Monitoring of membrane failure due to pinhole formation Viktor - - PowerPoint PPT Presentation

▶
monitoring of membrane failure due to pinhole formation
SMART_READER_LITE
LIVE PREVIEW

Monitoring of membrane failure due to pinhole formation Viktor - - PowerPoint PPT Presentation

Oct 09, 2023 256 likes •474 views

Monitoring of membrane failure due to pinhole formation Viktor Hacker, Eva Wallnfer Department of Chemical Engineering and Environmental Technology, TU GRAZ, Austria Peter Prenninger AVL List GmbH, Austria Trondheim, June 23 rd ,2009

slide-1
SLIDE 1

Monitoring of membrane failure due to pinhole formation

Viktor Hacker, Eva Wallnöfer Department of Chemical Engineering and Environmental Technology, TU GRAZ, Austria Peter Prenninger AVL List GmbH, Austria Trondheim, June 23rd,2009

slide-2
SLIDE 2

Professor Horst Cerjak, 19.12.2005

2

Diagnostic Tools for Fuel Cell Technologies

Overview

  • 1. Introduction
  • degradation of PEMFC membranes
  • influence of operating conditions
  • 2. In-situ Degradation Studies
  • perating conditions
  • characterization methods
  • 3. Conclusions
slide-3
SLIDE 3

Professor Horst Cerjak, 19.12.2005

3

Diagnostic Tools for Fuel Cell Technologies

Degradation of PEMFC Membranes – impacts of degradation

membrane decomposition (release of HF,

SO2, CO2, CO, C-F-compounds)

membrane thinning higher gas permeability platinum particle deposition in the

membrane

performance loss of the MEA decrease of life time

slide-4
SLIDE 4

Professor Horst Cerjak, 19.12.2005

4

Diagnostic Tools for Fuel Cell Technologies

Degradation of PEMFC Membranes – causes

thermal

degradation

mechanical

degradation

chemical

degradation

slide-5
SLIDE 5

Professor Horst Cerjak, 19.12.2005

5

Diagnostic Tools for Fuel Cell Technologies

Degradation of PEMFC Membranes – influencing factors

  • material

properties

  • cell assembling
  • operating

conditions

  • membrane thickness
  • gas pressure
  • temperature
  • gas humidity
  • cell potential
slide-6
SLIDE 6

Professor Horst Cerjak, 19.12.2005

6

Diagnostic Tools for Fuel Cell Technologies

In Situ Degradation Studies

slide-7
SLIDE 7

Professor Horst Cerjak, 19.12.2005

7

Diagnostic Tools for Fuel Cell Technologies

Operating Conditions

  • 5 to 1 fuel cells (in series), 25 cm2 each
  • perated under the same conditions up to

1300 h

  • permanent operating 24h/day, 7 days/week
  • interruptions only for electrochemical

characterizations

  • every one or two weeks, one cell was removed

(SEM analysis)

  • gas flow:
  • H2: λ = 1.5 (at OCV: 300 ml min-1)
  • Air: λ = 2.2 (at OCV: 300 ml min-1)
  • MEAs:
  • pt loading: A: 0.4 mg cm-2, C: 0.6 mg cm-2
  • membrane: bilayer membrane, reinforced with

PTFE, thickness: 35 µm

  • activation of the MEAs ( 6 h at 0.4 and 0.6 V)
slide-8
SLIDE 8

Professor Horst Cerjak, 19.12.2005

8

Diagnostic Tools for Fuel Cell Technologies

Characterisation Methods

performance (UI) cell potential (CP) membrane resistance (MR) fluoride emission rate (FER) pinhole detection (PD) membrane thickness and condition (SEM)

slide-9
SLIDE 9

Professor Horst Cerjak, 19.12.2005

9

Diagnostic Tools for Fuel Cell Technologies

2 4 6 8 10 12 14 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Potential / V Hydrogen Diffusion Current Density / mA cm

  • 2

2 4 6 8 10 12 14 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Potential / V Hydrogen Diffusion Current Density / mA cm

  • 2

2 4 6 8 10 12 14 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Potential / V Hydrogen Diffusion Current Density / mA cm

  • 2

2 4 6 8 10 12 14 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Potential / V Hydrogen Diffusion Current Density / mA cm

  • 2

2 4 6 8 10 12 14 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Potential / V Hydrogen Diffusion Current Density / mA cm

  • 2

2 4 6 8 10 12 14 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Potential / V Hydrogen Diffusion Current Density / mA cm

  • 2

Hydrogen Diffusion

  • anode: H2 flow / cathode: N2 flow
  • standard conditions H2 diffuses through the membrane and gets oxidised

with an increasing potential

  • the hydrogen diffusion current is limited by diffusion to < 5 mA cm-2
  • if there is a pinhole, the current increases with increasing potential
Po t e n t i a l / V

0 h 110 h 280 h 450 h 620 h 790 h 960 h 1130 h

slide-10
SLIDE 10

Professor Horst Cerjak, 19.12.2005

10

Diagnostic Tools for Fuel Cell Technologies

10 20 30 40 50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000 1100 time / h hydrogen diffusion current density between 0.2 amd 0.5 V / mA cm

  • 2

Hydrogen Diffusion - Results

  • the formation of a pinhole

can not be forecasted

  • end of membrane lifetime:

time interval, at which the hydrogen diffusion current density is in the range between 4 and 5 mA cm-2

standard low humidity low temperature high pressure 45 mA 90 mA 135 mA 405 mA 90 mA, low humidity

slide-11
SLIDE 11

Professor Horst Cerjak, 19.12.2005

11

Diagnostic Tools for Fuel Cell Technologies

Cell Performance

  • the cumulated performance of the stack was investigated; H2: λ = 1.5 / Air: λ = 2.2
  • no gas pressure; T: 70 °C
  • polarisation curves: changes with operating time

