PROJECT FINAL REPORT

PROJECT FINAL REPORTGrant Agreement number: 201711Project acronym: ELECTROCHEMProject title: FUEL CELL STACK ASSEMBLY AND DIAGNOSTICSFunding Scheme: FP7-MC-IRGProject start date: 01/12/2008Project end date: 30/11/2012Person in charge of scientific aspects: Title: Prof.First name: ALIName: ATATel: +90-262-6051776Fax: +90-262-6530675E-mail: ALIATA@GYTE.EDU.TRResearcher:Title: Dr.First name: SUHAName: YAZICITel: +90-555-8464575Fax: +90-262-6530675E-mail: suha.yazici@gmail.comProject website address: http://www.gyte.edu.tr/materials/default.aspx?pg=a0f54902-0386-4658-873e-34b412d4f5b0

4.1 Final publishable summary reportExecutive SummaryProton Exchange Membrane (PEM) fuel cells are a disruptive technology in the power generation market that can provide the energy for numerous portable, transportation, and stationary power applications. Commercial success mostly relies on improvements in system lifetime, higher power density and cold start-up. In spite of their enormous potential, the cost for PEM fuel cell systems remains too high for mass-market appeal. Fuel cell bipolar plates that are lighter weight, thinner and more robust can reach cost and lifetime targets set by the industry. This includes finding ways of lowering costs with existing materials, as well as developing new manufacturing technologies that will improve yields and quality in short durations. ELECTROCHEM has the objective of working towards expanded graphite fuel cell bipolar plate development that has commercially acceptable properties, manufacturability and cost structure. Flexible graphite has shown to have properties that favour commercially and technically acceptable properties such as low corrosion, processing flexibility, favourable mechanical and electrical properties. Electrochemical performance has been tested several different types of membrane electrode assemblies (MEAs) prepared using the coupled screen printing - decal transfer process. Cells are assembled with custom made expanded graphite-epoxy-silica composite material and tested under different fuel cell operating conditions and compared with commercially available molded graphite. Expanded graphite plates developed in this study gives better performance over commercial materials. Expanded graphite has shown to be easily processable form as production with less thickness, light weight and cost advantages.This project allowed us to look at the problem from various interdisciplinary perspectives. Semester course has been offered on "Electrochemical Energy Conversion and Engineering" to educate students and researchers for them to better understand fundamentals. In parallel in the laboratory, new bipolar plate material research infrastructure was set-up. Expanded graphite material with and without resin were acquired from the leading manufacturer and evaluated for various properties in the first phase of the project. While materials were obtained, analytical and mechanical equipment were acquired to characterize materials and components. Upon project completion, we expect future researchers with electrochemistry knowledge and hands-on experience working towards a new industry. Electrochemistry is used for understanding critical issues such as corrosion and lifetime. Material science played critical role on material development such as right types of polymers, processing conditions etc. Mechanical engineering discipline is used to design and characterize plates for their mechanical, electrical properties and flow parameters. Finally, joint effort is to put things together and diagnose product with multidisciplinary knowledge and approach. At the end of the project, researchers with knowledge and hands-on experience on the expanded graphite technology were able to develop new solutions for problems associated with fuel cell bipolar plate development.Main achievements of the project are:1. Regular semester course offered by Dr. Suha Yazici on "Electrochemical Energy Conversion and Engineering"2. Laboratory capabilities of Gebze Institute of Technology has been expanded to test, characterize not only bipolar plates but also other materials to continue research into the future.3. Silica impregnated expanded graphite – epoxy composites are developed as bipolar plates in proton exchange membran (PEM) fuel cells. These composite plates are prepared by solution, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance and contact angles are determined as a function of impregnation content.4. Manufactured plates were characterized at fuel cell setting for performance under developed fuel cell testing protocols.5. Plate properties are compared to commercially available materials and main conclusions in favour of expanded graphite has been established.

Project Content & ObjectivesFuel cells have several advantages; however it is still not competitive due to its high cost, durability and performance which can be overcome by innovative alternative materials. It must be noted that bipolar plates constitute 80% volume of a fuel cell system. This project has objectives to help fuel cell development through bipolar plate enhancement during reintegration of Dr. Suha Yazici.

