Fiber Optic Temperature Sensors for PEM Fuel Cells

Fiber Optic Temperature Sensors for PEM Fuel Cells

Timothy J. McIntyreW. P. Partridge, S. W. Allison, L. C. Maxey, M. R. Cates,C. L. Britton, R. Lenarduzzi, T. J. Toops, and T. K. Plant*

(* Oregon State University)

DOE Annual Program ReviewMay 23-26, 2005

This presentation does not contain any proprietary or confidential information.

Project ID# FC42

Project TimelineProject Overview

Partners

Project ID# FC42

January2003

January2004

January2005

Phase 1 - Concept Development

Phase 2 - Concept Validation

Phase 1 - Concept Utilization

Project Milestone

September2005

Advanced Concept Development

1 2

3 4

5

1 - Lab feasibility demo.Go/No-Go

2 - Concept complete3 - Field feasibility demo.4 - Field validation5 - Utilization in operating

system6 - Demonstrate novel 2

photon technique

6

Project Budget

FY 2005 = $405k, all DOE funds

Barriers - Transportation Systems B.• Automotive sensors required to meet performance and cost targets for measuringphysical conditions and chemical species in fuel cell systems.

• Current sensors do not perform within the required ambient and process conditions,do not possess the required accuracy and range, and/or are too costly.

Targets - Automotive Fuel Cell Systems, Temperature• Sensors must conform to size, weight, and cost constraints of automotive applications• Operating range: -40 to 150°C• Response time: -40 to 100°C range <0.5 seconds with 1.5% accuracy; 100 to 150°Crange <1.0 seconds with 2% accuracy

• Gas environment: high humidity reformer/partial oxidation: H2 30% - 75%, CO2, N2,H2O, CO at 1 - 3 atm total pressure.

• Insensitive to flow velocity.

Technical Barriers and Targets

http://www.gm.com/

Project ID# FC42

Overview of Reviewer FeedbackReview Comment: Develop a multiplexing approach for thermal mapping

• Demonstrated a 5 sensor platform that could easily be scaled to over 10

Review Comment: More interaction with auto companies

• Beginning collaborative efforts with GM

Review Comment: Focus more on robust measurement to acquire new information than low-cost system

Review Comment: Perform sensor durability/compatibility testingReview Comment: Demonstrate measurements in operating fuel cells, forget

about low cost• 2 parallel demonstration/evaluation programs (Plug Power and in-house)• Sensors have been demonstrated in operating fuel cells.

Project ID# FC42

Project Objective

Provide measurement and diagnostic tools to fuel cell developersfor system performance optimization and model validation.

Real-time intra-fuel cell measurements of temperature and species (Humidity) made within operating PEM fuel cells.

• Demonstrate intra-fuel cell transient temperature diagnostic

• Characterize ‘typical’ intra-fuel cell temperature distributions

• Demonstrate intra-fuel cell species diagnostic (developed in separate DOE program)

* Combining temperature and species measurements provides dynamic humidity distribution

• Identify performance characteristics of fuel cell that suggest operational/design limits

Technical Approach• Construct luminescence-based sensors w/micro-ruby transducers

• Instrument fuel cells (multiple testing platforms and sensor configurations)

• Operate fuel cells to characterize operational relationships

Fuel cell courtesy of

250 micron ruby sphere tipped fiber233 micron ruby rod straddling flow channel

OpticalFiber

Bi-polarPlate

Project ID# FC42

Project ID# FC42

Technical Accomplishments

• Demonstrated intra-fuel cell temperature and species measurements within operating fuel cell(s)

• Characterized spatial distributions of temperature and humidity• Demonstrated correlation between temperature and humidity

distributions• Characterized time and temperature dynamics for improved

diagnostics• Demonstrated approach for improving detailed understanding of

realistic fuel cell system kinetics/chemistry* Pathway for optimizing operational and design parameters

(e.g. flow rates, pressure, concentrations, Pt distribution, flow path geometry, materials characteristics, etc.)

