Nitrided Metallic Bipolar Plates. Research sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Hydrogen, Fuel Cells, and Infrastructure Technologies Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. - PowerPoint PPT Presentation
EffortD evoted to Scale U p and D em onstration of Thin Stam ped M etallic BipolarPlates Start-M ay 1,2007 Finish-M ay 1,2010 N ew Project A .D urability B .C ost Total projectfunding $4530 K (+ $400 K M atch) Funding forFY2007 $1200 K Tim eline Budget B arriers O R N L (Lead) A llegheny Ludlum A rizona State U niversity G enC ellCorp LANL NREL Team Mem bers Targets (2010) resistivity < 10 m ohm -cm 2 corrosion < 1 x10-6 A /cm 2 cost< $5/kW O bjective:Surface Treatm entto Protect Stam ped M etallic BipolarPlates O verall G oal: Demonstrate potential for metallic bipolar plates to meet 5000 h automotive durability goal at cost < $5/kW Year1 G oal: N o significantw arping or em brittlem entofthe stam ped plates by the nitriding-am enability ofapproach established forthin stam ped foils Year2 G oal: Single-cellfuelcelltestperform ance for~25 cm 2 stam ped and nitrided m etallic bipolarplates equivalentto thatofgraphite (~1000 h,cyclic) Year3 G oal: 10 cellstack testof250 cm 2 stam ped and nitrided m etallic bipolarplates underautom otive drive-cycle conditions (~2000 h) Potentialto m anufacture stam ped and nitrided m etallic bipolarplates at < $5/kW demonstrated Approach:Therm ally G rown C r-N itride forProtection • Surface conversion,nota deposited coating :High tem perature favors reaction ofallexposed m etalsurfaces -N o pin-hole defects (otherissues to overcom e) -Am enable to com plex geom etries (flow field grooves) • Stam p then nitride:Industrially established and cheap Cr-Containing Bipolar Plate A lloy Cr Nitrogen-containing gas Cr-Nitride Cr-Containing Bipolar Plate A lloy Cr Nitrogen-containing gas Protective C r-N itride Layer Metal Protective C r-N itride Layer Metal 10 m 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 Series1 Series2 Voltage C urrent(A /cm 2 ) Before D rive C ycle (break in 23 h/0.5 V,25 h/0.6V) A fter cycle + shutdow C ollaboration with LA NL M. Wilson and F . Garzon 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 S eries1 S eries2 G ood Single-C ell D rive-C ycle D urability Test R esults forM odel N itrided N i-50C rPlates • 1160 h ofdrive-cycle testing (afterinitial 500 h/0.7V/80°C testscreening) -0.94V/1 m in;0.60V/30 m in;0.70V/20 m in;0.50V/20 m in -additional 24 full shutdow ns superim posed •N o perform ance degradation/N o attack ofthe C r-nitride -trace level (2x10 -6 g/cm 2 )ofN i detected in M EA,suspectlocal CrN iN spots After~650 h ofdrive cycle + shutdow ns N eed Fe-Base Alloys to M eet $5/kW BipolarPlate C ostG oals • D ense C r-nitride surface form ation dem onstrated on a m odelFe-base alloy,Fe-27C r-6V w t.% – pre-oxidation key to protective surface nitride form ation – V segregation into C r-oxide m akes itm ore readily nitrided • A lloy C hallenges – Low erC rand V levels to reduce alloy cost – C o-optim ize preoxidation/nitridation to segregate C r,V to surface – D ow n selectto ferritic (cheaper)oraustenitic (m ore form able)alloy base 20 m A lloy (light) Nitride/O xide 3 m (Cr,V) x N N itride (light) (Cr,V) 2 O 3 O xide (dark) 3 m (Cr,V) x N N itride (light) (Cr,V) 2 O 3 O xide (dark) SEM C ross-Sections ofPreoxidized and N itrided Fe-27C r-6V D ense,C ontinuous N itride Surface O btained on a M odel Vanadium -M odified Stainless Steel • Low contact/through-thickness electrical resistance • Low corrosion currentdensities undersim ulated anodic and cathodic conditions Nitrided Metallic Bipolar Plates M .P.B rady,P.F.Tortorelli ,K .L.M ore,J.A .Pihl,T.J. Toops,H .M .M eyer,T.R .A rm strong Oak R idge National Laboratory D .F.G ervasio,A .N .M ada K annan A rizona S tate University J.M .Rakow ski ATI Allegheny Ludlum D .C onnors Gencell Corp M .S.W ilson,F.G arzon,R .L.B orup,T.R ockw ard Los Alamos National Laboratory H .W ang and J.A .Turner National R enewable E nergy Laboratory Team ing and Prim ary R esponsibilities • O ak R idge N ational Lab: Alloy design,nitridation optim ization,characterization • Arizona State U niversity: Single-cell testing (assisted by G encell,O RNL) • ATIAllegheny Ludlum : Alloy foil m anufacture • G enC ell C orp: D esign and stam ping ofbipolarplate flow field features • Los Alam os N ational Lab: Stack testing/perform ance assessm ent,characterization • N ational R enew able Energy Lab: C orrosion/contactresistance evaluation