The general objective of this project was to give Gebze Institute of Technology research capabilities in the area of fuel cells and educate graduate students on “Electrochemical Systems” through reintegration of Dr. Yazici. Outcome of this research was expected to result several highly educated and trained engineers and researchers with state of the art knowledge of fuel cell systems with hands on experience.More specific objective was to develop a new type of flow field plate material for fuel cell performance, durability and cycle life under various operating conditions. The following action steps were implemented:

Developing fuel cell research and development (R&D) capabilities with the potential to become best scientific institution in Turkey on fuel cell research.

Integration of Dr. SuhaYazici into research community in Turkey has been achieved through various interactions in the scientific and academic community. Dr. Yazici has started to offer graduate level semester course titled "Electrochemical Energy Conversion and Engineering" during 2010 winter semester with participation of 14 students. In 2011, a graduate level class was offered with 12 students participating. In 2012, two undergraduate level courses (Hydrogen Energy Systems and Fuel Cell Technologies” were offered in English with more than 40 students registering. Dr. Yazici has influenced many students to continue their research in other countries including Europe.Dr. Yazici was also invited various scientific and technical panels by Turkish Scientific and Technical Research Council (TUBİTAK). Educational activities with training and participation at conferences took place.Research results were shared with scientific community on Electrochemical Society Meeting. A manuscript is in preparation for submitting to a scientific journal.

Preparing diagnostics methods for thorough evaluation of fuel cell performance and durability.In order to carry out fuel cell development with manufactured plates, research capabilities of Gebze Institute of Technology (GYTE) were enhanced with several new equipments.Development of new capabilities and new infrastructure allowed group to initiate new projects. In past two years, GYTE has made significant achievements towards this objective. The following capabilities are utilized in this research: Three-point flexural strength (Instron Model 5569 universal testing machine); In-plane electrical conductivity (Jandel RM3-AR four point probe electrical conductivity measurement tool); Through-plane electrical conductivity (custom designed equipment with probes); Hydrostatic press; Keithley Model 2000 digit digital multimeter; Corrosion testing ( in-house 3 compartment electrochemical cell); Potentiodynamic experiments (Volga PGZ4 potentiostat); Contact angle measurements (KSV CAM 200 Optical Contact Angle and Surface Tension Meter); ATMA AT-45PA semi-automatic screen printer and CNC machine for plate manufacturing.

Using the best weight and volume efficient flow filed plate technology to meet or exceed current fuel cell performance and cost targets.

At the research front, plate manufacturing, fuel cell assembly and testing were project objectives and has successfully accomplished. Several different graphite substrates were inquired from manufacturers before testing with several different resin formulations. Suitable composites were manufactured and machined, molded for electrical, thermal and mechanical measurements. At the

end measurements with fuel cell assembly was carried out to compare performance with commercially available materials. Light weight, flexible and thin single layer epoxy impregnated expanded graphite bipolar plates with 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. The low thickness (~0.5 mm) and density (~1.2 g/cm3) values of the prepared composite plates put them one step ahead of competition. Performance up to 1 W/cm2 was obtained with these plates. Approximately 4W was obtained from 1 rectangular MEA of 4cm2 with double serpentine design with 1mm channel thickness, 1mm distance between channels and 0.3mm anode and 0.5 mm cathode channel depth. The thickness of the custom made plate was around 1.5mm. At least 25 of these MEAs were needed to obtain 100W net power.

S&T ResultsPolymer electrolyte member fuel cells (PEMFC) are promising candidates for future’s alternative energy technologies, since they are environmentally friendly and highly efficient. No greenhouse gas is vented from PEM fuel cells, during conversion of electrochemical energy to electrical energy. Only water is produced as product. Additionally, PEM fuel cells enable noise and vibration-free technologies. Furthermore, overall efficiency and compactness of PEM fuel cell systems are much better than internal combustion engine systems.

