Stainless Steel Alloys for

1
Stainless Steel Alloys for Polymer Electrolyte
Membrane (PEM) Fuel Cells Keegan Duff November
22, 2005
2
Overview

• What is a fuel cell
• Subcategories of low temperature PEM FC
• Basic advantages and disadvantages of fuel cell
• Show slides of fuel cell
• Comparison of austenitic stainless steels in
  PEMs
• Consideration to stainless steel for current
  collectors

3
What is a fuel cell?

• A fuel cell is a electrochemical device that acts
  as a high efficiency electrical storage device.
• Chemical energy is stored in a fuel and
  continually supplied to the device and chemically
  consumed. In the case of PEM fuel cells, hydrogen
  and oxygen out of the air are reacted producing
  electricity, water, and heat.

4
Low temperature (PEM) proton exchange
membrane are subcategories of fuel cells
2 Source US DOE, Office of Energy Efficiency and
Renewable Energy
5
Fuel Cell Categories

• 2 Source Renewable Energy Policy Project

6
SGL Carbon Group Fuel Cell Animation http//www.
sglcarbon.com/sgl_t/fuelcell/
7
Chemical Images Making Membrane Electrode
Assembly PEM FC
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Fuel Cells are not Ideal

• The cells do suffer from voltage degradation with
  time
• Gaskets Fail
• Pin hole leaks form in separator materials/ion
  exchange membranes
• Catalysts become clogged with impurities, in
  particular carbon monoxide, sulfur and
  phosphorus compounds reduce performance

• The ion exchange membranes like NAFION (Dupont)
  , PRIMEA (GORE) the industry standards have
  limited lives. 1000hrs
• Hydration of membranes is complicated
• cost of machining bipolar plates
• Optimization of current collection

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Nafion

• Perfluorinated polymer that contains small
  proportions of sulfonic or carboxylic ionic
  functional groups
• Its general chemical structure can be seen where
  X is either a sulfonic or carboxylic functional
  group and M is either a metal cation in the
  neutralized form or an H in the acid form.

• Figure 1.
• Nafion Perfluorinated Ionomer
• http//www.psrc.usm.edu/mauritz/nafion.html

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Operating conditions for PEM fuel cells
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Power density of Fuel Cell

• D.P Davies et al. (journal of power sources
  86(2000) 237-242

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Austenitic Stainless Steelcurrent density vs.
cell potential

• D.P Davies et al. (journal of power sources
  86(2000) 237-242

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Schematic of test assemblycomparing
electrical surface resistance of each material
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Stainless Steel Grade Compositions for Austenitic
Stainless
Grade UNS No. C Mn Cr Mo Ni Others() Description and applications


301 S30100 0.10 1 17   7   Primarily for deep drawn components and high strength springs and roll-formed panelling.
302HQ S30430 0.03 0.6 18   9 Cu 3.5 Wire for severe cold heading applications such as cross-recess screws.
303 S30300 0.06 1.8 18   9 S 0.3 Free machining grade for high speed repetition machining. Also available as "Ugima" 303 improved machinability bar for even higher machinability.
304 S30400 0.05 1.5 18.5   9   Standard austenitic grade - excellent fabrication characteristics with good corrosion resistance. Also available as "Ugima" 304 improved machinability bar.
304L S30403 0.02 1.5 18.5   9   Low carbon version of 304 gives resistance to intergranular corrosion for heavy section welding and high temperature applications.
308L S30803 0.02 1 19.5   10.5   Filler wire for welding 304 and similar grades.
309 S30900 0.05 1.5 23   13.5   Good corrosion resistance and good resistance to attack by hot sulphur compounds in oxidising gases. Filler for welding dissimilar metals.
310 S31000 0.08 1.5 25   20   Good resistance to oxidation and carburising atmospheres in temperatures 850-1100C.
316 S31600 0.05 1 17 2 11   Higher resistance than 304 to many media, particularly those containing chlorides. Also available as "Ugima" 316 improved machinability bar.
316L S31603 0.02 1 17 2 11   Low carbon version of 316 gives resistance to intergranular corrosion for heavy section welding and high temperature applications.
321 S32100 0.04 1 18   9 Ti 0.5 Titanium stabilised grade resists intergranular corrosion during exposure at 425-850C. High strength in this temperature range.
347 S34700 0.04 1 18   9 Nb 0.7 Niobium stabilised grade resists intergranular corrosion as for 321, but more commonly used as a filler for welding 321.
904L N08904 0.02 1 20 4.5 24 Cu 1.5 Super austenitic grade with very high corrosion resistance, particularly to sulphuric acid and warm chlorides.
2111HTR S30815 0.08 0.6 21   11 N 0.16Ce 0.06 Excellent scaling and creep resistance at temperatures up to 1150C.
Reference 7
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Tin and Lead phase diagramgeneration of
microstructure without equilibrium cooling

• http//www.sv.vt.edu/classes/MSE2094_NoteBook/96Cl
  assProj/sciviz/contracts/booncon.html, accessed
  on November 21, 2005

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Twin Boundary in Austenitic Stainless Steel

