Cost-Effective Surface Mo

For Metallic Bipolar P

M.P. Brady, B. Yang, P. F. Torto

K.L. More

Oak Ridge National Labora

H. Wang and J.A. Turne

National Renewable Energy La

May 18, 2006

This presentation does not contain any proprietary or confidential informa

NREL/PR-560-41724Presented at the 2006 DOE Hydrogen, Fuel Cells & Infrastructure Technologies Program Annual Merit Review in Washington, D.C., May 16-19, 2006.
Overview

Timeline Barr

• A. Durability• B. Cost• Targets (20

– resistivi

– corrosio– cost < $

• Start- Oct 2001 (small 

exploratory $ in 1999/2000)

• Finish- Sept 2006• 90% complete• Total project funding 

– $1650K

• Funding for FY05

– $300K

• Funding for FY 06

– $300K

Budget

– Addtl. $150K linked w/NREL

• DANA Co

Energy, GJadoo Po

• Los Alam

TN Tech, de Paris (

Primary 
Objective: Surface Treatment 

Metallic Bipolar Plate

• Overall Goal: Demonstrate potential for 

plates to meet 5000 h durability goals at 

• FY 06 Goals:

– Demonstrate cyclic fuel cell test durabilit

grown Cr-nitride surfaces (nitrided Ni-ba

– Demonstrate protective Cr-nitride on Fe-

meet cost goals

• establish mechanism of nitride formation 

to provide basis for scale up (cost, repea

• deliver plates for single-cell fuel cell testi

• Completion of effort in FY06 to provide b

Go decision for scale-up activities (propo
Approach: Thermally G

Cr-Nitride for Protect

Cr-Nitride

Cr-Containing Bipolar Plate Alloy

Cr

Nitrogen-containing gas

Prote

10 

μ

m

•Surface conversion, not a deposited coat

temperature favors reaction of all expose

-No pin-hole defects (other issues to o-Amenable to complex geometries (flow 

•Stamp then nitride: Industrially establish
Durability/Performance Studied w

Surfaces Formed on Ni-C

•Protective Cr-nitride surfaces achieve

commercial Ni-(30-50)Cr base alloys

-Used to establish whether thermally grown 

meet DOE corrosion, contact resistance, a

•Formation of similar Cr-nitride surfac

alloys needed to meet cost goals (Ni-

-More difficult to do than for Ni-base alloys-Lower Cr level alloys, interference from Fe-Focus of FY 05 and 06 efforts
0

0.10.20.30.40.50.60.70.80.9

1

Voltage

Current (A/cm2)

Before Drive Cycle(break in 23 h/0.5 V, 25 h/0.6V) 

After ∼650 h of drive

cycle + shutdowns

Good Single-Cell Drive-Cycle Du

Results for Nitrided Ni-50Cr 

• 1160 h of drive-cycle testing (after initial 500 h/0.7

-0.94V/1 min; 0.60V/30 min; 0.70V/20 min; 0-additional 24 full shutdowns superimposed

•No performance degradation/No attack of the Cr-ni

-trace level (2x10-6 g/cm2) of Ni detected in MEA, suspect 

0 0.2 0.4 0.6
Good Single-Cell Performance 

G35TM(Ni-30Cr base) for Dry/W

(40%/100% RH) Test a

Current Density (mA/cm2)

Time (h)

200 300500400100

0010

0 200 400 600 800

Current Density (mA/cm2)

Time (h)

200 300500400100

0010

0 200 400 600 800

•Dry/wet cycling accelerates MEA degradation/hig

to produce aggressive bipolar plate conditions

•No metal ion contamination and low resistance: c

to Poco graphite plates (post-test examination of 
Need Fe-Base Alloys to 

$6/kW Bipolar Plate Cost 

Status at FY05 Review

•Dense Cr-nitride formation demonstrated 

base alloy

-low corrosion current densities in 1st pol

-low interfacial contact resistance

•At that time:

-repeatability issues encountered-surface layer microstructure not well c-mechanism of formation not well unde(needed to improve repeatability and o
Problem: Internal Nitridation 

