Overview of the FP7 Project DECODE Results and Recommendations › 71438 › 1 › Thessaloniki_Friedrich_V1.pdf · 2013-12-12 · low temperature polymer electrolyte fuel cell membrane”,

Degradation Workshop, Thessaloniki, 21 September 2011

K. Andreas Friedrich

2nd International Workshop on

Degradation Issues of Fuel Cells

Thessaloniki, Greece

21 - 23 September 2011

Overview of the FP7 Project DECODE Results and Recommendations

DECODEDECODEDECODEDECODE

Project general information

Project full title: Understanding of Degradation

Mechanisms to Improve

Components and Design of PEFC

Coordinator: K. A. Friedrich, DLR

Project major Opel, Volvo, SGL, Solexis, DANA,

partners: CEA, ZSW, JRC, Uni. Erlangen,

Chalmers Uni.

Starting Date: 01.01.2008

Ending Date: 31.03.2011

Budget Total/Funding: 5.5 MEUR / 3.7 MEUR

Type of project: CP


Project General Information

Page 3

Motivation and Goals

First main goal of DECODE is to assess the relevance of

the degradation processes of polymer electrolyte fuel

cell based on the extensive analysis performed in

DECODE

Second goal is to identify and implement improvements

for fuel cell durability based on:

Understanding of degradation processes

Improved materials

Improved operation conditions

Third goal is the development of prediction tool for

degradation based on modelling (different

modelling approaches)



Interactions of Work Packages


Page 5

Identification and Ranking of CCM Degradation Mechanisms

Mechanism

• Structural degradation

Mechanical degradation

of the membrane

Loss of electrochemical

activity at the cathode

Loss of “electrochemical

activity” at the anode

• Chemical degradation

Importance

++++

+++

?



Page 6

Mechanical + Chemical Stress: Edge Failure

Degradation issues:

Gas X-over on the edges leads to chemical degradation

Mechanical shear stress during dynamic operation (membrane

expansion/shrinkage)

Membrane exposed to GDL fiber puncture

Suitable edge/gasket designs will avoid these failure

modes

Simple gasket design:


Page 7

Stabilized AquivionTM Membrane

0.0

1.0

2.0

3.0

4.0

5.0

0 50 100 150 200 250 300 OCV duration (hrs)

Hy

dro

ge

n C

ros

so

ve

r (m

A/c

m²)

70 °C 50 % RH std

70 °C 50 % RH stab

90 °C 50 % RH std

90 °C 50 % RH stab

standard

grades

stabilized grades

Polarisation curves E79-03S + LT250EW (25cm² cell)

0.6 V constant (=~1A/cm²)

100% reactant humidification - 75°C - 2.5 Bar abs

0,40

0,50

0,60

0,70

0,80

0,90

1,00

0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40

Current Density (A/cm²)

Cell V

olt

ag

e (

V)

BOL Hour 1000 Hour 2000 Hour 3000 Hour 4000

Open Circuit Voltalge at 75 °C

Accelerated aging test for membranes



Page 8

Stabilized AquivionTM Membrane


Experimental MEA made by CEA using

unstabilized AQUIVION membrane

without edge protection (2009)

Experimental MEA made by CEA using

reinforced AQUIVION membrane

with edge protection (2010)


DECODE Final Workshop March 24rd, 2011 Page 9

Ageing of MEAs in single cell

• Ageing test of DECODE CCB MEA (E87-05S + sub-gaskets) + Segmented-cell (DLR)

Constant load i = 676 mA.cm-2


Folie 6 > DECODE > Reissner

Stuttgart 28.01.2011

Current density distribution

676 mA/cm2 0 mA/cm2 96 mA/cm2

19 h:

833 h:

-45-81-53-36-41-51-31

3-8-9-9-8-45

192-1-11518

33147681530

24118791424

16118891216

6-8-25447

-1-100-2-20

1100-1-10

00-1-1-100

00-1-1011

0000010

0000010

-1-100-2-20

Current density distribution:

Air

H2 average current density = 676 mA/cm2 BAqPP923

conditions: counter-flow; single serpentine cell+segm. cell; 1500 mbar at cell

outlet; 80°C; RH 100/100%; stoich 1.7/2.0

0

100

200

300

400

500

600

700

800

900

1000

-100 100 300 500 700 900

Time after start of constant conditions [h]

vo

lta

ge

[m

V]

0

112

225

456

680

long term

676

1136

OCV

operation

>10 min

current density

[mA/cm2]

No OCV degradation

Faster reversible degradation

Small irreversible degradation

Counter-flow – 100/100%RH

Cell voltage at OCV, low and high

current densities

26 h 574h + 10min OCV

Possible recovery strategy

for flooded electrodes:

10min OCV operation

Page 10

Dynamic Test of Membrane and Electrodes

Results with ELAT electrodes (SLX) – E87-05S edge protected

• Dry DECODE conditions


Evidence of better mechanical stability with increased membrane

crystallinity & edge protection


Anode side

Cathode side

50 nm

0,5 µm

Page 11

Electrode Characterization

• TEM observations (CEA)

Active layers degradation: after cycling and membrane damaged


Air inlet

Air outlet

H2 outlet

H2 inlet

Cathode side: more degradation

Fresh MEA

6,3 nm

XRD : 6,3 nmXRD : 3 nm

Pt particles growth by Ostwald ripening at air outlet

C corrosion and massive Pt dissolution + reduction in AL or membrane at air inlet


Characterization: Conductive AFM

Page 12

Solexis E87-05S Comparison baseline after 24 h and after 20000 h stationary Operation

left: right:

reference outlet baseline, 24 h 20000 h stationary operation

0

5

10

15

20

25

30

35

40

45

50

Nafion 112 Solexis 20000 hstationary

Solexis 2000 hcycling air outlet

Solexis 2000 hcycling air inlet

Solexis 24 hreference

Mean structure size size / nm

Other Methods in DECODE:

• EIS, CV, LSV

• Raman spectroscopy

• XPS

Page 13

Identification and Ranking of GDL Degradation Mechanisms

Mechanism

• Chemical degradation

Loss of hydrophobicity

Carbon / structure corrosion

• Structural degradation

Change in (gas phase)

transport parameters

Change in wetting behaviour

Importance

++++

++++

+++

Observed, but influence on

performance limited


Page 14

Chemical Degradation of Electrodes and GDL


Loss of hydrophobicity

Partial decomposition of PTFE identified by XPS

PTFE decomposition mainly on the anode

Decrease of hydrophobicity

Changed water balance

Reversible loss of performance Degradation Workshop, Thessaloniki, 21 September 2011

Page 15

Chemical Degradation - Carbon Corrosion

OHCOOHC 2222 22

23323 )(HCOCaCOHCaCO

OHCaCOCOOHCa 2322)(

Chemical reactions:

• Carbon corrosion could be detected

• No fluoride was found -> No PTFE

decomposition for this chemical

degradation experiment

• Mass loss study for quantification


In DECODE:

Comparison of naturally aged and

artifically aged GDLs!

Page 16

Hydrohead Measurements for Testing Hydrophobicity


GDL type ∆p

(mbar)

New GDL 25BC 86.3 ±

3.0

Naturally aged GDL

25BC for 1000h

70.1 ±

6.2

Artificially aged GDL

25BC for 24h in H202

76.2 ±

4.8

Modified new GDL 25BC 78.9 ±

5.3

Modified artificially aged

GDL 25BC for 24h in

H202

79.4 ±

2.1

New GDL 25BA 15.7 ±

1.2

hgp fluid


Other Characterization methods:

• Mercury porosimetry

• Capillary flow porosimetry

• EDX mappings

• Contact angle

Page 17

IR Spectroscopy Inhomogenity in the Intensity of the C-F Vibration


Recommendation: Improve homogeneity of hydrophobic agent distribution


Page 18

Artificial and natural ageing

In Situ Single Cell Tests (SGL)



Short Stack Long Term Test – Temperature Cycling Test


DECODE 25– Voltage time chart over 700 h

º Very low degradation of cells with modified GDLs compared to cells with

standard GDLs

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800

time [h]

T [

°C]

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

U [V

]

ave T KW Ein [°C]

standard U1

standard U2

7609 neu U3

used (1500 h) U4

used (1500 h) U5

aged standard U6

aged standard U7

7609 aged U8

7609 aged U9

standard neu U10

7609 neu U11

standard neu U12

25 BC, modified

aged 25 BC, mod.

25 BC, modified

aged 25 BC, mod.

Page 20

Identification and Ranking of Bipolar Plate Degradation Mechanisms

Mechanism

• Contamination of the Ionomer from

external sources via port region

• Change of contact resistance

• Water accumulation in areas of low

flow and low pressure difference

• Potential MEA contamination from

the plates

• Release of silicon from the seal

material

Importance

++++

++++

++

+

?


Corrosion products

degradation products (AISI316L) degradation products (composite)

Total sum of metallic cations in the stack

968 ppm

Total sum of metallic cations in the stack

1172 ppm

comparable metallic contamination of both materials – can this be possible?