Transcript
Effort Devoted to Scale Up and Demonstration of Thin Stamped Metallic Bipolar Plates
Start- May 1, 2007 Finish- May 1, 2010 New Project
A. Durability B. Cost
Total project funding $4530 K (+ $400 K Match)
Funding for FY2007 $1200 K
Timeline
Budget
Barriers
ORNL (Lead) Allegheny Ludlum Arizona State University GenCell Corp LANL NREL
Team Members
Targets (2010) resistivity < 10 mohm-cm2
corrosion < 1 x10-6 A/cm2
cost < $5/kW
Objective: Surface Treatment to Protect Stamped Metallic Bipolar Plates
Overall Goal: Demonstrate potential for metallic bipolar plates to meet 5000 h automotive durability goal at cost < $5/kW
Year 1 Goal:No significant warping or embrittlement of the stamped plates by the nitriding-amenability of approach established for thin stamped foils
Year 2 Goal:Single-cell fuel cell test performance for ~25 cm2 stamped and nitrided metallic bipolar plates equivalent to that of graphite (~1000 h, cyclic)Year 3 Goal:10 cell stack test of 250 cm2 stamped and nitrided metallic bipolar plates under automotive drive-cycle conditions (~2000 h)Potential to manufacture stamped and nitrided metallic bipolar plates at < $5/kW demonstrated
Approach: Thermally Grown Cr-Nitride for Protection
•Surface conversion, not a deposited coating: High temperature favors reaction of all exposed metal surfaces
-No pin-hole defects (other issues to overcome)-Amenable to complex geometries (flow field grooves)
•Stamp then nitride: Industrially established and cheap
Cr-Nitride
Cr-ContainingBipolar Plate Alloy
Cr
Nitrogen-containing gas
Cr-Nitride
Cr-ContainingBipolar Plate Alloy
Cr
Nitrogen-containing gas
Protective Cr-Nitride Layer
Metal
Protective Cr-Nitride Layer
Metal
10 m
00.10.20.30.40.50.60.70.80.9
1
0 0.2 0.4 0.6
Series1
Series2
Volta
ge
Current (A/cm2)
Before Drive Cycle(break in 23 h/0.5 V, 25 h/0.6V)
After 650 h of drivecycle + shutdowns Collaboration with LANL
M. Wilson and F. Garzon
00.10.20.30.40.50.60.70.80.9
1
0 0.2 0.4 0.6
Series1
Series2
Good Single-Cell Drive-Cycle Durability Test Results for Model Nitrided Ni-50Cr Plates
• 1160 h of drive-cycle testing (after initial 500 h/0.7V/80°C test screening)-0.94V/1 min; 0.60V/30 min; 0.70V/20 min; 0.50V/20 min-additional 24 full shutdowns superimposed
•No performance degradation/No attack of the Cr-nitride-trace level (2x10-6 g/cm2) of Ni detected in MEA, suspect local CrNiN spots
After ~650 h of drivecycle + shutdowns
Need Fe-Base Alloys to Meet $5/kW Bipolar Plate Cost Goals
• Dense Cr-nitride surface formation demonstrated on a model Fe-base alloy, Fe-27Cr-6V wt.%
– pre-oxidation key to protective surface nitride formation– V segregation into Cr-oxide makes it more readily nitrided
• Alloy Challenges– Lower Cr and V levels to reduce alloy cost– Co-optimize preoxidation/nitridation to segregate Cr, V
to surface– Down select to ferritic (cheaper) or austenitic (more
formable) alloy base
20 m
Alloy (light)Nitride/Oxide
3 m
(Cr,V)xN Nitride (light)
(Cr,V)2O3 Oxide (dark)3 m
(Cr,V)xN Nitride (light)
(Cr,V)2O3 Oxide (dark)
SEM Cross-Sections of Preoxidized and Nitrided Fe-27Cr-6V
Dense, Continuous Nitride Surface Obtainedon a Model Vanadium-Modified Stainless Steel
• Low contact/through-thickness electrical resistance• Low corrosion current densities under simulated anodic
and cathodic conditions
Nitrided Metallic Bipolar PlatesM.P. Brady, P. F. Tortorelli, K.L. More, J.A. Pihl, T.J.