Nitrogen Away from Surface Lay

Fe-Cr Base Alloys

Typical Nitrided Cross-Section

for a Fe-27Cr wt.% Base Alloy

Typical Nitri

(aerate

-400-200

0

200400600800

1000

1.E-7 

Curr

Potential (mV, SHE) Corro

Goa

Cr2N

10 μm

•Mechanical property, cost, and phase stability issof Fe-Cr base alloys to < 30 wt.% Cr•High alloy N2 permeability prevents dense Cr-nitr
Vanadium Additions to Fe-27

in Protective Cr-Nitride S

Polarization in Aerated pH 3 Sulfuri

•Corrosion resistance comparable to nitrided Ni-50

nitrided Fe-27Cr-2V and Fe-27Cr-6V (850-900

°C

-Meets goal corrosion current density up to 

∼ 900m

-Low corrosion current densities also observed und

0

200400600800

1000

1.E-09 1.E-08 1.E-07 1.E-06 

310 S

(25Cr/

Ni-50Cr

Metal

NitridedNi-50Cr

Nitrided

Fe-27Cr+V

Goal

Potential (mV, SHE)

Corrosion Current Density (A
Nitrided Fe-27Cr+V Meets and 

Contact Resistance G

Nitrid

H

2S

0

102030405060

0 

As-

2 x ICR (mohm-cm2)

Compa

1

10

100

1000

10000

0 100 200 300

1

10

100

1000

10000

0 100 200 300

Nitrided Fe-27Cr-6V

Goal ICR

Compaction Stress (N/cm

2

)

316 Metal

446 Metal

Fe-27Cr-6V Metal

Fe-27Cr Metal

ICR (mohm-cm2)

•Nitridation significantly reduces interfacial contac•Slight increase in ICR on polarization-still meets g•Untreated stainless steels don’t meet ICR goals 
Little Effect of Polarization o

Chemistry of Nitrided Fe-2

Auger Electron Spectroscopy of Nitrid

After 

0

20406080

0 50 

Sputter

O

V 

N

Concentration, At. %

As-Nitrided

0

20406080

0 50 100 150 200

Concentration, At. %

Sputtering time, min

Fe

O

V Cr

N

•Polarized 7 h at 0.84 V SHE in pH 0 H

2SO4 + 2 p

70 

°C (similar results under H

2-purged anodic co

•No Fe detected in nitrided surface, oxygen pres
Surface Layer on Nitrided Fe

Contained Nitrides and O

Cross-Section of Fe-27Cr-6V wt.%, 900

°C

(V,Cr)

2

O

3 (da

(Cr,V)

2N (light)

2.5 

μ

m

Alloy

•O

2 Impurity level in nitriding gas sufficient to form 

•Nitrogen stayed at surface, no internal nitridation

•(Cr,V)

2N overlying mixed (V,Cr)

2

O

3 + (Cr,V)

2N at 
Reducing O2 in Nitriding Gas R

Surface Gaps/Extensive Intern

Fe-27Cr-6V Nitrided at 900°C for 4 h in 

10 μm

Surface

Cr Gaps 2N

10 

10 μm

Cross-Se

Internal 

•Indicates O2 impurity/oxide formation favors den

surface formation by reducing N2 penetration into 

•Variations in O2 impurity level cause of initial rep
Initially Formed Oxide Conv

Nitride: Easier with Van

SEM Cross-Sections after 24 h at 85

CrN

0.5 

μ

m

0.5 

μ

m

(V,Cr

Fe-27Cr F

Cr

2

O

3

•Oxide formed initially during heat up followed by 

-V and Cr co-segregate into initially-formed (V,

-V addition adds extra degree of freedom- inter

•Nitrided Fe-27Cr showed inadequate corrosion re

many non-uniform areas and thin spots 
V Additions Destabilize Oxid

to Nitride Compared to 

900

°C Predominance Diagra

-6-5-4-3-2-1

0

Log pN2

-30 -28 -26 -24 -22 -20 -18 -16

Log pO

2

CrN

Cr

2

N

Cr

Cr

1 ppm O

2

O

3

2

10 ppm O2

100 ppm O2 VN

1 ppm O2

-30 -28 -26 

-6-5-4-3-2-1

0

Log pN2

•Order of magnitude greater O

2 impurity stability fo

CrN at 900

°C in N

2-4H

2 (100 vs 10 ppm O

2

)

•V works because Cr

2

O

3-V

2

O

3; Cr

2N-V

2N; CrN-VN 

•V

2

O

3 and Cr-doped V

2

O

3 also conductive-combin

morphology and N

2-doping yields good ICR value
Insights for Alloy/Nitridation O

•Use of O

2 to segregate Cr and V to the surface 

significant decrease in Cr and V level to minimiz

-Fe-27Cr-6V studied as model (Fe-27Cr-2V also -Decrease to 18-20 wt.% Cr and 1-2 wt.% V like(Cr-V oxides very stable, low O

