fuel cell diagnostics for automotive application4+fuel+… · startup sequence: minimization of...

FUEL CELL DIAGNOSTICS FOR AUTOMOTIVE APPLICATION

DR. SEBASTIAN KIRSCH, DR. MAREN RAMONA KIRCHHOFF 13TH INT. AVL SYMPOSIUM ON PROPULSION DIAGNOSTICS │ BADEN-BADEN │ 26.06.2018

2 VW Group Research | Propulsion and Energy Systems | Dr. Sebastian Kirsch, Dr. Maren R. Kirchhoff

ZOOMING INTO A FUEL CELL SYSTEM

Membrane-Electrode-Assembly and Bipolar Plates

Fuel Cell Vehicle Fuel Cell Stack

endplate

cells

clamping system

endplate

Fuel Cell System

stack

turbo- compressor

gas diffusion layer (GDL)

membrane

gas diffusion layer (GDL)

bipolar plate (BPP)

gas conditioning


MEMBRANE ELECTRODE ASSEMBLY (MEA)

O2 from ambient air

H2

from tank

Current for electric motor

heat & water GDL 180 µm

GDL 180 µm

Cathode 15 µm

Anode 5 µm

Membrane 18 µm

UCell ≈ 0.6 - 1V e-

BPP 600 µm

Summerschool 2017

Overall reaction: H2 + ½ O2 H2O

Abbreviations: BPP: Bipolar plate GDL: Gas diffusion layer MEA: Membrane Electrode Assembly

H2 → 2H+ + 2e- 2H+ + ½O2 + 2e- → H2O


OPERATION FAILURES

H2

coolant

air

Anode Flooding due to bad water management

Cathode degradation

14 µm 7µm

SEM Post-Mortem Analysis

A HYPOTHETIC COUNTER FLOW SETUP

dry out as relative humidity (rH) at the inlets is too low

Performance reduction

70°C Fast Transient Polarizations at varying inlet rH

20% 40% 60%

80%

100%

Mechanical Stress due to humidity cycling:

Cracking of the membrane

SEM Post-Mortem Analysis


CONTENT

1. Motivation: Things that go wrong during fuel cell operation

2. Some Diagnostic Tools Required During Development: 1. Polarization Curve Comparisons 2. Infrared Imaging 3. Cell Voltage Monitoring & Temperature mapping 4. Something advanced: X-ray and FIB-SEM sampling

3. Some Fundamental Diagnostic Strategies for Fuel Cell System Operation 1. System Setup Overview 2. System Operating Conditions 3. Diagnostics in Fuel Cell System 4. Examples for Diagnostics in Fuel Cell System

4. Summary


ANALYSIS OF DIFFERENCES IN POLARIZATION CURVES

Two polarization curves Four characteristic scenarios

volt

age

[V]

current density [A/cm²]

0,??

1,25 1,18

DU(i)

pol. curve 1

pol. curve 2

The shape of DU(i) helps to identify the origin of the failure.

FUNDAMENTALS

DU

[V

]

i [A/cm²]

0,10

0

DU

[V

]

i [A/cm²]

0,10

0

DU

[V

]

i [A/cm²]

0,10

0

► Membrane failures (pin-holes & cracks)

DU

[V

]

i [A/cm²]

0,10

0

► Loss of activity (Pt-loss, de-Alloying)

► Additional (quasi-) Ohmic losses (contam., rH)

► Additional transport losses (contam., C-corrosion)


Polarization curves difference

DU

[V

]

0,10

0,00

Activity

(Quasi -) Ohmic

Transport

Pin-holes / cracks

current density [A/cm²]

ANALYSIS OF DIFFERENCES IN POLARIZATION CURVES FUNDAMENTALS

By fitting DU(i) onto the four characteristic scenarios the individual losses can be quantified.

0,05

Four characteristic scenarios

DU

[V

]

i [A/cm²]

0,10

0

DU

[V

]

i [A/cm²]

0,10

0

DU

[V

]

i [A/cm²]

0,10

0

► Membrane failures (pin-holes & cracks)

DU

[V

]

i [A/cm²]

0,10

0

► Loss of activity (Pt-loss, de-Alloying)

► Additional (quasi-) Ohmic losses (contam., rH)

► Additional transport losses (contam., C-corrosion)


INFRARED IMAGING

Fixture for pin-hole & crack detection

FUNDAMENTALS

Example

► IR-imaging can be used to detect pin-holes and cracks

► From the findings failures in the MEA- or BPP design or operation strategy can be anticipated

IR-camera

MEA

H2

Air


Risk of overheating

Time [s]

MEA

Tem

p [

°C]

Co

ola

nt

Tem

p [

°C]