Fuel cells have several advantages; however it is still not compatitive with other energy storage devices for portable applications, due to its high cost, durability and fuel procurement. Platinum catalyst and semi permeable membrane make up the biggest portion of the total cost. Unfortunately, these components must be used for high performance and durability. On the other hand, performance and durability barriers for bipolar plates, another important component of a fuel cell stack, could be overwhelmed with innovative alternative materials. It must be noted that bipolar plates constitute 80% volume of a fuel cell system.

Bipolar plates must be vulnerable to acidic environments and mechanical forces they face during flow channel machining and assembly. Metal materials such as, gold, titanium, stainless steel may seem to be ideal candidates as bipolar plate material, due to their high mechanical strength and conductivity. However, their limited corrosion resistance, weight and coating micro cracks prevent their use in PEM fuel cells. Natural graphite – polymer composites were studied by several researchers. The filler content in these composites have dramatic role in performance. High filler content is required for desired mechanical strength and gas permeability values, but it also increases the electrical resistance, too. As an alternative to widely used natural graphite, expanded graphite stepped forward. Expanded graphite has a structure similar to natural graphite, but with extremely high interlayer distances. Longer interlayer distances improve electrical and thermal conductivity. The porous structure of expanded graphite foams facilitates impregnation of epoxy and a continuous expanded graphite structure minimizes gas permeability. The most important advantages of expanded graphite – epoxy composite bipolar plates is their low density and manufacturability at low thicknesses. These composites can lead to dramatic improvements in PEM fuel cell stack weight (W/kg) and volume (W/L). Technical targets for bipolar plates are listed in Table 1.

TABLE 1. DOE Technical Targets for Bipolar Plates.Characteristic Units 2015

Cost $/kW 3Weight kg/kW <0,4

System Power Density W/L 650H2 Permeation Flux cm3 sec-1 cm-2 @ 80°C, 3 atm <2X10-6

Corrosion μA/cm2 <1Electrical Conductivity S/cm >100

Resistivity Ohm-cm 0,01Flexural Strength MPa >25

Flexibility % deflection at mid-span 3 to 5

Expanded graphite’s porous structure has a negative effect on mechanical strength which necessitates addition of a filler material. Various thermoplastic, polyvinylidene fluoride (PVDF), polypropylene (PP), poly(ethylene terephthalate) (PET) and poly (phenylene sulfide)(PPS) and thermoset, resols and novalak epoxy resins, and vinyl esters polymers have been studied by many researchers. Among other polymers epoxy resin stepped forward with its high mechanical and chemical strength. These properties enabled their use in several industries such as, coating, composite materials, electronics, fiberglass reinforcement and so on. In this project, expanded graphite substrates were obtained from GrafTech Inc. in foam form. Bisphenol-A-epichlorhydrin was used as epoxy precursor and Triethylenetetramine was used as epoxy hardener. Later in the project, silica impregnated expanded graphite – epoxy composite plates were prepeared using four different starting materials, which were expanded graphite foams (GrafTechInc.), epoxy resin, hardener and methyltrimethoxysilane (MTMS, H3C-Si-(OCH3)3. Commercially available MGS® L 285 epoxy resin (Bisphenol-A-epichlorhydrin) and MGS® H 285 curing agent (Triethylenetetramine), which were received fromHexionTM, as well as methyltrimethoxysilane (MTMS, H3C-Si-(OCH3)3), obtainedfrom Alfa Aesar, were used as additives. First of all, 4.5 mm thick expanded graphite foams into desired shapes. The epoxy resin, hardener and MTMS were dissolved in acetone by using magnetic stirrer, ultrasonic bath and ultrasonic homogenizer, respectively. Expanded graphite foams were added into the prepared solution, followed by 30 minute magnetic stirring, which is required for effective impregnation. The specimens were dried in a BINDER FD55 forced convection drying oven at 35 °C for 2 hours. Four of the epoxy impregnated plates were placed in a mold and compressed by a hydraulic press at 150 °C. The compression pressure of 2000 N/cm2 was applied intermittently for 15 minutes. Cross-linking of the epoxy resin was also completed during this process. The surfaces of the bipolar plate samples were polished using fine grade abrasive paper and chemically cleaned with acetone to remove any excess dust and epoxy particles.The composite bipolar plates were characterized in terms of mechanical (flexural) strength, electrical conductivity, corrosion resistance and contact angle. Experiments were repeated with several specimens to ensure repeatability.