Corrosion products: nickel, iron, chromium

Fe

Ni

Page 22

Distribution of contaminants

peaks are allocated to the coolant inlet and coolant outlet region

direct contact of the ionomer to the medias trough the port cut-outs

design proposal elaborated to avoid

this contamination

Page 22 Degradation Workshop, Thessaloniki, 21 September 2011

Page 23

DECODE - Stack Contaminations

Contamination of the ionomer from external sources via port

region

• Step one introduce Solvicore 5 Layer MEA (Membrane

Solexis, Catalyst, Sub gasket, Membrane extended to the

edge of the bipolar plate

• Step two change of MEA design to Ionomer free Sub gasket,

Port area



Page 24

Stack Tests with Improved Stack Design

• Durability run with AISI316L blank

and new MEA with old configuration –

at DANA

• Durability run with AISI316L blank

and new MEA with new configuration

– at DANA

• Durability run with conductive coating

and new MEA configuration

• Durability run with modified

conductive coating, new MEA design

and further developed conditions

Conclusions of WP6 durability runs:

• Comparable behavior between new and old MEA configuration

• Higher cell voltage with conductive coating, irregular cell behavior

• Modified coating and further developed conditions with excellent performance results


Page 25

Contaminations in MEA

Corrosion products: nickel, iron, chromium

Page 25

DECODE 15 (AISI316L bipolar plates)

60µV/h

DECODE 24 (AISI316L bipolar plates

with organic coating, new MEA

Design and new operating conditions)

0µV/h


Page 26

Modelling and Lifetime Prediction

Page 26



Modelling and Lifetime Prediction


Modelling activities and results

Porous media:

• Molecular Dynamics

• Lattice Boltzmann

• Monte-Carlo

• Performance modelling

Bipolar Plates:

• CFD

• Movement of droplets by

VOF (volume of fluid)

DECODE Final Workshop March 24rd, 2011 Page 28

Membrane and Electrodes:

• Multiscale elementary kinetics simulation with coupling to

microscopical structure

Page 29

Summary

• Improvement achieved by materials: Reinforced membrane with higher crystalinity

Modified gas diffusion layer

• Improvement achieved by design: Edge protection of membrane

Blocking of external contermination by new sealing concept

• Improvement achieved by operation conditions: Avoiding liquid water phase

Excursion to open circuit conditions to recover reversible voltage losses

• Different models with life time prediction capability


Page 30

THANK YOU FOR YOUR ATTENTION

DECODE




Acknowledgement to the

partners of DECODE:

• M. Schulze, A. Haug, E. Gülzow, K.A. Friedrich, „Investigation of Local

Degradation Effects”, ECS Transactions 26 (2010) 237-245

• K. Seidenberger, F. Wilhelm, J. Scholta, „Monte-Carlo-Simulation -

Wasserhaushalt in der GDL einer PEM-Brennstoffzelle“ article (German), HZwei

(April 2011), pages 17-19

• S Pulloor Kuttanikkad, J.Pauchet, M.Prat; „Pore-network simulations of two-

phase flow in a thin porous layer of mixed wettability”, Journal of Power Sources

196 (2011) 1145

• K. Seidenberger, F. Wilhelm, T. Schmitt,W. Lehnert, J. Scholta, „Estimation of

water distribution and degradation mechanisms in polymer electrolyte membrane

fuel cell gas diffusion layers using a 3D Monte Carlo model“ J. Power Sources

196 (2011) 5317

• M. Holber, P. Johansson and P. Jacobsson, “Raman spectroscopy of an aged

low temperature polymer electrolyte fuel cell membrane”, Fuel Cells, 2011,

accepted

• J. Pauchet, M. Prat, P. Schott, S. Pulloor Kuttanikkad, „Analysis of the effect of

hydrophobicity loss of GDL on performance of PEMFC by coupling pore network

and performance modelling”, Submitted to the Journal of Power Sources

Page 31

Cathode side

Anode side

inner side

outer side

outer side

inner side

Division of membrane in 2 layers of 15 μm

after storage in water

Height

DMT

Height

Phase

Platinum particles with high

phase shift and high DMT

modulus (~elasticity) at inner

side of anode with mean

diameter of 21 nm

(11 nm - 44 nm)

40 nm 20 nm

Phase

Height

DMT

Height profile

Overall high density of

particles with small phase

shift: probably no Pt

AFM Analysis of Solexis E87-05S, 20000 h



Documents

Overview of the FP7 Project DECODE Results and Recommendations › 71438 › 1 › Thessaloniki_Friedrich_V1.pdf · 2013-12-12 · low temperature polymer electrolyte fuel cell membrane”,