Durable Catalysts for Fuel Cell Protection During Transient … · 2010. 6. 24. · 3 Durable...

1

Durable Catalysts for Fuel Cell Protection during

Transient ConditionsRadoslav Atanasoski

3M

DOE/3M Award DE-EE0000456

2010 DOE Vehicle Technologies Program Review

Washington DC, June 8, 2010

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project ID: FC006

22

Overview

Durable Catalysts for Transient Conditions – DOE Annual Review – Washington DC, June 8, 2010 3M

Timeline

• Project start date: August 1, 2009• Project end date: July 31, 2013• Percent complete: ~ 15%

(03/31/2010)

Partners• Dalhousie University (subcontractor)

- Dr. David Stevens; High-throughput catalyst synthesis and basic characterization

• Oak Ridge National Lab (subcontractor)- Dr. Karren More; TEM characterization

• 3M:- George Vernstrom- Greg Haugen- Theresa Watchke - Radoslav Atanasoski

BarriersElectrode Performance:Catalyst durability under 30,000+ start-up&shut-down events

Budget

Total: $5,782,165- DOE Share: $4,625,732 Funding Received in FY09: $ 900,000- Contractor Share: $1,156,433 Funding for FY10: $1,260,000

3


Objectives and RelevanceDevelop catalysts that will enable PEM fuel cells systems to weather the damaging conditions in the fuel cell at voltages beyond the thermodynamic stability of water (> 1.2 V) during the transient periods of start-up/shut-down and fuel starvation by favoring the oxidation of water over the dissolution of platinum and carbon.

Such catalysts are required to make it possible for the fuel stacks to satisfy the current 2010 and 2015 DOE targets for performance and durability.

More than 30,000 start-up/shut-downs have been estimated to take place during stack lifetime.

Recent HONDA and GM presentations singled out start-ups and the shut-downs as being the most damaging for the durability of the catalysts (ECS Fall Meeting, 2009)

4


Approach: Problem Statement

*) Modified after Gu et al, ECS Transactions, 11 (1) 963, 2007

Absence of hydrogen and simultaneous presence of oxygen in separate regions of the anode is necessary to provoke and maintain cathode potential > 1.23 V.While important for durability, Pt partial dissolution current is negligible in comparison.

PEMFC with fuel starved regionElectrochemical reactions leading to carbon corrosion and Pt dissolution

A, C; normal FC operation; B, D; operation in fuel starved region.As presented, region AC acts as a power source imposing the same voltage in region BD. Thermodynamically favored reaction in the AIR area (D) is ORR. Protons required in ORR have to come from carbon and/or water oxidation at cathode. Abnormal operation lasts until at the anode- during shut-down: hydrogen is exhausted;- during start-up: H2/H+ prevails to bring the anode potential negative enough for normal FC state.

H2/Air FrontStop Start

A

CH2 → 2 H+ + 2e-

O2 + 4H+ + 4e- → 2 H2O

H+

Air

Hydrogen

H2

A

CH2 → 2 H+ + 2e-

O2 + 4H+ + 4e- → 2 H2O

H+H+

Air

Hydrogen

H2

Cathode

Anode

Membrane

B

DO2 + 4H+ + 4e- → 2 H2O

C + 2H2O → CO2 + 4H+ + 4e-

2H2O → O2 + 4H+ + 4e-

Air

Air

O2 H+

Cathode

Anode

Membrane

B

DO2 + 4H+ + 4e- → 2 H2O

C + 2H2O → CO2 + 4H+ + 4e-

2H2O → O2 + 4H+ + 4e-

Air

Air

O2 H+H+

e-

e-

e-

e-

>> H+>> H+

Normal Operation Starved Operation

5


The two catalyst material concepts:1. Catalysts with high oxygen evolution reaction (OER) activity2. Anode catalysts with low oxygen reduction reaction (ORR) activity

Alleviate the damaging effects from within the fuel cells by• modifying both the anode and the cathode catalysts to favor the oxidation of water over carbon corrosion.• maintaining the potentials close to the thermodynamic for wateroxidation.

1. Presence of highly active OER catalyst on the cathode reduces the overpotential for a given current demand (region B).

- Key requirements: Implement the OER catalyst with negligible inhibition of the ORRon existing cathode catalyst and with minimal additional PGM.