Mechanical Strength Analysis: Bipolar plates must possess good mechanical properties to support thin membranes and electrodes, and to withstand high clamping forces for the stack assembly. The mechanical failure of bipolar plates could be examined ex situ with several test methods, such as tensile strength test method, compression test method and three point bending method. Among various alternative methods three point bending method was chosen, in parallel with several researchers working on bipolar plates for PEM fuel cells. This method was representing the tensile and compression stresses occurring simultaneously at bipolar plates during assembly or compression of PEM fuel cell stacks. Three-point flexural strengths of the custom made bipolar plates were evaluated using Instron Model 5569 universal testing machine. Mechanical strength measurements were recorded according to ASTM D790 standard. 16 x 60 mm2 sized specimens prepared for mechanical measurements. The supporting span distance is 40 mm wide moving at a constant cross-head speed of 1 mm/sec. Schematical view of the experiment setup is shown in Figure 1.

Figure 1. Schematical Flexural Strength Measurement Setup

The EG foam plates that were impregnated with epoxy resin, curing agent and other additives were compressed under huge pressure which filled the pores. The epoxy amount was selected as 50 wt% similar with other studies. In general epoxy filler material might improve the flexural strength of expanded graphite specimens; however they tend to shrink during the curing process which resulted in local stresses. Dimensional changes increased with increasing epoxy content which increased total stress. Flexural strength of only epoxy impregnated EG bipolar plates were found to be 12 MPa with 1.64 mm thickness. In order to improve the flexibility of the plates methyltrimethoxysilane (MTMS) as a precursor of silica was also added before the hot press process. Addition of MTMS improved the mechanical properties of the plates up to 20MPa. MTMS and epoxy impregnation into the EG foam was studied by trying different amount of MTMS, a 5 wt%, 10 wt% and 15 wt%. Optimum MTMS amount in terms of flexural strength was found to be 5 wt%. The results indicated that further increase in the amount of MTMS caused a decrease in flexural strength. Change of flexural stress values obtained during the 3 point bending test is shown in Fig. 2.

Fig. 2 Effect of MTMS content on flexural strength

Flexural strength values up to 17.41 MPa and flexural modulus values up to 6.28 GPa with 0.45 mm thick bipolar plates were obtained with the impregnation method. Interestingly, impregnation amount was not changing linearly with time. Effect of epoxy impregnation time on epoxy content, flexural strength and flexural modulus is shown in Figure 3. Flexural strength values showed paralelity with flexural modulus values. In general epoxy filler material might improve the flexural strength of expanded graphite specimens; however they tend to shrink during the curing process which resulted

in local stresses. Dimensional changes increased with increasing epoxy content which increased total stress.

Figure 3. Effect of epoxy impregnation time on flexural properties and impregnation amount

The plates gained flexibility with the epoxy impregnation process. Deflection at mid-span (%) values for epoxy impregnated expanded graphite bipolar plates were 4.02, 4.38, 4.23, 4.18 for 0.5h, 1h, 2h and 4h epoxy impregnated plates, respectively. Current flexibility values met the DOE 2015 flexibility targets. Besides mechanical strength flexibility also has an important role in fuel cell stack assembly and impact durability.

Electrical Conductivity Measurements: Through plane conductivity values of the prepared specimens were measured by custom designed two plates, each including 4 gold plated copper probe, and an adjustable hydrostatic press (Figure 4a). The conductivity measurements from all 4 probes were recorded with Keithlay 2000 digital multimeter. In plane conductivity measurements were conducted with Jandel RM3-AR 4 point probe electrical conductivity measurement device (Figure 4b). Mechanical strength measurement specimens (16 x 60 mm2) were used for electrical conductivity measurements.