Project ID# FC42

Fuel Cell Platform(Plug Power)

2530354045505560657075

90 100 110 120 130 140Time (minutes)

Tem

pera

ture

(°C

)

MEA Centered Temperature Sensor Monitoring Cooldown

Water droplet passing sensor due to nitrogen purge

Water droplet events observed prior to shutdown

Project ID# FC42

50

55

60

65

70

75

150 170 190 210 230 250 270 290Time (minutes)

Tem

pera

ture

(°C

)Temperature Sensor at MEA Center

50

55

60

65

70

75

150 170 190 210 230 250 270 290

Temperature Sensor Near Gas Inlet

Time (minutes)

Tem

pera

ture

(°C

)

Thermography Data from Experiments at Plug Power

Water droplet formation rate varies with Operating Parameters

Cell temperature varieswith applied load and operating parameters

And position in cell

Sensors show similar trends in fuel cell temperature.

Project ID# FC42

Fuel Cell Platform(in house)

• Commercially available 2-cell stack• 7-cm x 7-cm active area per cell• Flow path: 13-pass, 918-mm dual-serpentine, crossed anode-cathode flows,

~1.27-mm diameter half channel, 0.633-mm2 flow area

Probes toInstruments

BPRBPR

MFCMFC

Gas BottlesExhaust

PEM

Fue

l Cel

l

Project ID# FC42

Probe Access for Intra-Fuel Cell Measurements• Fiber and capillary probes were installed at the inlet, 2x, 6x, 8x,

10x, (0, 0.2, 0.4, 0.6, 0.8, and 1L) and outlet positions• Temperature Probes ~0.4-mm OD: 19.9% flow area (next

generation 80 micron probe: 0.8% flow area)• Species Probes ~0.15-mm OD: 2.8% flow area• Thermocouples at fuel cell inlet and outlet

Ruby-tippedtemperature sensor

Micro-capillaryfor species measurements

Project ID# FC42

Experimental ConditionsThe fuel cell was evaluated at :

• Two temperatures: 30° and 72°C• Three gas flow rates: 50, 100 and 200 sccm• Two power levels: Low Power (LP), & High Power (HP)

Room Temp High Temp

Nominal Inlet/Outlet FC Temp (°C)

Water Bath Temp (°C)

Inlet Relative Humidity (%)

Anode (dry)

Cathode (dry)

30 72

27 58.9

84 56

50% H2 in N2, 10 psig 50% H2 in N2, 10 psig

20% O2 in N2, 12.5 psig 20% O2 in N2, 12.5 psig

Project ID# FC42

High-Temp Operation Shows Stepped Temperature Changes

Fuel Cell Conditions

Slow cooling, ~4°C/hr

All temperature measurements show stepped behavior

Inlet heats up too –strong front-end reaction?

High Temp PEM Fuel Cell Heating : 100sccm Case

70

71

72

73

74

75

300 320 340 360 380 400 420 440 460 480 500 520Time (min)

Tem

pera

ture

(C)

InletOutlet20pt Avg (10x Temp)20pt Avg (6x Temp)

Spac

iMS

'1O

hm',

100s

ccm

Spac

iMS

'Sho

rt', 1

00sc

cm

H2, O2 On,Very LP

LPH2, O2 Flow Off H2, O2 Flow OffHP

• Fuel cell heating ~ on the order 3-5°C• Interior temperatures can be > or < inlet and outlet temperatures• Temperature dynamics occur on 1-10 minute time scales• Even fast dynamics occur on the order of ~1 minute

Project ID# FC42

Phosphor Thermography Resolves Transient Intra Fuel Cell Temperature Distributions

Slow heating, ~5°C/hr

Species Measurements

Room Temp PEM Fuel Cell Heating

27

29

31

33

35

0 20 40 60 80 100 120 140 160 180 200 220Time (min)

Tem

pera

ture

(C)

InletOutlet20pt Avg (6x Temp)20pt Avg (10x Temp)