- Approach: Deposit the OER catalyst as a separate phase - as nanoparticles.

2. Inhibition of the ORR on the anode side lowers the ORR current (region D). Through reduced proton demand this then decreases the OER current on the cathode (region B) resulting in reduced cathode potential.

- Key requirement: Implement the ORR inhibiting component with negligible inhibition of the HOR, either as a mixed or a separate phase.

Approach: Proposed Solutions

6



Schematic illustration ORR/OER catalyst The Model:•Achieve 1cm2 of OER catalyst on 1 cm2geo with OER nano-cubes of 3 nm sides to withstand 1 mA/cm2 OER at <1.4 V.•Number of catalyst particles needed: 2.2x1012.•Ru content: 0.41 µg/cm2 RuO2 or 0.31 µg/cm2 Ru.•ORR catalyst surface area blocked: 0.2 cm2

or 0.5% of NSTF entitlement.•With TiO2 as support the blocked ORR catalyst area is ~1%.(further background info in slides 29&30)

Most active, cost effective, and stable OER catalystsActivity: RuO2 High exchange c.d.; 40 mV/decade Tafel slope; good charge capacity

Activity and stability: RuO2 + IrO2: Good stability; Activity with up to 75% surface IrO2 is acceptable

Stability and cost: TiO2, MnO2, etc. RuO2 - TiO2 interfacial stability improves from 400 oC to 600+ oC

All the components are isostructural, rutile.

Morphological considerations:Discrete nanoparticles in order to minimize blocking of the base ORR catalysts.

7


ORR suppression on the anode

ORR curves for Pt1-xTax sputter-deposited onto glassy carbonmeasured at 1600 rpm, 30 C in 0.1 M HClO4.

Bonakdarpour et al.J. Electrochem. Soc., 153,A2304,2006.

Hydrogen oxidation Overpotentials: 500 mA/cm2 ; 80 C; 64-electrode cell

Stevens et al,J. Electrochem. Soc., 154, B566, 2007.

Only 12% Ta inhibits ORR by a factor of 10. HOR has practically no voltage losses even with 30+ % Ta.

Ta or similar elements built into or on the surface of the anode (HOR) catalyst are going to be produced.


∆E1/2 = - 70 mV

8


Approach: Catalysts Synthesis and CharacterizationCatalysts Synthesis

• Use Pt - NSTF as an ideal real catalyst substrate: no carbon interference• Implement vacuum deposition processes fully compatible to the existing NSTF fabrication. • Use high throughput approach for broad material synthesis and initial evaluation (RDE).• Produce enough catalysts for evaluation of 3 - 4 cells with 50-cm2 MEAs, eliminating the need for the first scale-up requirement.• Use direct particle deposition for proof of concept.Instrumental Characterization

• Extensive in-depth XPS for surface compositional characterization, oxidation state in particular• XRF for total elements content• TEM for particle identification and composition and structure characterization.

Functional Characterization (FC and electrochemical test details: slide #31)

• Comprehensive testing to ensure the catalyst performs well for intended use (OER on cathode, ORR inhibition on anode) and the level of obstruction of the basic catalyst layer performance (ORR or HOR)

• Start-stop testing under real life conditions (to be defined with the Tech Team)

9


3M – All tasks. Lead, determine, scale-up, and fabricate quantities of the standard (stock) starting and new catalysts. MEA assembly and testing.

Dalhousie – Task 1 and 2. Composition spreads via sputter deposition; ex situcharacterization; 64-electrode fuel cell testing; RRDE on NSTF grown on GC.

ORNL – All tasks. Structural and compositional TEM characterization, before and after testing.

Timeline and Participant RolesQtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 2 Qtr 3

1 Efficient OER Catalysts Mixed PGM oxide spreads 50 cm2 FC mixed oxides Morphological characterisation Laser ablation - nanoparticles Integrated OER/ORR catalyst

2 Low ORR activity anode catalysts Pt-M intermix screening Pt overlayer screening Morphological characterisation 50 cm2 FC intermixes and overlayers

3 Scale-up and project outcomes Best catalysts - scale-up Full size FC MEA Prepare >=100 cm2 MEAs Short stack assembly and delivery Final Report

Milestones and Go/No Go Decisions Milestone 1 Milestone 2 Go/no goMilestone 3

Qtr 1TASK DESCRIPTION Year 4Qtr 4

Year 1 Year 2 Year 3

10


MILESTONES AND GO/NO-GO DECISION

Until DOE targets for this topic are established, the milestones have been defined by the following project goals (Year 1 highlighted):

Milestone #1: OER of 1 mA/cm2 at 1.45 V; 10 mA/cm2 at 1.5 V; PGM: 2 µg/cm2.

