dynamic water management studies by means of perforated … · 2014. 11. 17. · schmallenberg st....

Dynamic Water Management Studies by means of Perforated GDLs and In-situ ESEM Observations

Robert Alink, Dietmar Gerteisen, Christian Sadeler, Christopher Hebling

Fraunhofer Institute for Solar Energy Systems ISE Freiburg, Germany

Diagnostic Tools for Fuel Cell Technologies 24.06.2009, Trondheim

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DIAGNOSTIC TOOLS FOR FUEL CELL TECHNOLOGIES 2009

Overview

Test scope: Examination of the water transportproperties of laser perforated of gas diffusion layers

In-situ single cell experiments and stack experiments

Ex-situ visualizing of water transport in untreated and perforated GDLs in ESEM

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The Fraunhofer Society58 Institutes - 12 600 Employees – 1.2 Bio € Budget7 Alliances

MikroelectronicsProduction TechnologyInformation and Communication TechnologyMaterials, DevicesLife Sciences

Surface Technology and Photonics

Defense and Security Research

Itzehoe

BerlinGolm

Magdeburg

Hannover

Braunschweig

Bremen

OberhausenDortmund

Duisburg

AachenEuskirchen

SchmallenbergSt. Augustin

IlmenauJena

Dresden

Chemnitz

Würzburg

Erlangen

Pfinztal

DarmstadtKaiserslauternSt. Ingbert

SaarbrückenKarlsruhe

Stuttgart

Freiburg

Freising

Rostock

Teltow

CottbusHalleSchkopau

Paderborn

Nürnberg

Efringen-Kirchen

MünchenHolzkirchen

Leipzig

Itzehoe

BerlinGolm

Magdeburg

Hannover

Braunschweig

Bremen

OberhausenDortmund

Duisburg

AachenEuskirchen

SchmallenbergSt. Augustin

IlmenauJena

Dresden

Chemnitz

Würzburg

Erlangen

Pfinztal

DarmstadtKaiserslauternSt. Ingbert

SaarbrückenKarlsruhe

Stuttgart

Freiburg

Freising

Rostock

Teltow

CottbusHalleSchkopau

Paderborn

Nürnberg

Efringen-Kirchen

MünchenHolzkirchen

Leipzig

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DevelopmentComponents

Products, PrototypesSystems, Processes

Fraunhofer ISEResearch & Development, Services

ServicesConsulting, Tests

MonitoringQuality Assurance

ResearchMaterialsModellingMethods

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Development of fuel cell systems, stacks and autonomously controlled systems

Characterizing and modelling single cells, stacks and systems

Control and safety technology

Fuel Cell Systems

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As consequence:water hinders oxygen

diffusion

How can perforation of GDLs help to enhance theperformance?

Water is generated in thecatalyst layer

Water flows throughsmall cavities

Small filled cavitiesmerge to larger cavities

Void space gets filled byliquid water

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How can perforation of GDLs help to enhance theperformance?

Pressure needed forthrough-plane transportof liquid water is higherthan that for in-planetransport

Water transport channels(WTCs) support thethrough-plane transport

Decrased saturation and increased oxygen

diffusivity

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Investigation of singlecell with an active area of1 cm2

Cathode GDL „under thechannel“ was perforatedby laser treatment

Holes have a diameter of 80 μm and a gap distance of 1 mm

Investigation of single cell

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forward

backward

* without anode polarization

different operatingconditions

sweep rate 10 mV/s

Dynamic polarisation curves @

show hysteresis effect

Enhancing liquid water transport by laser perforation of a GDL in a PEM fuel cellJournal of Power Sources, Vol 177, Issue 2, 1 March 2008, P 348-354D. Gerteisen, T. Heilmann, C. Ziegler

In-situ characterising of GDL water transport properties

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Potential sweepmeasured with non-modified GDL

Improving the liquid water transport in the GDL


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Hysteresis knee due to flooding effects


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Hysteresis knee due to flooding effects

Perforated GDL showslowered pore flooding

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Chronoamperometriy

700 400 mV

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Performance improvement ~15%



Chronoamperometriy

700 400 mV

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Chronoamperometriy

600 300 mV

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Performance improvement ~20%



Chronoamperometriy

600 300 mV

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Investigation of fuel cell stack

Air cooled stack

6 cells

Active area of 6 x 31 cm2

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Cell stability at 0.71 A/cm2

Stability test at 0.71 A/cm2 and 63 °C

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Cell stability at 0.71 A/cm2

Stability test at 0.71 A/cm2 and 63 °C

Voltages of outer cellstend to collaps due to flooding

Higher overallperformance

3 times less purging steps

Increased stabilityand performance

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Polarisation curve

Higher Voltage at constant current

Less variation of singlecell-voltage


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Chronovoltametry


Higher Voltage afterswitching to highercurrent

Lower temperature dueto lower mass transportlosses

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Examination of degradation by freezing water in ESEM

ESEM working in watervapor athomsphere

All 3 phases of waterpossible by adjustingtemperature and pressure

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bef

ore

Freeze / thaw cycling of GDLs


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bef

ore

10 x freeze / thaw

afte

r



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bef

ore

10 x freeze / thaw 10 x freeze / thaw

afte

r


Freeze / thaw cycling of MEAs


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bef

ore

10 x freeze / thaw 10 x freeze / thaw 10 x wet / dry

afte

r


Freeze / thaw cycling of MEAs

Wet / dry cycling of MEAs as reference


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Liquid water examination in ESEM

ESEM working in watervapor athomsphere

All 3 phases of waterpossible by adjustingtemperature and pressure

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Ex-situ visualization of liquid water breakthrough in ESEM

Water is „sucked“through a porousmembrane and the GDL

Visulization of waterbreakthrough near theGDL surface

800 Pa absolute

1x105 Pa absolute

E-beam

GDL

water

GDLGDL

porous membrane

ESEM

800 Pa

1 °C

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Transportation of water within an untreated GDL

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Transportation of water within a perforated GDL

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Summary

Single cell experimentsconsistant with stackexperiments

Significant increase in cellperformance and stabilityachieved

New method found to visualize water transportin GDLs in ESEM

dynamic water management studies by means of perforated … · 2014. 11. 17. · schmallenberg st....

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