Spac

iMS

'1O

hm' ,

100s

ccm

Spac

iMS

'Sho

rt', 5

0scc

m

Spac

iMS

'Sho

rt', 2

00sc

cm

Spac

iMS

'Sho

rt', 1

00sc

cm

H2,O2 On,100 sccm,Very LP

100 sccm,LP

H2, O2 Flow Off 100 sccm,HP

50 sccm,HP

200 sccm,HP

100 sccm, Very LP

Fast Transients occur on 1-2 minute timescale

Intermittentcooling event(s)

Project ID# FC42

SpaciMS Resolves Transient Intra Fuel Cell Water and Species Distributions

Fuel cell power shows dynamic behavior at ‘stationary’ conditions

Local N2 ~ mirrors O2

Humidity increases inside fuel cell

O2 increases in outlet manifold to ~ inlet value

• un-instrumented cell inactive or degraded

Room Temp, 100 sccm, High Power

0.0E+00

2.0E-10

4.0E-10

6.0E-10

8.0E-10

1.0E-09

1.2E-09

1.4E-09

7 9 11 13 15Time (min)

H2O

, N2,

O2

and

Blan

k S

igna

l (A)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

FC O

utpu

t Pow

er (W

)

H2ON2O2BlankPower

10xOutlet 8x 6x 2x Inlet

With temperature and pressure can determine relative humidity from H2O

Project ID# FC42

High Humidity at 6x Location for Room Temp 200 sccm Case

Distinct and localized high humidity

8% Power increaseRoom Temp, 200 sccm, High Power

0.0E+00

2.0E-10

4.0E-10

6.0E-10

8.0E-10

1.0E-09

1.2E-09

1.4E-09

8.5 10.5 12.5 14.5 16.5Time (min)

H2O

, N2,

O2

and

Bla

nk S

igna

l (A

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

FC O

utpu

t Pow

er (W

)

H2ON2O2BlankPower

10xOutlet 8x 6x 2x Inlet

O2 depletion is greater in lower-flow case

Project ID# FC42

Without Condensation, Temperature and Relative Humidity Profiles are Flat within Fuel Cell

Largest temperature and relative humidity gradients occur in front 2x of fuel cell

Temperature and relative humidity decrease at outlet

• consistent with degraded parallel cell


30

31

32

33

34

Inlet 2x 6x 8x 10x OutletPosition Along FC Cathode Flowpath (x : number of passes)

Loca

l Tem

pera

ture

(C)

70

75

80

85

90

95

100

Loca

l Rel

ativ

e H

umid

ity (%

)

Temp%RH

Project ID# FC42

Locally Condensing Conditions Create Localized Cooling

Relative humidity = 100% Locally Condensing Conditions

Localized cooling : Condensation orEvaporative cooling?


30

31

32

33

34


Loca

l Tem

pera

ture

(C)

70

75

80

85

90

95

100

Loca

l Rel

ativ

e H

umid

ity (%

)

Temp%RH

Project ID# FC42

Increasing Reactant Flow Rate Cools Fuel Cell and Decreases O2 Consumption Rate

6% power increase

Major heating is in fuel cell front end (like at room temperature)

Overall cooling trend

O2 rate difference primarily 6x to 10x

O2 rate similar at fuel cell front

Output power increases despite less O2 consumption• Due to cooling effect?

Halving residence time did not half O2 consumption• Not reactant limited at 100sccm; maybe diffusion limited

Heating Rate and Oxygen Consumption, High Temp, High Power100sccm base flow (2Y mpm), HF:200sccm (4Y mpm), LF:50sccm (1Y mpm)

0

0.4

0.8

1.2

1.6

2


Rel

ativ

e H

eatin

g R

ate

and

O2

Con

sum

ptio

n

dT/dt, 100sccmdT/dt, 200sccm-dO2/dt, 100sccm-dO2/dt, 200sccm

P(100sccm, HP) : 1.16 WP(200sccm, HP) : 1.23 W

Project ID# FC42

Decreasing Reactant Flow Rate Cools Fuel Cell and Increases O2 Consumption Rate

Heating Rate and Oxygen Consumption, High Temp, High Power100sccm base flow (2Y mpm), HF:200sccm (4Y mpm), LF:50sccm (1Y mpm)

