Transcript Slide 1

Stainless Steel Alloys for
Polymer Electrolyte Membrane (PEM) Fuel Cells
Keegan Duff
November 22, 2005
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
PEM’s
• Consideration to stainless steel for current
collectors
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.
Low temperature (PEM) proton exchange membrane
are subcategories of fuel cells
2 Source: US DOE, Office of Energy Efficiency and Renewable Energy
Fuel Cell Categories
2 Source: Renewable Energy Policy Project
SGL Carbon Group Fuel Cell Animation
http://www.sglcarbon.com/sgl_t/fuelcell/#
Chemical Images:
Making Membrane Electrode Assembly
PEM FC
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
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
Operating conditions for PEM fuel cells:
Power density of Fuel Cell
D.P Davies et al. (journal of power sources 86(2000) 237-242
Austenitic Stainless Steel:
current density vs. cell potential
D.P Davies et al. (journal of power sources 86(2000) 237-242
Schematic of test assembly:
comparing electrical surface resistance of
each material
Stainless Steel Grade Compositions for Austenitic Stainless
Grade
UNS No.
301
S30100
302HQ
S30430
C
Mn
Cr
Mo
Ni
0.10
1
17
7
0.03
0.6
18
9
Others(%)
Description and applications
Primarily for deep drawn components and high
strength springs and roll-formed panelling.
Cu 3.5
Wire for severe cold heading applications such
as cross-recess screws.
S 0.3
Free machining grade for high speed repetition
machining. Also available as "Ugima" 303
improved machinability bar for even higher
machinability.
303
S30300
0.06
1.8
18
9
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 850-1100°C.
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 425-850°C. 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
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 0.16
Ce 0.06
Reference 7
4.5
Excellent scaling and creep resistance at
temperatures up to 1150°C.
Tin and Lead phase diagram:
generation of microstructure without equilibrium cooling
http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/sciviz/contracts/booncon.html, accessed on November 21, 2005
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-1.43Mn0.33Si-0.56Cr-0.23Mo- 0.056V-0.064Al-0.062Ni
wt%.
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
Simulation of
Dendritic Growth in Nonequlibrum Cooling
• Simulation of phase field simulation of the dendritic solification
of an austenitic stainless steel:
– Sequence formation of δ-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.mov
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.
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/industry_background.aspx?id=12
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.html
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
7.
Metals and Alloys, Annealing Twins,T. Sourmail, P. Opdenacker, G. Hopkin and H. K. D. H. Bhadeshia
University of Cambridge-shows twin boundrys. http://www.msm.cam.ac.uk/phase-trans/abstracts/annealing.twin.html
8.
Atlas Steels Australia http://www.azom.com/details.asp?ArticleID=1147 accessed on 20 November 2005
9.
http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/sciviz/contracts/booncon.html, accessed on November
21, 2005
10.
University of Cambridge http://www.msm.cam.ac.uk/phase-trans/abstracts/annealing.twin.html. accessed on
November 17, 2005
11. 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/abstract/304/5669/422
12. Obtained from university of Cambridge http://www.msm.cam.ac.uk/phase-trans/2005/vitek.mov ,
http://www.msm.cam.ac.uk/phase-trans/2005/vitek.html,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