• Grain structure of austenitic stainless steel
  NF709, observed using light microscopy on a
  specimen polished and etched electrolytically
  using 10 oxalic acid solution in water. Many of
  the grains contain annealing twins. NF709 is a
  creep-resistant austenitic stainless steel used
  in the construction of highly sophisticated power
  generation units.
• Annealing twins formed in austenite from a
  low-alloy steel. Austenite is unstable in such
  steels so it is not ordinarily possible to look
  at the austenite grain structure except at
  temperatures in excess of 900oC. This particular
  sample was prepared metallographically to a 1
  micron finish and then heated at 1200oC in a
  vacuum containing only a trace of oxygen. The
  heat gives thermally grooves the surface to
  reveal the austenite grains, and the oxygen
  slightly oxides the surface to give an etching
  effect. The sample is then cooled to room
  temperature but the transformation of the
  austenite to ferrite does not influence the
  grooves or the oxide-etching, thus revealing the
  austenite grain structure. Notice the annealing
  twins. The chemical composition of the steel is
  Fe-0.16C-1.43Mn-0.33Si-0.56Cr-0.23Mo-
  0.056V-0.064Al-0.062Ni wt.

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Ultrahigh Strength and High Electrical
Conductivity in Copper

• Research using twining in Cu alloys shows promise
  of manipulating the microstructure to improve
  mechanical properties with out significantly
  increasing the electrical resistance.
• Ultrahigh Strength and High Electrical
  Conductivity in Copper Lei Lu, Yongfeng Shen,
  Xianhua Chen, Lihua Qian, K. Lu
  http//www.sciencemag.org/cgi/content/abstract/304
  /5669/422 Originally published in Science Express
  on 18 March 2004

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Simulation of Dendritic Growth in Nonequlibrum
Cooling

• Simulation of phase field simulation of the
  dendritic solification of an austenitic stainless
  steel
• Sequence formation of d-ferrite dendrites
• nucleation and growth of austenite as the
  temperature decrease
• austenite finally overwhelms the ferrite and
  becomes the leading phase to solidify
• http//www.msm.cam.ac.uk/phase-trans/2005/vitek.mo
  v

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In Conclusion

• Many aspects of low temperature fuel cells need
  optimization before they can be implemented.
  These are engineering and chemistry problems that
  can be solved.
• The type of stainless steel used for the current
  collector effects the PEM performance.
• Non equilibrium cooling results in concentration
  gradients and microstructure having significant
  effects on the corrosion of stainless steels.
• Currently research does not consider how changes
  in microstructure of alloys effect performance in
  fuel cells.
• Additional work is need to understand the resins
  for these differences.
• I would like to thank Dr. Coia at PSU for
  allowing the use of slides of PEM fuel cell
  prototypes that we constructed.

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• References
• 1. Felten, Rick. Scanning Electron Microscopy.
  Stainless steel screen (image SEM used on cover
  page), acessed on November 19, 2005
  http//www.semguy.com/gallery.html
• 2 . (Had doe diagram of PEM cell, and doe
  comparison chart), acessed on November 20, 2005
• http//www.greenjobs.com/Public/info/indu
  stry_background.aspx?id12
• 3. SGL Carbon Group Fuel Cell Animation, accessed
  on November 19, 2005
• http//www.sglcarbon.com/sgl_t/fuelcell/
  
• 4. Image and description of Nafion, accessed on
  November 21, 2005
• http//www.psrc.usm.edu/mauritz/nafion.htm
  l
• 5. Davies, D.P., P.L. Adcock, M. Turpin, and S.J.
  Rowen. Stainless steel as a bipolar plate
  material for solid polymer fuel. Journal of power
  Sources 86(2000) 237-242 Fuel cell Research
  group, department of aeronautical, Automotive
  Engineering and Transport Studies, Loughborough
  Univesity, Loughbororugh, Leicestershire LE11
  3TU, UK
• 6. Davies, D.P., P.L. Adcock, M. Turpin, and S.J
  Rowen, Bipolar plate materials for solid polymer
  fuel cells
• Fuel cell Research group, department of
  AAETS, loughborough university, loughborough,
  leicestershire, Le11 3TU,
• Great Britain, journal of applied
  Electrochemistry 30 101-105, 2000

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• 10. University of Cambridge http//www.msm.cam.
  ac.uk/phase-trans/abstracts/annealing.twin.html.
  accessed on November 17, 2005
• Lu, L., Yongfeng Shen, Xianhua Chen, Lihua Qian,
  and K. Lu. Ultrahigh Strength and High Electrical
  Conductivity in Copper. Science. March 18th
  2004. http//www.sciencemag.org/cgi/content/abstra
  ct/304/5669/422
• 12. Obtained from university of Cambridge
  http//www.msm.cam.ac.uk/phase-trans/2005/vitek.mo
  v ,
• http//www.msm.cam.ac.uk/phase-trans/2005/vitek.ht
  ml,accessed on 22 November 2005
• 13. Kim, J.S. W.H.A. Peelen, K. Hemmes, R.C.
  Makkus. Effect of alloying elements on the
  contact resistance and the passivation behavior
  of stainless steels. Corrosion science 44(2002)
  635-655
• Concludes that schottky contscs have to be
  considered rather than just omic resistance
• 14. Schottky contacts
• http//www.ee.sc.edu/research/SiC_Research/papers
  /schottkycontacts.pdf