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Synthesis and durability of CNT based MEAs for PEM fuel cellsNanoduramea
SusEn Seminar, Espoo 22 September 2011Dr. Pertti KauranenVTT Technical Research Centre of Finland
228/09/2011
Presentation lineout
1. Motivation2. Partners 3. Work packages4. Materials and methods5. Highlights by the partners6. Summary
328/09/2011
1. Motivation (2008)* Durability of carbon supported Pt catalyst and Nafion@ membrane
electrolyte are the key factors limiting more wide spread use PEMfuel cells.
* The catalyst life is limited by growth of the Pt nanoparticles on thecarbon support and corrosion of the support itself.
* Degradation of the Nafion@ membrane can be caused by local dryingor overheating due to uneven current distribution or membrane puncturing due to mechnical failure.
* Durability of the membrane is a complex function of humidity andtemperature.
* Degradation of recast membrane in the catalyst layer is more severethan that of the bulk membrane.
* Corrosion is caused by peroxide intermadiates of the oxygen reductionreaction.
428/09/2011
2. Partners
Dr. Pertti Kauranen
Prof. Esko Kauppinen
Prof. Göran Lindbergh
Prof. Svein Sunde
Prof. Eivind Skou
Dr. Magnus Thomassen
528/09/2011
3. Work packages (WP)
WP1 Synthesis of CNT,
CNF and CNB, By Aalto
WP3 Surface scientific characterizationBy Aalto, VTT, NTNU and SDU
WP2 Pt and Pt alloy deposition By Aalto, VTT and NTNU
WP4 Ex-situ electrochemical
characterization By NTNU, SINTEF and SDU
WP5 MEA preparation
By KTH and IRD Fuel Cells
WP6 Single cell testing and
effluent analysis By VTT, KTH, SINTEF and SDU
WP7 Post mortem analyses
By Aalto, KTH, NTNU and SDU
628/09/2011
4. Materials and methods
1. Carbon supports- carbon blacks (e.g. Vulcan XC-72), commercial- single and few walled carbon nanotubes by Aalto University- graphitized multi walled carbon nanotubes, commercial- graphitized carbon nanofibres (VGCF), commercial
2. Surface treatment of carbon- acid treatment- plasma treatment- polyaniline treatment
3. Platinum deposition- impregnation, polyol, electrodeposition
4. Physical characterization- XRD, TG, FTIR, XPS, ESR, NMR, SEM, EDS, TEM
5. Electrochemical characterization- CV, EIS, CO stripping, EQMB, start-stop on RRDE and in PEMFC single cells
5.1. Aalto: Pt on graphitized carbon nanofibers (GNFs)
1. Preparation of 2g batches of catalyst with ∼20% Pt on Showa-Denko GNFs by the polyol method for IRD FC to prepare MEAs. Activated in 2M HNO3 /1M H2SO4 1:1 at120°C, 6hTransmission electron microscopy (TEM) and scanning electron microscopy (SEM) ESA: ∼30 m2/g
2. Deposition of ∼ 20% Pt on several batches of Showa-Denko GNFs with different activation treatments carried out by VTTCharacterization by Raman spectroscopy and EDS-SEM.
Pt on few-walled carbon nanotubes (FWCNTs)
Preparation of catalysts with ∼20% Pt on FWCNTs (grown by CVD at Aalto Univ.) by the polyol method with different activation treatments.
Activated in 2M HNO3 /1M H2SO4 1:1 at120°C for: 0, 2, 4 and 6h.Characterization by Raman spectroscopy, TEM and EDS-SEM.ESA: 40-60 m2/g
untreated 4h 6h
9
5.2. NTNU: Effect of Chlorides on Pt dissolution by EQMB
Potentiostatic at 1.2 V (RHE)
10
Improved Polyol Deposition Method (Ex-Situ)15 % Pt/XC-72 by In-Situ Polyol (old) 20 % Pt/Xc-72 by Ex-Situ Polyol
5.3. SDU:Thin film Rotating Ring Disc Electrode
11
CV on Thin film RDE
12
Potential (V) vs. RHE
Cur
rent
(uA
)
Pt 20% on XC-72 Vulcan, BASF
0.0 0.5 1.0
V
-500
0
500
µA
Peroxide formation on carbon supports
13
14
5.4. KTH:PEMFC Degradation due to Catalyst Support Corrosion
Alejandro Oyarce
Applied electrochemistrySchool of Chemical Science and Engineering
Royal Institute of Technology (KTH)
Applied electrochemistry
15
Fuel cell performance
Humidifier temperature:83 oC Humidifier temperature:64 oC
Conditions: Nafion 115 (127μm), Cell temperature 80 oC, gases:H2 (CE/RE)/ O2 or Air (WE), flow rates: 120 ml/min (CE/RE), 60 ml/min (WE). Sweep rate: 1 mV/sEIS: Frequency: 100kHz-0.1Hz, amplitude:5% of idc.
