1 / 21

Chemical Degradation of Seal Materials in PEM Fuel Cell Environment

Chemical Degradation of Seal Materials in PEM Fuel Cell Environment J. Tan, Y. J. Chao , Woo-Kum Lee, CS Smith, JW Van Zee and CT Williams NSF-I/UCRC for Fuel Cells College of Engineering & Information Technology University of South Carolina, USA. Cracking. Virgin silicon gasket.

elias
Download Presentation

Chemical Degradation of Seal Materials in PEM Fuel Cell Environment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chemical Degradation of Seal Materials in PEM Fuel Cell Environment J. Tan, Y. J. Chao, Woo-Kum Lee, CS Smith, JW Van Zee and CT Williams NSF-I/UCRC for Fuel Cells College of Engineering & Information Technology University of South Carolina, USA

  2. Cracking Virgin silicon gasket Background • GM found that their silicone gaskets are failing after 2,000 hours (by cracking and increasing roughness). • Outlet water from a stack has a pH of 3-4. • 1-2 ppm HF was found in the outlet water from the stack. • Will seal integrity be one of the major next technological barriers in commercializing Fuel Cells ?

  3. Ambient Gasket or Seal Pressure Temperature Chemicals Gasket/seal as a structural member • Characteristics of gasket/seal : • Under compression, exposed to chemicals, high temperature, pressure, cyclic conditions, etc. • Loss of functionality : by cracking and /or stress relaxation • Cracking : due to corrosion under compression (Chemical stability) • Stress Relaxation : material degradation… loss its sealing ability (mechanical stability) • Leachants :detrimental sometimes (chemical stability)

  4. Objective: Develop design guidelines for gasket materials in fuel cell stacks • Studies: Investigate the long term mechanical and chemical stability/durability of PEM fuel cell gasket materials • Scope of work: • Testing commercially available elastomeric seal materials • Identifying leachants into the soaking solutions • FEM analysis of seal profiles to understand the mechanical stresses in test specimens and seals during operation • Investigating the degradation mechanisms • Investigating changes in mechanical properties as a function of stress state and soak environment • Developing Accelerated Durability Testing (ADT) methodologies, and confirming similar failure mechanisms (ADT vs. fuel cell)

  5. Flow Chart of Studies : Current and intended -

  6. PROJECT ACCOMPLISHMENTS • Bend Strip Tests for commercially available elastomeric seal materials (Silicone S, Silicone G, EPDM and Fluoroelastomer T) • Constant load compressive test on gasket samples • ATR-FTIR test to elucidate the material surface chemical degradation • XPS test to analyze the degradation mechanisms for gasket materials • FEA modeling for the bend strip specimens –stress state • Atomic adsorption spectrometry analysis to identify leachants into the soaking solutions

  7. Summary of bend experiments performed Silicone S Silicone G EPDM Fluoroelastomer Bending Angle 180° , 120°, 90°, 0° 80°C 60°C Simulated Solution ADT Solution Simulated Solution ADT Solution 4x4x2x2=64

  8. Two Solutions used in the Tests • Regular solution - similar to that in PEM FC 12 ppm H2SO4, 1.8 ppm HF and reagent grade water • ADT solution – for short term accelerated testing 1M H2SO4, 10 ppm HF and reagent grade water

  9. Gasket sample Fuel cell solution Fixture for 120° bend Polypropylene bottle Experimental setup for bend tests Bottles are placed in an oven with the desired temperature Specimens dimensions: 4cm long x 1 cm wide Fixture for 90° bend Fixture for 180° bend

  10. 10 m 10 m 10 m 10 m 10 m 10 m 10 m 10 m Optical micrographs for Silicone S samples with bend angle of 120° exposed to ADT solution at 60°C, 500× (showing the degradation of the surface) Without exposure 6 weeks exposure 10 weeks exposure 12 weeks exposure 14 weeks exposure 17 weeks exposure 23 weeks exposure 19 weeks exposure

  11. Sample Results - Gasket Degradation in ADT solution (120o bending , 80 oC vs. 60 oC) Failed at 4 w Started cracking at 3 w Delta weight (%) Started cracking at 3 w Started cracking at 14 w Started cracking at 6 weeks for Silicone G at 60°C Failed at 6 w Time of exposure (weeks) Silicone S and Silicone G degraded; but not EPDM and Fluoroelastomer T

  12. 1010 10 1080 7 1260 1150 5 1210 868 3 1420 1 0 Wavenumber (cm-1) ATR-FTIR results for Silicone G before and after exposure to ADT solution at 80°C (showing little chemical degradation) Absorbance Little Change – degradation primarily from stress (--bend tests)

  13. 1020 0.32 1150 0.30 0 1090 0.28 1210 0.26 1260 0.24 0.22 0.20 0.18 866 0.16 1 0.14 Absorbance 0.12 0.10 3 0.08 0.06 5 0.04 0.02 7 0.00 10 -0.02 -0.04 1400 1300 1200 1100 1000 900 Wavenumbers (cm-1) Wavenumber (cm-1) ATR-FTIR results for Silicone S before and after exposure to ADT solution at 80°C (showing chemical degradation) vibration of  (Si-O-Si) stretching (Si-CH3) bending mode (Si-OH) stretching vibration Absorbance Degradation from change of chemistry (and stress)

  14. X-ray Photoelectron Spectroscopy (XPS) was used to obtain qualitative and quantitative information on the surface of the four gasket materials before and after exposure to ADT solution at 80C and 60C. Surface atomic concentration of each element and ratios of atomic concentrations of O and C to Si for Silicone S sample before and after exposures to ADT solution at 80C

  15. no exposure XPS Survey Spectra Silicone S sample before and after exposure to ADT solution at 80C 1 week exposure

  16. CH3 OH Fuel cell environment O Si O O Si O + CO2 Oxidation CH3 CH3 C decreased and O increased Possible oxidation mechanism of Si-CH3 groups

  17. no exposure XPS (High Resolution) Silicone S sample before and after exposure to ADT solution at 80C 1 week exposure

  18. CH3 CH3 Fuel cell environment O Si O O Si OH H+ CH3 CH3 Possible mechanism of Chain Scission in the Backbone - A intensity decreased (backbone chain scission) - B intensity increased

  19. Leachants detection Calcium (mg/l) from 120bend tests in ADT solution Calcium values(mg/l) Time of exposure (weeks)

  20. Conclusions and Future work • Chemical Stability Optical microscopy, FTIR and XPS tests to reveal the attack of the chemicals to the materials. Silicone materials are not good. • Mechanical Stability – Ductility, hardness, constitutive law, cracking • Degradation of Sealing Capability of gasket materials Stress relaxation tests of gaskets in fuel cell solutions • FEA modeling whenever needed • Selection and fabrication of new seal materials for FC applications

  21. Thank you for your attention !Questions ?

More Related