Milestone #2: OER of 1 mA/cm2 at 1.42 V; 20 mA/cm2 at 1.5 V; PGM: 1.5 µg/cm2.

Anode ORR current reduced by a factor of 2.

Demonstrated ORR and HOR performance with integrated catalyst will be substantially the same as the base-line NSTF catalyst.

Go/No-Go: OER of 1 mA/cm2 at 1.40 V; 100 mA/cm2 at 1.5 V; PGM: 1 µg/cm2.

Anode ORR current reduced by a factor of 5.

Integrated catalyst system meets DOE metrics for durability, performance and PGM loading demonstrated by 50-cm2 FC testing.

Milestone #3: Short stack for delivery to DOE designated site for testing.

Year One Goal: Explore the space (Ru, Ir, Ti) around the OER model catalyst.

11


Combination: Pt Ti Ru Ir O2Pt:Pt 150 - - - -

Pt:Ti 150 2 - - -Pt:Ti 150 10 - - -Pt:Ru 150 - 2 - -Pt:Ru 150 - 10 - -Pt:Ir 150 - - 2 -Pt:Ir 150 - - 10 -Pt:Ti,Ir 150 1 - 2 -Pt:Ti,Ir 150 2 - 3 -Pt:Ti,Ir 150 2 - 4 -Pt:Ti,Ir,O2 150 1 - 2 1 sccm

Pt:Ti,Ir,Ru 150 1 2 2 -Pt:Ti,Ru,Ir,O2 150 1 2 2 1 sccmPt:Ru,Ir,Ti,O2 150 1 2 2 2 sccmPt:Ti,Ir,Ru,O2 150 1 2 2 7 sccmPt:Ir,Ru,O2 150 - 2 2 7 sccm

Pt:Ru,Ir 150 - 0.5 1.5 -Pt:Ru,Ir 150 - 1.0 1.0 -Pt:Ru,Ir 150 - 1.5 0.5 -Pt:Ru,Ir,O2 150 - 0.5 1.5 2 sccmPt:Ru,Ir,O2 150 - 1.0 1.0 2 sccmPt:Ru,Ir,O2 150 - 1.5 0.5 2 sccm

Element (ug/cm2)

Accomplishments: The model-based OER catalysts

Individual components:To enhance the OER effect, 10 µg/cm2 of PGM were used

Effect of PGM and Ti:2; 3; 4 µg/cm2 of Ir1; 2 µg/cm2 of Ir(data in Supplemental #32-35)

The four elements:2 + 2 µg/cm2 of Ir +Ru with Ti and Oxygen

Year One milestone PGM: 1 + 1 µg/cm2 of Ir +Ru with Oxygen

Baseline performance

12


OER of single components

The major findings: Ru the most active

Ir less active but much more stable

Ti is inactive; same as Pt substrate

Tafel plot of Initial Ru scan (2 mV/s): Well defined ~66 mV/dec slope

Ru 10

Ru 2Ir 2

E, V vs 1% H2

E, V vs 1% H2

10 µg/cm2 Ru

10 µg/cm2 Ir

OER onset

OER activityexpressed as current at verticies

Pt

Accomplishments: Results

15 curves @ 2 mV/s

E, V vs 1% H2

I, m

A/50

cm

2

I, m

A/5

0 cm

2I,

mA

/50

cm2

OER onset

13


Accomplishments: OER Summary of Single ComponentsVertices currents of 3 consecutive sweeps at milestones potentials of

1.45 V and 1.50 V

2 µg/cm2

Ru2 µg/cm2

Ru2 µg/cm2

Ir

With exception of Ti and bare Pt, all other catalysts are above the milestoneactivity at 1.45 V: 1 mA/cm2.