galvanostatic measurement at 0.2 A/cm2
Humidifier temperature:77 oC
At 0.2 A/cm2 the decrease in voltage performance is:-7% decrease for O2/H2-15% decrease for air/H2
At 0.2 A/cm2 the decrease in voltage performance is:-5% decrease for O2/H2-13% decrease for air/H2
At 0.2 A/cm2 the decrease in voltage performance is:-4% decrease for O2/H2-12% decrease for air/H2
The results are an indication that the mass transport losses upon the support degradation are mainly due to changes in the electrode morphology, specifically the large decrease in porosity
16
Carbon agglomeration of Pt/Vulcan
Fresh-Pt/Vulcan low RH Degraded-Pt/Vulcan low RH Degraded-Pt/Vulcan at high RH orhigh current densities
Fresh-Pt/Vulcan at high RH or high current densities
O2H2O
O2O2
O2
H2OH2O
H2O
17
Carbon nanofibers (Pt/GNF)
After degradation
Before degradation
Materials and Chemistry
Humidification of gases with membrane humidifiers
Fuel cell under test
70 °C, 100%RH
Heated 2μm filter and sample gas
line
FTIR spectrometer for detection of CO2, CO, SO2, CHOH, CHOOH and HF
in cathode exhaust
5.5. Sintef: In situ carbon corrosion measurement by FTIR
Carboncorrosion
• 70°C, 100% RH100 mL/min H2/Air
• 0.6 – 1.5 V, 40 mV/s, 300 cycles• 1 minute FTIR resolution
Recovery
• H2/N2, 100 mL/min OCV for 10h• Pt area CV every 2h
Reactivation
• H2/H2, 100 mL/min• -0.2 – 0.2 V, 20 mV/s, 3 cycles
Materials and Chemistry
Results – accellerated carbon corrosionPotential cycling 0.6-1.5V vs RHE, 300 cycles
19
Pt / Vulcan Pt / CNF
0
2
4
6
8
10
12
14
0
20
40
60
80
100
120
‐50 0 50 100 150 200 250
Carbon
loss / wt%
CO2 c
oncentratio
n / p
pm
Time / min
CO2 ppm ‐MEA1CO2 ppm ‐MEA2C loss ‐MEA1C loss ‐MEA 2
0
2
4
6
8
10
12
14
0
20
40
60
80
100
120
‐50 0 50 100 150 200 250
Carbon
loss / wt%
CO2 c
oncentratio
n / p
pm
Time / min
CO2 ppm ‐MEA 1CO2 ppm ‐MEA 2C loss ‐MEA 1C loss ‐MEA 2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Cell V
oltage / V
Current Density / mAcm‐2
InitialAfter corrosionInitial ‐MEA2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Cell V
oltage / V
Current Density / mAcm‐2
Initial ‐MEA 1After corrosion ‐MEA 1Initial ‐MEA 2After corrosion ‐MEA 2
135 mΩcm-2 96 mΩcm-2
Materials and Chemistry
Results – real start stop cycling15 min purge cycles for 20 h at OCV
20
Pt / CNF
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Cell V
olta
ge / V
Current density / A cm2
Before start/stopAfter start/stop
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Cell V
olta
ge / V
Current density / A cm2
Before start/stopAfter start/stop
Pt / CB
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700 800
CO2co
ncen
tratio
n / pp
m
Time /min
Vulcan XC72CNF
2128/09/2011
5.6. VTT: Analysis of GNF surface treatments by FTIR
Acid treatments ↑
Polyaniline treatments ↓
2228/09/2011
Multisinglecell
Optimization and testing of the setup and components for the new 3 cm2 multisinglecellInstead of start-stop operation testing with automotive drive cycleResult: Problems in MWCNT ink preparation
2328/09/2011
6. Summary
1. Vulcan XC-72 and FWCNT are not stable at potentials above 1.4 V (RHE) and during start-stop cycling.
2. Temperature and high relative humidity promote carbon corrosion.3. The pore structure of Vulcan collapse due to carbon corrosion leading to electrode
thinning and mass transport limitations.4. Graphitization of the carbon support and especially use of graphitized nanofibres
can improve the catalyst stability by a factor of 5 under severe operating conditions.5. Potential cycling at high potentials and presence of even traces of chlorides promote
platinum dissolution.6. Acid treatment has only minor effect on graphitized GNF surface. 7. Oxide functionalization is harmful for MWCNT.8. N-doping by PANI decomposition was not successful.9. Three summer schools were organized.10. The two PhDs educated have been hired by Nordic FC industries.11. It makes perfect sense to join forces in Nordic FC&H2 research.
2428/09/2011
2528/09/2011
VTT creates business from technology