2 permeability in 

•Positive early results with pre-oxidation followed 

-800

°C, < 20 minutes to form oxide (want 

≤ 0.2-

-May be accomplished on commercial scale by 

containing purge gas followed by introduction o(can also leverage shifting oxide/nitride bounda

•Total temp./time cycle < 900

°C and < 24 h 

-cost estimates difficult at this stage-not a conventional hardening cycle (cheaper), -very dependent on # and size of plates, furnac
Stamped Fe-Cr-V Alloys Ca

$6/kW Transportation Cos

GenCell Corp Cost Estimates for Stampe

(Nitriding Costs Not Include

Foil Density

Thick. (in) kg/kW $3/lb Alloy $5/lb Alloy 

0.002 0.26 $2.31 $3.47 0.004 0.38 $3.15 $4.26 

0.008 0.64 $4.86 $7.69 

Bipolar Plate Cost 

•High Cr ferritic alloys $3-7/lb: potentially viable 

-E-BRITE

® (Fe-26Cr-1Mo wt.%): $5-7/lb commerc

-Alloy 444 (Fe-18Cr-2Mo wt.%): $3-5/lb commerci

-Above alloys comparable to Fe-Cr-V alloys as Mo 

Assumptions: 360 cm

2 active area plate (494 cm

2 total area)

for cooling (nested stacking), parallel flow field 0.025” depth, 2010 
Future Work

•Delivery of nitrided Fe-27Cr-6V plates for fuel collaborators (thick machined plates for compa•Better establish range of oxygen-nitrogen con

protective Cr-nitride base surfaces

-Includes exploration of lower Cr and V alloys

•Manufacture foil for stamping assessment with •Complete post fuel cell test microstructure ana

Ni-Cr plates run with collaborators

-Establish limits of Cr-nitride by cycling nitride

plates at > 1V (such conditions can be encou

•Project ends in Sept 2006: Go/No Go decision 

proposal submitted for recent DOE fuel cell ca
Summary

•Single-cell fuel cell testing of model nitrided N

good performance and durability of thermally g

surfaces under cyclic test conditions (voltage, 

•Promising results with protective Cr-nitride fo

V-modified Fe-Cr alloys that can meet DOE co

-Behavior in range of contact resistance and pcorrosion screening targets met-Dense Cr-nitride surface formation aided by o

to reduce nitrogen penetration/internal nitrida

-Key to V effectiveness is mutual solubility in Cand high relative stability of V-nitride, V2O3 als
Responses to Previous Year 

Comments

•Need for coatings for metal plates not establishe

fuel cell tests with untreated metal plates

-Under some mild/static conditions and applicationmay be acceptable: not the case for automotive aprimary focus of this program-Limited $/time prevent fuel cell testing of untreateplates (collaborators use past graphite plate perfo

i) extensive corrosion and ICR studies of 

ii) no untreated stainless steel can meet I

•Limited alloy, cost estimate, road mapping detaicollaborations but proactively seek more stack de

-Project wrapping up development stage, not yet in -Cost estimate details added this year with GenCe

i) Input also obtained from alloy manufactuii) Exploratory discussions w/many fuel ce
Publications

Publications/Manuscripts: 9 journal papers published, in press, or in manusince 2002 1) M.P. Brady, B. Yang, H. Wang, J.A. Turner, K.L. More, M. Wilson, F.GarzoProtective Nitride Layers for PEM Fuel Cell Bipolar Plate Applications”, invited for the August 2006 Issue of JOM 2) B. Yang, M.P. Brady, D.J. Young, K.L. More, P.F. Tortorelli, E.A. Payzant, HJ.A. Turner, “Growth of Multi-Functional Protective Nitride Layers on Fe-Cr BPEM Fuel Cell Bipolar Plates”, to be submitted to Acta Materialia 3) M.P. Brady, H. Wang, B. Yang, J.A. Turner, K.L. More, M. Bordignon, R. M“Nitridation of Comercial Ni-Cr and Fe-Cr Base Alloys for PEM Fuel Cell BipoApplications”, to be submitted to International Journal of Hydrogen Energy 4) I. Paulauskas, M.P. Brady, H. M.Meyer III , R.A. Buchanan, L.R. Walker, “CBehavior of CrN, Cr2N and π Phase Surfaces Formed on Nitrided Ni-50Cr with 