Toops, H.M. Meyer, T.R. ArmstrongOak Ridge National Laboratory
D. F. Gervasio, A.N. Mada KannanArizona State University
J.M. RakowskiATI Allegheny Ludlum
D. ConnorsGencell Corp
M. S. Wilson, F. Garzon, R. L. Borup, T. RockwardLos Alamos National Laboratory
H. Wang and J.A. TurnerNational Renewable Energy Laboratory
Teaming and Primary Responsibilities• Oak Ridge National Lab:
Alloy design, nitridation optimization, characterization•Arizona State University:
Single-cell testing (assisted by Gencell, ORNL)•ATI Allegheny Ludlum:
Alloy foil manufacture•GenCell Corp:
Design and stamping of bipolar plate flow field features•Los Alamos National Lab:
Stack testing/performance assessment, characterization•National Renewable Energy Lab:
Corrosion/contact resistance evaluation
Research sponsored by the U.S. Department of Energy,Research sponsored by the U.S. Department of Energy,
Assistant Secretary for Energy Efficiency and Renewable Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Hydrogen, Fuel Cells, and Infrastructure Technologies Office of Hydrogen, Fuel Cells, and Infrastructure Technologies
Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.
Nitrided Fe-27Cr-6V Meets and MaintainsContact Resistance Goal
• Polarized 7 h at 0.84 V SHE in 1M H2SO4 + 2 ppm F- air purged at 70 C (similar results under H2-purged anodic conditions)
• No Fe detected in nitrided surface
Little Effect of Polarization on SurfaceChemistry of Nitrided Fe-27Cr-6V
Auger Electron Spectroscopy of Nitrided Fe-27Cr-6VAs-Nitrided
0
20
40
60
80
0 50 100 150 200
Con
cent
ratio
n, A
t. %
Sputtering time, min
FeO
V CrN
As-Nitrided
0
20
40
60
80
0 50 100 150 200
Con
cent
ratio
n, A
t. %
Sputtering time, min
FeO
V CrN
After Polarization
0
20
40
60
80
0 50 100 150 200 250
Sputtering time, min
FeO
V CrN
Con
cent
ratio
n, A
t. %
900°C Predominance Diagrams
V Additions Destabilize Oxide Relativeto Nitride Compared to Cr
-6
-5
-4
-3
-2
-1
0
Log
pN
2
-30 -28 -26 -24 -22 -20 -18 -16Log pO2
CrN
Cr2N
Cr
Cr2O31 pp
mO
2
10 p
pmO
2
100
ppm
O2
VN
VO
1 pp
mO
2
10 p
pmO
2
100
ppm
O2
-30 -28 -26 -24 -22 -20 -18 -16-6
-5
-4
-3
-2
-1
0
V2O3
Log
pN
2
Log pO2
•Order of magnitude greater O2 impurity stability for VN relative toCrN at 900°C in N2-4H2 (100 vs 10 ppm O2)
•V works because Cr2O3-V2O3; Cr2N-V2N; CrN-VN all mutually soluble
•V2O3 and Cr-doped V2O3 also conductive – combined with intermixedmorphology and N2-doping yields good ICR values
Stamped Fe-Cr-V Alloys Can Meet $5/kW Transportation Cost Goals
GenCell Corp Cost Estimates for Stamped Bipolar Plates(Nitriding Costs Not Included)
Assumptions: 360 cm2 active area plate (494 cm2 total area), 2 mil secondary foilfor cooling (nested stacking), parallel flow field 0.025” depth, 2010 MEA target power density