0

0.4

0.8

1.2

1.6

2


Rel

ativ

e H

eatin

g R

ate

and

O2

Con

sum

ptio

n

dT/dt, 100sccmdT/dt, 50sccm-dO2/dt, 100sccm-dO2/dt, 50sccm

P(100sccm, HP) : 1.16 WP(50sccm, HP) : 0.36 W

69% power decrease

Overall cooling trend

O2 is depleted by the 2x position

Back >80% of the flow path is inactive

Relative humidity was near or at saturation throughout fuel cell

Significant heating at 50 sccm indicative of strong spatially confined reaction?Doubling residence time completely depleted O2

• Reactant limited at 50 sccm • Further indicates diffusion limitation at 100 sccm

Project ID# FC42

Intra Fuel Cell Temperature and Species Measurements can Identify Performance Limitations

• The performance-limiting process can vary across the fuel cell (e.g., reactant depletion, diffusion, product surplus, localized site blocking,…)

• Intra fuel cell measurements can identify the local limiting processes

• More detailed experiments required* Change anode and cathode flows individually* Change concentration at constant residence time* Change residence time at constant molar flow rate

• Better understanding of these processes in realistic systems may improve performance via improved design and materials selection

* Temperature profile, Pt distribution, transport characteristics (O2, H2, H+, H2O)

Project ID# FC42

Fuel Cell Performance can be Dynamic Even at ‘Stationary’ Conditions

• Power dynamics may indicate regulation by limiting process

• O2 dynamics correlate with fuel cell output power

• Temperature and humidity may also correlate similarly

• Power-chemistry relationships are observable

Suggests meaningful chemical insights are accessible

Correlation of PEM FC O2 Use and Power, High Temp, 100sccm

0.0E+00

5.0E-11

1.0E-10

1.5E-10

2.0E-10

2.5E-10

3.0E-10

0 20 40 60 80 100Time (min)

O2

Sign

al (A

)

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

FC O

ut P

ower

(W)

O2Power

LP,6x

HP,6x

HP,8x

Project ID# FC42

Summary Conclusionsand Technical Accomplishments

• Intra-fuel-cell measurements demonstrated* Temperature* Humidity* Species including H2, O2, H2O, N2, Ar (others possible)

• Dynamics are slow, ~ minutes, and temperature changes are small, ~5°C

• No localized dry zones were observed

• Dynamic behavior routinely observed under stationary conditions* Symptomatic of detailed process limitations?

• Diffusion layer appears to efficiently transport water along flow path

• Methods demonstrated for achieving next-level performance understanding and improvements

Project ID# FC42

Future WorkMore extensive spatial mapping

• Stacks, not just cells?• Does feed gas short circuit flow path via diffusion layer?

Anode and cathode side instrumentation• Balance of reactants and products?

More extreme operating conditions to highlight barriers• Localized drying/flooding?

More controlled operation variations (drive cycle) to identify origins of local efficiency limitations.

Further instrument improvements• Advanced measurement methods instead of single probes, probe size,

signal-to-noise, temperature and time resolution, etc.

Project ID# FC42

Presentations, Publications and PatentsPresentationsFiber Optic Temperature Sensors for PEM Fuel Cells: Progress Report, Fuel

Cell Expo, San Antonio, TX, 2004.

Publications1. Development of Fiber Optic Sensors for Fuel Cells: Issues and Results,

Cates, M. R., S. W. Allison, L. C. Maxey, and T. J. McIntyre, Instrument Society of America, 2005.

2. Development of Optical Fuel Cell Temperature Measurements, Maxey, L. C., and T. J. McIntyre, Instrument Society of America, 2005.

