University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Oct. 30, 2007

Mech 549

Fuel Cell Technology

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Fuel Cell Stack Design

• Fuel Cells are “stacked” to place bipolarcells in series and increase voltage andpower

• Major stack issues:– Volume and weight

– Cooling methods

– Sealing

– Clamping

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Stack Design Objectives

Minimize Volume, Weight, Cost

Satisfy other constraints to maintain high fuel

cell performance

Conventional Stack Layout

• Bipolar plate / MEA in alternating arrangement

• Some internal humidification

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Stack Assembly

• Built up from discrete MEA, Bipolar

plate components.

• Discrete seals at each layer

• Compression applied through tie rods or

straps

• Manual Assembly

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

• 3 cell un-humidified stackMEA Layer

Bipolar Plate

Seal

Current Collector

Insulator

Compression Plate

Stack Components

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

PEM Stack Evolution

• Major advances in fuel cell power have

not been in the area of electrochemistry!!!

• Cost and performance targets have been

reached through better engineering:• Tighter integration of components

• Reduced materials use

• Better integrated manufacturing

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

PEMFC Stack Power Density

Source: Ballard Power Systems

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

PEMFC Stack Cost

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Compression & Clamping

Source: F. Barbir, PEM Fuel Cells, Elsevier, 2005

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Early Stack Layout

Tie Rods

Bulk Manifolds

Active Area

Seals

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Alternative Clamping

Internal Tie Rods

Bulk Manifolds

Active Area

Seals

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Humidification

Source: F. Barbir, PEM Fuel Cells, Elsevier, 2005

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Cooling

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30 Cooling Requirements and

Bounded Design Space

85 kW Automotive Fuel Cell Design Space

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Current Density [A/cm2]

Ce

ll V

olt

ag

e [

V]

0.0

3.0

6.0

9.0

12.0

15.0

18.0

21.0

To

tal

Ac

tiv

e A

rea

Re

qu

ire

d t

o

Pro

du

ce 8

5 k

W [

m2]

MEA Active Area @ Full Specified Stack Power [ m2 ]

Cell Voltage [ V ]

Automotive Fuel Cell Design Space

Courtesy: Pat Hearn, Ballard Power Systems

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.70 0.95 1.20 1.45 1.70 1.95 2.20 2.45

Current Density [A/cm2]

Cell V

olt

ag

e [

V]

0.0

3.0

6.0

9.0

12.0

15.0

18.0

21.0

To

tal A

cti

ve A

rea R

eq

uir

ed

to

Pro

du

ce 8

5 k

W [

m2]

Cell Voltage [V] Thermal constraint, Vc min (V) Total stack active area required [m2]

Design Space: Baseline Example

Cell R = 159 mohms- cm2

V0 = 0.829 V

1.0 mg/cm2 Cat Load @ $20/g,

$50/m2 Membrane, $20/m2 GDL,

4.4 m2 affordable

Power Density = 1700 W/LMax Active Area = 10.6 m2

Cooling Capacity = 1800 W/K @

90 C Coolant, 35 C ambient = 99

kW, Minimum Voltage = 0.58 V

Active Area Gap = 5.7 m2

~ 2x Stack Cost Target !Power Density and ThermalConstraints are Compatible

Heat Rejection Constraint

Power Density Constraint

Cost Constraint

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Baseline

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.70 0.95 1.20 1.45 1.70 1.95 2.20 2.45

Current Density [A/cm2]

Cell V

olt

ag

e [

V]

0.0

3.0

6.0

9.0

12.0

15.0

18.0

21.0T

ota

l A

cti

ve A

rea R

eq

uir

ed

to

Pro

du

ce 8

5 k

W [

m2]

Cell Voltage [V] Thermal constraint, Vc min (V) Total stack active area required [m2]

Cost Constraint, $45/kW FCS [m2] Power Density Constraint [m2]

4.4 m2 affordable active area

Cell R = 159 mohms- cm2

V0 = 0.829 V

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Baseline with +25% Cooling Capacity