Only Ir catalysts exhibit activity above the milestone (2 µg/cm2 PGM) line at 1.5 V:10 mA/cm2.

Pt:Ti, Ru, or Ir

05

10152025303540

1450 1500

Voltage (mV, SHE)

Cur

rent

Den

sity

(mA

/cm

2)

16482 2ug Ti

16452 10ug Ti

16622 10ug Ti

16580 2ug Ru

17039 2ug Ru

16527 10ug Ru

16642 10ug Ru

16511 2ug Ir

16577 2ug Ir

16648 10ug Ir

16795 10ug Ir

16926 10ug Ir

16599 Pt

milestone

milestone

2 µg/cm2

Ir

14


Electrochemical surface properties changes during OER testingCyclic voltammograms before OER, after exposure to 1.45 V and 1.65 V

(Catalyst with 10 µg/cm2 Ru; Voltammograms #2 and #20 presented)

100 mV/s

CVs dominated by Ru initially 1.25 V:

Large capacitive current in Pt double layer region;

Pt Hupd and Pt oxide suppression

Small change in CVs cycled to 1.25 V

Exposure to 1.45 V:

Features due to Ru are substantially but not completely diminished

Exposure to 1.65 V:

CVs resemble Pt as if Ru were completely removed;

Well pronounced Hupd peaks, double layer and Pt oxidation appropriate for Pt.

Disappearance of Ru from the catalysts explains fully the change in the OER behavior

E, V vs 1% H2

I, A

/50

cm2

RuOxCapacitive

Accomplishments: Ru OER explained

15

Ti, Ir, Ru Series: ORR- Peak Activity (DOE Protocol)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

1648

2-Pt

:Ti

2ug

1645

2-Pt

:Ti

10ug

1662

2-Pt

:Ti

10ug

1651

1-Pt

:Ir2u

g

1657

7-Pt

:Ir2u

g

1664

8-Pt

:Ir

10ug

1679

5-Pt

:Ir

10ug

1658

0-Pt

:Ru

2ug

1652

7-Pt

:Ru

10ug

1664

2-Pt

:Ru

10ug

mA

/cm2 @

0.9

Vol

ts

Before OER After OER

10µg Ru


Within the reproducibility of the FC testing, OER added catalysts fall in two groups:

• No interference with ORR (all Ir and Ru with 2 µg/cm2)

• High impact: Ti and high content Ru (10 µg/cm2) before OER test.

• Due to losses, Ru (10 µg/cm2) is the only catalyst that moves to low impact group after OER testing.

FC polarization curves (Air) and ORR activity at 900 mV (Oxygen; lower graph)10 ug/cm2 Series: Fuel Cell Polarization Curves

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Current Density, A/cm2

Cel

l Vol

tage

, V

Pt:Pt (0.15/0.15) BOER Pt:Pt (0.15,0.15) AOER

16452: Ti- 10ug BOER 16452: Ti- 10ug AOER

16795: Ir- 10ug BOER 16795: Ir- 10ug AOER

16642: Ru- 10ug BOER 16642: Ru- 10ug AOER

16527: Ru- 10ug BOER 16527: Ru- 10ug AOER

100407

Accomplishments: Impact of OER catalyst on the FC performance

Ti

ORR activities at 0.9 V follow the same pattern as the FC polarization curves. With exception of 10 µg/cm2 Ru, the catalysts activities are slightly lower after the OER test.

10µg Ru

16

Coverage Evaluation

0

1

2

3

4

5

6

7

8

9

10

11

12

Ti/Pt Ir/Pt Ru/Pt

Ato

mic

ratio

s va

lues

10 mg/cm2 Ti on Pt-NSTF

10 mg/cm2 Ir on Pt-NSTF

10 mg/cm2 Ru on Pt-NSTF

Coverage Evaluation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Ti/Pt Ir/Pt Ru/Pt

Ato

mic

ratio

val

ues

2 mg/cm2 Ti on Pt-NSTF

2 mg/cm2 Ir on Pt-NSTF

2 mg/cm2 Ru on Pt-NSTF


Sample ID C O Ti Ir Ru Pt Ti/Pt Ir/Pt Ru/Pt O/Ti O/Ir O/Ru O/Pt C/Ti C/Ir C/Ru C/Pt Comment2 µg/cm2 Ti on Pt-NSTF 37 36 11 16 0.7 3.3 3.4 15 % at of O bound to C