Figure 4. In Plane (a) and Through Plane (b) Conductivity Measurement Setups

The electrical conductivity of the epoxy impregnated bipolar plates were affected by the second polymer additive content. MTMS had a positive influence on the electrical conductivity values of the plates. Change in the amount of MTMS content was monitored while epoxy content was kept at a constant value that was accepted as the optimum value due to previous studies. (Table 2) The presence of epoxy had a negative influence on the conductivity, but it was required to obtain the desired mechanical strength.

TABLE 2. In-plane conductivity and through-plane resistivity of prepared specimens

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The in-plane conductivity values of the prepared specimens meet the DOE target (> 100 S / cm), however a similar success couldn’t be achieved with through-plane resistivity values. (DOE Target: < 0.01 Ω·cm) The high through plane resistivity values might seem to be negative for fuel cell applications, whereas the flexibility of these plates might lead to a decrease in contact resistance. The bulk resistance of the bipolar plates is accepted to be much less important than the contact resistance of these plates with GDLs. It is also known that flexible plates make better contact with GDLs.The final products were prepared by attaching 4 independently impregnated plates. The increase in MTMS amount might have decreased the contact resistance between these plates, since higher MTMS containing plates were probably more flexible, which enabled better adhesion and contact between these individual plates. The decrease in through-plane resistivity can be explained with this phenomenon. On the other hand, the in-plane conductivity had also improved with increasing amount of MTMS. This fact could be explained with the presence of more MTMS and less epoxy on the surface layer, since epoxy is electrically less conductive than MTMS. The continuous electrically conductive matrix of expanded graphite enabled to achieve high in plane conductivity values up to 136.6 S/cm with epoxy impregnated expanded graphite plates. (Figure 5) In-plane electrical conductivity of the composite plates decreased with increasing epoxy impregnation time. The surface quality of the bipolar plate was protected with water solvent based adhesive which was critical to achieve high conductivity. As expected, the electrical conductivity values showed worse performance with increasing polymer content. The impregnated polymer was probably blocking the electrically conductive zones of expanded graphite. Furthermore, shrinkage after the curing process might also had a negative effect on the electrical conductivity. 30 minute epoxy impregnated expanded graphite plates were selected for further measurements. Through plane conductivity measurements were conducted under 140 N/cm2 pressure. Through-plane resistance of 0.027 Ohm-cm was measured with 30 minute epoxy impregnated expanded graphite plates, which was slightly higher than DOE 2015 target.

Figure 5. In-plane electrical conductivity as a function of impregnation time (Jandel RM3-AR)

Corrosion Measurements: Corrosion behavior of the epoxy impregnated expanded graphite bipolar plates were analyzed by potentiodynamic method. Volta PGZ4 potentiostat was used to apply and measure the current and voltage. The experiments were conducted at 80 °C in a three compartment electrochemical cell setup with epoxy – expanded graphite specimen as working electrode, platinum plate as counter electrode and calomel electrode as reference electrode. 0.5 M H2SO4was used as the electrolyte to represent the acidic environment of PEM fuel cells. The potential of the working electrode was increased from -700 mV vs. Ref to 800 mV vs. Ref with 1 mV/s scan rate. The experimental setup is shown in Figure 6. The corrosion current value was calculated with Tafel extrapolation method at the corrosion potential. Corrosion current values as low as 1.09µA/cm2were obtained with these plates. Corrosion behavior of various plates is summarized in Table 3. The plate with 50 wt% epoxy and 5 wt% MTMS was found to be the most corrosion resistant plate.

Figure 6. Corrosion Experiment Setup

Table 3 Corrosion Current Values of Prepared Specimens

Further corrosion experiments were conductied with different epoxies. Very low corrosion as low as 0.5 µA/cm2 values were obtained. Comparison of several epoxies is shown in Figure 7.

Figure 7. Corrosion Current Calculation Using Different Epoxies

Contact Angle Measurements: Static contact angle values were obtained with Sessile Drop Technique. The images were recorded with KSV CAM 200 Optical Contact Angle and Surface Tension Meter. (Figure 8) Contact angles of several specimens were measured to investigate repeatability. Bipolar plates with low surface energy and high water contact angle (>80°) can prevent liquid water formation in the channels. The hydrolytically stable methyl group in silica prepared from MTMS resulted in high contact angle (θ). The sessile drop contact angle measurements of the prepared specimens are summarized in Table 4. Increase in hydrophobicity with increasing amount of MTMS can be explained with the effect of organic groups (Si-CH3) attached to the MTMS which made the surface non-polar and hence hydophobic.