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Current Density / A cm

  • 2

Potential / V standard

Po t en t i al / V

0 h 110 h 280 h 450 h 620 h 790 h 960 h 1130 h 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Current Density / A cm

  • 2

Potential / V low humidity (40 % rH) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Current Density / A cm

  • 2

Potential / V low temperature (40 °C) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Current Density / A cm

  • 2

Potential / V 45 mA cm

  • 2

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Current Density / A cm

  • 2

Potential / V 135 mA cm

  • 2
slide-12
SLIDE 12

Professor Horst Cerjak, 19.12.2005

12

Diagnostic Tools for Fuel Cell Technologies

Cell Performance - Results

maximum power density

▫ changes with operating time ▫ the performance loss is related to the membrane degradation, but also influenced by the electrode degradation ▫ the formation of the first pinhole is not exactly related to a certain loss of performance

standard low humidity low temperature high pressure 45 mA 90 mA 135 mA 405 mA 90 mA, low humidity

slide-13
SLIDE 13

Professor Horst Cerjak, 19.12.2005

13

Diagnostic Tools for Fuel Cell Technologies ▫ OCV decreases with the

  • perating time (non-linear)

Cell Performance - Results

OCV

▫ normalised OCV (to 0.95 V) ▫ the formation of the first pinhole is related to a loss of 30 - 70 mV (mostly ~ 50 mV)

  • f the initial OCV of the “stack”

because of the increasing gas diffusion through the degradated membrane ▫ a certain influence of the electrode degradation may exist

standard low humidity low temperature high pressure 45 mA 90 mA 135 mA 405 mA 90 mA, low humidity

slide-14
SLIDE 14

Professor Horst Cerjak, 19.12.2005

14

Diagnostic Tools for Fuel Cell Technologies ▫ FER in the anode and cathode exhaust water was nearly the same, even though the degradation

  • f the anode side was higher

(→ SEM investigations) ▫ FER was slightly decreasing with

  • perating time

Fluoride Emission Rate - Results

0.000 0.002 0.004 0.006 0.008 0.010 100 200 300 400 500 600 700 800 Time / h FER / mg F - cm -2 h -1

Anode Standard Cathode Standard

slide-15
SLIDE 15

Professor Horst Cerjak, 19.12.2005

15

Diagnostic Tools for Fuel Cell Technologies

Fluoride Emission Rate - Results

▫ accumulation of the total anode and cathode FER: ▫ the formation of the first pinhole is related to a certain cumulated FER:

standard low humidity low temperature high pressure 45 mA 90 mA 135 mA 405 mA 90 mA, low humidity

slide-16
SLIDE 16

Professor Horst Cerjak, 19.12.2005

16

Diagnostic Tools for Fuel Cell Technologies ▫ the resistance does not correlate clearly to ▫

  • perating conditions

▫

  • perating time

▫ pinhole formation ▫ membrane thickness (SEM) ▫ a slight increase of the resistance could be observed at higher degradation/ long operating time in most cases

Membrane Resistance - Results

▫ the resistance is influenced by ▫ the loss of proton conducting, hydrophilic functional groups ▫ the structural changes of the hydrophobic phase ▫ the thinning of the membrane ▫ change of the resistance with the operating time

standard low humidity low temperature high pressure 45 mA 90 mA 135 mA 405 mA 90 mA, low humidity

5.0E-03 6.0E-03 7.0E-03 8.0E-03 9.0E-03 1.0E-02 1.1E-02 1.2E-02 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 time / h membrane resistance / Ω

slide-17
SLIDE 17

Professor Horst Cerjak, 19.12.2005

17

Diagnostic Tools for Fuel Cell Technologies

Scanning Electron Microscopy - Results

membrane thickness

▫ the thinning of the membrane is not clearly related to operating conditions ▫ membrane thinning occurs under moderate and harsh conditions ▫ pinhole formation is not related to a significant membrane thinning

5 10 15 20 25 30 35 100 200 300 400 500 600 700 800 900 1000 1100 time membrane thickness / µm standard low humidity low temperature high pressure 45 mA 90 mA 135 mA 405 mA

slide-18
SLIDE 18

Professor Horst Cerjak, 19.12.2005

18

Diagnostic Tools for Fuel Cell Technologies

Conclusions

  • a low cell current and a low gas humidity accelerate membrane

degradation

  • a lower temperature and higher cell currents slow membrane

degradation

  • the current density influences the impact of other parameters (e.g. gas

humidity)

  • the end of lifetime of the MEA was indicated by the detection of the first

pinhole (at moderate performance losses)

  • an exceed of a certain value of cumulated FER could indicate the

formation of pinholes

  • a drop of OCV below a certain value could indicate the formation of

pinholes

  • membrane thinning at the anode side occurred at long-time operation

even under moderate operating conditions

  • the membrane resistance did not correlate clearly to the membrane

degradation, the formation of pinholes and the membrane thinning

slide-19
SLIDE 19

Professor Horst Cerjak, 19.12.2005

19

Diagnostic Tools for Fuel Cell Technologies

future research activities

evaluate and understand the complex interactions of fuel cell operating conditions, membrane parameters and membrane lifetime

  • bserve membrane and electrode

degradation separately find a (simple) analysis instrument to observe membrane ageing during fuel cell operation

slide-20
SLIDE 20

thank you for your kind attention!