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.70 0.95 1.20 1.45 1.70 1.95 2.20 2.45

Current Density [A/cm2]

Cell V

olt

ag

e [

V]

0.0

3.0

6.0

9.0

12.0

15.0

18.0

21.0

To

tal A

cti

ve A

rea R

eq

uir

ed

to

Pro

du

ce 8

5 k

W [

m2]

Cell Voltage [V] Thermal constraint, Vc min (V) Total stack active area required [m2]

Cost Constraint, $45/kW FCS [m2] Power Density Constraint [m2]

4.4 m2 affordable active area

Cell R = 159 mohms- cm2

V0 = 0.829 V

Active AreaGap=4.5 m2

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Baseline

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.70 0.95 1.20 1.45 1.70 1.95 2.20 2.45

Current Density [A/cm2]

Cell V

olt

ag

e [

V]

0.0

3.0

6.0

9.0

12.0

15.0

18.0

21.0T

ota

l A

cti

ve A

rea R

eq

uir

ed

to

Pro

du

ce 8

5 k

W [

m2]

Cell Voltage [V] Thermal constraint, Vc min (V) Total stack active area required [m2]

Cost Constraint, $45/kW FCS [m2] Power Density Constraint [m2]

4.4 m2 affordable active area

Cell R = 159 mohms- cm2

V0 = 0.829 V

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Base Case –20% Cell Resistance

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.70 0.95 1.20 1.45 1.70 1.95 2.20 2.45

Current Density [A/cm2]

Cell V

olt

ag

e [

V]

0.0

3.0

6.0

9.0

12.0

15.0

18.0

21.0

To

tal A

cti

ve A

rea R

eq

uir

ed

to

Pro

du

ce 8

5 k

W [

m2]

Cell Voltage [V] Thermal constraint, Vc min (V) Total stack active area required [m2]

Active AreaGap=4.1 m2

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Other Stack Designs

• The ‘Plate & Frame’ stack is popular

and is the only stack being

contemplated for large volume

production

• Other approaches to stack design can

be considered and may have merit in

the long run.

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Alternate Geometries:

Virtually everybody does this

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Alternate Geometries:

A simple change

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Alternate Geometries:

The Wave Cell

Ref: W.R. Merida, G. McLean, N. Djilali, ‘Non-Planar architecture for

proton exchange membrane fuel cells’, Journal of Power Sources, 102, pp.

178-185, 2001

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Integrated MEA / Bipolar Plate

Metal

Screen

E l e c t r o l y t e

M a t e r i a l

S o l d e r e d

S u r f a c e T r a c eV i a

P h e n o l i c

R e s i n B o a r d

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Volume Comparison

Conventional

plate and

frameCorrugated

Waved tube cell

V

(m

m3/

m

m2)

Horizontal Axis represents critical minimum thickness (mm)

Vertical Axis

represents

volume per

active area

(mm3/mm2)

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Wave Cell Prototypes

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Wave Cell Power Density

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Current Density (Acm-2

)

Po

we

r D

en

sity (

W c

m-3

)

Baseline

WTC1 Prototype

WTC2 Prototype

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Other Stack Issues

• Contact between plates and MEA must

be good:

– Seals must not separate MEA from plates

– Gaps between MEA and plates cause a

low pressure drop path from inlet to outlet

– Reactants and coolant must be separated

and remain unmixed

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Correct Gasket

Substrate

Layer

Electrolyte

Flow Field Plate

Compressed

Gasket

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Gasket Casting

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Stack Design…

• Big step from single cells to stacks

• Engineering dominates chemistry inthese areas

• Stack design requires integration ofmany disciplines

• There are lots of opportunities forimproved fuel cells through better stackdesign

University of Victoria Department of

Mechanical Engineering IESVic

Oct 30

Market Penetration Strategies

Current Market Price/Power Envelope (source: Manhattan Scientifics)