2 µg/cm2 Ir on Pt-NSTF 22 24 10 43 0.2 2.4 2.2 ~ 6 % at of O bound to C

2 µg/cm2 Ru on Pt-NSTF 39 23 13 25 0.5 1.8 3 20 % of O bound to C

10 µg/cm2 Ti on Pt-NSTF 19 55 23 2 11.5 2.39 0.8 ~ 6% at of O bound to C

10 µg/cm2 Ir on Pt-NSTF 15 16 46 22 2.1 0.3 0.3 no data

10 µg/cm2 Ru on Pt-NSTF 46 20 27 8 3.4 0.7 1.7 ~20 % of O bound to C

0.15 mg/cm2 Pt-NSTF 22 4 74 0.05 0.3 ~5 % at of O bound to C

XPS Atomic Concentrations and Atomic Ratios of Ti, Ir and Ru Coatings vs. Pt

Accomplishments: Oxidation state and coverage of OER catalyst on Pt-NSTF

O/Ti ratios indicate that Ti is present as TiO2. Ir is as IrO2 only in 2 µg/cm2.Atomic concentrations of oxidized C, O and Ru indicate that Ru may be present as organo-metallic compound through Ru-O-C bonds for both 2 and 10 µg/cm2 on Pt-NSTF (details in #36)

Scale: 15X

17


02468

10

1214161820

1450 1500

Voltage (mV, SHE)

Cur

rent

Den

sity

(mA

/cm

2 )

17214 1 Ti 2 Ru 2 Ir no O2

17215fc 1 Ti 2 Ru 2 Ir no O2

17216 1 Ti 2 Ru 2 Ir no O2

16842fc 1 Ti 2 Ru 2 Ir 1sccm

16903 1 Ti 2 Ru 2 Ir 1sccm

16965 1 Ti 2 Ru 2 Ir 2sccm


16967 1 Ti 2 Ru 2 Ir 2sccm


16974 1 Ti 2 Ru 2 Ir 7sccm

16975 1 Ti 2 Ru 2 Ir 7sccm

17040 2 Ru 2 Ir 7sccm

17041fc 2 Ru 2 Ir 7sccm

17042 2 Ru 2 Ir 7sccm

Milestones:Red horizontal lines

Accomplishments: Ru – Ir – Ti – Ox OER catalyst

Vertices currents of 3 consecutive sweeps at:1.45 V and 1.50 V

ORR- Peak Activity (DOE Protocol)

0.05.0

10.015.020.025.030.035.0

1721

5-Pt

:Ti

,Ir,R

u(1

,2,2

ug; N

o O

2)

1684

2-Pt

:Ti,I

r,Ru,

O2

(1,2

,2ug

;1s

ccm

)

1696

6-Pt

:R

u,Ir,

Ti,Ir

,O2

(2,1

,1ug

;1pa

ss;

2scc

m)

1697

3-Pt

:Ti,I

r,Ru,

O2

(1,2

,2ug

;7s

ccm

)

1704

1-Pt

:Ir,R

u,O

2(2

,2ug

; 7sc

cm)

mA

/cm2 @

0.9

Vol

ts


More O2/Less Ti

Ti,%at: 12 7 3 0.0

The presence of oxygen during the deposition conditions correlates with changes in FC performance rather than on the OER activity or stability.

• The polarization curves as well as ORR activity are affected by the presence of Ti on the OER catalysts.

• Based on XPS, the presence of oxygen during the catalyst depositiondecreases the amount of Ti (XPS Ti % at. on Si wafer indicated on lower graph).

• As a result, better ORR activity and FC polarization performance is attained where more oxygen is present in the deposition system.