High Cr ferritic alloys $3-7/lb: viable nitriding costs– E-BRITE® (Fe-26Cr-1Mo wt.%): $5-7/lb commercial price for foil– Alloy 444 (Fe-18Cr-2Mo wt.%): $3-5/lb commercial price for foil– Above alloys comparable to Fe-Cr-V alloys as Mo and V costs similar
Above shown for molten carbonate fuel cell bipolar plates, approach currently being extended to PEM and SOFC
Related J ournal Publications1) B. Yang, M. P. Brady, H. Wang, J. A. Turner, K. L. More, D.J. Young, P. F. Tortorelli, E.A. Payzant, and L.R. Walker, “Growth of Cr-Nitride Surfaces to Protect Stainless Steels for Proton Exchange Membrane Fuel Cell Bipolar Plates”, submitted to Acta Materialia. 2) M.P. Brady, B. Yang, H. Wang, J.A. Turner, K.L. More, M. Wilson, F.Garzon, “Growth of Protective Nitride Layers for PEM Fuel Cell Bipolar Plate Applications”, JOM, 50-57 (August 2006) 3) M.P. Brady, H. Wang, B. Yang, J.A. Turner, K.L. More, M. Bordignon, R. Molins, “Nitridation of Comercial Ni-Cr and Fe-Cr Base Alloys for PEM Fuel Cell Bipolar Plate Applications”, International Journal of Hydrogen Energy (in press) 4) I. Paulauskas, M.P. Brady, H. M.Meyer III , R.A. Buchanan, L.R. Walker, “Corrosion Behavior of CrN, Cr2N and Phase Surfaces Formed on Nitrided Ni-50Cr with Application to Proton Exchange Membrane Fuel Cell Bipolar Plates”, Corrosion Science 48 (10), pp. 3157-3171 (2006) 5) M.P. Brady, P.F. Tortorelli, K.L. More, E.A Payzant, B.L. Armstrong, H.T. Lin, M.J. Lance, F. Huang, and M.L Weaver, “Coating and Surface Modification Design Strategies for Protective and Functional Surfaces”, Materials and Corrosion, 56 (11), 748-755 (2005) 6) M.P. Brady, K. Weisbrod, I. Paulauskas, R.A. Buchanan, K.L. More, H. Wang, M. Wilson, F. Garzon, L.R. Walker, “Preferential Thermal Nitridation to Form Pin-Hole Free Cr-Nitrides to Protect Proton Exchange Membrane Fuel Cell Metallic Bipolar Plates”, Scripta Materialia, 50(7) pp.1017-1022 (2004). 7) H. Wang, M P. Brady, K.L. More, H.M. Meyer, and J. A. Turner, “Thermally Nitrided Stainless Steels for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates: Part 2: Beneficial Modification of Passive Layer on AISI446”, Journal of Power Sources, 138 (1-2), 75 (2004) 8) H. Wang, M. P. Brady, and J. A. Turner, “Thermally Nitrided Stainless Steels for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates: Part 1 Model Ni-50Cr and Austenitic 349TM alloys”, Journal of Power Sources, 138 (1-2), 86 (2004) 9) M. P. Brady K. Weisbrod, C. Zawodzinski, I. Paulauskas, R. A. Buchanan, and L. R. Walker, “Assessment of Thermal Nitridation to Protect Metal Bipolar Plates in Polymer Electrolyte Membrane Fuel Cells”, Electrochemical and Solid-State Letters, 5, 11, A245-A247 (2002)