Figure 8. Contact Angle Measurement Setup

TABLE 4 Average contact angle values of prepared specimens

Plate Machining: Serpentine gas flow channels were machined on epoxy impregnated expanded graphite plates with a CNC milling machine, to evalujate the were machinability of the plates. Both single sided and double sided 0.3 mm deep flow channels were successfully machined on 2mm thick plates with a benchtop CNC milling machine (Figure 9). Several different flow field designs were machined on expanded graphite specimens (Figure 10).

Figure 9. Bench top CNC Milling Machine

Figure 10. Machined Expanded Graphite Plates

MEA Preparation and Fuel Cell Experiments: Commercial Nafion XL membrane and Tanaka catalyst (38 wt% Pt/C) were used to prepare MEAs. MEA’s were prepared using the coupled screen printing - decal transfer process. Catalyst slurries were coated on Teflon sheets using the ATMA AT-45PA semi-automatic screen printer (Figure 11). Anode and cathode catalyst layers were prepared with a platinum loading of 0.3 mgPt / cm2 using the slurry of the same commercial catalyst. The coated sheets were sandwiched with a Nafion XL membrane in between and placed in a hot press. The sandwich was compressed up to 150 Bar at 130 °C for 8 min. The catalyst layers were transferred on the membrane and the Teflon sheets were peeled off. Several MEAs were prepared at same conditions to test bipolar plates. The active area of the MEAs was 450 mm2 (10 mm x 45 mm).

The MEAs were tested in a custom designed cell with different bipolar plate materials. The custom single cell design is shown in Figure 12. This design was made to show the effect of bipolar plate on overall performance. Freudenberg CX-316 was used as the gas diffusion layer (GDL) material and 0.5 mm thick silicon gaskets were used for sealing. All of these experiments were conducted in the fuel cell lab in Nanotechnology Center of Gebze Institute of Technology (Figure 13).

Figure 11. ATMA AT-45PA Semi Automatic Screen Printer

Figure 12. Custom Designed Test Cell

Figure 13. The Fuel Cell Lab in GIT

The experiments were hold at 60 °C while hydrogen and oxygen was purged fully humidified at 58 °C. The gas flow rates were kept constant both for the anode and cathode and they were 0.2 l/min and 0.4 l/min, respectively. The MEAs were conditioned before recording a data. Performance tests were conducted with a Scribner 850C compact fuel cell test station (Figure 14). Polarization curves were obtained while decreasing the potential slowly by withdrawing current. Polarization data were recorded after six continuous cycles. Custom made expanded graphite-epoxy-silica composite material was tested and compared with other commercial alternatives. The results are compared in Figure 15.

Figure 14. Fuel Cell Test Station

Figure 15. Polarization Curves Obtained With Several Bipolar Plate Materials

Performance improvement can be explained as the insulating property of the polymer in the commercial plate material and the conductivity improvement with MTMS addition in the custom plate material. For further investigation, impedance spectroscopy experiments were conducted. This experiment was important to observe the effect of contact resistance and through plane conductivity values of the bipolar plate. This experiment was also important to measure if the MEA is conditioned or not. The frequency was decreased from 10 kHz to 100mHz while withdrawing constant current (1 A) from the test cell. The Nyquist plots of the MEAs run with different bipolar plate materials are compared in Figure 16.