Nominal composition:2 + 2 + 1 µg/cm2 of Ir +Ru + Ti; Sputter deposition with oxygen flow: 1; 2; 7 sccm

18


NSTF-Pt withTi/Ru/Ir_7 sccm O2: Sample prepared by scraping NSTF off substrate

• On a closer examination, a thin, continuous layer is observed on the surface of the Pt “cap” • The ~2 nm thick layer is crystalline, contains Ti, Ir, and Ru and is primarily on the “cap” surface

5 nm

Pt cap

• Pt “cap” is ~40nm thick whereas thickness of Pt along sides of NSTF ~10nm• NO individual particles containing Ti/Ru/Ir were identified on the surface of Pt coating along the sides

Accomplishments: TEM of Ru – Ir – Ti – Ox OER catalyst

19


PtRu

PtIr

PtTi

Amount of Ru in the surface layer is greater than either Ti or Ir, in agreement with XPS findings. Oxygen also detected, indicating possible presence of oxides.Some lattice/ordering but not completely crystalline phase exhibited.

Accomplishments: TEM of Ru – Ir – Ti – Ox OER catalyst

Distribution of individual elements

20


Ru-Ir: No O2

0

2

4

6

8

10

12

14

1450 1500

Voltage (mV, SHE)

Cur

rent

Den

sity

(mA

/cm

2 ) 17324 0.5 Ru 1.5 Ir17325 0.5 Ru 1.5 Ir17326fc 0.5 Ru 1.5 Ir17380fc 0.5 Ru 1.5 Ir17235 1.0 Ru 1.0 Ir17236 1.0 Ru 1.0 Ir17237fc 1.0 Ru 1.0 Ir17435fc 1.0 Ru 1.0 Ir17348 1.5 Ru 0.5 Ir17349 1.5 Ru 0.5 Ir17350fc 1.5 Ru 0.5 Ir

Ru-Ir: 2 sccm O2

02

46

81012

14

1450 1500

Voltage (mV, SHE)

Cur

rent

Den

sity

(mA

/cm

2 )

17357 0.5 Ru 1.5 Ir

17358 0.5 Ru 1.5 Ir

17359fc 0.5 Ru 1.5 Ir

17351 1.0 Ru 1.0 Ir

17352 1.0 Ru 1.0 Ir

17353fc 1.0 Ru 1.0 Ir

17354 1.5 Ru 0.5 Ir

17355 1.5 Ru 0.5 Ir

17356fc 1.5 Ru 0.5 Ir

Accomplishments: Ru – Ir – (Ox) OER catalyst

There is indication that the presence of oxygen during the deposition process might be beneficial to the stability of some of the compositions Ru – Ir (1:1 by weight).

Ru (% at.): 85 67 38 85 67 38

Total PGM loading of 2 µg/cm2

Ru:Ir ratio from 3:1 to 1:3 w/w

Vertices currents of 3 consecutive sweeps

1.45 V 1.50 V

milestone

milestone

milestone

milestone

milestone

milestone

All catalysts achieved the milestone at 1.45V and some at 1.5 V.

21


Accomplishments: Ru-Ir Series - No O2 vs. O2ORR- Peak Activity (DOE Protocol)

0.0

10.0

20.0

30.0

40.017

350-

Pt: R

u,Ir,

No

O2

(1.5

,0.5

ug)

1743

5-Pt

: Ru,

Ir,N

oO

2 (1

,1ug

)

1738

0-Pt

: Ru,

Ir,N

oO

2 (0

.5,1

.5ug

)

1735

6-Pt

: Ru,

Ir,O

2(1

.5,0

.5ug

;2sc

cm)

1735

3-Pt

: Ru,

Ir,O

2(1

,1ug

;2sc

cm)

1735

9-Pt

: Ru,

Ir,O

2(0

.5,1

.5ug

;2sc

cm)

mA

/cm

2 @ 0

.9 V

olts


1.5,0.5

Ru-Ir, No O2

1.0,1.0

0.5,1.5

1.5, 0.5 1.0,1.0 0.5, 1.5

Ru-Ir, 2 sccm O2

Samples prepared with oxygen during the deposition process behave the same way. Obvious dependence on the Ru to Ir ratio exists in the absence of oxygen.

22

50 nm/cm2 deposit of Ru1-xIrx on 0.15 mg/cm2 Pt (i.e. 5 µg/cm2 Ru to 10 µg/cm2 Ir)Peak current density decreases as Ru:Ir ratio decreasesMost noticeable at high potential, increasing Ir content increases stability.RDE has produced very similar results and trends as did FC testing.