Proton Exchange Membrane Fuel Cell Bipolar Plates”, Corrosion Science (in pr

5) M.P. Brady, P.F. Tortorelli, K.L. More, E.A Payzant, B.L. Armstrong, H.T. LF. Huang, and M.L Weaver, “Coating and Surface Modification Design Strategiand 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. WanGarzon, L.R. Walker, “Preferential Thermal Nitridation to Form Pin-Hole Free CProtect Proton Exchange Membrane Fuel Cell Metallic Bipolar Plates”, Scripta M

pp.1017-1022 (2004). 7) H. Wang, M P. Brady, K.L. More, H.M. Meyer, and J. A. Turner, “Thermally Stainless Steels for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates: ParModification of Passive Layer on AISI446”, Journal of Power Sources 138 (1-2)

8) H. Wang, M. P. Brady, and J. A. Turner, “Thermally Nitrided Stainless Steels Electrolyte Membrane Fuel Cell Bipolar Plates: Part 1 Model Ni-50Cr and Auste

alloys”, Journal of Power Sources , 138 (1-2), 86 (2004) 

9) M. P. Brady K. Weisbrod, C. Zawodzinski I. Paulauskas,R. A. Buchanan,and 

Assessment of Thermal Nitridation to Protect Metal Bipolar Plates in Polymer EMembrane Fuel Cells”, Electrochemical and Solid-State Letters, 5, 11 2002 

Since Last Review
Presentations

Presentations: 2 Conference Presentations with Proceedings Papers, 9 tpresentations not including DOE Hydrogen Program Reviews, 3 poster several additional university/student presentations not listed for effort s1) B. Yang, M. P. Brady, P.F. Tororoelli, K. L. More, H. Wang, J. A. Turner “Nitrided Stainless Steels for PEM Fuel Cell Bipolar Plates”, TMS Annual MAntonio, TX, March 15, 2006 2) (Invited) M.P. Brady, B. Yang, Peter Tortorelli, K. L. More, H. Wang and “Thermally Nitrided Metallic Bipolar Plates for PEM Fuel Cells”, Materials Technology 2005, Pittsburgh, PA, September 26, 2005. 3) B. Yang, M. P. Brady, D. J. Young, K. L. More, H. Wang and J. A.TurneNitrided Stainless Steel Bipolar Plates for Proton Exchange Membrane Fuel Meeting of the Electrochemical Society, October 22-26, Los Angles, CA, U1007. 4) (Invited) M.P. Brady, “Multi-component/multi-phase alloys as precursors protective/functional surfaces via gas reactions", Gordon Research ConferenTemperature Corrosion”, July 2005 Colby Sawyer, NH. 5) M.P. Brady, H. Wang, I. Paulauskas, B. Yang, P. Sachenko, P.F. TortorelBuchanan, “Nitrided Metallic Bipolar Plates for PEM Fuel Cells”, Proceedin

International Conference on Fuel Cell Science, Engineering and Technology

(June 14-16, 2004). 6) M. P. Brady, I. Paulauskas, R. A. Buchanan, K. Weisbrod, H. Wang, L. RMiller “Evaluation of Thermally Nitrided Metallic Bipolar Plates for PEM FProceedings of 2nd European Fuel Cell Forum, Lucerne, Switzerland, June 37,8) Two presentations at Spring Electrochemical Society, Orlando, FL (2009) ASM, Pittsburgh, PA (2003) 10) Fall Meeting of The Materials Research Society (2002). 11,12) Fuel Cell Seminar 2003, 2004 poster presentations 

Since Last Review
Critical Assumptions and 

•Potential for warping of thin stamped foil during n

-significant warping not observed thus far-slight warping at corners: could cause stack seali-bigger issue appears to be nitridation embrittleme

be controlled by limiting internal nitridation

a) b)

a) Oxidized 2 mil FeCrAlY Foil (20-500 h cycles/800

°C

b) Stamped and nitrided G-35TM foil (Ni-30Cr alloy; co
Critical Assumptions and Issu

•Durability of Cr-nitride surface under stack condit

- transient excursions > 1V could degrade nitri- 10-5 A/cm

2 corrosion current densities in coup

+ 2 ppm F- at 70

°C and 1.4 vs SHE (dynamic 

- literature suggests transpassive dissolution v

- vanadium additions may further stabilize Cr-n- will examine via > 1V cycling at LANL- current MEAs and carbon supports degrade a

•Repeatability of protective nitride on Fe-Cr-V allo

-a concern but use of initial formation of oxide promising