1. Design of Fuel Cell Membrane Test Stand for Advanced Fuel Cell Research Rebekah Achtenberg, Brandon Darr, Luke Roobol Western Michigan University College of Engineering and Applied Sciences Mechanical and Aeronautical Engineering Department ME 1004-07 April 20, 2010
2. Outline of Presentation Scope of the Project Fuel Cell Background Design Sensors Instrumentation Experimental Methods Evaluation Methods
3. Scope of the Project A fuel cell membrane test stand was designed and fabricated to evaluate solid polymer electrolytes at the reactant-catalyst-electrolyte interface Three new membranes from the Institute of Macromolecular Chemistry in Kiev, Ukraine were tested and analyzed C-40 N-172 229 Characterizations were made of the membranes and gas diffusion electrodes. The membranes were compared to the Nafion 117 membrane.
4. What is a Fuel Cell A Fuel Cell works by combining Hydrogen and Oxygen Gas to produce electricity and the only byproduct is water and heat. Fuel cells have also been called Gas Batteries The reaction within a Fuel Cell the opposite of electrolysis. Fuel Cells are classified by the type of electrolyte utilized There were two types of Fuel Cells that were tested Proton Exchange (PEM – acid) Hydroxyl Exchange (Alkaline Fuel Cell)
6. Fuel Cell Membrane Test Stand A Test Stand was fabricated by modifying an existing fuel cell manufactured by Parker Hannifin TekStakTM Fuel Cell. A fuel cell membrane test stand was designed to evaluate solid polymer electrolytes. The test stand allows for the measurement at the reactant-catalyst-electrolyte interface. Temperature Pressure Humidity Oxygen concentration
8. Material Selection Gas Diffusion Electrode Carbon Cloth Porous and Flexible Platinum Catalyst Layer Pt is the most reactive and expensive catalyst Robust design (4 mg/cm2) To isolate membrane performance Gaskets 20 mil Silicone Rubber 30% compression
9. Sensors Temperature E type thermocouple Humidity Honeywell relative humidity sensor Compact size Low Cost Pressure Absolute Gas Pressure Sensor 3-36 psi range Temperature Compensated Easy Integration 5 V supply voltage Oxygen Advanced Micro Instruments Model 60 Oxygen Probe electrochemical sensor type 0-25% oxygen range
11. Design Flow plate Serpentine Pattern High channel velocity Good water removal High Performance Graphite The flow plate was redesigned to accommodate the sensors Humidity Sensor Needle Oxygen Sensor Pressure Sensor
18. Characterizations Characterizations of the membrane materials and the gas diffusion electrodes were completed. Optical Microscopy Basic morphology of membranes and GDL’s Scanning Electron Microscopy (SEM) Catalyst loading Detailed Morphology of GDL Atomic Force Microscopy (AFM) Topography of Membranes
19. Optical Microscopy Capability to magnification up to 400 and 1000 times the object’s original size Alkaline Membrane Catalyst Layer
20. Scanning Electron Microscopy In SEM electrons are used to capture an image instead of light SEM scans the sample with a high energy beam of electrons As electrons hit a sample, other electrons are ejected and converted into other forms typical resolution of SEM is around 5 nm
22. Atomic Force Microscopy AFM consists of a cantilever with a probe mounted at the end The probe is brought near the surface of the specimen and the deflection of the cantilever is measured AFM has a resolution of 0.1 nanometers and can be used to view atoms
23. Performance Evaluation Polarization Curve Plot of the voltage vs current density Shows “polarization” losses Activation losses Ohmic Losses Concentration Losses Power Curve Plot of power on a voltage vs current graph
27. Results: Experimental Membranes C-40 Generate voltage of .856 V with no measurable current Ionic conductivity of 4.1(10-3) S/cm at 15C 229 (Alkaline) Generated voltage of .153 V with no measurable current Ionic conductivity of .0112 S/cm when hydrated at 60-80C Nafion 117 Generated of .95 V Ionic conductivity of .083 S/cm
28. Experimental Membranes Voltage of experimental membranes show promising results Still in the initial testing stages Experimental membranes are designed to operate at higher temperatures than Nafion which is limited to below 100C The experimental membranes are thicker than Nafion increasing their resistance Recommend that membranes be made thinner
29. Challenges and Solutions Electronic Fuel Cell Load Little knowledge of how to use machine Spent hours on phone with manufacturer for weeks Leakage Different gasket shapes Did many leak tests to find out where the fuel cell was leaking Applied vacuum grease to the O-rings
30. Challenges and Solutions Humidity Sensor GDL’s were not as flexible as originally thought and caused humidity sensor to not fit into it’s designated space Humidity Sensor kept shorting out Added varnish to the flow plate and leads of humidity sensor Added silicone to flow plate and the leads Insulated the leads with jackets Used a Dremmel to shave off any unnecessary plastic from the humidity sensor. Pressure that was safe for the fuel cell stack was much lower than the pressure that the experiments were supposed to take place at
31. Challenges and Solutions Bolts If the bolts are tightened too much, the gaskets block the channel If the bolts are too loose, then the GDL and membrane don’t have enough contact and there is no current Found optimal torque to be 6 lb-in After one use, Nafion becomes deformed and is pushed into the flow channels by the gaskets and blocks the channel. Thermocouple picking up signals from the EFCL
32. Design Recommendations Deeper channels Allow for gasket to deform into channel without restricting flow Change flow channel design Eliminate the need for holes in the membranes and gaskets to prevent leakage and cross over of gases Use sensors specifically made to be in a conductive environment Prevent sensors from short circuiting between flow plates or Gas Diffusion Electrodes
33. Design Recommendations Use a larger fuel cell Add polyurethane coating to thermocouple for “insulation” Know the mechanical properties of the GDL is before designing a modified flow plate
34. Conclusions A Fuel Cell Test Stand was successfully designed, fabricated, and tested. A data acquisition system was designed and implemented to measure Pressure, Temperature, Oxygen Concentration, and Relative Humidity. Characterizations of Gas Diffusion Electrode and Membrane materials were made. Advanced Laboratory Techniques were learned including Optical Microscopy, Scanning Electron Microscopy, and Atomic Force Microscopy.
35. Acknowledgements Our Advisors – Dr. Shrestha, Dr. Ghantasala, and Dr. Bliznyuk Dr. V. Schevchenko – Institute of Macromolecular Chemistry Dr. Hathaway Pete Thannhauser Abraham Poot Glenn Hall Rex Harding Melissa Wagner
