MEA Fabrication

James Fenton

University of Central Florida-FSEC

May 18, 2009

1

Outline

• Test Protocol • FSEC Responsibilities • Electrode Background • Previous Studies • FSEC Baseline Fabrication Procedures • Cell Assembly • CCM Fabrication from Team Membranes • Membrane Tests and Test Results

2

MEA Test Protocol

• Hard copies available

• First presented at fall meeting inHawaii

• Additional tests run to verify procedure

3

FSEC Responsibilities

• Make a good MEA according to membrane developers specifications

• Work closely with developer to apply an appropriate electrode for their membrane – FSEC has a baseline electrode application

process – Ink composition, electrolyte type, loading,

application conditions (e.g. heat), hot press conditions, etc.

4

Membrane Electrode Assembly (MEA)

5Gas Diffusion Layer

300-500 μm

Catalyst Layer 10-30 μm

Membrane 25-50 μm

Carbon paper fiber

Ionomer supplies/removes H+

Catalytic Pt

Carbon supplies/removes e-

CCM 35-80 μm

Electrode Components

•Kinetics (activation) •Ohmic (ionic, electronic) •Mass Transport (O2)

Catalyst (Active Site + Electronic)

Ionomer (Proton Transport)

Reactant (Gas Transport)

Anode: H2 Æ 2 H+ + 2 e-

Cathode: ½ O2 + 2 H+ + 2 e-Æ ½ H2O

MOST Losses 3-phase reaction

H+

6

Complex Interplay Among Key Elements

Catalyst loading

Electrode thicknessPt content in Pt/C

Ionomer loading and EW

Ohmic lossesKinetic losses Transport losses

7

Previous Studies of CCM Fabrication: Effect of Ionomer Loading and EW

0.80

Ionomer 800EW

Cel

l Vol

tage

at 4

00m

A/c

m2 (V

) Nafion® 1100EW

Nafion® 920EW

0.75

0.70

0.65

0.60

120/35/35 0.4mg/cm2 Pt H2/Air 1atm

0 10 20 30 40 50

88

Ionomer Content (%)

FSEC-1 CCM FSEC-3 CCM 0.00

0.10

0.20

0.30

0.40 0.50

0.60

0.70

0.80

0.90

1 10 100 1000 10000 Current density (mA/cm2)

Volta

ge (V

)

FSEC3_25% ionomer FSEC3_27% ionomer

120/35/35 0.4mg/cm2 Pt H2/Air 1.5 atm

*H. Xu, H.R. Kunz, L. Bonville, J.M. Fenton, J. Electrochem. Soc., 154, B271-B378 (2007).

Effect of Ionomer EW and Content on Performance at 120 oC and 35%RH

1.0

0.8

0.6

0.4

0.2

0.0

15% Nafion 1100EW 25% Nafion 1100EW 32% Nafion 1100EW 35% Nafion 1100EW 40% Nafion 1100EW

1100EW (optimized content 32%)

Cel

l Vol

tage

(V)

1.0

0.8

0.6

0.4

0.2

0.0

15% Nafion 920EW 25% Nafion 920EW 28% Nafion 920EW 32% Nafion 920EW 35% Nafion 920EW

920EW (optimized content 28%)

0 200 400 600 800 1000 1200 1400 1600 0 200 400 600 800 1000 1200 1400 1600

Current Density (mA/cm2) Current Density (mA/cm2)

Cel

l Vol

tage

(V)

0.0

0.2

0.4

0.6

0.8

1.0 10% Ionomer 800EW 15% Ionomer 800EW 25% Ionomer 800EW 28% Ionomer 800EW 32% Ionomer 800EW

800EW(optimized content 25%)

Membrane: Nafion®-Teflon®-Phosphotungstic Acid (NPTA) 25μm

Cathode: 0.4mg/cm2 Pt (Tanaka Pt/C)

Anode: 0.4mg/cm2 Pt (Tanaka Pt/C)

Cel

l Vol

tage

(V)

Reactant: H2 (stoic 4)/air (stoic 3) 0 200 400 600 800 1000 1200 1400 1600 9Total pressure: 1atm

Previous Studies of CCM Fabrication: Hydrocarbon Membranes

• Drying the membrane before and after

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spraying resulted in a brittle membrane