RDE OER Assessment of Ru1-xIrx on Pt-coated NSTF disks


0

4

8

12

16

20Curr

ent

Den

sity

at

Ver

tex

(mA/c

m2) Ru0.9Ir0.1

Ru0.7Ir0.3

Ru0.5Ir0.5

Ru0.3Ir0.7

Ru0.1Ir0.9

1400 mV 1500 mV 1600 mV

5 mV/s1600 rpmArgonR.T.

Ru Ir

23


Collaboration and CoordinationPartners

• Dalhousie University (subcontractor)- Dr. David Stevens; High-throughput catalyst synthesis and basic

characterization• Oak Ridge National Lab (subcontractor)

- Dr. Karren More; TEM Characterization

– The project has been fully integrated since its inception, during the proposal phase.

– It continues to be run as one single program.– Participants influence project directions based on their own data as

well as experimental results obtained by all. – Results are reviewed during weekly scheduled teleconferences and

many more unscheduled contacts between participants.

24


Future Work

Immediate/remaining of Year 1• Improve the reproducibility of the FC testing for both FC performance and OER activity• Modify/simplify test procedure to reflect “real life”, taking into account the Freedom Car Tech Team inputs• Start the high throughput anode work• Explore further the model system space by changing deposition conditions• Attempt catalyst post-processing• Initial attempts to produce the catalysts in discrete rather than continuous form

Year 2/ Long Term• Reaching the Project milestones as stated (slide # 10) or modified according to new DOE performance targets in this area.

25


• OER catalysts with 2 mg/cm2 PGM achieved First Year milestone for OER activity of 1 mA/cm2 at 1.45 V; Several catalysts initially met the milestone of 10 mA/cm2 at 1.5 V.

• Integrated OER catalysts with up to 2 mg/cm2 Ru + Ir do not interfere with the ORR.

• Canvassed the space around the components for the model OER durable catalyst in real PEM FC environment.

• Produced and characterized > 40 OER coatings and > 100 MEAs of Ir, Ru and Ti as individual elements, binaries and ternaries, with and without oxygen.

• Ru coatings are most active, while Ir are more stable.

• Combinations of Ru + Ir retain some of the properties of the two.

• Catalyst deposition under oxygen improves some of the properties of Ru + Ir.

• Presence of Ti inhibits the FC performance the most.

• Fully characterized coatings with XPS (ESCA) show indications of interaction of the OER catalysts with the substrate, potentially favorable from a durability point of view.

• High resolution TEM depicting the distribution of Ru, Ir, Ti on NSTF (ORNL) provides insight into the observed fuel cell performance and ORR activity.

Summary

26


Supplemental slides

29


Background for OER Catalyst: IrAs presented at DOE Annual review 2008

1.2 1.3 1.4 1.51E-4

1E-3

0.01

0

5

15

J (A

/cm2

)

E v. NHE @ 80C (Volts)

60OER polarization curves on NSTF PtCoMn (0.1mg/cm2 Pt) catalyst over-coated with 1, 3, and 12 nm/cm2 geo Ir.

50-cm2 FC

Counter electrode: same as working without Ir.Test conditions: FC 80 oC, Working: N2; counter/reference: 1% H2 in N2; 1000 sccm, 0 psig, 100% RH;Potential scan rate: 1 mV/s.

At 1 mA/cm2 only 1.1 µg/cm2 Ir depolarizes OER by 100 mV!

14

3.4

1.1

Ir, µg/cm2

14.0

3.4

1.1

30


Fundamentals – most active OER catalysts

Polarization curves for oxygen evolution on (a) Pt, (b) RuO2 singlecrystal, and (c) RuO2 film. 1M HClO4 at 25 oCTrasatti, Electrochim. Acta 36, 225, 1992

Dependence of Tafel slopes for OER on surface composition of RuO2 + IrO2. PGM precursors dissolved in aqueous (open symbols) and non-aqueous solvents (closed symbols). PGM content determined by XPS.

Atanasoska et al, Vacuum, 40, 91, 1990.

31


Approach: Electrochemical Characterization (OER Catalyst)1. Fuel cell performance before and after OER testing2. OER testing (under nitrogen) via quasi-steady state (2 mV/s or 1 mV/s) polarization measurements3. Surface area measurements and characterization via cyclic voltammetry4. Durability assessment at end of testing via constant voltage polarization

Fuel cell configuration: OER catalysts are deposited on 0.15 mg/cm2 PtThick, 35 µm 3M membrane, no additive. Counter/reference electrode: 0.15 µg/cm2 Pt under diluted hydrogen. Gas flows: 1,000 sccm 110% rh; cell: 70 oC.