Figure 16. Nyquist Plots Of Single Cells With Different Bipolar Plate Materials

The impedance measurement conducted with the custom made expanded graphite – polymer material performed better than the commercial expanded graphite – polymer material at 1 A (222 mA/cm2) constant current. The result was in parallel with the performance improvement observed in Figure 5 at low current region (<1 A/cm2). A custom test apparatus was designed for testing these materials. Performance up to 1 W/cm2 was obtained with these plates. The MEAs used in these tests were prepared with commercial membranes and catalysts. Several different bipolar plates were prepared with different flow field designs. Single serpentine, Double serpentine, triple serpentine and straight channels were machined with a CNC. Approximately 4W was obtained from 1 rectangular MEA of 4cm2 with double serpentine design with 1mm channel thickness, 1mm distance between channels and 0.3mm anode and 0.5 mm cathode channel depth. The thickness of the custom made plate was around 1.5mm. At least 25 of these MEAs were needed to obtain 100W net power. However lower power densities could be obtained at stack studies. So several more MEAs and bipolar plates were needed to obtain 100 W net power.

Conclusions: Epoxy impregnation into expanded graphite foam process was optimized by changing the stirring time from 30 minutes to 4 hours. The effect of impregnation time on weight of the specimen was used for optimization. The densities of the specimens varied in between 1.2 – 1.3 g/cm3 which corresponded to 5 – 15 wt% epoxy content. Furthermore, thickness of the specimens varied in between 0.4 – 0.5 mm under certain compression pressure. A correlation between epoxy content and thickness of a specimen was observed. Surface quality of the specimens had severe effect on corrosion and contact angle measurements. Non-uniform surfaces resulted in high corrosion current and low contact angle values. The specimens were polished with 1200 and 2500 sand papers. The corrosion current value of the 30 minute epoxy impregnated expanded graphite plate was measured as 2.74 µA/cm2 which was quite higher than the DOE 2015 target for corrosion (<1 µA/cm2). Interestingly, epoxy impregnated expanded graphite plates showed similar behavior with pure expanded graphite plates which had a corrosion current value ofb 2.69 µA/cm2. Average contact angle value for 30 minute epoxy impregnated expanded graphite plates was 64 °.

Potential ImpactComposite materials have been easing the human life for more than 6000 years and met the demand for advanced technology and quality of life standards. They have an important role in several sectors including energy applications. Latest advances and constraints in technology, regardless of the subject, depend on the material used. Energy sector is also an important sector which composites came into prominence. One of the most promising clean energy technology topic is Proton Exchange

Membrane (PEM) fuel cells. These electrochemical systems are composed of important components such as membrane and catalyst layer. These layers should be supported with other components which will provide sufficient gas, electron, product and heat transfer and protection from mechanical and physical effects. Bipolar plates are the components which undertake these important tasks in PEM fuel cells. Thus, the material and production method of bipolar plates should be optimized.Bipolar plates need to be lightweight, that will effect the power density (W/kg) of a fuel cell system, which is crucial for commercialization. In order to build a thin, lightweight, mechanically and chemically resistant composite material, expanded graphite matrix can be used with some additives. Expanded graphite plates step up with their low density and their adequate mechanical properties. As an additive, epoxy resin is one of the most common material to prepare a solid composite material. Several different epoxy resins and other additives were used to fullfill the requirements for PEM fuel cells bipolar plates. The composite plates were prepared with impregnation of the additives followed by hot pressing.Results hav shown material developed in this research has promising properties and this group will continue implement this material at different projects. Further tests with different resins and additives will continue.

Educational front, Dr. Yazici has offered several classes on electrochemical systems. In the first year of course offering, 7 registered and 8 unregistered graduate students participated in the course. This number increased in following years. In 2011, a graduate level class was offered with 12 students participating. In 2012, two undergraduate level courses (Hydrogen Energy Systems and Fuel Cell Technologies” were offered in English with more than 40 students registering. The infrastructure for bipolar plate research at Gebze Institute of Technology was significantly improved with this project. Laboratory capabilities were enhanced by adding electrical conductivity equipment and CNC machining for plate processing, laser cutter for gaskets and several molds.

In summary, this project transferred the studies that Dr.Suha Yazici was conducting in United States and enabled an infrastructure for further studies. Several undergrad and grad students had a chance to attend electrochemistry classes of Dr. Yazici. Furthermore, a Ph.D. thesis and 2 M.S. thesis were completed on this topic, which enabled transfer of knowledge to new researchers.