Patents1. Duel-mode Optical Temperature and Humidity Sensor for PEM Fuel

Cells.2. 2-photon Induced, Spatially Resolved Temperature Sensing.3. Embedded Waveguide Sensors and Thin Polymer Membranes.

Project ID# FC42

Project SummaryRelevance: Help to answer fundamental questions necessary for energy-

efficient PEM fuel cell implementation.

Approach: Develop and apply intra-FC diagnostics to characterize transient performance characteristics

Technical Accomplishments and Progress: Demonstrated dynamic temperature, humidity and species distributions throughout an operating PEM fuel cell

Technology Transfer/Collaborations: Active partnership with Plug Power and others, new partnership with GM, presentations, publications and patents

Proposed Future Research: Apply intra-FC diagnostics to identify performance barriers and pathways for performance

Tim McIntyre865-576-5402

[email protected]

Project ID# FC42

Hydrogen SafetyThe most significant safety risk would be a hydrogen supply gas leak or mishandling of unutilized hydrogen exhausted from the fuel cell.

• All project activities at ORNL are covered by a formal, integrated work control process for each project/facility

– Definition of task– Identification of hazards– Design of work controls– Conduct of work– Feedback

• Each work process is authorized on the basis of a Research Safety Summary (RSS) reviewed by ESH subject matter experts and approved by PI’s and cognizant managers

• RSS is reviewed/revised yearly, or sooner if a change in the work is needed• Staff with approved training and experience are authorized through the RSS

To minimize any potential safety risks on this project the following actions are taken:

Project ID# FC42

Interesting Observations via Multiple DiagnosticsHigh Temperature Fuel Cell Operation

FC@~71C, Anode 50%H2 50%N2 ~10psig, Cathode 20%O2 80%N2 ~12.5psig, H2Osat@~58.9C100sccm base flow, HF:200sccm, LF:50sccm

0

2

4

6

8

10

12

14

16

18

20

Inlet 2x 6x 8x 10x OutletLocation along 13-Pass Serpentine Fuel Cell Cathode Channel

Oxy

gen

Con

cent

ratio

n (%

V/V

)

1 OhmShort1 Ohm, HFShort, HF1 Ohm, LFShort, LF

High Temperature Fuel Cell OperationFC@~71C, Anode 50%H2 50%N2 ~10psig, Cathode 20%O2 80%N2 ~12.5psig, H2Osat@~58.9C

100sccm base flow, HF:200sccm, LF:50sccm

20

30

40

50

60

70

80

90

Inlet 2x 6x 8x 10x Outlet

Location along 13-Pass Serpentine Fuel Cell Cathode Channel

Rel

ativ

e H

umid

ity (%

)


High Temp PEM Fuel Cell Exp.

70

70.5

71

71.5

72

72.5

73

73.5

74

Inlet 2X 6X 8X 10X OutletPosition Along PEM Cathode Serpentine Flowpath (x : number of passes)

1Ohm, 100sccmShort, 100sccm1Ohm, 200sccmShort, 200sccm1Ohm, 50sccmShort, 50sccm



-30

-20

-10

0

10

20

30

40

Inlet 2x 6x 8x 10x Outlet

Location along 13-Pass Serpentine Fuel Cell Cathode Channel

Cal

cula

ted

Wat

er G

ener

atio

n (b

ased

on

O2

Use

) (%

V/V

)


Project ID# FC42

Under Differing Operational Conditions the Fuel Cell Thermal Profile Varies

Average FC Heating Rate

0.015

0.020

0.025

0.030

0.035

0.040

Inlet 2X 6X 8X 10X Outlet

Position Along PEM Cathode Serpentine Flowpath (x : number of passes)

50sccm100sccm200sccm

Project ID# FC42

Observed Power Outputfrom Fuel Cell During Testing



0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1 Ohm Short 1 Ohm, HF Short, HF 1 Ohm, LF Short, LF

Fuel Cell Load and Flow Conditions

Fuel

Cel

l Out

put P

ower

(W)

Fiber Optic Temperature Sensors for PEM Fuel Cells

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