1. Initial 20 CVs, 100 mV/s, from 1.25 V – 0.05 V, after 50 s at 1.25 V before the first CV

2. ECSA determination3. 2 Polarization curves at 2 mV/s and 1 at 1 mV/s, from 0.6 V – 1.45V4. Repeat steps 1 – 3 to positive end point of 1.5, 1.55, 1.60, and 1.65 V5. 300 s constant voltage at every 50 mV form 1.45 to 1.65 V6. Repeat step 2

OER Test Protocol

Time the cathode is over 1.25 V: ~ 6,000 s.

32


Ti – Ir OER catalyst: OER Polarization curvesOER activity improves with Ir content

Ir content: 1, 2, and 4 µg/cm2

Ir % at.: 34; 25; 34

E, V vs 1% H2

I, A/

50 c

m2

33


Ti-Ir Series: Current at vertex of 3 consecutive OER Polarization curves

Besides increasing with Ir content, OER activity improves when the catalyst is made in the presence of oxygen. This is more prominent at higher voltages.

Pt:Ti, Ir

0

2

4

6

8

10

12

1450 1500

Voltage (mV, SHE)

Cur

rent

Den

sity

(mA

/cm

2 )

16906 1Ti 2Ir no O2

16907 1Ti 2Ir no O2

16689 2Ti 3Ir no O2

16774 2Ti 3Ir no O2

16904 2Ti 4Ir no O2

16905 2Ti 4Ir no O2

16901 1Ti 2Ir 1sccm O2

16841 1Ti 2Ir 1sccm O2

Milestones:Red horizontal lines

34


Ti-Ir Series: Fuel Cell Polarization Curves

0.500.550.600.650.700.750.800.850.90

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Current Density, A/cm2

Cel

l Vol

tage

, VPt:Pt (BOER)Pt:Pt (AOER16689- Pt:Ti,Ir, No O2 (2,3 ug)-BOER16689- Pt:Ti,Ir, No O2 (2,3 ug)-AOER16774- Pt:Ti,Ir,No O2 (2,3 ug)-BOER16774- Pt:Ti,Ir,No O2 (2,3 ug)-AOER

100407

Ti-Ir Series: ORR- Peak Activity (DOE Protocol)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

1668

9-Pt

:Ti,I

r(2

,3ug

)

1677

4-Pt

:Ti,I

r(2

,3ug

)

mA

/cm2 @

0.9

Vol

ts


Both the polarization curves as well as the ORR activity are lower due to the Ti coverage of the ORR catalysts (Pt)

35


Ti-Ir Series: TEM of

100128Pt-Ti/Ir

Both Ti and Ir are clearly observed on the Pt surface, as a thin layer

PtTi

PtIr

NSTF Pt w/ Ti- 2 µg/cm2, Ir- 4 µg/cm2

• Ti/Ir “nanocrystalline” layer observed on surface of Pt “cap” and ~50nm down sides of Pt/NSTF• Thickness of Ti/Ir layer ~4-5nm (2X thicker than Ti/Ru/Ir layer; slides 18&19)

Pt capNSTF

36


XPS: Rigorous curve-fitting procedure for Ru and Carbon

2752802852902950

0.2

0.4

0.6

0.8

1

1.2

1.4310 DOE0013.spe

Binding Energy (eV)

Nor

mal

ized

Inte

nsity

ML100310 on Pt-NSTF

ML100310 on Si wafer

Curve fitting analysis of Ru 3d-C 1s core level photoemission for ML100310-1 on Pt-NSTF and Si wafer

Curve fitting analysis step of Ru 3d-C 1s core level photoemission including Ru 3d contribution onlyOverlapped Ru 3d-C 1s core level photoemission for Si wafer and Pt-NSTF substrates

O/(O/(Ir+RuIr+Ru =0.8 (Si wafer)=0.8 (Si wafer)

O/(O/(Ir+RuIr+Ru =1.3 (Pt=1.3 (Pt--NSTF)NSTF)

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