetric energy of non-porous graphite bipolar plates. To resolve this problem, a bilayer coating consisting of Ni and Ni–Cr–P is deposited on AISI 1020 low-carbon steel using pulse electrodeposition. Ni/Ni–Cr–P-coated AISI 1020 is evaluated as a bipolar plate material for PEMFCs. Ni/Ni–Cr–P-coated substrates exhibit better corrosion resistance in both cathodic (air-purging) and anodic (H2-purging) environment than the bare AISI 1020 substrate and lower interfacial contact resistance (ICR) than bare AISI 1020 and stainless steel. Further, it is expected to show better water management as the Ni/Ni–Cr–P coating is more hydrophobic than the bare substrate. Preliminary studies show that Ni/Ni–Cr–P-coated AISI 1020 plate can be a suitable candidate for replacing graphite as the bipolar plate of PEMFCs.

In Silico Screening and Design of Coating Materials for PEMFC Bipolar Plates

Methods used to design coating materials for polymer electrolyte membrane fuel cells (PEMFCs) are unsystematic and time-consuming because current materials research relies on scientific intuition and trial and error experimentation. In this study, a feasible and more efficient scheme of screening and designing coating materials is established based on density function theory (DFT) utilizing the fast-growing computing capacity. The scheme consists of four steps: Elements selection by calculation of Pilling–Bedworth ratio and electrical resistivity, corrosion resistance assessment leveraging the Pourbaix diagram approach, running BoltzTrap code to calculate electrical conductivity ( σ / τ ), and interface binding strength evaluation by calculation of separation work. According to the calculation results, TiCo and TiCo3 are proposed to be the two most promising candidates because of relatively better properties required by harsh working environment of PEMFC. The high-throughput screening strategy established in this study makes the ideal of rapidly evaluating hundreds of thousands of possible coating materials candidates into reality and helps to indicate the direction of further synthesis efforts.

PENGARUH PENAMBAHAN IRON MILL-SCALE DAN TEMBAGA SEBAGAI MATERIAL PELAT BIPOLAR

Bipolar plate is an important component of proton exchange membrane fuel cell (PEMFC), which provides fuel and oxidant to reactive sites, collect produced current, and mechanical support for the cell in the stacks. This study concerns to find the optimum composition and sintering temperature of iron mills-cale in matrix aluminium as bipolar plate material. This work firstly carried out by downsizing aluminium flake from scrap into powder using high energy milling for 120 min and treated the iron mill-scale at 300 and 1000 oC for 60 min. The waste aluminium powder, after sieving of 150 mesh, was mixing with iron mill-scale containing 30 to 50 vol.% using shaker mill for 10 min. The mixed powders were then pressed 300 MPa and sintered with temperature of 500-600 oC for 60 min and flowed with N2 gas. The structural changes, physical, and mechanical properties of the sintered sample were studied by optical micrograph, density, porosity, hardness Vickers, and electrical conductivity test. The result showed that the optimum composition Fe is 40 vol. % and sinter temperature is 550 oC. Conductivity value of 45.406 S/cm and hardness 183.96 HV hasn’t meet expectation. Cu added containing 4-10 vol. % Fe aims to improve physical properties composites as bipolar plate material PEMFC. The result showed Cu 4 vol. % Fe can increase conductivity value 64.481 S/cm and hardness 340.13 HV.

Comparison of Carbon Based Bipolar Plate Materials for Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells can be separated into two types, the high-temperature (HT) PEM and low-temperature (LT) PEM fuel cell. As main advantages operating at higher temperatures improved tolerances to impurities like carbon monoxide, easier heat rejection and simpler water management can be mentioned. In comparison to LT-PEM fuel cells where sulfuric acid is applied polybenzimidazole (PBI) membranes doped with phosphoric acid (PA) were used in HT-PEM fuel cells. Nevertheless, degradation and long term stability are still major challenges. Here, it is necessary to understand the degradation mechanisms regarding membrane and catalyst degradation, carbon corrosion as well as loss of phosphoric acid and degradation of bipolar plates (BPP). Titration investigations of carbon based bipolar plates after operation in PEM fuel cells showed that phosphoric acid can be found within the composite matrix [1, 2] which can lead to corrosion of the graphite material. In this work, a variety of graphite-polymer composite bipolar plate materials for PEM fuel cells were tested for their stability and compared with different methods. The electrochemical stability was investigated by means of corrosion measurements within a three-electrode cell setup. The bipolar plate material was applied as working electrode and a platinum wire with an activated felt was served as counter electrode. Potentials are shown with respect to the standard hydrogen electrode (SHE). Two different methods of aging were used: chemical storage and potentiostatic treatment. For determination of stability and corrosion rates OCP, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were evaluated. Additionally, the bipolar plate materials were compared by electrical conductivity measurements (in-plane and through-plane), contact angle measurements as well as structural changes of the surface area. Here different imaging methods like scanning electron microscopy (SEM), micro-computed tomography (µ-CT), atomic force microscopy (AFM) and confocal microscopy were applied. First results of two graphite composite bipolar plate materials with different types and amount of polymer binder show different electrochemical behavior after chemical aging for 3 and 7 days in 0.5 M H2SO4. The bipolar plate material with higher polymer content (BPP-01) reveals lower double layer capacitance and a lower amount of oxygen functional groups in the potential range between 0.5-0.7 V vs. SHE (Figure 1) in comparison to the bipolar plate with higher polymer content (BPP-02). The reason for this behavior could be the lower amount of electrochemical active graphite at the BPP/electrolyte interface from BPP-01 in comparison to BPP-02. In addition, conductivity measurements show that BPP01 has a higher sheet resistance (53.6 +/- 5.6 mOhm) compared to BPP-02 (46.2 +- 4.5 mOhm) in good agreement to the content of polymer and graphite in the composite materials. The various methods can be used to identify the difference of graphite compound materials and correlate it to degradation mechanism. Further results will be given. [1] C. Hartnig and T. J. Schmidt, Electrochim. Acta, 56 (2011), 4237-4242.[2] N. Pilinski, M. Rastedt and P. Wagner, ECS Trans., 69 (2015), 323-335. Figure 1