CELL VOLTAGE MONITORING & TEMPERATURE MAPPING DURING FREEZE START

performance reduction

Eq. S

tack

Po

wer

[%

] C

oo

lan

t Te

mp

[°C

]

Min

Cel

l Vo

ltag

e [V

]

Time [s]

Cathode ice-blockage

► start load: 10% Pel,max

► start temperature: -21.5°C

progress of cathode electrode ice front

Anode ice-blockage Overheating

► start load: 50% Pel,max ► start temperature: -15°C ► (too) wet ShutDown

► inserted temperature sensors to measure the local temperature (between cathode-BPP and GDL)

Time [s]

Eq. S

tack

Po

wer

[%

]

Min

Cel

l Vo

ltag

e [V

]

-1.5V: emergency stop

Global H2-Starvation

inlet middle outlet


HARD X-RAY CT (SYNCHROTRON) & FIB-SEM (FOCUSED ION BEAM…) A VLIES-BASED GAS DIFFUSION LAYER

GDL (left): ► Vlies-Substrate and MPL ► Resolution: 0,35 µm MPL (right): ► Microstructure ► Resolution: 5 nm

Motivation: ► Flooding and 2-phase flow in the electrodes and the gas

diffusion layer causes voltage losses (especially at high current densities) and degradation

Targets: ► Sub µm-detailed reconstruction of GDL & MPL ► Modeling of flooded areas in GDLs & MPLs

Fiber H2Oliquid Binder/PTFE

Reconstruction of fibers and binder in the substrate, as wells as the different components in the MPL. [Göbel et al., J. Power Sources 355, 2017, 8 ]


CONTENT




4. Summary

DU

[V

]

i [A/cm²]


SYSTEM: SETUP OVERVIEW

H2-Supply

Supply the fuel cell with H2

Remove water from the anode

Hydrogen recirculation

Hydrogen safety

Examples of Components

Recirculation blower

Jetpump

Water separator

Pressure regulator

Sensors (T, p, dp, concentration)

Cooling

Heat removal

Ensure insulation resistance

Examples of Components

Coolant pump

Radiator

Heater

Thermostat

Deionization filter

Sensors (T, p, conductivity) Air Supply Examples of Components

Supply the fuel cell with air Compressor

Humidify the supplied air Humidifier

Remove liquid water Throttle valve

Minimize sound emissions Sensors (T, p, dp, mass flow)

PEMFC

H2 supply

Cooling

Air supply

Cat

ho

de

An

od

e

Sensor system/ controller


SYSTEM: OPERATING CONDITIONS

Cooling

Coolant inlet temperature

Coolant differential temperature

Conductivity

Air Supply

Cathode inlet temperature

Cathode inlet pressure

Relative humidity

Air mass flow

H2-Supply

Anode inlet temperature

Anode inlet pressure

Anode differential pressure

Relative humidity

Gas mixture

Stoichiometry

PEMFC

H2 supply

Cooling

Air supply

Cat

ho

de

An

od

e

Sensor system/ controller


Operating Strategy ► Sequence control

► (Freeze) Startup ► Start/Stop ► Shutdown

► Control of operating conditions ► Adaptation of the operating conditions set

► Provision of the requested power ► Fault reaction

DIAGNOSTICS IN FUEL CELL SYSTEM

Fuel cell stack ► Deviation from power forecast ► Cell voltage monitoring

► State-of-health, cell quality index ► Degradation models ► Impedance spectroscopy

Environmental effects ► Ambient pressure ► Ambient temperature ► Standing time ► Contamination

Fuel cell system: components and media supply ► Status messages from components ► Control deviation ► Model deviation ► Limit value monitoring

Diagnosis


EXAMPLES FOR DIAGNOSTICS IN FUEL CELL SYSTEM

Diagnosis: Single operating parameter outside the permitted range

Reaction: 1. Adaptation of operating conditions set 2. Power reduction

Diagnosis: State-of-health (Cell voltage monitoring)

Reaction: 1. Regeneration measure 2. Power reduction 3. Forced Shutdown

Diagnosis: O2-Concentration on the anode side

Reaction: Startup sequence: Minimization of air/air-start degradation

Humidity adjustment by means of operating conditions set

Provision of the requested power Startup sequence

Diagnosis

PSoll ISoll

1,0 1,1 0,9

Startup request

Protected

Air/Air O2

y

n


SUMMARY




DU

[V

]

i [A/cm²]

1,0 1,1 0,9

17 VW Group Research | Propulsion and Energy Systems | Dr. Sebastian Kirsch, Dr. Maren R. Kirchhoff Thank you.

fuel cell diagnostics for automotive application4+fuel+… · startup sequence: minimization of...

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