Cracks developed during electrode application

Previous Studies of CCM Fabrication: Hydrocarbon Membranes

• Solvents used in spraying caused significant swelling – The CCM never relaxed back to its original

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shape

Previous Studies of CCM Fabrication: Hydrocarbon Membranes

• Lower drying temperature and slower rate of spraying resulted in better CCM

12

FSEC CCM Baseline Fabrication Procedure

45.5 wt % Pt/C (45.5 wt % Pt/C (TTKK)KK)1. Spraying PFSAPFSA ionomerionomer sosolluuttiioonn

2. Cs+ treatment

3. Heat treatment 75 psi Cs exchanged CCMs, hot press at 180 oC Non Cs exchanged CCMs, hot press at 136 oC

4. Protonation

5. Cleaning

Cs+ 0.1 N Cs2CO3

H+

0.5M H2SO4

DI

SolventSolvent

- both membrane & electrode

-CCM is melt processed

- ionomer regains its protonic form

- remove residual acid

1313 High performance, interfacial stability and improved durability

Ink Preparation

3 wt% Pt/C +

10 wt% Water +

65 wt% Methanol +

22 wt% 1100 EW 5% Nafion® Dispersion

Homogenize 19,000 rpm

5.5-6 h

Store in a vial, stirring, for no more than

one week

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Membrane Spraying Setup

The lamp enables solvent

evaporation

Airbrush (X-Z movement) Computer controlled axes. Parameters controlled: • gas pressure • spray rate and pattern • distance to membrane (Y) • temperature

The carrier gas propels onto membrane

surface.

Final catalyst layer contains 68 wt% Pt/C and 32 wt% 1100 EW Nafion®

IR lampMembraneSpray gun

Car

rier G

as (N

2 )

Heating Plate

gun

membranes

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From Membrane to Testing

Membrane Catalyzed Electrode MEA in

Membrane Membrane Assembly Cell Hardware

Mem

bran

e Spray

Catalyst M

embr

ane

+ Flow Fields & Hardware Set + 2 GDLs

Mem

bran

e

Electrocatalyst: 45.5 % Pt/C (TKK); 0.4 mg Pt/cm2 for both the anode and cathode

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1

2

3

4 5

6

4

3

2

1

7

5

Cell Assembly

1. End plate 2. Gold coated copper plate 3. Bipolar plate 4. Teflon gaskets to provide pinch

- Total pinch = 228-254 μm (9-10) mil 5. Gas Diffusion Media

- 10 BB SGL Carbon (SigracetTM) 6. CCM 7. Bolts

Assembly verification – Check for electrical short using a

multimeter – Leak check 17

CCM Fabrication & Testing of Your Membranes

Check Membrane Viability Visual inspection-bubbles, debris, fogginess, stretches, cracks, thickness variations, gas crossover, flexibility, solvent effects

Conductivity FSEC, Bekktech, and

Scribner

Materials Characterization

TG/DTA-MS FTIR

Water uptake

Prepare CCM Develop ink, apply

electrode, hot press, protonate in close collaboration with

supplier Untested CCM &

Coupon

Tests 9-day performance

100 hr OCV durability

H2O Analysis

FER, NMR, GC-MS

Materials Characterization SEM/EDAX of CCM and cross-section Visual inspection

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Provided to Supplier

• All the data collected – MEA manufacturing issues as they arise

– Conductivity, performance and accelerated durability data with analysis

• An untested CCM for your evaluation • Coupon for ex situ testing

– SEM, FTIR, XPS, etc.

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4 cm

Membrane Sample Size

CCM

Conductivity #1

Conductivity #2

Coupon

Extra 12 cm

12 cm

8 cm

4 cm

4 cm

5 cm 5 cm

4 cm

8 cm

4 cm

• CCM piece used forMEA

• Conductivity piecestested at FSEC Bekktech, and Scribner

• Coupon piece prepared withelectrode at same time as CCM – Could be used to

examine effects of post spray treatment,electrode/membrane interface, electrode surface, etc

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Electrode Development In Collaboration With Suppliers

• Solvent in ink mixture – Type, ink content

• Ionomer in electrode – Type, final electrode loading

• Cure rate of ink on membrane – Heat, distance from heat, ink application rate

• Catalyst

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How Can You Help Us?

• Membrane temperature limits? • Membrane solvent tolerance? • Membrane/ionomer interactions?

• What ionomer do you want in your electrode?

• Additional questions for discussion?

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